Abstract:
A multifunctional breath analyzer includes a receptor unit for receiving a breath sample from a test subject, a sensing unit providing a signal corresponding to the concentration of at least one volatile substance within the sample, elements for providing a signal indicative of the dilution of the breath sample, and an analyzing unit/processing unit for the identification and quantification of the volatile substance of the breath sample. The signal processing unit is configured to perform at least two different calculations for the quantification, and the signal processing unit is also configured to automatically display the result of a selected calculation, the selection being based on the signal indicating dilution.

Description:
TECHNICAL FIELD 
     The invention relates to the analysis of breath (exhalation air) from a test subject. The analysis comprises the identification and quantification of one or several volatile substances, e.g. ethanol, methanol, acetone, carbon monoxide, carbon dioxide, ammonia, nitric oxides. It may have medical, social, security, or judicial purposes, depending on the situation, and the substances involved. The situation may call for different requirements with respect to measuring accuracy, specificity, speed of response, etc. In particular the invention relates to an apparatus for such analysis. 
     BACKGROUND 
     Breath analyzers according to the state of the art are designed for specific situations and application areas. A variety of products exists for applications in screening, clinical diagnostics, and for evidential purposes for the determination of breath alcohol concentration. For the latter category, high priority requirements are measuring accuracy and specificity. For screening purposes, speed of response and simplicity for the test person are more important, especially when the fraction of positive response, i e concentration exceeding a certain threshold value, is expected to be small. This is the case in testing of sobriety of vehicle drivers, including alcolocks or similar devices. 
     In evidential instruments and qualified diagnostic instruments, infrared spectroscopy is being used as the measuring principle, resulting in very high accuracy and specificity. For screening purposes, simpler sensors based on catalysis, e.g. fuel cell or semiconductor elements, are being used. They are advantageous with respect to production cost, but have drawbacks when it comes to reliability. The catalytic function is difficult to control, and the sensors have limited life time. In most breath analyzers the test subject is required to deliver forced expiration into a tight-fitting mouthpiece. The procedure is time consuming and problematic to persons with impaired respiratory function. 
     SUMMARY OF THE INVENTION 
     The present invention is concerned with a multifunctional breath analyzer which simultaneously fulfills the seemingly conflicting requirements mentioned above within one single enclosure. The breath analyzer according to the invention can be used for a number of different purposes that have hitherto called for different pieces of equipment. Thereby increased flexibility is obtained, along with reduced time consumption, and lower cost for the user. Both screening and more demanding tasks may be carried out with one and the same piece of equipment. 
     In the breath analyzer according to the invention, screening may be performed without physical contact between the breath analyzer and the test subject, with the benefits of easy and fast operation, and requiring a minimum effort of the test subject. However, it also means that the breath sample is being diluted with ambient air. By measuring the concentration of a tracer substance, e.g. carbon dioxide (CO 2 ), within the sample, the degree of dilution may be estimated, allowing an estimation of the true breath concentration. 
     According to the invention the breath analyzer comprises a receptor unit for receiving a breath sample from a test subject, a sensing unit providing a signal corresponding to the concentration of at least one volatile substance within the sample, means for providing a signal indicative of the dilution of the breath sample, and an analyzing unit/processing unit for the identification and quantification of the volatile substance of the breath sample. The signal processing unit is configured to perform at least two different calculations for the quantification, and the signal processing unit is also configured to automatically display the result of a selected calculation, the selection being based on the signal indicating dilution. 
     The means for indicating dilution may either comprise a sensor responsive of the tracer substance or one responsive of the tightness of connection between the respiratory organs of the test subject and the sensing unit. 
     The device according to the invention is defined in claim  1 . 
     In a preferred embodiment, the breath analyzer according to the invention comprises an autonomous, handheld unit which is simple to use independently of the position, posture and condition of the test person. 
     In another preferred embodiment the breath analyzer can be installed and embedded in the instrumentation at the driver&#39;s position of a vehicle. In the screening mode of operation, no active participation of the driver is required. However, if the estimated substance concentration exceeds a certain threshold, the driver may be urged to provide a second breath test using a tight-fitting mouthpiece connected to the same breath analyzer. 
