A Block Diagram, Graphical and Microcomputer Analysis of the - PDF by aij20926

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									                                                               various medical specialties and the potential critical
                                                               nature of abnormal values.
                                                                   In this paper a systematic description and block
                                                               diagram for O2 transport is developed that allows a
                                                               rigorous interpretation   of important clinical variables
                                                               such as the alveolar, arterial, and mixed venous PO,
                                                               (PA*,, Pao,, and PRO,, respectively) and the alveolar COs
                                                               partial pressure (PA~~J. In addition,          a graphical
                                                               analysis is developed using a total O2 content vs. PO,
                                                               graph so that the total system can be treated. The graph-
A Block Diagram, Graphical                                     ical analysis supplements the block diagram and pro-
                                                               vides a method to determine the effect of any sys!em
and Microcomputer Analysis                                     parameter [Hb concentration, pH, cardiac output (QT)]
                                                               on the clinical variable of interest. This material and
of the O2 Transport System                                     presentation has been used for 2 years in a medical
                                                               physiology course.
DAVID A. MILLER AND WESLEY M. GRANGER                              The block diagram is an excellent integrating tool for
                                                               the material     developed    early in the respiratory
Department of Physiology                                       physiology section including the gas laws, mechanics,
Medical College of Georgia
                                                               gas exchange, and transport. Later respiratory control
Augusta, Georgia 30912                                         mechanisms are easily discussed in terms of the founda-
                                                               tion established by the block diagram. A laboratory ses-
   MILLER, DAVID A., and WESLEY M. GRANGER. A sion is used to introduce the microcomputer                       system to
Block Diagram, Graphical and Microcomputer Analysis of the     the students. Several demonstration         exercises and
0, Transport     System. Physiologist     (25(2):   000-000,   clinical cases are discussed in this laboratory session.
1982.-The systematicdescription of O2 transport from the This session gives the students the opportunity            to try
                        involves a variety of environmental, therapeutic measures that they have either read or heard
ambientair to the tissues
pulmonary, heart, tissue,and blood parameters.    Using essen- about.
tially the law of conservationof mass   and the total blood O2
content vs. O2partial pressure (PO*)relationship,the variables     System Description
                 of
and parameters 0, transport can be relatedin the form of a
block diagram. This systemblock diagramhasproved useful                The O2 transport system has been formulated on the
to examine factors that influence O2 transport. A mathe-           basis of the conventional three-compartmental       model
maticaldescriptionof the system beenprogrammed an
                                  has                     on       for pulmonary gas exchange (4) that includes dead-
Apple II microcomputer.The computercan be usedto predict           space, alveolar and shunt compartments and a tissue
the relationshipbetweenalveolar, arterial, and mixed venous        compartment that utilizes O2 (Fig. 1). Since this is a
PO, and any given system parameter. To augment our                 steady state model tissue O2 utilization is assumed to be
understandingof some of the more complex findings, we              equal to O2 uptake at the lungs. The transport of 0, to
developeda graphical analysisthat involves manipulation on         the gas exchange region is dependent on the tidal
the total 0, content vs. PO, diagram. Even though the
graphicaltechniqueis less  exactthan the computer, it provides     volume (VT), breathing frequency (F), and the inspired
better insight into the characteristicfeaturesof a given result.   fraction of O2 (FIOJ. The dead-space compartment is
This techniquereinforcesthe understanding the equations
                                              of                   represented by a dead-space volume, which is the por-
usedin the block diagramand providesan in-hand methodfor           tion of the VT that does not reach perfused alveoli. Thus
determining the effect of any system parameter on the              for this portion of the breath no gas exchange occurs,
alveolar, arterial, or mixed venousPO,.                            and consequently the effective ventilation is reduced
                                                                   particularly when this volume is large. The volume of
    The transport of O2 from ambient air to the tissue is          the conducting airways normally accounts for the major
affected by a variety of environmental,      lung, heart,          portion of the dead-space volume. Examples of in-
tissue, and blood parameters. Because of the large                 creased dead-space volume would include breathing
number of parameters and relationships involved in this            through a tube or pulmonary emboli that block perfu-
system, its analysis or understanding often cannot be              sion to ventilated areas. The alveolar compartment is
dealt with adequately using word arguments or singular             represented by a gas exchange space that is both ven-
aspects (e.g., the O2 dissociation curve) of the total             tilated and perfused. In this compartment it is assumed
system. An inadequate analysis can result in wrong                 that the blood comes into perfect equilibrium     with the
answers or possibly right answers for the wrong reasons.           alveolar gas concentrations. The shunt compartment is
For example, if a patient has a lowered arterial O2 par-           represented by a shunt flow (Qs), which is the portion of
tial pressure (Pad, =60 mmHg) and a low hemoglobin                 the venous return that would have to be added to the
concentration (hb = 10 g/100 ml), is the low Pao, ac-              arterial blood to account for the difference between the
counted for entirely by the low Hb? The answer is not a            O2 arterial content (Cao,) and the O2 content of tpe
simple yes or no, since it depends on the adequacy of gas          blood equilibrated with the alveolar space (CA~,).~ QS
exchange. With normal gas exchange low Hb does not                 divided by QT yields the shunt fraction (Fs), which is a
 appreciably affect Pao,, whereas with impaired gas ex-            quantitative measure of an O2 exchange abnormality
 change it can significantly influence the Pao,. This ex-
 ample illustrates the complex behavior possible in the O2
 transport system. The importance of interpreting var-
 ious blood gas measurements (e.g. arterial and mixed
 venous PO,) is underscored by their widespread use in

