Abstract:
A calibration apparatus for checking the accuracy of DLco testing machines includes a pair of syringes mounted side by side in a frame and joined by a valve controlled gas passageway to a coupling adapted to mate with the testing machine. The first syringe receives gas from the testing machine and the second syringe has a chamber from which gas of a known concentration is returned to the testing machine. The chamber of the second syringe is flow connected by a valve to a source of test gas. The gas passageway is constructed in such a manner to reduce dead air space and to allow purging with test gas to eliminate contamination with ambient air or gas of previous tests.

Description:
BACKGROUND OF THE INVENTION 
     The present invention is directed to a calibration apparatus for allowing the user of a DLco testing machine to check the ability of the machine to correctly measure carbon monoxide levels in a gas sample. 
     There are many different types of tests that are available to today&#39;s medical practitioners and pulmonary rehabilitation practitioners for testing various functions of the lung. Many types of diseases, such as emphysema, and injuries reduce the ability of gasses to transfer across the membrane that separates the interior gas spaces of the lungs from the pulmonary-capillary system. This membrane is often referred to as the alveolar-capillary membrane. 
     A number of somewhat related tests have been developed in order to test the function of this membrane without invasion into the lung by surgery or apparatus. These non-invasive tests take advantage of the manner in which carbon monoxide transfers across the membrane and in general measure the rate at which carbon monoxide diffuses across the human lung. The rate of carbon monoxide diffusion then provides the testor with information as to diffusion of other gasses, especially oxygen and carbon dioxide. Because the carbon monoxide reacts in certain ways with the hemoglobin, concentrations of the carbon monoxide in the blood (at least at the levels utilized in testing) are not relevant and a practitioner can calculate the diffusion of carbon monoxide across the membrane by knowing such factors as the initial concentration of carbon monoxide in the lungs, an elapsed time, and the final concentration of the carbon monoxide after the elapsed time. Such tests allow the calculation of a gas transfer factor for carbon monoxide which is generally referred to as the pulmonary diffusing capacity (DLco). While one principal testing technique is used for determining this factor, other techniques have been used in the past, have been proposed or may be developed in the future. 
     Various types of machines have been developed for conducting the pulmonary diffusion capacity test. Such machines typically deliver a known quantity of a test gas with known concentrations of various components to a patient wherein the test gas includes a small non-harmful and specific initial concentration of carbon monoxide, along with a tracer gas that does not cross the lung membrane and allows a user to calculate dilution of the test gas in the lungs. Some DLco testing machines require that the person being tested take several breaths from the machine before the testing begins to start programming. Other machines provide only a single test breath. Subsequently to receiving a test breath from the machine, the patient breathes out or exhales the gas that has been received from the machine back into the machine after a specific elapsed period of time. The machine then performs certain analysis on the test gas exhaled by the patient, normally to determine fairly accurately the exhaled concentration of carbon monoxide which will be less than the inhaled concentration since some will cross the lung membrane. 
     The present invention is not directed to the machine that delivers the test gas to the patient and receives the subsequent exhaled gas for analysis, but rather to an apparatus for testing the machine to insure that it is correctly analyzing the exhaled gasses. In order to check the calibration of the testing machine to determine whether it is accurate in measuring the carbon monoxide concentration in the exhaled gasses, it is important to mimic the testing procedure as much as possible in order to locate and identify problems not only with the carbon monoxide analyzer, but with the procedure for delivering the gas to the carbon monoxide analyzer. 
     While simply delivering a gas stream of a predetermined concentration of carbon monoxide to the carbon monoxide analyzer of the machine allows a technician to determine whether or not the machine can accurately determine the carbon monoxide concentration, such a test does not take into account other factors which may affect the analyzed carbon monoxide concentration when the test is run in a true medical environment with a patient. For example, it may be found that the testing machine is not correctly receiving the exhaled gas from the patient or that the tubing to the testing machine is too long and contains too much extraneous gas which then dilutes the gas sample, so as to provide an inaccurate analysis. 
     Consequently, it is important for the calibration apparatus to both provide a standardized gas of known carbon monoxide concentration, but also to provide the gas in a manner that is as realistic to the actual use with a patient as possible in order to insure that other factors do not cause the tester to incorrectly analyze the carbon monoxide gas concentration. 
