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					Add-on Mixing Chamber for
  Mechanical Ventilator




Team Members: Missy Haehn, Laura Sheehan,
       Ben Sprague, Andrea Zelisko

         Client: Matt O’Brien, RPT

        Advisor: Professor Webster

               May 5, 2004
Abstract:
        The metabolic rates of critically ill patients can vary drastically from typical metabolic rates.
This can cause problems for health care providers when determining the correct amount to feed the
patient. Matt O’Brien, RRT, performs metabolic tests on these critically ill patients to determine
their metabolic rate and food intake needs. This is done with indirect calorimetry, measuring the
concentration of oxygen of the inspired and exhaled air of the patient. In order to stabilize the
inspired oxygen level produced by the ventilator, our final design is an air mixing chamber placed
within the series of sir flow from the ventilator to the patient.

Problem Statement:
        To develop a mixing chamber to help stabilize oxygen percentage delivered from mechanical
ventilators to critically ill patients; this chamber would allow for increased accuracy of metabolic
measurements.

Background:
       Metabolism is defined as the amount of energy one uses throughout the course of a day (1).
The body’s metabolism is similar to a scale balance in that the calories fed to a person must equal
the amount of heat energy produced by the patient’s body (Figure 1).



                                                                  Figure 1: The balance of caloric
                                                                  intake and energy output (6).




         Contrary to popular belief, critically-ill patients receiving supplemental oxygen via a
mechanical ventilator “resting” in bed actually have a much greater metabolic rate than healthy
resting individuals (2). Due to the higher metabolic rate of a ventilated patient, a different caloric
intake needs to be calculated tailored to the patients needs. This is very important because of the
incidence of malnutrition among critically ill patients on mechanical ventilators (3). This
malnourishment can lead to lengthened hospital stays and unnecessary ventilator support (4). The
vital task of determining the caloric needs of a patient falls to the Pulmonary Respiratory Technician.
Calculating this need is done by a method called “indirect calorimetry.” According to The American
Association for Respiratory Care, metabolic measurements use indirect calorimetry “to reduce the
incidence of overfeeding and underfeeding and to decrease costs associated with total parenteral
nutrition (5).” Indirect calorimetry is performed by measuring the dimensionless respiratory
quotient, RQ, which is the CO2 produced divided by the O2 consumed (4). From this value, one can
determine if the patient is receiving too few or too many calories, because what someone eats affects
the level of CO2 production. For example, a patient consuming a diet consisting of primarily
carbohydrates produces a significantly higher amount of CO2 from metabolism. Because of this
high level of CO2, it is harder to maintain a sufficient level of ventilation and can result in either
respiratory failure or difficulty in weaning the patient from the ventilator due to a reduction in
respiratory muscle strength (2). Ideally, a reasonable adjustment in the patient’s diet is to reduce the


                                                                                                        2
carbohydrates and increase the lipids consumed, thus reducing the amount of CO2 produced by the
patient’s metabolism and making ventilation easier. The patient’s diet is modified accordingly and
metabolic measurements are repeated shortly afterward to determine the effectiveness of the new
nutritional regimen.
         The validity of the metabolic measurement can be assessed by looking to see if the RQ is
appropriate for the patient’s diet and if it is within the “normal” physiological range, this being 0.67
to 1.3 (5). Generally, overfeeding increases this value while underfeeding decreases it (3).
Occasionally, a technician finds him or herself with an RQ outside the “normal” range and must
determine why this unusual data is occurring. Recalling that RQ is the ratio of carbon dioxide
expired to oxygen inspired, one would expect to theoretically find the percent oxygen inspired by
the patient (also called the fractional inspirational oxygen or FIO2) equal to what percent oxygen the
ventilator is delivering. However, often the FIO2 value is inconsistent due to the varying
concentrations of oxygen delivered to a patient from breath to breath. This can be caused by one of
two factors: the mixing of the gasses or changes in gas pressure between one end to another
(pressure drops). Therefore, the FIO2 must be measured on a breath-to-breath basis during these
metabolic tests and the inconsistencies from gas concentration and pressure must be made as small
as possible in order to have appropriate RQ values. The Association of American Respiratory Care
states that this can be done by either a blender for high-pressure gas or “an inspiratory mixing
chamber between the ventilator main flow circuit and the humidifier (5).” Lastly, to ensure
complete understanding of how the testing of these metabolic measurements is performed, the set-
up of the hardware involved should be explained in more detail.
         The critically ill patient is breathing via a mechanical ventilator. This ventilator has two
scissors valves, which, from the percent oxygen entered by the technician or physician on the
ventilator display, calculate the respective amounts of air and oxygen to be mixed and subsequently
delivered to the patients. This mixture of gas leaves the mechanical ventilator and heads to the
humidifier device where it is heated and humidified. From the humidifier the gas travels down a
tube to the patient’s lungs. However, before it reaches the patient it enters a pneumotach during
metabolic measurements. The pneumotach is a device that determines the rate of flow of the gas.
In order to measure the FIO2, there is a gas sample line that constantly is sucking out a tiny amount
of the gas mixture to be delivered to the patient (figure 2). This gas sample is then analyzed on a
breath-by-breath basis by the metabolic measurement software (our client’s is made by
MedGraphics, Figure 3) and from this data, the RQ is determined and the necessary nutritional
adjustments can be made. The mixing chamber, which is recommended above to create a more
uniform gas mixture, would be placed between the ventilator and humidifier. The improvement
made from the addition of this chamber would be seen from the sample taken at the site of the
pneumotach and its analyzation. Theoretically, a more stable FIO2 should be found with the
addition of this mixing chamber.