The Physiologist, Vol. 25, No. 2, 1982                                                                                    111
                                                                                                blood and its PO,. This relationship is influenced by
      Figure 1
      O2 transport compartmental model.                                                         blood pH, temperature,           and Pco~. Although
                                                                                                2,3=diphosphoglycerate can also influence the curve, its
                                               FIO,,   F-VT                                    concentration is assumed to remain constant in the
                                                                                               model, because clinical data on this parameter are
                                                                                               generally not available. The blood that perfuses the
                                                                                               alveolar compartment        is assumed to reach perfect
                                                                                               equilibrium with the alveolar gases. Therefore, the total
                                                                                               O2 content of that blood has been designated CAM,. In
                                                                                               block 4, the total Cao, is calculated using a combined
                                                                                               form of the FS equation and Fick’s principle. For
                                 I
                5

                                                                              ’       Left
                               (QT-QS,    -             CA02
                                                                                      Heart
                                                                                               normal values of FS (0.02), Cao, will approach CAM,;
                                                                                               however, when FS increases their difference will increase
            ’              J                                                  Lcoo2
                               QS -           Shunt            ciio,                           and also be influenced by fo, and OT. In block 5, work-
                                                                                               ing backward through the total O2 content vs. PO,
        I
                                                                          l



                                                                                       QT
                                         FS = QS/QT
                                                                                               graph will yield one of the desired variables, Pao,. This
       QT
                                                 vo2
                                                                                               variable is heavily relied on as a clinical index of the
                    PJO,                           I                   PO02
                                                                                               general state of oxygenation of the individual. In block
                                                                                               6, the mixed venous O2 content (CVO,) can be obtained
                                              Tissue
                                                                                               from Cao, and parameter values by using Fick’s princi-
                                                                                               ple. In block 7, PRO, can be obtained from GO, via the
                                                                                               total O2 content vs. PO, graph. Pvoz is used clinically as
(3). However, the FS does not specify the abnormality.                                         an index of tissue oxygenation.
An increased FS can indicate I) an anatomical shunting                                             PACT, can also be calculated from FA~o,
of blood that bypasses the alveolar space (e.g., atelec-                                                      PAco,=FAco,(PB-PH20)                   (0
tasis), 2) a diffusion abnormality,   3) a ventilation-
perfusion abnormality, or 4) some combination of the                                          where FA~o, =fCO&A.          CO* production @CO,) is ob-
above.                                                                                        tained from R~+o~, where R, the respiratory exchange
                                                                                              ratio, is assumed to be equal to 0.8 and.all gas volumes
                                                                                              are measured under BTPS conditions. VA is calculated
O2 Transport Block Diagram                                                                    from F+VT-VD).          Since PACT, is determined from a
    Conventional      equations and relationships (6) are’                                    fixed relationship (Eq. 1) with other system parameters
 available to describe the above compartments of the O2                                       (R, +o,, F, VT, VD, PB, PH,o), it is not input separately
 transport system and include 1) the alveolar gas equa-                                       as a parameter. Alveolar, arterial, and mixed venous
 tion, 2) the definition of a dry gas fraction, 3) total O2
 content vs PO, diagram, 4) FS equation, and 5) Fick’s
 principle. Each of these five relationships can be ex-                                           Figure 2
                                                                                                  Block diagram for O2 transport system.
 pressed in several forms. The form utilized in our                                                                                            FlO2
 analysis allows each new variable to be expressed in
 terms of the previously introduced variable and one or
 more system parameters (Fig. 2). In this way the
 dependency of any variable can be determined by obser-
ving the variables or parameters that appear in a                                                                                              FA02
previous block. In addition, variables and parameters
 are introduced at a level that is most consistent with
their structural or functional appearance in the system.
                                                                                                                                               PA02
    The system block diagram provides an orderly and
logical way to view the relationships of the O2 transport                                                                                             AFFECTED      BY:
                                                                                                                                                            PH
system. Accordingly, the beginning point in the diagram                                                                                                     TEMP.
                                                                                                                                                             PCO*
is FIN,, which is a frequently manipulated parameter                                                                                                         HGB

