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Breath Analysis as Technique in Clinical Chemistry

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					 CUN. CHEM. 20/8,     966-972(1974)




 Breath Analysis as a Technique in Clinical Chemistry

Kurt   M. Dubowskl

Breath possesses unique advantages as a specimen for                              body constituents,             metabolic       products,    and exogen-
clinical chemical analyses, including the continuous                              ously    introduced     compounds.
equilibrium of gases and volatile substances between                                This presentation    seeks to delineate    certain as-
expired alveolar air and the pulmonary blood circulation.                         pects of the current state-of-the-art  of breath analy-
Substances amenable to analysis in breath include 02,                             sis for substances       of clinical        significance    and to stim-
C02, CO, and other gases, volatile organic compounds,                             ulate further advances in this field by indicating                    like-
and many drugs with sufficiently high vapor pressures at
physiological temperatures. Practical aspects of breath                           ly avenues for developments.
sampling and breath analysis are discussed, exemplified                           Breath Analysis-General                    Considerations
by breath-alcohol analysis. The requirements for ob-
taining breath samples in equilibrium with the pulmonary                              Breath, as a physiological specimen for routine use,
blood circulation      are delineated, and experimental                   data    offers several unique advantages:         rapid, simple, non-
are presented for the significant breath-sample charac-                           traumatic   and frequently       repeatable     sampling; real-
teristics bearing on design of breath collection and stor-                        time functional     distribution      equilibrium       with the
age systems (end-expiratory temperature, breath vol-                              pulmonary circulation for many substances; potential
umes).                                                                            for rapid analyses with greatly simplified               primary
AddItional Keyphrases:     toxicology             #{149} alveolar   and   dead-
                                                                                  separation   steps, because the substances            of interest
space gas #{149} nalysis of volatiles
               a                                                                  are present   in the gaseous or vapor state; and capa-
                                                                                  bility for immediate       “field” analysis by portable,
    The adult lung is a most efficient boundary organ-                            bedside devices for many substances,              or for sample
as might be anticipated    from the presence of 3 X 108                           retention and subsequent         laboratory     analysis. There
alveoli with a total surface area of about 70 m2 in                               are also several inherent limitations:         only substances
contact with capillaries, pulmonary      blood flow con-                          capable of penetrating       the capillary-alveolar         mem-
sisting of the total cardiac output averaging about 6                             brane are present, often in low concentrations;             coop-
liters/mm,   and a mean daily respiratory      volume of                          eration is required from the patient for proper speci-
iO liters (1). It follows that the breath should faith-                           men collection (to an extent varying with the nature
fully reflect the body burden and the concentration                               of the required       breath      specimen);       precautions    may be
in the pulmonary   capillary circulation of those sub-                            required      to avoid sample       contamination      from extra-
stances that are capable of ready transfer across the                             neous sources such as eructation;              and sampling     and
alveolar-capillary   membrane.                                                    analytical esults
                                                                                                 r        forsome substances are potentially
    For many substances distribution     equilibrium     is, in                   affected by respiratory         disease or pulmonary insuffi-
fact, attained between the pulmonary circulation and                              ciency.
the alveolar air. While recognition of this fact has led                             A wide range of substances            of clinical significance
to widespread practical application     of breath analysis                        has been identified as present in breath, and practi-
to determination    of the plasma Pco2 and estimation                             cal methods         have been developed           for analysis of
of the blood-alcohol     concentration,   only occasional                         many such substances            in breath specimens.         Repre-
use has been made of breath as a specimen for other                               sentative      current schemes for a variety of breath
analyses. With the recent development        of a variety of                      analyses     (2-23) are listed in Table 1, and suggested
rapid and sensitive chemical detectors, it is now pos-                            applications      that are considered practical at present
sible to overcome the prior practical limitation of the                           are functionally grouped in Table 2.
low concentration     in breath of many substances           of                      Analysis of breath for alcohol, primarily to deter-
clinical interest. Hence, breath analysis could become                            mine the absence or presence of alcoholic influence in
the preferred procedure for analysis for many normal                              traffic-law enforcement,          is probably the most com-
                                                                                  mon application        of breath analysis and has attained a
                                                                                  high state of technical sophistication,            especially with
                                                                                  respect to the instrumental            detection and quantita-
   Departments    of Medicine,   Biochemistry    and Molecular Biology,
                                                                                  tion    of ethanol.    Table      3 itemizes       the major     methods
and Pathology,     College   of Medicine,     University  of Oklahoma,
Oklahoma City,    OkIa. 73190.                                                    that have been used for alcohol analysis                    in commer-
  Received May     8, 1974; accepted May 24, 1974.                                cially available instruments, to illustrate                 how various