                                                           Figure 2: Pneumotach and sample
                                                           line for analyzing gas (7).




                                                                                                       3
                                                                           Figure 3: Delivered
                                                                           Oxygen percentage
                                                                           measured when gas is
                                                                           just exiting the
                                                                           ventilator (Servo 300).
                                                                           FIO2 dialed in on
                                                                           ventilator was 52% (15)




Motivation:
        Our client, Matt O’Brien, is a Pulmonary Respiratory Technician at the UW Hospital who
performs metabolic measurements and is interested in having more accurate and reliable data in the
tests he performs. He believes that the inadequate mixing of oxygen and air could be to blame for
some inconsistent RQ measurements he has made. Thus, he has requested our team to design and
build him a small mixing chamber to sufficiently mix the gas in hopes for a more stable FIO2 value
and thus logical RQ data. This will aid in a more accurate nutritional assessment of mechanical
ventilator-dependent patients and help prevent over and underfeeding of these critically ill patients.

Client and Design Requirements:
         Our client has made a number of requests and requirements for the design of the mixing
chamber. The first and foremost requirement was an improved method of mixing the gas, resulting
in more stable FIO2 measurements. The chamber to be built is to be reduced in size from the
existing chamber he owned (dimensions: 15.9 x 5.1 x 8.3 cm). The inlet and outlet ports of the
new chamber must have an outer diameter of 22mm and inner diameter of 15mm in order to
adequately fit the tubes leaving the ventilator and entering the humidifier and maintain an airtight
seal. Another client requirement was for the chamber to be able to be sanitized yet maintain its
airtight seal. This is important because according to The American Association for Respiratory
Care, “connections used in the inspiratory limb of the circuit proximal to the humidifier should be
wiped clean between patients (4).” The chamber should be constructed of a transparent material,
most likely Plexiglas. Lastly, the device must be able to withstand use approximately once a week.

Design Alternatives:

Design #1:
        The objective of our new design is to create a better mixing environment for the air coming
out of the ventilator. Because air is a fluid, we can use fluid flow to model turbulence and to
calculate what dimensions we need for a prototype.



                                                                                                         4
        The Reynolds number is a dimensionless number that determines what type of flow is
present, either laminar or turbulent. Laminar flow can be described as organized and comprised of
streamlines; turbulent flow can be described as unidirectional. Using turbulent flow (or turbulence)
is one way to induce mixing within a container. Nonetheless, turbulence is not the same as mixing.
The ratio of inertia forces to viscous forces within the fluid is the factor that determines which type
of flow is present and is expressed by the following equation.

                                              R= ρVD/μ

In an open cylindrical container, if the number is less than 2000, then the flow is laminar. However,
if the number is above 4000 the flow is completely turbulent. Anything in between these two values
is a mixture of both laminar and turbulent flow (8). When calculating our Reynolds number using
the inlet size as the diameter for the equation, we obtained a Reynolds number of approximately
724. This was a clear indication that turbulence would not be created alone in the tube. We then
thought of inserting a grid inside a cylinder to create grid turbulence. According to Tim Shedd,
assistant professor of mechanical engineering at the University of Wisconsin - Madison, the
Reynolds number only needs to be between 10 and 100 to create turbulence with a grid. The
diameter used to calculate this number is the diameter of the grid rods because the separation
between the openings is what causes vortices to form in the space after the grid and therefore fuel
turbulence. After recalculating this number, we obtained a number of approximately 36. Grid
turbulence would be possible in our situation.
        The second alternative design would consequently be a cylindrical container with a grid
made up of cylindrical or square rods inserted inside the container (Figure 4).