during O2 therapy. In block 1, the alveolar gas equation                                                                                        PO2


is used to express the alveolar fraction of .02 (FA~J as a                                                                                       1
                                                                                                                                               CA02
function of the FIO*, O2 consumption (VO,), and the                                                                                              4                        4
ventilatory parameters, F, VT, and the physiological                                                                              cao,    = CA02-
dead-space volume (VD). Alveolar ventilation (+A) is                                                                         r

given by F(VT- VD). In block 2, FAO~ is converted to
PAN, by utilizing the definition of a dry gas fraction.                                                 c               6

PAN, is expressed as a function of the barometric                                                   IC302         = Ca02-        V02/QT    I
pressure (PB) and the partial pressure of water vapor                                                                  4
(P&O). PB is altered in diving and at altitude, and PH~O                                                             cc0
                                                                                                        7              k2


                                                                                                         1/
varies with temperature. Since there can be variation of
local PAN, across the lung due to local diffusion or
ventilation-perfusion
be viewed as compartmental
and 90,.
                          differences, FAO* and PAN, should
                                   values consistent with +A
              Block 3 represents the relationship
tween total O2 content (dissolved + Hb carriage) of the
                                                          be-                                           cl  co2


                                                                                                                       PO2


                                                                                                                        i
                                                                                                                     Pi02
                                                                                                                                                            Pab2