966    CLINICAL     CHEMISTRY         Vol   20   No   R 1n74
       Table 1. Representative Current Breath                                  Table 2. Breath Analysis: Typical Applications
                  Analysis Schemes                                                            Clinical diagnosis
     Analytical   technique               Substance             Reference
                                                                                                 Acetone
  Chemical reaction +          Ethanol                              (2)                          Alcohols and volatile drugs
    photometry                                                                                   Carbon monoxide
  Gas chromatography           Acetone                 (3)                                       Respiratory           gases
                               Alcohols                (4)
                                                                                              Forensic      uses
                               Aldehydes               (5)
                               Anesthetics             (6)                                       Ethanol
                               Fattyacids              (7)                                       Volatile drugs
                               Hydrogen                (8)                                    Occupational          health monitoring
                               Mercaptans & sulfides (9)
                               Methane                                                           Carbon monoxide
                                                     (10)                                        Halogenated             hydrocarbons
  Gasometry                    Carbon dioxide        (11)
                                                                                              Physiological         and metabolic studies
  Infrared absorpti.           Acetone                             (12)
                               Anesthetics                         (13)                          Aldehydes
    ometry
                               Carbon dioxide                      (14)                          Ammonia
                               Carbon monoxide                     (15)                          Hydrogen
                               Ethanol                             (16)                          Ketones
                               Solvents                            (17)                          Mercaptans
                                                                                                 Methane
  Mass spectrometry            Anesthetics                        (18)
                                                                                                 Respiratory           gases
                               Respiratory      gases             (19)
                                    l
                               Volati es                          (20)                        Therapeutic          monitoring
  Solid-state     sensing                                                                        Acetone
    Catalytic     oxidation    Ethanol                            (21)                           Volatile anesthetics
    Fuel cell                  Ethanol                            (22)                           Volatile drugs
    Metal oxidesemi-           Ethanol                            (23)
       conductor
                                                                              Table 3. Principal Analytical Methods Used for
                                                                                       Breath-Alcohol Determination
                                                                                                                                    Typical
                                                                                              Method                              instrument          Reference

