Patent Publication Number: US-9897590-B2

Title: Breath capture and sampling system

Description:
BACKGROUND 
     Exhaled human breath typically comprises approximately 78% nitrogen, 15-18% oxygen, and 4-6% carbon dioxide. The remaining small fraction of exhaled breath generally consists of saturated water vapor and trace levels of more than 1000 volatile organic compounds (VOCs) with concentrations ranging from parts per trillion (pptv) to parts per million (ppmv). 
     The specific composition of a person&#39;s breath can indicate various health conditions. For example, acetone is a VOC in exhaled human breath that can indicate diabetes, heart disease, epilepsy, and other conditions. A person who is in a state of ketosis will have an increased breath concentration of acetone resulting from the body&#39;s production of ketone bodies. Acetone is also produced by ketosis resulting from a restricted calorie weight loss and/or exercise program. This acetone production is the result of metabolism of fat. Hence, a breath acetone content measurement can be used as an indication of a medical condition or of fat burning during a diet and/or program to show the effectiveness of the program. 
     Sensors such as those for detecting acetone in breath samples can be particularly sensitive to the manner in which the sensor is exposed to the sample being tested. While repeatable and accurate results can be obtained in a lab setting by exposing the sensors to a sample in a controlled manner, it is often desirable to analyze a breath sample outside of a lab setting. 
     Consumer devices and/or portable devices for testing breath samples are typically used outside of a controlled laboratory setting. Such devices generally take a live breath sample and expose the sensor directly to the exhaled human breath, resulting in readings that are neither repeatable nor accurate. Collecting live breath samples, particularly from multiple subjects, causes factors to vary that can otherwise be held relatively constant in the lab gas setup described above. These factors include velocity of exhaled breath, dynamic vapor pressure, duration of exhalation, total volume and individual size of exhaled droplets, and variable oxygen and acetone concentrations that are dependent on which part of the exhaled breath is sampled from (i.e. mouth air, deep lung air, or somewhere in between). Collectively and individually, these variables contribute to poor repeatability and inaccurate measurements. 
     Known sensors also suffer from designs that inhibit accuracy and repeatability, even when exposed to a controlled, consistent flow of a breath sample. One example of a known acetone sensor  600 , shown in  FIG. 18 , includes tungsten trioxide (WO 3 ) disposed on an alumina or anodic aluminum oxide (AAO) substrate. This and similar sensors have typically been packaged in cylindrical leaded components, such as a standard TO-5 header  602 , like the one shown in  FIG. 16 . While TO-5 and similar headers are readily available, they are expensive, even at high manufacturing volumes. In addition, gas sensors housed in a TO type header are typically exposed to an air sample via diffusion, either through a mesh screen  604  or a hole in the case. As a result, such sensors are typically not well-suited for applications involving a sample having a controlled mass flow. 
     Acetone sensors are useful for detecting various health conditions and/or for monitoring the efficacy of diet and exercise programs. The acetone level for diet and exercise is lower than that caused by diabetes. Accordingly, a more sensitive, accurate, and repeatable sensor is required in order to monitor increased acetone levels caused by diet and exercise. 
     The present disclosure is directed to a breath capture and sampling system that captures a breath sample and provides it to a sensor in a manner that produces accurate and repeatable detection of various breath components. Although the described embodiment is directed toward the detection of acetone in a breath sample, it will be appreciated that alternate embodiments are possible wherein other sample components are sensed, and such embodiments should be considered within the scope of the present disclosure. 
     SUMMARY 
     A first exemplary embodiment of a disclosed device for capturing a breath sample has a mouthpiece with a chamber that receives a breath sample through a breath inlet aperture. The device further includes a pump that withdraws a portion of the breath sample from the chamber and discharges the portion of the breath sample to the sensor. 