112
Pco2 (PACT,, Pace,, and PVCO,, respectively) are assumed
equal for the calculations involving the total O2 content       Table 1
vs. Po2 graph.                                                  Parameters of O2 Transport System
    Since pH is related to Pco~, one might consider             Parameter           Anatomical of Functional Component
calculating pH also. However, this relationship is very         F                   Respiratory center, central and peripheral
complex. For example, in respiratory and metabolic                                  respiratory receptors
disturbances, there is not a fixed relationship between         VT                  Respiratory center, central and peripheral
the two variables. Even in a respiratory disturbance                                respiratory receptors, respiratory
                                                                                    muscles and elastic properties of the
alone, such a hyperventilation,    the relationship between                         lungs and chest wall
pH and PCOz can vary with time and Hb. Thus, because            YD,   Fs             Lungs
of the complexity involved, pH is not calculated from           QT                   Heart
PCO~ in the computer program but must be input                  to,                  Body tissues
separately. Arterial and mixed venous pH are also as-           Hb, pH, Pea,
                                                                  temperature       Blood
sumed equal for calculations involving the total O2 con-        FIO,, PHzO, PB      Environment
tent vs. PO, graph. Since the PH~O is determined solely
by the temperature, it is calculated in the computer pro-
gram from the input value of temperature.                       Table 2
                                                                Normal Values and Disturbances
    With the systematic description complete, it is of in-      to System Parameters and Variables
terest to examine the various system parameters to
determine what anatomical or functional components                    Parameter          Altered by Condition or Influence
they represent. Table 1 indicates that a variety of organs
                                                                to, = 250 ml/min    Temperature (1 1°F - 7% $0, I),
influence the behavior of the O2 transport system, and it                               abnormal. thyroid function
is this spectrum of components that must be initially           irco, = 200 ml/min  Related to Vo, by R
considered in abnormal states as opposed to immedi-             R = Vco,/Vo, = 0.80 Substrate for Metabolism (fat, protein,
ately focusing on the lungs or heart. As such, the initial                              or carbohydrate)
clinical assessment should be to establish the abnormal         VD = 150 ml/breath  Pulmonary embolus
                                                                Fs = 0.02           Diffusion abnormalities, ventilation-
anatomical or functional component so that some ap-                                    perfusion maldistribution, anatomical
propriate therapeutic regimen can be implemented.                                      shunts (bronchail veins, Thebesian
Table 2 shows the normal values that have been used for                                veins), alveolar shunts (collapsed
the system parameters and variables along with some of                                 alveoli)
the typical conditions or influences that might change          or = 5 .O l/min     Blood volume, sympathetic system,
                                                                                    drugs
the parameter values.                                           Flo, =0.21          O2 therapy
    The block diagram has proved to be extremely useful         PH,O = 47 mmHg      Temperature
for answering very basic questions that students have           PB = 760 mmHg       Altitude or diving
had about the O2 transport system. For example,                 Hb= I5 g/100 ml     Polycythemia, anemia
                                                                Temperature = 37 “C Fever, drugs, environment
   I) What are all the parameters that affect Pao,? This        pH = 7.40           Metabolic or respiratory acid-base
question is esily answered by just listing all the                                      disturbance
parameters that appear above Pao,in the block diagram,          F = 10 breaths/min  Disturbance of respiratory center or
since each of these parameters would influence the                                     receptors
                                                                VT = 500 ml/breath  Disturbances of respiratory center or
calculation of Pa0,. This list would also include the                                   receptors, abnormal chest or lung
parameters that affect the total O2 content vs. PO,                                    compliance, or abnormal respiratory
graph.                                                                                  muscle function
   2) What parameters affect the arteriovenous O2 con-          Normal Values for Variables
tent difference? Small rearrangement of block 6 shows           PAO, = 100 mmHg      PACO~ = 40 mmHg
that this difference is only influenced by to, and GT.          Pao, = 94 mmHg       CAoz= 20.6~01%
   3) With normal gas exchange (Fs = 0.02), why does            Pvo, =40 mmHg        Cao, = 20.5 ~01%
                                                                Pa~o, = 40 mmHg      ci;(), = 15.5 VOW0
$0, have a large effect on Pao, and OT does not? The ef-
fect of ?o, and OT on Cao, in block 4 of the block
diagram is modified by the factor Fs/( 1 - Fs). When FS       This is a combined form of blocks 1 and 2 in Fig. 2.
ii small (Gormal = 0.02), it minimizes the influence of       KnOwingPA 02, C~~,is obtained graphically in Fig. 3 (see
Voz and QT on Cao, in block 4. However, 90, also ap-          arrows). Knowing CAM, and the parameters of the
pears in block 1 of the diagram and has a major influ-        equation designated as (2) in Fig. 3, Cao, is calculated*
ence on PAN, and CAM, only in block 4 and therefore has       This value is used on the graph (see arrows) to obtain
a minimal influence when FS is small.                         Pao,, which is an important clinical variable. Knowing
                                                              Cao,, and the parameters of the equation designated as
Graphical Analysis                                            (3) in Fig. 3, Go, is calculated; from this P%, is ob-
   In our efforts to examine and to understand the            tained graphically.
system, we developed a graphical analysis that utilizes              Figures 4-6 show how this basic graphical analysis
the total O2 content vs. PO, relationship. All of the          can be used to determine the effects of parameter varia-
system relationships of Fig. 2 can be taken into account       tions     on PAoz, Pao,, and PVo,. In Fig. 4, the effect of
using this graphical technique. Therefore the effect of        two different concentrations of Hb is examined. The
perturbing any system parameter can be examined. The          curves relating PO, and total O2 content are shown for
total O2 content vs. PO, graph is shown in Fig. 3. The         Hb concentrations of 15 and 7.5 g/100 ml. Variables
entry point on the graph is PAN,, which can be                associated with the lower Hb are denoted by a prime.
calculated from the equation designated as (I) in Fig. 3.     I%,, which is the entry point on the graph, is the same
The Physiologist, Vol. 25, NO.2, 1982                                                                                            113
       Figure 3                                                                                                                                                                      Figure 5
       Graphical analysis of O2 transport.                                                                                                                                           Graphical analysis of effect of pH on O2 transport.
                                               22
                                 CA02               -L