                                                                              Chemical reaction+                            Drunkometer                      (24)
                                                                                visual endpoint detection
analytical   approaches     can be applied to detection                       Chemical reaction+                            Breathalyzer                      (2)
and quantitation     of a single compound of interest in                        photometry
breath. The methods are listed in chronological order                         Column chromatography                         Hermes                       (25)
of appearance         during   the past      40 years,   with     the six     Gas chromatography                            GC Intoximeter               (26)
most recent having been utilized only within the past                         Infrared    photometry                        Intoxilyzer                  (16)
five years. In several automated             breath-alcohol       in-         Electrochemical      oxidation                Alco.Limiter                 (27)
struments     (28-30), manual manipulations             have been             Catalytic oxidation                           H.A.L.T.                     (21)
virtually eliminated       and the results are obtained by                    Solid.state    (MOS) sensing                  A. L. E. R .1.               (23)
mechanized,      internally-controlled       sequential      opera-           Fuel.cell sensing                             Alco.Sensor                  (22)
tions. It has been possible recently to develop several
highly reliable, sophisticated,        yet moderately        priced
breath-alcohol      devices. Table 4 lists various ad-
vanced features of current commercial                 devices for           tention   of whole-breath                specimens       or of breath             com-
breath-alcohol     analysis. Although not all of these fea-                 ponents    are listed         in Table        5. These        clearly      fall into
tures are found in any single current production                  in-       two principal       categories:                         storage
                                                                                                                     (a) Direct temporary
strument,    they do illustrate the degree of success al-                   of whole-breath            (in collapsible            laminat-
                                                                                                                                polymeric        or
ready attained        in dedicated       instrumentation         for        ed containers, gas pipettes and syringes, vacuum can-
breath analysis in a cost range of $1000-$3000              (31). It        nisters, or indium capsules), and (b) separation             and
deserves mention that these developments                  occurred          retention   by physical or chemical means (condensa-
for an application       with demanding         special require-            tion, adsorption,    or adsorption      on suitable columns
ments, including intended use by nontechnical                   per-        or in appropriate     liquid reagents) of selected breath
sonnel, in nonlaboratory          environments,        and under            components     of interest. For the latter category, it is
the probative value constraints         of forensic sciences.               necessary to measure or fix the breath volume from
   It is often necessary or desirable to collect breath                     which the desired component          is removed and stored.
specimens or selected breath components                 for subse-          This can readily be accomplished          with a field collec-
quent analysis in a different location, or for retention                    tion apparatus     (41, 45) combined       with suitable ab-
for various purposes. Many procedures have been de-                         sorption or adsorption       columns or by modifications
veloped for this purpose, and typical systems for re-                       of the indium encapsulation       technique (26).