     SUMMARY OF THE INVENTION 
     A DLco calibration syringe apparatus is provided for calibrating and insuring the accuracy of pulmonary testing machines that allow a patient to inhale a gas containing a low percentage of carbon monoxide and then, subsequently, receive back and analyze the exhaled gas from the patient to determine the percentage concentration of carbon monoxide after a given time period or sequence of events. The calibration apparatus includes a pair of adjacent syringes joined on one end by a gas flow passage that also communicates during use with the DLco testing machine. Flow through the gas passageway is controlled by a multi-position valve. The first of the syringes includes a piston slideably mounted in a chamber that is joined to the gas flow pathway and which receives a quantity of gas from the testing machine upon proper positioning of the valve. The receipt of the gas from the testing machine by the first syringe is designed to simulate inhalation of a breath by a patient of a predetermined amount of gas having a preselected concentration of carbon monoxide. The first syringe is calibrated by volume and may be utilized to simulate taking and delivering several breaths from the machine in a pre-breathing mode required by certain of such machines. 
     The second syringe also includes a cylinder with a piston mounted therein so as to form a chamber in communication with the gas flow passageway. The second chamber is filled with a quantity of test gas wherein the percentage concentration of at least the carbon monoxide in the test gas is known and, preferably, all of the concentrations of the components of the test gas are known with some precision. Normally, the remainder of the gasses in the test gas will include an inert gas that generally does not cross the lung membrane, such as methane, neon or helium and will have a concentration of oxygen similar to ambient air. The test gas may have other gasses in concentrations found in typical exhaled breaths. After a given period of time, for example, ten seconds, or after a series of events occurs, the valve in the gas passageway is routed so as to communicate the second syringe with the test machine and the syringe is operated by a user to discharge the test gas therein into the testing machine. 
     The apparatus also includes a fill system joined with a test gas sample tank that can be selectively flow connected with the second syringe chamber by the person administering the test, as well as a bleed valve to allow some of the test gas to pass through the gas passageway to purge other gasses positioned therein and a relief valve to prevent the second syringe from being over-pressurized. 
     OBJECTS AND ADVANTAGES OF THE INVENTION 
     Therefore, the objects of the present invention are: to provide a syringe calibration apparatus for calibrating DLco testing machines comprising a pair of closely mounted syringes having internal pistons slideably mounted within a cylinder to form a variable volume chamber therein; to provide such an apparatus wherein the internal chambers of the syringes are joined by a flow controllable gas passageway with each other and with the testing machine during usage; to provide such an apparatus wherein the first of the syringes is sized and shaped to receive a preselected volume of gas from the testing machine and the second syringe is sized and shaped to return a preselected volume of test gas to the testing machine with a preselected concentration of carbon monoxide; to provide such an apparatus wherein the gas flow passageway has relatively very little dead space between the second syringe and the test machine; to provide such an apparatus wherein the gas flow passageway provides a purge valve to allow purging of the passageway with test gas prior to usage; to provide such an apparatus wherein the first syringe chamber is operably joined with a supply of test gas under control of a fill valve; to provide such an apparatus wherein the syringe that receives gas from the test machine can be set to receive varying amounts of gas and designed to allow an operator to return the gas from the cylinder to the machine in certain pre-breathing modes; and to provide such a calibration apparatus which is relatively inexpensive to produce, easy to use, and especially well adapted for the intended usage thereof. 
     Other objects and advantages of this invention will become apparent from the following description taken in conjunction with the accompanying drawings wherein are set forth, by way of illustration and example, certain embodiments of this invention. 
     The drawings constitute a part of this specification and include exemplary embodiments of the present invention and illustrate various objects and features thereof. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a DLco syringe calibration apparatus in accordance with the present invention shown schematically joined with a test gas source and with a DLco testing machine. 
     FIG. 2 is a cross-sectional view of the calibration syringe apparatus, taken along the line  2 — 2  of FIG.  1 . 
     FIG. 3 is a fragmentary side elevational view of the syringe calibration apparatus. 
     FIG. 4 is a front elevational view of the syringe calibration apparatus. 
     FIG. 5 is a rear elevational view of the syringe calibration apparatus. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed structure. 
     The reference number  1  generally indicates a calibration apparatus in accordance with the present invention. The calibration apparatus  1  is illustrated in FIG. 1 as schematically joined to a standard test gas source  5  and a DLco testing machine  6 . 
     The calibrating apparatus  1  includes a first syringe  10  and a second syringe  11  mounted in a frame  12  with a gas manifold  13  located on the front of the frame  12 . 
     The first syringe  10  includes a cylindrical shaped body  17  within which is mounted a piston  18 . The piston  18  includes a sealing member  19  around the perimeter thereof and is sized and shaped to slide within the interior surface  20  of the cylindrical member  17  in a manner such that the sealing member  19  seals as the piston  18  moves along the cylindrical member  17 . 