                       (2)        coofol

                                               18                                                                                                                                                 18     -

                                               16
                     (31         CGO,
                                               I   4’                                                                                                                              Total
                                               12                                                                                                                                    02
             Total                                                                                                                                                                 Content
                                               IO
                  O2                                                                                                                                                               (Vol. %)
                                                    8
        Content                                                                                            FS=    0.12
        (Vol. %)                                    6

                                                    4


                                                    2


                                                                                                                                                                                                     0        IO      20    t 30     f40       50      6Ot     701    80          90        IO0            II0
                                                            0           IO          20       30     f 40         50      60      70          80    90          100          II0                                                                                                        f
                                                                                                                                                                                                                           POb*      PP 02               Pa’02    Pa02                     PA02
                                                                                                                                                                                                                                                                                            and
                                                                VO,     (PB - PIi,                Pii02                         Pa 0,                          PA 0,
       (I)        PA02       =          PI02            -                                                                                                                                                                                                                                  PA/O2
                                                                 FtVT          - VD)                                                                           (I 1
                                                                                                                                                                                                                                             PO,      (mm Hg)
                                                                                                           PO,        (mm      Hg)
      (2)         CaOZ            = CAOz-
                                                                 (3(3

      (3)         Cii02          = Co02                     -    VO,         / OT



        Figure 4                                                                                                                                                                    Figure 6
        Graphical analysis of effect of hemoglobin concentration on O2                                                                                                              Graphical analysis of effect of fraction of inspired O2 on O2
        transport.                                                                                                                                                                  transport.

                             do,22


                                                                                                                                                                                                                                             PI02     = 357mm     Hg (primed)                      ,
                                                                                                                                                                                                                                             P IO2 - I49 mm Hg (unprimed)
                                                                                                                                                                                                                                                PoCO2 = 40mm     Hg
      Total
                                                                                                                                                                                                                                                      R = 0.8
                                                                                                                                     PI02    = 149 mm Hg
             02                                                                                                                                                                                                                                       FS= 0.26
       Content                                                                                                                       PoCO2 = 40mmHg                                                                                          VO/QT        = 5.0      Vol.   %
                                                                                                                                         RzO.8             ,
      (Vol. %)
                                                                                                                                        FS = 0.12




                                                                                                                                                                                                       I         11*1111,,,1,,,,,,                                                                     4
                                                                                                                                                                                              0       f32        (‘64                    128    160     192       224       256        288         t320
                                                                                                                                                                                                  Pi02        f Pa02     t 962     PA02
                                           0                    IO           20       3.Of     f40         50      f60        170           80    90    flO0          IIO                                                                                                                   PA/O2
                                                                                                                                                                                                         Piibp
                                                                                     p+o;     PiiO2              PdO2         PO02                      ‘PAOz                                                         Pdo2         (FlO2= 0.21)                                        (F102=0    5)
                                                                                                                                                           ond
                                                                                                  PO2hn                  Hg)                              Pd02
                                                                                                                                                                                                                                     PO2(mm            Hg)