                                                                                              CLINICAL       CHEMISTRY.          Vol.
                                                                                                                                    20.      No.8.    1974          967
                                                                                             sidered to consist of physiological                       dead-space        gas and
      Table 4. Typical Features of Current Devices                                           alveolar gas. In subjects without                         respiratory       disease
               for Breath-Alcohol Analysis
                                                                                             or pulmonary    dysfunction,      the composition     of the ex-
          End-expiratory
        #{149}             breath sampling                                                   pired air is, therefore,     approximately      constant    after
                    by
        #{149}Analysis GC, IR, or solid-state sensing                                        the dead-space     gas has been expelled, reflecting the
          Direct
        #{149} digital concentration     readout and                                         alveolar-air   phase of expiration (the so-called”alveo-
            resultprintout                                                                   lar plateau”).   The practical problem is how to know
          Rapid
        #{149} results (5-15 s) and short turn-                                              when         this    has occurred          during       any single       expiration
            around time (30-60 s)                                                            or how to arrange                 matters           so that    breath-specimen
          Direct
        #{149} or stored-specimen      analysis capability                                   collection occurs only after                         all physiological           dead-
          Portable, self-contained,
        #{149}                        hand-held devices                                      space gas has been discarded.                         It is impossible          consis-
                                                                                             tently       to obtain     expired          alveolar     air by collecting             the
       Table 5. Typical Schemes for Collection and                                           breath        remaining         after     discard      of any fixed      volume         of
             Storage of Breath Specimens or                                                  dead-space    air. However, four different schemes can
                   Breath Components                                                         provide practical means for determining     when the al-
        Device    or procedure                      Application           Reference
                                                                                             veolar plateau has been reached during a continuous
         container
Metal-Foil                                  Alcohol                             (32)
                                                                                             expiration,  or for securing breath specimens   that are
Rubberized             “Douglas”            Respiratory        gases            (33)         essentially          alveolar          or equivalent          to alveolar        air    in
  bag                                                                                        composition:
Polymeric         film bag                  Metabolic       products            (34)                  The expiration
                                                                                                 #{149}                             can be monitored           with a rapidly
                                            Alcohol                             (35)         responding     analysis    device   sensitive      to a suitable
                                            Halogenated                         (36)         breath    component     (e.g., carbon      dioxide     or oxygen)
                                              hydrocarbons
                                                                                             until breath     composition      becomes       essentially    con-
Condensation             of volatiles       Methanol                            (37)         stant, or the rate of composition          change approaches
                                           Volatile    fatty      acids          (7)         zero.
Glass gas pipette                          Carbon monoxide                      (38)               A phenomenon        that is known         to have a time
                                           Alcohol                              (39)         course that parallels      changes    in breath      composition
                                           Trichloroethylene                    (40)         (e.g., breath temperature)       can similarly      be monitored
Column       adsorption          on                                                          with rapidly           responding          instrumentation.
  Activated          charcoal              Volatilecompounds                    (20)            e A small or moderate                     breath volume (e.g., 250 ml
  Ascarite                                 Carbon dioxide                       (24)         or less) can be collected                   at or near the end of a pro-
  Calcium chloride                         Alcohol
                                                                                p42)         longed, uninterrupted       full expiration,      by means of a
  Magnesium             perchlorate         Alcohol
  Silica gel                                Alcohol
                                                                                (43)         device that traps an end-expiratory          specimen.
                                                                                                e A small    or moderate       breath   volume     can be ex-
Indium encapsulation                       Alcohol
                                                                                (26)         haled into a suitable      collapsible     container,    and in-
Vacuum container                           Alcohol                              (44)         spired         and     expired          several       times     until    this      “re-
                                                                                             breathed   air” has attained       a composition identical    or
                                                                                             equivalent   to alveolar air, with respect to the compo-
                                                                                             nent of interest.
Breath Sampling                                                                                 In the practical      application    of such breath     sam-
   Proper         breath sampling is fundamental      to all ap-                             pling schemes,      consideration      must be given to the
plications        of breath analysis, but this aspect of breath                              presence   of water vapor in breath specimens,          and to
analysis         has    often      been    neglected        as attention               has   breath temperature,    volume, and pressure   factors.
been focused on the detection and quantitation              of a                             Experimental   data bearing on design and use of such
component      in the sample.        Theoretically,     several                              breath       sampling      systems          follow.
types of expired breath specimens            are suitable for
chemical analysis: expired alveolar air, end-tidal air,                                      Materials and Methods
end-expiratory     air, and re-breathed       air. Mixed ex-                                    Studies were          conducted         on healthy        volunteer
pired air is generally    not suitable   for breath-compo-                                   human subjects         (40     age 21-50 years; 15 9, age 23-
                                                                                                                                ,


nent      analysis       inasmuch         as it contains           variable       pro-       46 years) by methods            previously       described     (46) for
portions         of alveolar       air and of dead-space                air, which           measurement        of breath volumes and temperature.
does not reflect           the body        burden      or pulmonary             blood           Composition        of expired       air in each expiration           of
contents of respired compounds     because a consider-                                       healthy    subjects     was measured          by continuous       mass-
able part of the inspired air comes to rest in the con-                                      spectrometric        analysis,      in the single-breath             test
ducting air passages and does not participate     in (al-                                    mode, with a Model 1100 Medical Gas Analyzer                       (Per-
veolar) gaseous exchange. For the same reason, CO2                                           kin-Elmer       Corp.,      Medical       Instruments,        Pomona,
measurements              cannot        be used     to determine          the     pro-       Calif. 91767). The CO2 and 02 content                  of the expired
portion      of alveolar         air in a mixed expired                air sample            air at constant        breath    flow rates were recorded,              in
(31).                                                                                        percent    by volume, against time.
   In highly simplified                 terms, an expirate            may be con-               Carbon     dioxide content         of expired     breath was de-