     A rod  23  is centrally attached to the piston  18  and has an operator handle  24  located opposite the piston  18  an external of the cylindrical member  17 . The rod  23  both provides stability to the piston  18  and allows an operator to position the piston  18  within the cylindrical member  17 . The rod  23  includes a first fixed stop  26  which limits the range of motion of the piston  18  within the cylindrical shaped member  17  for purposes of stability. The rod  23  also has positioned thereon an adjustable second stop  27  which is positionable therealong to allow a user to select an initial position for the piston  18  within the cylindrical member  17 . Located along the rod  23  is a calibrated rule  26  that allows a user to visually and accurately determine the position of the piston  18  relative to the cylindrical member  17 . 
     The second syringe  11  also includes a cylindrical member  33  within which is mounted a piston  34  with a stabilizing and position adjusting rod  35 . The rod  35  is mounted and secured to the center of the piston  34  and extends through the frame  12 , as will be discussed below. The piston  34  also includes a circumferential and peripheral sealing O-ring  36  that seals with the cylindrical member  33  during use. The rod  35  includes a stop  37  to limit the maximum position to which the piston  34  may move within the cylindrical member  33  and an operator handle  38  located opposite the piston  34  outside of the cylindrical member  33 . 
     The frame  12  comprises a front plate  43  and a rear plate  44  joined by six tie rods  45  located in opposing corners of the front plate  43  and rear plate  44  and between the cylindrical members  17  and  33 . The front plate  43  includes a first recess  47  that is sized and shaped to snugly receive the cylindrical member  17  and a second recess  48 , which is likewise sized and shaped to receive the cylindrical member  33 . Sealing O-rings  49  and  50  also are positioned about the cylindrical members  17  and  33  respectively, and seal with the recesses  47  and  48  respectively. The rear plate  44  also includes a pair of recesses  54  and  55 . The recess  54  is sized and shaped to snugly receive the cylindrical member  17  and includes an O-ring  56  for purpose of stability. Likewise the recess  55  is sized and shaped to receive the cylindrical member  33  and also includes an O-ring  57  for stability. The rear plate  44  also has apertures  60  and  61  therein which are aligned to slideably receive the rods  23  and  35  respectively. Positioned around the aperture  60  is a series of vent openings  64  passing horizontally through the rear plate  44  and connecting the rear interior of the cylindrical member  17  with ambient air. Likewise positioned around the aperture  61  are a series of vent openings  65 . 
     The front plate  43  in the illustrated embodiment is integrally formed with the gas manifold  13 , although it is foreseen that the two elements could be manufactured separately. The front plate  43  functions in cooperation with the pistons  18  and  34  and their associated cylindrical members  17  and  33  to form variable sized chambers  68  and  69  respectively. When the pistons  18  and  34  are positioned as close to the gas manifold  13  as possible and to the left as seen in FIG. 2, the chambers  68  and  69  are relatively very small in volume and the volume of the chamber  69  preferably approaches a zero volume as closely as possible when the piston  34  is near the manifold  13 . As the pistons  18  and  34  move away from the gas manifold  13  and to the rear or right, as seen in FIG. 2, the chambers  68  and  69  grow in volume and function to receive selected gasses therein. 
     The gas manifold  13  extends forward of the front plate  43 , as is seen in FIGS. 1,  2 , and  3 . The gas manifold  13  includes a first gas passageway  72  and a second gas passageway  73  joined at a frontward end thereof by a multi positional valve  75 . Ends of the passageways  72  and  73  opposite the valve  75  operably flow connect with the chambers  68  and  69  respectively. The valve  75  is also flow connected with a forward projecting coupling  76  that is sized and shaped to join with the gas discharge and receiving nozzle of a DLco testing machine  6 . In this manner, the valve  75  may be set to allow flow from the testing machine  6  to the chamber  68  or alternatively, to allow flow from the chamber  69  to the testing machine  6 . The valve  75  includes an operator control knob  78 . 
     Third, fourth and fifth gas passageways  81 ,  82 , and  83  also flow connect with the second gas passageway  73 , as is shown in FIG.  2 . The third gas passageway  81  is joined with a quick operating flow control valve  85  mounted on the front of the gas manifold  13 . The valve  85  also operably flow connects with the standardized test gas source  5  during use and operably provides for an operator using gas from the source  5  to fill the chamber  69  by depression of the valve  85 . 