                            Figure 4: Diagram of Alternative Design 1
When the gases from the ventilator are inserted into this device, the grid would allow the air to
become turbulent (Figure 5). According to William Easson, professor of fluid mechanics at the
University of Edinburgh, turbulence will be fully mixed about 30 to 50 diameters downstream of the
rod diameter in the design. Therefore, the length of the cylindrical container would need to equal
this in length.
         An advantage to this design alternative would be the simplicity of the device. It would be
fairly easy to manufacture and low in cost. As for cleaning the device, one of the ends of the
cylinder could be removable so that it could be sanitized, yet maintain an airtight seal.
         After initially speaking with Professor Chesler, assistant professor of biomedical engineering
at the University of Wisconsin – Madison, this design alternative seemed to be the simplest, most
direct way to mix the gases from the ventilator. Professor Chesler definitely supported the use
turbulence in order to fully mix the gases, but did not know if this was obtainable due to our design
constraints. However, after speaking with Professor Shedd and confirming grid turbulence, our
design would work. Using the cylinder alone would not be possible, but modifying this design by
adding a grid would create enough vortices to create turbulence and thus induce mixing. A


                                                                                                          5
                                                                              Figure 5: Grid
                                                                              Turbulence (10)




disadvantage of this design is that the mixing is completely dependent on the grid turbulence
created; there are no other forces mixing the air within this design. It is also known that any induced
turbulence will quickly die out. To account for this problem multiple grids can be inserted into the
cylinder, but in theory if the number of grids is infinitely increased a filter will result and pressure
drop will be a concern. However, the only actual way to determine the pressure drop would be to
test the design.

Alternative #2:
         During the research phase of our design, Mechanical Engineering Professors Jaal Ghandi
and Chris Ruthland were consulted. Due to their involvement in mixing gases for internal
combustion engines, they were able to provide useful background information.
         Jaal Ghandi provided a few things to consider. He said that there isn't any specific medium
that helps promote mixing, and there aren't any properties of gases that would be useful to focus on
in our design. He suggested focusing on the fluid mechanics and dimensional analysis areas instead.
Also, by optimizing hole sizes and possibly making them smaller, we could create uniform flow
through all of the holes. The design currently used isn't very effective, because a large proportion of
the gas is most likely going through the hole closest to the input port. Professor Ghandi
recommended that we take advantage of the small pressure difference between the entrance and exit
and create turbulence by logically placing holes, wall heights, etc. This would have the same effect
as having an electrically powered fan.
         After coming up with a few ideas, Chris Rutland was asked to provide some feedback. One
idea that he had was to make the gas flow over or under a barrier. This technique would help add
some turbulence. He also said that it's important to consider both the large and small scale. Having
large holes and small holes incorporated into the design would address large scale and small-scale
levels of mixing.
         This design’s prototype involves a setup similar to the design currently in use. A diagram of
the prototype with dimensions is shown in Figure 6. In order to create more mixing, the first
divider was made with a slit across the top and the bottom. This forces some the gas to rise and
some of it to sink. The next divider has large holes and is very similar to the dividers from the
original design. However, one major improvement has been made. A concern with the initial design
is that since the air flows in one side of the container, the gas flow isn't uniform throughout. More
gas was flowing through the holes closest to the input port than the holes on the opposite end of the
chamber. To combat this problem, the new divider has holes of increasing size. The holes closest


                                                                                                      6
to the input valve are smaller than the holes farther away. Ideally, after the gas goes through this
divider, the airflow should be uniform throughout the length of the container. The last divider has a
number of small holes. These small holes will help mix patches of air and oxygen that were not




                                                         Figure 6: Diagram of Alternative
                                                         Design 2




mixed well enough by the first two dividers. The divider with the large holes will break up big
patches of air and oxygen, and the divider with the small holes will repeat what the big screen did
but on a smaller scale. Therefore, the small holes break apart small patches of oxygen and air. Chris
Rutland suggested that using a screen instead of a divider with small holes might be more effective.
During the testing stage, we will test the prototype with the divider and then replace it by a screen to
compare the results. This will be easy to do, because the dividers and screen will slide in and out of
tracks on the side of the container.
        The advantages of this design are that it is simple, easy to clean, and deals with both large
scale and small scale mixing problems. However, there is no way of knowing how much better this
design will work than the previous one without testing it first. It is based on the suggestions of
professors in the field, but there is not any other information to currently support this design. Also,
the pressure drop across this design is going to be higher than the pressure drop against the current
product. This could potentially be an issue if the pressure drop is significantly more than the current
chamber.