     A second exemplary embodiment of a disclosed device for capturing a breath sample includes a mouthpiece with a breath inlet aperture in fluid communication with a chamber. A pump assembly delivers a breath sample from the chamber to a sensor. The pump assembly comprises a manifold in fluid communication with the chamber and the sensor and a cylinder coupled to the manifold. The cylinder is rotatable between a first position and a second position. The cylinder is in fluid communication with the chamber in the first position and is in fluid communication with the sensor in the second position. A piston is slidably disposed within the cylinder and moves in a first direction when the cylinder is in the first position and in a second direction when the cylinder is in the second position. 
     Also disclosed is an exemplary method of providing a sample of exhaled gases to a sensor. The method includes the steps of passing the exhaled gases through a chamber for a predetermined duration and sensing a duration that exhaled gases are passed through the sample cavity. The method further includes the step of opening an orifice when the sensed duration reaches the predetermined duration, wherein opening the orifice provides a fluid connection between the sample cavity and the sensor. 
     This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This summary is not intended to identify key features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same become better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein: 
         FIG. 1  shows a front isometric view of a breath analysis device with a breath sampling system according to one exemplary embodiment of the present disclosure; 
         FIG. 2  shows a partially exploded view of the breath sampling system of  FIG. 1 ; 
         FIG. 3  shows a partial, side cross-sectional view of the breath sampling system of  FIG. 1 ; 
         FIG. 4  shows a partially exploded, side cross-sectional view of the breath sampling system of  FIG. 1 ; 
         FIG. 5  shows a front isometric view of a pump assembly of the breath sampling system of  FIG. 1 ; 
         FIG. 6  shows a rear isometric view of the pump assembly of  FIG. 5 ; 
         FIG. 7  shows a partially exploded front isometric view of the pump assembly of  FIG. 5 ; 
         FIG. 8  shows a side view of the pump assembly of  FIG. 5  in a first position; 
         FIG. 9  shows partial cross-sectional view of the pump assembly of  FIG. 8 ; 
         FIG. 10  shows a side view of the pump assembly of  FIG. 8  in a second position; 
         FIG. 11  shows partial cross-sectional view of the pump assembly of  FIG. 10 ; 
         FIG. 12  shows a partially exploded isometric view of the breath analysis device of  FIG. 1  with a sensor module removed; 
         FIG. 13  shows an isometric view of the sensor module of  FIG. 12  according to one exemplary embodiment of the present disclosure; 
         FIG. 14  shows a partially exploded isometric view of the sensor module of  FIG. 13 ; 
         FIG. 15  shows a side view of the sensor module of  FIG. 13 ; 
         FIG. 16  shows a first cross-sectional view of the sensor module of  FIG. 13 ; 
         FIG. 17  shows a second cross-sectional view of the sensor module of  FIG. 13 ; and 
         FIG. 18  shows an isometric view of a known breath acetone sensor. 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 1 and 2  show front and rear isometric views, respectively, of an exemplary embodiment of a breath analysis device  30  that utilizes a breath sampling system  100  according to the present disclosure. The device  30  includes housing  40  that contains the components of the breath analysis device. The housing  40  provides an ergonomic surface that makes the device  30  self-contained and easily portable. 
     The breath sampling system  100  collects a breath sample from a user and provides it to a sensor module  400  for analysis. The sensor module  400 , best shown in  FIGS. 13-17 , is operatively connected to a processor  60  shown in  FIG. 6 . As described in further detail below, the processor  60  receives data from the sensor module  400  that can include data related to sensed breath components, breath flow, sensor temperature, and other operating characteristics. In one contemplated embodiment, the processor  60  processes the data and selectively displays information on a display  70  based on the data received from the sensor assembly  400 . 
     In the illustrated embodiment, the display  70  comprises a plurality of lights  72  that can be selectively illuminated to indicate operating conditions, such as state of battery charge, readiness of the device to collect a breath sample, success of a breath sample collection, or any other information that would be desired by the user. The color, display duration, and pattern of the lights can be varied to indicated different conditions. Further, it will be appreciated that disclosed embodiment can incorporate any suitable type of displays and signals to relay information to a user, including LCD screens, LED screens, audible signals, haptic signals, or any other type of combination of displays and signals. 