     The fourth gas passageway  82  is joined to a relief valve  86  also mounted on the gas manifold  13  to safely relieve over-pressure in the chamber  68 , should the chamber  68  inadvertently become over-pressurized. Furthermore, the fifth gas passageway  83  is joined by a valve  88  to a vent  89  mounted on the front of the gas manifold  13 . The operation of the valve  88  and vent  89  function to allow a user to purge gas that enters the chamber  69  through the valve  85  and also through the second gas passageway  73  in order to assure that the gas in the second gas passageway  73  has a composition that is essentially consistent with the gas composition in the chamber  69 . 
     In use the calibration apparatus  1  is joined to any of numerous types of DLco testing machines, such as are illustrated by the block  6  and to a source  5  of standardized test gas. The calibration apparatus  1  is then utilized much to mimic testing with a patient. In particular, the DLco testing machine will normally discharge a quantity of test gas into the patient, sometimes after offering several breaths of normal air to the patient in order to start machine programming or in other cases without such pre-breathing. 
     For pre-breathing, the operator manipulates the piston  18  in the syringe  10  to mimic breathing by a patient. The test gas will be similar in composition to air which may be humidified or otherwise treated to make it similar to a normal breath composition and which will include a small concentration of carbon monoxide, as well as a known quantity of an inert tracer gas. The carbon monoxide concentration may be varied with subsequent tests to insure the machine  6  is able to correctly analyze carbon monoxide from a range of patients who have different membrane diffusion, such as athletes and persons with emphysema. The valve  75  is initially set to allow the gas from the testing machine  6  to enter or flow into the chamber  68  through the first passageway  72 . The piston  18  moves away from the gas manifold  13  as gas enters the chamber  68  thereby enlarging the chamber  68 . The piston  18  may be pre-positioned relative to the cylindrical member  17  away from the gas manifold  13  by location of the second stop  27  therealong. Such positioning will be in accordance with the particular testing being conducted. 
     Once the gas has been delivered from the testing machine  6  to the chamber  68 , either an elapsed time, such as 10 seconds, is allowed to occur or some series of events is allowed to occur, after which an exhalation of gas into the testing machine  6  occurs. 
     In particular, a quantity of a test gas with a known concentration of carbon monoxide, which is lower than the concentration of carbon monoxide in the gas discharged by the testing machine  6 , is placed in the chamber  68  by operation of the valve  85 . 
     Normally, the chamber  68  will have several volumes, for example 250 milliliters of test gas delivered to it which is then discharged to purge the chamber  68  and gas manifold  13  prior to final filling for conducting the test. The gas in the chamber  68  causes the piston  34  to retract or move away from the gas manifold  13  a preselected distance or until the stop  37  engages the rear plate  44 . The valve  88  and vent  89  may then be operated in such a manner as to discharge some of the gas entering through the valve  85  in such a manner as to sweep or purge the second passageway  73  and thereby remove any stagnant or gas remaining therein, such as ambient air or from a previous test, if a purge has not already been completed. In this way the gasses in both the chamber  69  and the second passageway  73  have essentially the same composition, especially with respect to concentration of carbon monoxide. Normally gas will be positioned within the chamber  69  before the calibration or testing is done, but this step could be taken subsequent to the discharge of gas from the machine  6 . 
     Subsequent to the lapse of a given period of time or a series of events, the valve  75  is set to flow connect the coupling  76  with the second passageway  73 . The piston  34  is then urged toward the front of the cylindrical member  33 , that is toward the gas manifold  13 , by an operator pushing on the handle  38 . This urges the gas that is then in the chamber  69  out of the chamber  69  due to compression of the chamber  69  and through the second passageway  73  to the DLco testing machine  6 . The DLco testing machine then performs one or more analyses on the test gas to determine whether the DLco machine is correctly analyzing the concentration of carbon monoxide in the gas and/or whether there are any other problems associated with the system that cause the machine  6  to incorrectly analyze the carbon monoxide concentration within the test gas. 
     The coupling  76  is mounted as close to the valve  75  as possible, such that dead space, that could hold contaminated or ambient air is reduced to a minimum between the DLco testing machine  6  and the apparatus  1 . Because the second gas passageway  73  is purged with test gas and the chance for contamination at the coupling  75  is reduced as much as possible, the gas analyzed by the testing machine  6  has very little likelihood of being contaminated or diluted with ambient air or other gas in the calibrating apparatus  1 . 
     It is to be understood that while certain forms of the present invention have been illustrated and described herein, it is not to be limited to the specific forms or arrangement of parts described and shown.