Alternative #3:
        This design includes the use of three stationary turbines, oriented in opposite rotation
directions to the one preceding it (Figure 7). All three turbines will be mounted on a slender rod



                                                                                   Figure 7: Diagram of
                                                                                   Alternative Design 3




                                                                                                      7
running down the center of a section of clear plastic tubing. This tubing will be an alteration of a
screw-top plastic container, with a hole in each end for the inlet and outlet ports, and an airtight seal
surrounding the screw joint. The entire tubing length will be approximately 10cm with a diameter of
3cm. The slender center rod will be mounted within the container by attaching a three-branch
prong on either end that rests on the inside of the container to keep the rod centered. Each one of
these turbines will be approximately 2.5 cm in diameter and be spaced along the rod 3 cm apart.
Because these turbines will not be spinning, we don’t have to worry about bearings or the precise
position of the turbines within the tube. These turbines will be acting strictly as an obstacle to the
air flow, forcing it to travel in one direction as it passes the first turbine, in the other direction to
pass the other and then back in the first direction to pass the third.
        The advantages of this design are that it is rather simple, small, and because of its screw top,
it can be easily dismantled and the inside of the tubing, rod, and turbines clean easily. By using a
tube shape, this design minimizes the amount of glued joints where a potential leak could occur.
Keeping this in mind, using pre-made plastic products limits our own construction error in cutting
and forming the plastic that could lead to lower quality or reliability. Such a design with a long
slender shape would be very inconspicuous and would not get in the way of the technician.
        However, it is difficult to gauge the effectiveness of this design in mixing the gases
compared to the other designs until testing is done. In addition, it is unknown to what degree the
pneumotach oxygen analyzer can measure the mixing of the gases and how many obstacles are
necessary for consistent measurements from the analyzer.

Further Research:
        After our midsemester presentation, we contacted representatives at Mayo Clinic to receive
feedback based on our design prototype. We received lots of new suggestions, information, and
ideas. The three main categories discussed were volume, indirect measurement, and timing.
        One aspect emphasized by Kris Hammel, a respiratory therapy supervisor, involved the
possibility that leaks in the system were the cause of the fluctuations in the FIO2 value. Humidifiers
tend to cause leaks in the system, and it was suggested to test the setup without the humidifier inline.
To check for other leaks, we were instructed to examine the tubes, make sure the cuff is inflated,
and check to make sure the adapter is inline. Leaks also occur if medication is delivered through the
ventilator, heated-wire circuits are used, or the patient is on a chest tube. When leaks are present,
introducing a mixing chamber will make the patient feel a high need to pressurize his or her lungs,
deliver more flow, and magnify the leaks in the system. It is important to eliminate leaks in order to
keep an accurate measurement of volume.
        Determining the RQ is meant to be done through indirect metabolic measurements.
Introducing a mixing chamber increases the resistance in the system and alters the patient’s steady
state. Therefore, if the resistance is changed too much, the measurements won’t be accurate even if
the FIO2 value is stable. Minimizing the resistance across the mixing chamber will help maximum
the accuracy of the metabolic measurements. For this reason, a filter shouldn’t be used.
        The timing of the inhalation and exhalation is important in the functional modes of the
ventilator. When testing, this should be a consideration. The mixing chamber must not interfere
with any modes of the ventilator.
        A mixing chamber from an older metabolic chart was given to us by Kris Hammel from
Mayo Clinic. This type of design had been proven most effective for their purposes. It had an extra
chamber attached to it, because it was originally used for a different purpose. We cut the chamber
off and plugged the extra inlet holes in order to make testing on it feasible.