968      CLINICAL        CHEMISTRY.        Vol. 20. No.8,      1974
termined   in physiological    samples     (at body tempera-
ture, without    removal of water vapor) and under am-
bient conditions1      by nondispersive       infrared       absorb-
ance measurement        with a Model KK146 Godart Cap-
nograph     (Instrumentation        Associates,        Inc.,     New
York, N. Y. 10023). The capnograph    response for
each complete expiration was recorded on a Model
194     10-inch      potentiometric           strip-chart         recorder
(Honeywell, Inc., Ft. Washington,     Pa. 19034). After a
period of resting-state   normal  respiration,    the non-
fasting, standing subjects performed a maximum ex-
halation following a normal inspiration.       The breath
CO2 was monitored,       using a by-pass mouthpiece,
with the flow-through          cell of the capnograph    (0.44-ml
sample-cell   volume,       2 liters/mm    flow-rate, 80 ms full-
scale response).
                                                                                Fig. 1. Single-breath mass spectrometric expirogram ob-
Results                                                                         tained with a Model 1100 Perkin-Elmer Medical Gas Analyzer
                                                                                Upper and lower curves show the breath 02 and CO2 content, respectively.
   Key characteristics       of the principal          method      we           (in vol per 100 volumes) during a single continuous full expiration at constant
                                                                                breath-flow rate
used in these studies,         including     their precision        in
nonbiological     reference   systems,    have been previous-
ly reported    by us (46).
   Table 6 summarizes         the breath       temperature       and
breath volume data. All temperatures              shown were re-                                                        H
                                                                                                          C-.)

corded at the end of an expiratory           vital-capacity     ma-
neuver2     and are, therefore,     end-expiratory        tempera-
                                                                                                                 20
tures. The breath volume data consist                of the maxi-                                                25
mum expiratory          volume        measured      by an expiratory                                      3o          -_I
forced vital capacity         maneuver2        in standing       subjects,                                       35
                                                                                                                  6
and of the maximum             expiratory        volume in the same
subjects    after a normal          inhalation.       Volumes       shown                                         5
are for breath        at physiological          temperature,        essen-
                                                                                                                  4
tially saturated        with water vapor,             and at ambient
barometric      pressure.                                                                                         3
    A typical single-breath          mass-spectrometric            expiro-
gram for CO2 and 02 is shown in Figure 1.
    Figure 2 illustrates        a typical simultaneous             in vivo
recording     of expiratory        temperature          and expiratory
CO2 during a single continuous               full expiration        after a                                       0   ----1
normal inhalation.          The same simultaneous               measure-                                                                       II

ments for an in vitro system are shown in Figure 3, il-                                                                     0           5      10          5
                                                                                                                                TIME,       SECONDS
lustrating    the thermistor        response       to a nearly instan-
taneous    transfer     from a 23.3 #{176}C 34.5 #{176}C
                                              to a                medium        Fig. 2. Typical simultaneous in vivo recording of breath tem-
                                                                                perature and CO2 during a single continuous full expiration
and capnograph            response      to nearly        instantaneous
                                                                                after a normal inhalation, demonstrating the simultaneous al-
change in gas flow from C02-free                 air to medical gas of          veolar plateau indication by both procedures
nominal     5.3% (by vol) CO2 content flowing at 2 liters!
mm.                                                                             ability    found          in the human                      subjects                studies        is, thus,
                                                                                not   attributable               to the         methods             of measurement.
Discussion
                                                                                    The basic breath-sample            characteristics         shown in
   The several       methods      used in this study have good                  Table 6 are of considerable            practical     significance       for
precision,    as previously        reported      (46),      and   the   van-    breath    sampling     and breath-storage           procedures.         In-
                                                                                formation      regarding        the temperature            of expired
  ‘The ambient barometric pressure over the duration of these
measurements  varied from 979 X 10 to 987 X 102 Pa (734.7 to                    breath    is required      to determine        the minimum            con-
740.7 Torr) (corrected  for temperature   and gravity) and room          tem-   stant temperature        at which breath collection,             storage,
peratures  varied between    24.0 and 24.2 OC. The instruments           were   and rebreathing       devices must be kept in order to pre-
frequently recalibrated, at ambient conditions, at the time breath
samples were analyzed.                                                          vent condensation           of water vapor and consequent
   2Vjtal capacity (VC) is the volume of air that can be expelled               loss of condensable          or water-soluble         breath      compo-
during a maximal     expiration after a maximum      inspiration;   Forced      nents, and to apply appropriate               Charles’      law correc-
vital capacity   (FVC) is the VC maneuver      performed       with expira-
tion as forceful    and rapid as possible.   In normal subjects,         VC
                                                                                tions to the breath volumes for calibration                  and analy-
equals FVC.                                                                     sis. This information         is also of significance        in applica-