     In another contemplated embodiment, the processor  60  stores the data locally, or makes the data available for transfer to a remote storage location or processor, such as a home computer, tablet, smart phone, etc. These and other processor functions suitable for receiving and processing diagnostic data are contemplated and should be considered within the scope of the present disclosure. 
     Referring now to  FIGS. 1-4 , the breath sampling system  100  includes a mouthpiece  110  and a pump assembly  140 . Generally speaking, a user exhales into the mouthpiece  110  so that the breath flows into a chamber  114  formed in the mouthpiece. The pump assembly  140  then draws a breath sample from the chamber  114  and supplies it to the sensor module  400  for analysis. 
     As best shown in  FIGS. 1 and 2 , the mouthpiece is removably coupled to the housing  40 . In the illustrated embodiment, a plurality of tabs  112  extend down from the base of the mouthpiece  110  and are received by corresponding slots  44  disposed in the housing  40  to releasably secure the mouthpiece to the housing. It will be appreciated that any number of suitable configurations are possible to secure the mouthpiece to the housing, and such embodiments should be considered within the scope of the present disclosure. Further, embodiments are contemplated wherein the mouthpiece is permanently secured to the housing  40  or integrally formed with the housing. 
     Referring now to  FIGS. 2-4 , a breath sample port  116  extends downward from a bottom portion of the mouthpiece  110 . The breath sample port  116  includes a generally cylindrical body  118  with a central passage  120  extending axially therethrough. The pump assembly  140  includes a manifold located within the housing  40 . The manifold  140  has a mouthpiece channel  152  with a mouthpiece channel inlet  154  sized and configured to receive the breath sample port  114 . When the mouthpiece  110  is attached to the housing  40 , the cylindrical body  118  of the breath sample port  116  extends into the mouthpiece channel inlet  154  so that the chamber  114  of the mouthpiece is in fluid communication with the mouthpiece channel  152 . 
     A breath detection port  124  also extends downward from the bottom portion of the mouthpiece  110 . Like the breath sample port  116 , the breath detection port  124  includes a cylindrical body  126  with a central passage  128  extending therethrough. The breath sample port  116  is sized and configured so that when the mouthpiece  110  is mounted to the housing  40 , the end of the breath sample port is proximate to a breath detection sensor  122 . The breath detection sensor  122  is mounted to the pump manifold  150  or another suitable component and is operatively connected to the processor  60 . 
     The disclosed breath detection sensor  122  is preferably a heated glass NTC (negative temperature coefficient) thermistor configured to operate as a hot-wire anemometer. Contemplated alternate embodiments utilize other temperature sensors capable of dissipating heat, such as resistance temperature detectors (RTDs) or PTC (positive temperature coefficient) thermistors. It will be further appreciated that the sensor  122  can also be a pressure sensor, a mass flow sensor, or any other suitable sensor for detecting that breath is being exhaled into the mouthpiece  110 . As will be described below, the breath detection sensor senses when a user is breathing into the mouthpiece. Data from the breath detection sensor  122  is received by the processor  60 , which determines when a breath suitable for sampling has been introduced into the mouthpiece  110 . 
     The mouthpiece  110  includes an inlet aperture  130  into which a user breathes to introduce a breath sample into the chamber  114  of the mouthpiece. A baffle  132  extends from the edge of the chamber  114  and redirects the breath within the chamber. The baffle controls the introduction of saliva into the chamber  114  and also makes the direction of airflow into the chamber more predictable, thereby providing more consistent breath sample characteristics within the chamber. 