                                                                                                       8
Testing, Results and Decision of Final Design:
          As we developed our three preliminary designs, we discovered that testing each of them in
the ventilator circuit with the equipment and measurement tools that the client uses would be the
most reliable and effective way to evaluate them. In addition, we found that much of the
information that we had obtained about the ventilator circuit and behavior of gases during
ventilation was contradicted by the information we had obtained from the Mayo Clinic. For this
reason, we decided it would be a good idea to test all of the variables of the ventilator circuit to look
for sources of leaks or other factors that would lead to the inconsistent FIO2 values.
          Measurements for all of our testing were taken at the patient mouthpiece, calculating the
instantaneous flow, and oxygen and carbon dioxide percentages of the air in the mouthpiece. All of
these values were displayed in a graph over time, making it very easy to observe the deviation values
of the FIO2 from the actual percentage delivered.
          Over two separate days, we tested the variation of FIO2 values of two different ventilators,
the Servo300a and Servo i. We also tested several different modes of ventilation including, Volume
Control, Pressure Control, Pressure Regulated Volume Control (PRVC) and SIMV with Pressure
Support. The mixing abilities of each preliminary design as well as of the chamber obtained from
the Mayo Clinic were tested all under the same conditions as well in order to evaluate their
properties.
          All of these elements were tested using a mechanical lung that simulated the breathing
rhythm but did not absorb any oxygen. This made it much easier to evaluate the consistency of the
FIO2 values because the oxygen percentage was simply a flat line.
          We also tested the effect of the humidifier upon the ventilator circuit, testing without it, with
it in line but turned off and with it turned on. In order to test this component, we had to use a test
patient, one of our group members, because the test lung would not work well with the humidifier.
This presented new challenges because the patient was absorbing oxygen from each breath, making
the oxygen percentage vary between two ranges over time. For these tests, we evaluated the
consistency of the oxygen percentage by looking at the consistency of the two values of oxygen
percentage, before a breath and after a breath. This is the form that the information is in when it is
used for the metabolic tests.
          The results of all of our testing can be seen in Appendix B, organized by the focus of the
graphs. From these tests, we found that the newer ventilator, Servo i, expelled air with less variations
in the FIO2 than the Servo300a. The ventilation modes involving pressure control caused a greater
variation in FIO2. The mixing chamber obtained from the Mayo Clinic was most efficient in mixing
gases, producing air with fluctuations of only 0.1%. The client’s prototype mixing chamber, much
like our Design 2, was second most efficient, +-0.2% fluctuations. The grid and filter design was the
least effective of the design possibilities, allowing fluctuations of +-1.0%.
          It was presented by the Mayo Clinic that the humidifier might be a source of leaks in the
ventilator system. However, from our testing, we saw no real difference in the FIO2 fluctuations
whether the humidifier was in line, turned off or turned on. Also, we found that the position of the
mixing chamber within the line made no difference to the consistency of the FIO2.




                                                                                                          9
        From this data, we determined that the Mayo Clinic design incorporated the best
arrangement of obstacles and dimensions of the chamber. Also, the position of the chamber made
no difference to chamber’s effectiveness however should probably be placed after the humidifier as
it was suggested by the Mayo Clinic. Using this data, we were able to decide on the specifications




                             Figure 11: System Diagram of Final Design

and set up of our final design (Figure 11). The other information we have collected will be useful to
our client for creating the best environment for obtaining good data.

Final Design:
       From the extensive testing performed, the final design of the mixing chamber was based
upon the design of the mixing chamber given to us by the Mayo Clinic, which had a maze-like
construction with air path obstructions. The dimensions were scaled to one third of the original
chamber, 12.0 x 12.0 cm length and width, 2.0 cm deep, while the inlet/outlet ports sizes were
maintained (Figures 8,9). In theory, a scaled version of the original sized design should generate as




                                                                             Figure 8: Final mixing
                                                                             chamber dimensions.




                                                                                                      10
sufficient turbulence and provide as adequate mixing. Scaling down the mixing chamber also allows
for the client specification of reduced size to be met. The inlet and outlet ports were placed on
opposite faces of the mixing chamber to make the device more easily integrated in the patient-
ventilator circuit. The placement of the inlet and outlet ports also makes for a vertical placement of
the mixing chamber and vertical airflow within the chamber, a suggestion from the Mayo Clinic, to
improve mixing of the gasses.