for both cases because this variable is unaffected by Hb.                                                                                                                            Figures 4-6 illustrate the use of the graphical techni-
The values for CAM, and C ‘Ao, are obtained from the                                                                                                                              que for evaluating the effects of Hb, pH, and F10,on O2
appropriate curve. Next Cao, and C ‘ao, are calculated                                                                                                                            transport. In a similar fashion, the effect of any other
from the alveolar O2 contents and parameter values and                                                                                                                            system parameter could be evaluated.
 then used graphically to determine Pao, and P ‘ao,. Then                                                                                                                            The graphical analysis has been particularly useful in
 CVO, and C 70, are calculated from arterial Ot con-                                                                                                                              helping students understand the following difficult
tents and parameter values and used graphically to                                                                                                                                points about O2 transport behavior.
determine PVO, and P 70,. These results can now be used                                                                                                                              I) With abnormal gas exchange (large Fs) Pao, is
to evaluate the effects of Hb. For this set of parameter                                                                                                                          significantly influenced by Hb or QT, whereas with
values the largest influence of Hb is on Pi;;o,.                                                                                                                                  normal gas exchange (small Fs) it is not. It is imperative
    In Fig. 5 the effect of pH on O2 tensions and contents                                                                                                                        to understand the complex behavior of Pao,, since this is
is evaluated in a manner identical to that used for Hb.                                                                                                                           a frequently measured and highly relied upon clinical
For the set of parameter values used, pH is shown to                                                                                                                              variable.
alter both arterial and mixed venous O2 tensions.                                                                                                                                    2) Some disturbances (i.e., t CO, 1 OT, T pH, 1
    The effect of FIO, on O2 transport is evaluated in Fig.                                                                                                                       temperature, and 1 Hb) decrease PVO, without signifi-
6. Since changing Fro, alters PAN,, the entry points on                                                                                                                           cantly affecting Pao,. The recognition and understand-
the graph are different. The influence of FIN, on the                                                                                                                             ing of these disturbances is important, because in these
arterial tension will be highly dependent on Fs, which                                                                                                                            cases tissue hypoxia that is undetectable by observing
affects the vicinity in which the arterial content falls.                                                                                                                         Pa0,- is occurring.
This in turn can markedly alter the arterial tension in the                                                                                                                          3) The clinical index (PAN, - Pao) for gas exchange is
saturation region of the curve. Since CVO, will usually                                                                                                                           extremely sensitive to FIO, and (Cao, -GO,) as well as
fall on the steep portion of the graph, mixed venous ten-                                                                                                                         the gas exchange function (Fs). Understanding the fac-
sions are affected by FIO, in a similar way for most sets                                                                                                                         tors that influence this difference allow better utility of
of parameter values.                                                                                                                                                              it as an index.

114
   The above behaviors as well as many others are read-                          PRO,    to change in opposite directions. Figure 8 shows the
ily understood by using the graphical analysis. In addi-                         compaiison-mode        graphics that appear for the condi-
tion the graphical analysis has seemed to help the                               tions QT = 6.0 l/min and FS = 0.3 (designated as 1st)
students gain confidence in using the microcomputer                              and for the conditions OT = 3.0 l/min and Fs = 0. I
program, since they know they have a tool they can fall                          (designated as 2nd). This particular demonstration
back on to explain the results.                                                  generally stimulates the student to return to the
                                                                                 graphical analysis and block diagram to explain this
Microcomputer Analysis                                                           result and also drives home the point that a logical and
    The O2 model has been programmed on an Apple II                              orderly approach is necessary to understand the O2
 microcomputer       with graphics. The computer graphics                       transport system.
 plots PAo,,   Pa0,,   PVo,, and PACT, on the Y-axis. The                              The following are notes about the O2 transport com-
 user can choose the parameter             to be changed                        puter program. The program has been written in Apple-
 systematically on the X-axis and then either keep the                           soft BASIC and can be run on a 48-K Apple II system
 normal values for the other parameters or enter known                          with an Applesoft BASIC language card.
values. In this mode the effect of each parameter on the                              I) The disk operating system (DOS 3.3) has been pro-
 O2 transport variables can be examined. The graphics                           grammed so that when the computer is turned on, the
that appear on the screen in this mode are shown in Fig.                        system will automatically begin to run the O2 transport
7. In this example the effect of the parameter @r on the                        program. Thus, after turning the computer on, the user
O2 transport variables is shown.                                                needs only to follow the instructions on the screen.
    Another program choice is the comparison mode,                                    2) Acceptable ranges for parameter values have been
which allows examination         of the effect of a single                      programmed into the computer. If a parameter value is
parameter change and then the additional effects that                           entered that is not within the acceptable range, the pro-
may result from concqmitant parameter or variable                               gram will continue to ask for reentry of the parameter.
changes. For example, VO, increases when body temp-                                   3) The O2 transport system has been programmed to
erature increases, and VT and F are altered by arterial                         automatically scale the Y-axis so that maximal utiliza-
pH, Pco,, and PO,. Thus parameter and variable in-                              tion of the screen is obtained.
terdependence can be examined in the comparison mode                                  4) The O2 saturation curve used in this model is that
in a stepwise manner that facilitates the understanding                         of Gomez (1). The corrections for pH, temperature, and
of the effects of the initial disturbance and the physical                      PCO~are those used by Kelman (2). The equation used
changes or physiological responses that accompany it.                           to calculate PH,O from temperature is from Siegel (5).
The comparison mode has also been used to demon-                                      5) Since the original program was too long to run
strate to the students unusual system behavior. One ex-                         without erasing the graphics page of memory, a utility
ample is a change in conditions that causes Pao, and                            program was applied to the Applesoft BASIC program
                                                                                to reduce it in length. A listing of this reduced program
                                                                                is unreadable, since all of the internal documentation
  Figure 7                                                                      has been eliminated. A flowchart of the computer pro-
  Microcomputer graphics showing effect of cardiac output on O2
  transport variables.                                                          gram is given in Figs. Al and A2 of the Appendix. A
                115   t                                                         diskette copy, which includes the symbols table and
                110
                                                                                character generator (both in binary) and additional
                105
                                                                                documentation of the program, is available by sending a
        MM HG                                                                   blank diskette to Wesley M. Granger, Dept. of Physi-
                100   t     + . . . . . . . + . :I.*. * . . * t
                                                                                ology, Medical College of Georgia, Augusta, GA 30912.
                                                                                      In conclusion, this presentation is viewed as an
                                                                                elementary but fundamental teaching package for O2
                                                                                transport. The block diagram allows a logical and
                                                                                orderly examination of influences that act on one or
        MM
                                                                                more parts of the system. The graphical analysis pro-
                                                                                vides a visual operational tool to predict the magnitude
                            10       7.5          5.0       2.5                 and direction of these influences. The microcomputer
                                     QT    (L/M      IN)                        program with graphics facilitates the examination of the
  Figure 8                                                                      system and provides ready access to correct responses.
  Microcomputer       graphics in comparison               mode (see text for     This work was supported in part by National Institutes of Health
  explanation).                                                                 General Research Support Grant 2507-RR05365- 19.