     The mouthpiece  110  further includes an outlet aperture  134 . A typical human exhalation has a volume of approximately 500 ml. The volume of the chamber  114  in the disclosed embodiment is approximately 30 ml. The outlet aperture  134  provides an escape path for excess breath so that a user can provide a longer breath to sample, thereby ensuring that early mouth air is discharged from the chamber  114  or sufficiently diluted with the end tidal air from the airway and lungs. The inlet and outlet apertures  130  and  134  are large enough to allow a user to exhale a breath through the mouthpiece  110 , but not so large that the breath becomes significantly diluted by ambient air after the breath is finished. 
     Referring now to  FIGS. 5-10 , the pump assembly  140  draws breath from the chamber  114  of the mouthpiece and supplies it to the sensor module  400  in a controlled manner that is consistent and repeatable, thereby improving the accuracy and repeatability of the sensor readings. 
     The pump assembly  140  includes a cylinder  180  rotatably coupled to the pump manifold  150  about an axis  500 . A piston  190  is slidably disposed within the cylinder  180  to define a volume  182  within the cylinder, wherein reciprocating movement of the piston within the cylinder increases and decreases the volume. A drive rod  200  is fixedly secured at one end to the piston  190 . A second end of the drive rod is rotatably coupled to a drive gear  210  about an axis  504 , which is parallel to axis  500 . The drive gear  210  is itself rotatably coupled to the pump manifold  150  or another suitable structure about an axis  502 , which is parallel to axes  500  and  504 . 
     A spur gear  220  is rotatably mounted to the pump manifold  150  or other suitable structure about an axis  506 . A motor  230  selectively rotates the spur gear  220  about axis  506 . The motor  230  is preferably a compact stepper motor; however, it will be appreciated that other motors may be used to selectively rotate the spur gear  220 , and such motors should be considered within the scope of the present disclosure. 
     The spur gear  220  is operatively engaged with the drive gear  210  so that when the motor  230  rotates the spur gear about axis  506 , the drive gear  210  rotates about axis  502 . A magnet  212  is mounted to the drive gear  210 . One or more sensors (not shown), such as a Hall effect sensor, senses the position of the drive gear  210 , and sends information about the drive gear position to the processor. It will be appreciated that any number of suitable sensors for sensing the position of the drive gear may be utilized within the scope of the present disclosure. 
     As best shown in  FIGS. 8 and 10 , rotation of the drive gear  20  reciprocates the drive rod  200  and the piston  190  out of ( FIG. 8 ) and into ( FIG. 10 ) the cylinder  180 , increasing and decreasing, respectively, the size of the volume  182  within the cylinder. Because the drive rod  200  is fixedly coupled to the piston  190 , rotation of the drive gear  210  also rotates the cylinder  180  back and forth about axis  500 . 
     As the cylinder rotates back and forth about axis  500 , a generally planar face  186  formed on the cylinder  180  moves back and forth along an arcuate path in sliding engagement with a face  158  formed on the manifold  150 . A channel  184  extends from the interior volume  182  of the cylinder  180  to the cylinder face  158 . The cylinder channel  184  moves back and forth with the face  186  to alternately engage a mouthpiece channel outlet  156  and a sensor channel inlet  162 , both of which are disposed on the manifold face  158 . 
     The mouthpiece channel outlet  156  is the end of the previously described mouthpiece channel  152 , shown in  FIG. 7 . When the cylinder  180  is positioned such that the cylinder channel  184  is engaged with the mouthpiece outlet channel  156 , the mouthpiece chamber  114  is in fluid connection with the interior volume  182  of the cylinder  180 . As best shown in  FIG. 8 , when the cylinder  180  is so positioned, the drive rod  200  and piston  190  are moving to increase the volume  182  within the cylinder, creating a vacuum that draws gasses from the mouthpiece chamber  114 , through the mouthpiece channel  152 , and into the interior volume  182  of the cylinder. As this occurs, the sensor channel inlet  160  is covered and sealed by the cylinder face  186 . 