                                                                          Figure 9: Photograph
                                                                          of Final Design




        Construction of the final design involved the use the following materials: Plexiglas, solvent,
caulk, hinge, and hooked loop catches. The Plexiglas was measured and cut to size using the band
saw and mill. Holes were drilled in the top and bottom of the chamber for the inlet and outlet
ports. Following this, solvent was applied with a dropper to glue and secure all the parts together,
creating an airtight seal between the chamber’s pieces. Solvent is a chemical solution that almost
“melts” the Plexiglas so that it fuses together with the adjoining piece. A layer of silicon along the
top of the chamber’s walls ensures an airtight seal between the walls and lid of the chamber. To
meet the client requirement of the chamber being easily sanitized, the lid was not permanently
attached to the rest of the chamber. Instead, a hinge was placed on one side with a hooked loop
catch (Figure 10) on the opposite side of the mixing chamber. The hinge was acquired from the tool
crib while the catch was a sample sent from Nielsen Sessions (18). The hinge would create an easy
opening, a less cumbersome chamber, and also maintain an airtight seal along one edge. The latch
would ensure that seals were maintained along the other edges.




                                                   Figure 10: Hooked loop catch
                                                   from Nielsen Sessions.



The total cost of the final design is relatively low. The hooked latch catches are $4.08 each (three
are necessary for each chamber) and the one hinge costs approximately $3.50. The Plexiglas needed
is available for about $22 for a 0.125'' x 24'' x 44'' sized piece while the cost of the rubber to line the
seal is unknown. Lastly, the solvent used is about $5 for a bottle, which can be used in the


                                                                                                         11
construction of at least four mixing chambers. Thus the total cost for the design materials is
approximately $20. The most expensive component of this device is not all the materials, but
instead the tedious labor necessary in the construction and assembly of each mixing chamber. Mass
production of this device would most likely further reduce the cost with the introduction of bulk
purchases and other less expensive materials.

Ethical Issues:
          Our design is created for the greater good of human patients. However, in order to reach
this stage where our design may be used on patients on a regular basis, human patients must be used
as test subjects for the prototype. Our design may be tested on healthy patients first, but in order to
obtain good, accurate data, critically ill patients must be used to test under actual conditions. This in
practice brings about many ethical concerns, one being the benefit to the patient weighed against the
risk. All these concerns must be outlined and submitted in a written form to the Health Sciences
Institutional Review Boards (19). The committee’s goal is to protect human patients while allowing
research to continue. They go about allowing this to occur by requiring a protocol to be written
before human testing may occur. This protocol must be very specific and must exactly relay all the
events that will occur as well as all the risks. However, even after writing a protocol, submitting it to
the board, and receiving approval, the ethical issues still remain. Due to the fact that we would need
to test critically ill patients, there is a concern of who can decide what the best option for the patient
is, if they themselves are unable to decide.

Future Work:
         As with all projects in life, there is always more that can be done, whether it be research or
testing, no project is complete. As in our case with our final design prototype, testing has yet to be
completed with our smaller 1/3 scale model of the Mayo mixing chamber with the client’s
equipment. In theory, we are led to believe that our smaller scale model will act in about the same
manner as the full version predecessor. However, variations in construction could cause
uncertainties within the new results.
         The main focus of our design project was to develop a mixing chamber that would improve
our client’s values being received from patients. However, another specification that was also
important to the client was that the chamber should be easily cleaned or sanitized. We dealt with
creating a hinge/latch system for this specification as described in the final design section of the
paper. However, more research needs to be completed in this area. For example, in our final design
set up, we have one hinge opposing one latch on the other side of the lid. Two additional latches
could be added around the other sides to ensure airtight seals for the entire chamber. Also, in our
setup, the latches are quite cumbersome and large due to our limited time and resources. This could
be improved upon to create smaller, more integrated latches. Right now we used caulk to create an
edge seal for the design prototype. In any future work, a thin layer of rubber would be smoother
and more level around the edges.
         Due to our limited resources and skills to manufacture our design prototype, we need to
look into having a company manufacture this design. The low cost of the design would allow for
multiple productions if an easily sanitized container (with a removable lid) couldn’t be constructed
without difficulty. Our client has already informed us that he does have a contact that would create
this device for him. However, along with construction comes the issue of patents and patent rights.
Our design is modeled directly off that of the Mayo Clinic’s. We would definitely have to contact
the Mayo Clinic and discuss such issues before proceeding in any direction.