                                                                  , P 2ND
                                                                                References
                                                                                  I. Gomez, D&l. Considerations of oxygen-hemoglobin equilibrium
                                                                                                                              200:
                                                                                in the physiological state. Am. J. HZJAS~OZ. 135-142, 1961.
                                                                                  2. Kelman, G.R. Digital computer subroutine for the conversion of
                                                                                oxygen tension into saturation. J. A@. Physiol. 21: 1375-1376, M6.
                                                                                  3. Nunn, J.F. Applied Respiratory     Physiology. Boston, MA: But-
                                                                                tersworths, 1978, p. 277-298.
                                                                                  4. Riley, R.L., and A. Cournand. Ideal alveolar air and the analysis
                                                                                of ventilation-perfusion relationships in the lungs. J. A&. Ph.Wol. 1:
                                                                                825,   1949.
                                                                                 5. Siegel, D. An improved program to calculate intrapulmonary
                                                                                shunting. Crit. Care Med. 7: 282-284,   1979.
                      0.2   0.4         0.6FIog.8                 1.0            6. West, J .B. Respiratory Physiology-     The Essentials. Baltimore,
                                                                                MD: Williams & Wilkins, 1979.

The Physiologist, Vol. 25, No. 2, 1982                                                                                                             115
                                                                                                                  BASED ON 1ST




                                                                                                                        I            4
                                        BLOAD                                                                 *

ASD CHARACTER 1                         BINARY                                                                 PLOT SCALE
GFSERATOR i-!RE 1                       PROGRAMS.                                                              AND FIRST AND
                                                                                                               LAST VARIABLE
                                                                                                               VALUES.
                                                                                                              c

                                                                                                                       v                                      ,                                        ,
                                                             EACH PARAMETER1                                                         .          CALCULATE
                                                                                                                    INCREMENT        ,,\       VARIABLES      ,+                    PLOT VARIABLE
                                                                                                                    X-AXIS                 '    FOR NEW VALUE                       VALUES.
                                                                                                                    PARAMETER                   OF X-AXIS                       .                      4
                                                                                                                                               b
                                                                                                                    VALUE.
                                                                                                              4                                                                           v