     As the drive gear  210  continues to rotate, the cylinder  180  rotates so that the cylinder channel  184  disengages with the mouthpiece outlet channel  156 , which is then sealed off by engagement with the cylinder face  186 . The cylinder channel  184  moves along an arcuate path until it engages the sensor channel inlet  162 , as shown in  FIGS. 10 and 11 . The sensor channel inlet  162  is disposed at one end of a sensor channel  160  formed in the manifold  150 . A sensor channel outlet  164  is disposed at a second end of the sensor channel  160  proximate to the sensor module  400 . More specifically, the sensor channel outlet  164  is in fluid communication with an inlet  472  to the sensor module  400  so that the sensor channel  160  provides fluid communication between the interior volume  182  of the cylinder  180  and the sensor module inlet  472 . 
     As best shown in  FIG. 9 , when the cylinder  180  is positioned so that the sensor channel inlet  162  is engaged with the cylinder channel  184 , the drive rod  200  and piston  190  are moving to decrease the volume  182  within the cylinder, thereby increasing the pressure in the cylinder to discharge gasses from the cylinder  180  through the sensor channel  160  and into the sensor module inlet  472 . As this occurs, the mouthpiece channel outlet  156  is covered and sealed by the cylinder face  186 . 
     It will be appreciated that the disclosed pump configuration is exemplary only and should not be considered limiting. In this regard, any known pump suitable for selectively providing a breath sample from the mouthpiece chamber  114  to the sensor module  400  can be utilized and should be considered within the scope of the present disclosure. 
     Referring now to  FIGS. 12-17 , the sensor module  400  will now be described. The presently disclosed sensor module  400  is preferably mounted to the breath analysis device  30  without the use of fasteners, welds, adhesives, etc., so that the sensor module can be easily removed and replaced. As shown in  FIG. 12 , the illustrated embodiment of the breath analysis device  30  includes a removable cover  42  releasably secured to the housing  40  to cover a slot  50 . As will be described in further detail, replacing a sensor module  400  is accomplished by removing the cover  42 , pulling on the sensor module to disengage the sensor module from the breath analysis device  30 , inserting a replacement sensor module into the slot  50  with enough pressure to seat the sensor module, and reattaching the cover. It will be appreciated, however, that the sensor module need not be removable, and alternate embodiments utilizing various permanent and non-permanent mounting configurations are contemplated. 
     As shown in  FIGS. 13 and 14 , the illustrated embodiment of a sensor module  400  includes a printed circuit board  410  (PCB) disposed between a first cover  440  and a second cover  450 . The PCB  410  has an edge connector  412  sized and configured to be releasably coupled to a socket  46 , shown in  FIGS. 6 and 11 . The socket  46  is operably connected with the processor  60  so that data can be sent between the PCB  410  and the processor. As best shown in  FIG. 14 , a first hole  414  and a second hole  416  are formed in the PCB  410 . A slot  418  extends between the first and second hole  414  and  416 . Although the holes  414  and  416  and slot  418  are illustrated as extending through the PCB  410 , alternate embodiments are contemplated in which one or more of these features extends only partially through the PCB. 
     An acetone sensor  430  is mounted to the PCB  410  so that the sensor spans the slot  418  formed in the PCB. In the illustrated embodiment, the sensor  430  is flat tungsten trioxide (WO 3 ) disposed on an alumina or anodic aluminum oxide (AAO) substrate. The described sensor  430  is suitable for detecting acetone in a breath sample; however, it is contemplated that other sensors suitable for sensing acetone may also be used. Further, sensors useful for sensing the presence, level, or other characteristics of other sample components may be utilized, and such sensors should be considered within the scope of the present disclosure. 
     A memory chip  432  is optionally mounted to the PCB  410 . In the illustrated embodiment, the memory chip  432  is an EEPROM that is programmed with sensor  430  parameters, authentication data, and other information to be communicated with the processor  60 . It will be appreciated that any number of other components may be mounted to the PCB  410  to provide functionality to the sensor module  400  and the breath analysis device  30  as a whole. 