                                                                                                     (I    IMICAI                AITPV              C-fM       00             P   1074    QQ
                          Table 6. Human Breath Characteristics: End-Expiratory Temperatures,
                                     Measured at the Mouth, and Expiratory Volumes
                                                                                                                                            Maximum      exhalation after
                                                 End-expiratory   temperature,     C       Forced    vital    capacity,     ml                normal    inhalation, ml

      Subjects                n                         Range              Mean              Range                    Mean                    Range               Mean

    Men                       40                 32.41-35.57               34.48          2245-6550                       4502              1180-4550              2951
    Women                     15                 33.53-35.69               34.68          1825-3200                       2800              1420-3000              2141
    Total                     55                 32.41-35.69               34.53          1825-6550                       4038              1180-4550             2730



                                                                                       attained, presumably  indicative of the alveolar pla-
                                                                                       teau. Any portion of the remaining breath will have
                                                                                       essentially           the same        composition         and can be used for
                                                                                       breath analysis. From the data in Table 6, a mean
                                                                                       breath volume of 2690 ml must be discarded before
                                                                                       sampling to obtain a substantially expired alveolar
                                                                                       air sample  in forced                     vital capacity sampling; and a
                        35                                                             mean breath    volume                     of 1818 ml must be discarded
                         6-                                                            for the same result in sampling a maximum exhala-
                                                                                       tion after normal inspiration.       These data demon-
                         5                                                             strate that an earlier accepted authoritative        state-
                                                                                       ment that “an expiration       of 400 cc will completely
                         4
                                                                                       wash out the respiratory dead space of a normal rest-
                         3                                                             ing adult, which is estimated     as 125 to 200 cc. There-
                                                                                       fore, in such persons all the air expired after the first
                         2                                                             400 cc is alveolar  air” (47) is quite incorrect and mis-
                                                                                       leading. The data in Table 6 show clearly that no sin-
                                                                                       gle fixed volume discard can assure collection of ex-
                         0                                                             pired    alveolar  breath,    and even end-expiratory
                                                    I       I                          breath collection   schemes     thus require either knowl-
                                   0       5       10       15                         edge of the subject’s    actual expiratory    volume at the
                                       TIME, SECONDS                                   time of sampling      or arrangements      to retain the ut-
Fig. 3. Typical simultaneous recording of temperature and                              most terminal   portion of an uninterrupted                                  expira-
CO2 for an In vitro system. illustrating the rapid response to                         tion.
essentially      Instantaneous         changes    In the measured      variables          We had observed that the rise in breath                                tempera-
                                                                                       ture, measured      with rapidly-responding          instruments,
tion of partition data between blood and breath for                                    approximately      paralleled    the rise in CO2 content          (or
volatile substances,   such as the alcohols or anesthet-                               alcohol content      after alcohol      intake)    of the breath
ics, to the estimation   of blood concentrations (or par-                              during   continuous       full expiration.      As illustrated     in
tial pressures)         of such compounds       from their breath                      Figure 2, which is typical of the findings,              both, end-