                                                                                                                                                     I           9                         I
                                                                                                                                               t
                                                                                                                                                   CONTINUE TO                      DISPLAY "PRESS
IGRAPHICS PAGE            i             ENTER
IDISPLAYED                1             GRAPHICS                                                                                           /       DISPLAY PLOT ,                   RETURN TO
  UNTIL PLOT IS           1                                                               ABNORMAL                                         '       UNTIL'RETURN'   .                CONTINUE" AT
                                                         /                      I                                                                  IS PRESSED.                      BOTTOM OF PLOT
[FINISHED.                1             MODE'           \                      \         VALUE FOR
                                                                                        PARAMETER
                                           \/                                       i



                                                                                                                                    SELECT PROGRAM OPTION:                                         1. DISPLAY GRAPH
                                                                                                         GO TO:A.               2                                                             1>     #FROM HIGH-RES
                                                                                                                            <   7, ' 1. REDRAW GRAPH.
                                                                                                         ABOVE.                      2. NEW GRAPH.                                                      MEMORY.
                                                                                                     I                               3. LIST PARAMETER VALUES.                                        .             1
1                         1       t                 1
                                                                                                                                     4. COMPARISON GRAPH.
                          I                                                                                                          5: EXIT PROGRAM.
ALSO LABELS                         DRAW X-AXIS,                                                                            ‘5,
                                                                                                                            \
WITH PARAMETER;                     Y-AXIS                                                                                      ,
SA.?:E AND VALUE1                 ! AND TICS.       I                                                                                             \,3.
----~~                                                                                                                              I\                              9

                                                                                                                                                      LIST VALUES
                                                                                                                                                      FOR ALL               I
                                                                                                                                                                        I             *
    ‘s’AI,L’E   DEPEND-       ’                                                                                                                       PARAMETERS.
    ISC       OS X-AXTS




                                      VARIABLES FOR                                                                                                                                       I                     I
                                      1ST AND LAST



                                                                                                           Figure Al
                                                                                                           Flowchart for first half of O2 transport computer program.
                                                                                                           RECALL
                                                                                                           VARIABLE
                                                                                                           VALUES FROM
                                                                                                      r-l  FIRST GRAPH



                                                                                                       SCALE Y-AXIS
                                                                                                       BASED ON BOT
                                                                                                       1ST AND LAST
                                                                                                       VALUES.
                                                                                                      I 1
                                                                                 1
                                                             ALSO PLOTS          I
                                                             FIRST AND LAST 1                          AND FIRST AND
                                       GRAPH                 \'AR IAKLE \'ALUEtj                       LAST VARIABLE
                                                             FRO?1    1S-I’     GRAPH.1




                                                                                                           PARAMETER
GRAPHICS PAGE
              I
DISPLAYED
LQTIL PLOT IS 'I
FISISHED.                               PAGE 2
                               ----     HIGH-RES
                                        GRAPHICS
n
                                                                                                                         1
                                                                                                       COSTINUE T O
                                      x                                                        \
                                                                                               '
                                                                                                       DISPLAY PLOT
                                                                                                       UNTIL'RETURN'
                                                                                                       IS PRESSED.


                                                                                                                                                           DETERMINE
                                                                                                                             LABEL GRAPHS                  POSITIONS
                                                                                                                             AS "1ST" AND      <   1       OF 1ST AND
                                                                                                                                                           2ND PLOTS.
                                                                                                                                                   l




                                                                                                                                   r

                                                             GO l-0                                                                 DISPLAY GRAPH
                                                                                                                             ' 1.                             1 T O FAR RIGHT
                                      INCREMENT    FOR       A. IS                             SELECT PROGRAM OPTION:          L >FROM HIGH-RES
                                                             FIGURE       Al.                   1. REDRAW GRAPH.                    MEMORY.
(,i,Et,,                                                 c                                      2. NEW GRAPH.                      6
1 FOR SECOND       SET     1                                                                    3, LIST PARAMETER VALUES.                              l
                                                                                   9
1 OF PARA?lETERS         , \                                                                    4. COMPARISON GRAPH.                   LIST ALL PAR-
                                                             GO T O                       4.    5. EXIT PROGRAM.                       AMETER VALUES'+
                                                             B. ABOVE.              +'




                                                                                               Figure A2
                                                                                               Flowchart      for second half of O2 transport          computer     program.

								
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