     A first cover  440  is made of foil or another suitable material and has a generally L-shaped profile. In this respect, the first cover  440  has a first portion  442  corresponding to the PCB  410  and a second portion  444  extending approximately 90° from the first portion  442 . A second cover  450  is similar to the first cover  440 , being made of foil or another suitable material and having a generally L-shaped profile. The second cover  450  further includes a first aperture  456  and a second aperture  458  extending therethrough and positioned to correspond to the first and second holes  414  and  416 , respectively, in the PCB  410 . The second cover  450  further includes a first dimple  460  and a second dimple  462  that are sized and positioned to correspond to the acetone sensor  430  and the memory chip  432 , respectively. 
     As shown in  FIGS. 13 and 15-17 , the sensor module  400  is assembled so that the PCB  410  is disposed between the first cover  440  and the second cover  450 . The first portion  442  of the first cover  440  covers one side of the PCB  410 , including the holes  414  and  416  and the slot  418 . Similar to the first cover  440 , the first portion  452  of the second cover  450  covers the other side of the PCB  410 , including the holes  414  and  416  and the slot  418 . The first and second apertures  456  and  458  of the second cover  450  are aligned with the first and second holes  414  and  418 , respectively, of the PCB  410 . As shown in  FIG. 17 , the PCB  410  cooperates with the first and second covers  440  and  450  to form pneumatic circuit defined from the first aperture  456 , through the slot  418 , and out the second aperture  458 . As best shown in  FIG. 16 , the first and second dimples  460  and  462  are positioned to provide clearance between the second cover  450  and the acetone sensor  430  and the memory chip  432 , respectively. 
     The illustrated embodiment also includes a protective cover  470  positioned over the second cover  450  so that the second cover is disposed between the protective cover  470  and the PCB  410 . The protective cover  470  is shaped approximately like the first portion  452  of the second cover  450  and has apertures  472  and  474  that correspond to the first and second apertures  456  and  458 , respectively, of the second cover. The protective cover  470  also has third and fourth apertures  476  and  478  that correspond to and provide clearance for the first and second dimples  460  and  462 , respectively. The protective cover  470  protects the second cover  450  which would otherwise be susceptible to tearing, particularly around the first and second apertures  456  and  458 . As such, the protective cover  470  is preferable made from a material having suitable strength and durability, such as a metal or polymeric material. 
     As shown in  FIGS. 12 and 13 , the second portion  444  of the first cover  440  and the second portion  454  of the second cover  450  extend laterally from an edge of the PCB  410  opposite the edge connector  412  to form a handle that facilitates insertion and removal of the sensor module  400 . Referring to  FIG. 12 , to replace a sensor module  400 , a user removes the cover  42  and, pulls on the sensor module to remove the module from the socket  46 . A new sensor module  400  is then inserted in the slot  50  until the edge connector  412  of the new sensor module is seated in the socket  46 . As best shown in  FIG. 6 , an optional spring clip  40  helps retain the sensor module  400  within the socket  46 . Known sensors are susceptible to a buildup of contaminants and/or interferents, which can negatively impact the accuracy of the sensor. Thus, a sensor module  400  that is easily replaceable by a user provides an advantage over known sensors. 
     A method for collecting and sampling breath using the previously described breath analysis device  30  will now be described. To begin, a user places his or her mouth over the inlet aperture  130  of the mouthpiece  110  and exhales. Referring to  FIG. 3 , the exhaled breath is deflected off of the baffle  132  and circulates around the mouthpiece chamber  114 . As the user continues to exhale, a portion of the breath escapes through the outlet aperture  134 , and a portion of the breath escapes through the breath detection port  124 . The pump assembly  140  is in the position shown in  FIG. 10 , so the mouthpiece channel  152  is sealed by the cylinder face  186 , and none of the breath sample passes into the cylinder  180 . 