concentrations          (or partial pressures).    The end-expir-                      expiratory            temperature            and end-expiratory             CO2 at-
atory air commonly used for breath analysis can be                                     tain their respective                 alveolar plateaus    at or near the
expected to have a significantly    lower vapor pressure                               same time. Figure                    3 illustrates  performance     of the
of volatile compounds at a mean temperature          of 34.5                           same temperature    and CO2 sensors     in tracking
#{176}C the air in the alveoli at 37.5 #{176}C. vapor
     than                                     These                                    abrupt changes in an in vitro system. The rapid rise
pressures will also fluctuate somewhat with changes                                    to the respective             final values indicates that                the slower
in deep body temperature        and in breath     pressure,                            responses   shown              in Figure 2 are the result                of biologi-
and as a result of other factors. In vitro air/blood par-                              cal phenomena     rather than of instrumental  artefacts.
tition data thus may not be useful for various theo-                                   The slightly slower initial increase in the breath tem-
retical calculations  of blood concentrations     or vapor                             perature,   compared with the time-course     of C02, is
tensions from results of breath analysis.                                              probably    largely attributable to the differences                            in re-
    The typical single-breath     expirogram     shown in                              sponse   time of the respective     sensors.   The                           capno-
Figure 1 demonstrates    that constant breath composi-                                 graph has a response time of 80 ms full-scale                                (in the
tion with respect to CO2 and 02 is attained at about 6                                 0-10% by vol range), while the time constant3                                 of the
s during  a continuous       expiration      period of 9.2 s, or                       thermolinear              probe,          designed       for air      temperature
after 65% of the total breath has been exhaled, as-                                    measurements,               is given       as 600 ms.
suming a constant     breath flow rate during the expira-
tion. This consistent      finding     indicates   that at least
                                                                                             Time constant,”     the standard     measure of temperature-probe
two-thirds         of the total expiratory volume must be                              response   time, is the time required     for a probe to indicate 63% of a
discarded         before constant breath concentrations are                            newly impressed     temperature    change.
        It thus appears feasible to use breath-temperature                          mass spectrometry      has been shown capable of simple
     measurement      by means of rapidly responding     device                     and rapid qualitative       and quantitative    analysis of
     to indicate     when the alveolar plateau       has been                       ethanol and other low-molecular-weight          compounds
     reached and the sample for breath analysis should be                           (50), with quantitation     accuracy of better than ±5%,
     taken. The regular and predictable        nature of the                        ample for many biomedical applications.        In a prelim-
     breath-temperature-time      curve would       allow, by                       inary feasibility study, Green (51) demonstrated        that
    means        of relatively         simple     electronic    circuitry,   the    a mass spectrometer       coupled to multi-stage    Liewel-
    rate of temperature    change                 or a function      thereof   to   lyn-Arnold   separators                  as the enrichment         device
    trigger valving for automated                   collection    of end-expir-     could be used to detect                diethyl ether, dimethylsulfox-
    atory, substantially   alveolar   breath  samples without                       ide, ethanol,          and methylparafynol                         in breath           after in-
    knowledge    of the available   breath   volume and inde-                       troduction    into the body of small quantities.   It was
    pendent of technician      judgment     or skill or of com-                     also possible     to identify and quantitate  many other
    plete subject cooperation.     A coincident end-expirato-                       common           drugs           (cannabinoids,                          chlorpromazine,
    ry breath temperature        indication    could be used, if de-                methamphetamine,                  opiates) in air at jig/liter or ng/
    sired, to signal the possibility         of undetected        abnor-            liter concentrations.                It has now been repeatedly
    malities   in deep-body     temperature       that might impair                 shown     that     drugs         and their               metabolites                 and other
    or vitiate the validity of an instrument            calibration     or          physiologically      important        compounds        can be identi-