    
    
     
       The present invention is defined in the appended claims, and a more detailed description is provided below, in relation to the enclosed drawings, wherein 
         FIG. 1  schematically shows the building blocks of the breath analyzer according to the invention; 
         FIG. 2  illustrates examples of use; 
         FIG. 3  shows typical signal patterns; and 
         FIG. 4  is a flow chart illustrating the calculations. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows the building blocks of a preferred embodiment of the breath analyzer according to the invention. The analyzer is physically built into an enclosure  1 , designed for handheld use. Its outer physical dimensions are modest, typically 150×50×30 mm. To obtain the necessary durability it needs to be resistant to environmental stress of various kinds, including extreme temperature, humidity, pressure, shock, vibration, and electromagnetic interference. In particular, the enclosure  1  comprises a structured metallic material, or a shock resistant polymer in order to fulfill its functional requirements. 
     The enclosure  1  includes a sensing unit  2  coupled to a signal processing unit  3 . The sensing unit  1  is equipped with an inlet  5  and an outlet  6  allowing the breath sample to be passed through it with or without the assistance of a fan  10 . The fan  10  may also supply a bias flow to assist the breath flow during measurement, and improve sensitivity of highly diluted samples. Preferably, a flap valve  11  at the outlet  6  secures that the flow is unidirectional. The volume of the sensing unit  2  is typically less than 100 ml. 
     The breath sample is fed into the inlet  5  of the sensing unit  2  via a receptor  4   a , which in  FIG. 1  is shown mechanically secured to the inlet  5  of the sensing unit  2 . When the receptor  4   a  is used for contactless reception of a breath sample at a distance of a few centimeters from the mouth and nose of the test person, it preferably has the shape of a scoop, mug, cup or funnel, which may be detachably secured to the enclosure  1 . 
     Another shape preferred for undiluted breath sampling, which is shown separately in  FIG. 1 , is tubular  4   b  with or without a flange to ensure tight connection between the sensing unit  2  and the test subject&#39;s lips and therefore also the respiratory organs. A tight connection may also be accomplished if the receptor has the shape of a face mask enclosing both the mouth and nose of the test subject. 
     A particle filter  12  consisting of a porous and permeable substance, typically a fibrous polymer, is preferably included in the sensing unit  2  or receptor  4   a, b  with two distinctive purposes. First it separates liquid droplets and solid particles that may accompany expired air from the volatile substances of main interest, thereby avoiding contamination of sensitive surfaces within the sensing unit  2 . 
     The second purpose of the filter  12  is to define, together with the pressure sensor  16 , means for providing a signal indicative of the tightness of connection between the respiratory organs of the test subject and the sensing unit  2 . Tightness is one indication of an undiluted breath sample. The filter  12  exhibits a small but well-defined flow resistance. The flow through the filter  12  is preferably nearly laminar, resulting in a linear or polynomial relationship between the flow and the differential pressure across the up- and downstream ends of the filter  12 . The differential pressure sensor  16  is included for the purpose of responding to this pressure. At the onset of a breath sample, the pressure peak corresponds to the respiratory driving force of the test subject, and is indicative of a tight connection between the sensing unit  2  and the subject&#39;s respiratory organs. The input openings  16 ′,  16 ″ of the pressure sensor  16  are preferably directed perpendicular to the main flow direction in order to minimize the influence of dynamic pressure built up according to the basic theory of Bernoulli. 
     An alternative embodiment of means for providing a signal indicative of tightening makes use of other gas flow sensing devices, e.g. based on hot-wire anemometry, vortex shedding, ultrasonic transit time measurement, or Doppler frequency shift. Necessary prerequisite are response time of 0.1 second or less, and immunity to environmental variations. 
     Preferably, the sensing unit  2  includes sensor elements  8 ,  9  responsive both to the substance of interest  9 , and a tracer substance  8 , e.g. CO 2  or water vapor. Indication of an undiluted breath sample is provided by the latter element  8 . If the CO 2  concentration exceeds a certain value, e.g. coinciding with the normal alveolar concentration, the sample may be considered undiluted. 
     In a first embodiment of the sensing unit  2 , it includes a source  7  of electromagnetic radiation within the infrared (IR) wavelength range, and IR detectors  8 ,  9  equipped with band pass type interference filters tuned to wavelength intervals which coincide with absorption peaks of the substances to be determined. For ethanol and CO 2  9.5±0.3 μm (1 μm=10 −6  m) and 4.26±0.05 μm, respectively, are suitable wavelength intervals. Other substances have other preferred wavelength intervals. 