                                                                                                       12
References:

1. Campbell, N.A., Reece, J.B. Biology. San Francisco: Benjamin Cummings. 2002.

2. Madama, Vincent C. Pulmonary Function Testing and Cardiopulmonary Stress Testing, Second
edition. Delmar Learning, 1997.

3. Harris, C.L. “Weaning With Indirect Calorimetry.” Clinical Window. 2003(12).

4. Disease Management with Gas Exchange. Medical Graphics Corporation. 2002.

5. “American Association of Respiratory Care Clinical Practice Guideline.” Respiratory Care Journal.
1994:39(12):1170-75.

6. The Hard Facts About Burning Calories (Metabolism). 17 Feb. 2004. LifeChek.
http://www.lifechek.com/HardFactsPage.php

7. MedGraphics Direct Connect preVent. 2 Feb. 2004. Medical Graphics Corporation.
http://216.122.201.195/datasheet_direct_connect.html

8. Smart Measurement. 2002. Fluid Mechanics: Overview [Online]
      http://www.efunda.com/formulae/smc_fluids/overview.cfm.

9. Shedd, Professor Timothy A. Personal Interview. 27 Feb. 2004.

10. Easson, William. 2001. Fluid Mechanics 4. [Online]
       http://www.eng.ed.ac.uk/~will/teaching/Fluids4/index.html.

11. Easson, William. “Re: Questions about a Biomedical Engineering Design.” E-mail to the
       author. 27 Feb. 2004.

12. Chesler, Professor Naomi. Personal Interview. 26 Feb. 2004.

13. Ghandhi, Professor Jaal B. Personal Interview. 6 February 2004.

14. Rutland, Professor Chris J. Personal Interview. 18 February 2004.

15. Servo 300/300a Ventilator Service Manual. Siemens Corp., Ventilation Modes Chapter.

16. Fox, Robert, Alan McDonald, Philip J. Pritchard. Introduction to Fluid Mechanics, Sixth
       Edition. Hoboken, New Jersey: John Wiley and Sons, Inc., 2000-2003.

17. Hammel, Kris. Personal Interview. 15 March 2004.

18. Nielsen Sessions – An Actuant Company. 2003. [Online]
       http://www.nielsensessions.com/index.asp.




                                                                                                   13
19. Fost, Norman MD. 2001. Health Sciences Institutional Review Boards [Online]
       www.medicine.wisc.edu/hsc.




                                                                                  14
Appendix A:
Mixing Chamber for Mechanical Ventilator
Team Members:       Andrea Zelisko
                    Ben Sprague
                    Laura Sheehan
                    Missy Haehn
May 4, 2004

Function: To develop a chamber to help stabilize oxygen percentage delivered from mechanical
ventilators to critically ill patients; the chamber would allow increased accuracy of metabolic
measurements.

Client Requirements:
     New method to mix the gas more efficiently and accurately
     Chamber reduced in size
     Chamber able to be cleaned and remain tightly sealed
     Be manufactured of a clear material

Design Requirements:

       1. Physical and Operational Characteristics
             a. Performance requirements: The device will be used during every ventilator
                study performed by our client, approximately once a week. It will be subjected
                to a pressure gradient and must be able to withstand a pressure drop of 600 Pa.
             b. Safety: The device should be able to be sanitized due to use on critically ill
                patients.
             c. Accuracy and Reliability: The device should provide uniform oxygen
                distribution to the patient every time it is used. It should have an airtight seal
                to prevent gas from leaking from the chamber and disturbing the accuracy of
                measurements. The resistance across the chamber should be minimized to
                ensure the patient’s steady state is maintained during testing.
             d. Operating Environment: The device will be used in a hospital environment
                by Respiratory Technicians. The device should be able to withstand pressure
                up to 600 Pa.
             e. Ergonomics: The device should be free of any sharp edges and be easily
                cleaned.
             f. Size: The device should be smaller than the current chamber, which measures
                15.9 x 5.1 x 8.3 cm. The inlet and outlet ports must have an outer diameter of
                22mm and inner diameter of 15mm.
             g. Materials: The device should be made from a clear material such as
                Plexiglas. Metal should not be used except in small quantities as in screws.
                Adhesives must provide an airtight seal.


       2. Production Characteristics



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      a. Quantity: Only one chamber is necessary, however additional models could
          serve as replacements if needed.
      b. Target Product Cost: Device should be able to be manufactured for under
          $100.
3. Miscellaneous
      a. Patient-related concerns: The chamber should be sanitized between patient
          uses.




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