    result conversion     dependent       on biological    factors.                 fied and quantitated               in nanogram          quantities        in
       Once proper sampling is achieved, attention         can                      microliter      samples      of such specimens             as plasma,
    again be directed to advances in recognition, identifi-                         urine, breast milk, and amniotic fluid (52, 53). Such
    cation, and quantitation    of breath components.     Sys-                      quantities     of many compounds             are likely to be pres-
    tematic observations    on exhalation of drugs were first                       ent in breath after therapeutic              intake or from meta-
    recorded by Cushny (48) in 1910, but the field has                              bolic sources.      Breath      therefore      becomes     a practical
    been largely neglected since. The respiratory     tract is                      specimen      for a large number          of substances       of clinical
    a major entry route into the body for gases and va-                             interest,   probably       including       most compounds            with
    pors, and it seems reasonable   to consider that this                           melting points to 75 #{176}C      or boiling points to 250 #{176}C,      as
    transport  is reversible for many   more substances                             well as sublimating          compounds.          Such drugs as the
    than      so far shown.           High      orders   of sensitivity      and,   amphetamines,         chloral hydrate,         ethchlorvynol,        glyc-
    often,     specificity       are required        for analysis      in breath    eryl trinitrate, and methadone   should be readily de-
    of those substances               only present       in trace quantities.       tectible in breath, and recent developments     in sim-
    Stewart    et al [e.g., Stewart          and Erley       (17)] have             plified mass spectrometry     and mass fragmentogra-
    shown that      infrared    analysis    of breath     with cells of             phy for drug analysis     in biological samples                                        (54,     55)
    long pathlength       can be used effectively        to detect hal-             should significantly  advance these studies.
    ogenated     hydrocarbons,         alcohols,    ethers,     ketones,               It also seems probable                 that solid-state                      devices such
    and gases, and this technique           can undoubtedly        be re-           as the Taguchi     gas-sensor,     now used successfully      for
    fined and extended           with modern        instrumentation.                breath-alcohol    screening    tests (56), will soon be made
    Gas chromatography           is an inherently        useful proce-              more specific,   to complement        their present   rapidity
    dure for analysis        of many organic         compounds        and           of response    and high sensitivity,       and thus become
    could well become universally usable for analysis in                            useful for many additional  breath analysis applica-
    breath of compounds   in ng/liter concentrations  by                            tions. Because of their rapid response,    both mass
#{149} of enrichment
    use                     or concentrating       techniques    based              spectrometry  and these sensors, as well as infrared
-  on physical      adsorption,      molecular     sieving, or easily               absorbance         measurement                     for     certain              compounds,
   reversible    chemical     reactions.    Zlatkis et al. (49) have                lend    themselves           well to real-time                       dynamic             breath
   recently   reported     use of a new porous polymer          adsor-              measurements.             Peak-holding               techniques                 can then         be
    bent, Tenax      GC, which efficiently          adsorbs   and de-               used to sense attainment     of the alveolar plateau by
   sorbs a large number          of volatile organic compounds.                     following the breath concentration      of the measured
   This adsorbent       has been used for air and breath sam-                       compound    and to indicate its alveolar plateau con-
    pling     with   an   adsorbent       trap    that   is subsequently      in-   centration.
    serted    directly      into a gas-chromatograph               injector            Breath analysis is a clinical chemical technique of
    inlet for desorption           and analysis.       Such a system                great merit and exceptional potential.
    could facilitate       breath    analysis    for volatiles      regard-            Supported   in part by Grant No. GM 16211 from NIGMS,         NIH,
    less of their original concentration,           by repetitive      sam-         USPSH;     by Grant No. DA-00402   from NIDA, ADAMHA,      USPHS;
    pling of fixed volumes            of end-expiratory         breath      to      by the Special Action Office for Drug Abuse Prevention,   EOP; and
                                                                                    by the U. S. Dept. of Transportation    and the Insurance  Institute
    the extent      required.     Demonstration        of reproducible              for Highway Safety.
    patterns    in particular      metabolic     abberrations        or d.is-
    ease states      could then permit         useful application           of      References
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