     The breath passing through the breath detection port  124  passes over the breath detection sensor  122 , which senses that a breath is being exhaled into the mouthpiece  110 . When exhalation has been sensed for a predetermined amount, the breath detection sensor  122 , which is operably associated with the processor  60  sends data to the processor indicating that an adequate sample has been collected. By having a user exhale into the mouthpiece  110  for a predetermined amount of time, it is assured that the breath sample within the mouthpiece chamber  114  is end tidal air, which yields more accurate readings. 
     The processor  60  controls the display to indicate to the user to stop exhaling into the mouthpiece  110 . It will be appreciated that the signal need not be visual, as indicated in the exemplary embodiment, but can be audible, haptic, or any other type or combination of signals. 
     Next, the pump assembly  140  works to provide the breath sample from the mouthpiece chamber  114  to the acetone sensor  430  in a controlled, repeatable manner. Referring to  FIGS. 8 and 10 , the motor  230  rotates the drive gear  210  in a counterclockwise direction. As a result, the cylinder  180  rotates back and forth about axis  500 . When the cylinder  180  is in the position shown in  FIG. 8 , the cylinder channel  184  is in fluid communication with the mouthpiece chamber  114 , and the piston  190  is moving downward in the cylinder. As a result, a portion of the breath sample is drawn from the mouthpiece chamber  114  into the volume  182  of the cylinder  180 , as shown in  FIG. 9 . Continued rotation of the drive gear  210  rotates the cylinder  180  about axis  500  to the position shown in  FIG. 10 , wherein the cylinder channel  184  is in fluid communication with the sensor channel  160 . The rotation of the drive gear  210  moves the piston  190  upward in the cylinder  180 , driving the breath sample from the cylinder volume  182  out through the sensor channel  160 , as shown in  FIG. 11 . 
     It will be appreciated that the disclosed configuration allows the flow rate of the breath sample to the sensor module  400  to be controlled. In the disclosed embodiment, the preferred flow rate is in the range of 5 ml/min.-100 ml/min. It will be appreciated, however, that the motor  230 , which is controlled by the processor  60 , can increase the rotational speed of the drive gear  210  to increase the flow rate or decrease the rotational speed of the drive gear to decrease the flow rate. Thus, the flow rate can be tailored to provide optimal accuracy for a particular sensor type or application. 
     Still referring to  FIG. 11 , the breath sample is discharged from the sensor channel  160  into the inlet (aperture  472 ) of the sensor module  400 . When installed, the protective cover  470  of the sensor module  400  preferably contacts a portion of the manifold  150  so that the connection between the sensor channel  160  and aperture  473  is sealed. In this manner, the breath sample can flow through aperture  472  into the slot  418  in the sensor module  400  with no loss of the sample. It will be appreciated that other sealing configurations are possible and that some loss of the breath sample can be acceptable, provided that the accuracy and repeatability of the readings is not impacted too greatly. 
     The breath sample passes through the slot  418  where it flows over the acetone sensor  430  and then out the sensor module outlet (aperture  474 ). The motor  230  continues to rotate the drive gear  212  until a suitable breath sample has been passed over the acetone sensor  430 . It will be appreciated that the speed and duration of the pump assembly  140  operation can be varied to provide optimum exposure of the particular sensor contained within the senor module  430 . 
     When the analysis of the breath sample is completed, the motor  230  reverses direction, and rotates the drive gear  210  in a clockwise direction. Reversing the rotation of the drive gear  210  reverses the direction of flow through the pump assembly  140 . Accordingly, ambient air is drawn into the sensor module outlet, through the sensor module  400  and sensor channel  160  into the cylinder  180 . The ambient air is then discharged into the mouthpiece  110  and out the inlet aperture  130  and outlet aperture  124 . In this manner, the breath sample is purged from the sensor module  400  and the mouthpiece  110 , ensuring that one breath sample will not influence the results of the next breath sample. 
     While illustrative embodiments have been illustrated and described, it will be appreciated that various changes can be made therein without departing from the spirit and scope of the invention.