     It is schematically indicated in  FIG. 1  that the detectors  8 ,  9  are reached by the IR beam emitted by the source  7  after reflections against the inner wall of the measuring volume which is preferably covered by a thin film of gold or aluminum, or other highly reflecting material, and having appropriate shapes to collimate the beam. The IR beam is reflected once before reaching the detector  8 , and reflected three times before reaching the detector  9 . Thus the optical path is much longer for the detector  9 , resulting in a higher sensitivity to absorption. Therefore, detector  9  is used for detecting the volatile substance of primary interest, whereas the detector  8  is used for the tracer substance. Moreover, it is desired to optimize the optical path and aperture to the expected concentration of the substance to be analyzed in accordance with principles described by J. U. White (J. Opt. Soc. Amer., vol 32, 1942, pp 285-289). 
     The IR source  7  is preferably generating repetitive pulses of IR radiation with a repetition frequency of 5-100 Hz, which determines the time resolution of the analyzer. The IR source  7  preferably includes a black body radiating thin membrane in order to allow high repetition frequency. The IR detectors  8 ,  9  are preferably thermopiles in order to provide maximum signal to noise ratio, and consequently maximum sensitivity and resolution. 
     In a second embodiment of the sensing unit  2 , a catalytic sensor including an electrochemical cell or a semiconductor element is being used for identifying and quantifying the volatile substance of interest, and the tracer substance. 
     The signal processing unit  3  preferably includes integrated analog and digital circuit elements for signal processing and control. Preferably one or several microprocessors are included for signal processing, management of signals to a display  14  for indication of measurement results, and for data communication with external equipment, e.g. a personal computer or other peripheral equipment connectable by a dedicated connector  15 . 
     In a preferred embodiment, the breath analyzer according to the invention is operating as an autonomous, handheld unit. Power supply is provided by a battery  13  which is preferably rechargeable via a mains adapter. In another preferred embodiment, the breath analyzer is embedded into an instrument panel, and used together with other equipment. 
     As already mentioned, estimation of the dilution of the breath sample is performed by the use of a tracer substance, e.g. CO 2 . The partial pressure of CO 2  within deep (alveolar) breath air is typically 4.8 kPa, corresponding to 4.8% by volume, whereas the background ambient concentration seldom exceeds 0.1% v/v. The degree of dilution therefore can be calculated from the ratio CO 2alv /SO 2meas , where CO 2alv  and CO 2meas  are the alveolar and measured concentrations, respectively. The variability of CO 2alv  between different individuals expressed as one standard deviation is relatively modest, of the order of 10% of the average. 
     In the present invention, the measured concentration of a substance in a diluted sample is multiplied by CO 2alv /CO 2meas  in order to obtain an estimated value of the undiluted concentration. This mode of operation is extremely rapid and convenient for the test person, but exhibits a relatively large error due to the variability of CO 2alv . Water vapor can be used as an alternative tracer substance, however with the addition of careful determination of the background concentration which at unfavorable conditions may nearly coincide with the signal. 
     Transfer from a screening mode of operation into one of higher measuring accuracy is accomplished in the present invention by identifying an undiluted breath either by the sensor element  8  responsive of the tracer substance, or by means of a signal indicative of a tight-fitting connection between the respiratory organ and the sensing unit of the breath analyzer. This signal is provided by the pressure sensor  16 . 
     In the absence of a signal indicating an undiluted sample, an estimation of the sample dilution is used in the calculation of the substance concentration. In the presence of such a signal the estimation of dilution may be omitted, resulting in higher accuracy. Thus the dilution signal is enabling the breath analyzer to be automatically switching between screening operational modes and those of high accuracy. 
       FIG. 2  schematically shows two operating modes, or functionalities, of the breath analyzer according to the invention. In  FIG. 2   a ) contactless measurement is being performed with the enclosure  1  handheld at a distance of a few centimeters from the test person. By the funnel-shaped receptor  4 , expiratory air flow is being captured, however with some dilution of ambient air. By the previously described ratioing procedure or algorithm, the concentration of the substance of primary interest can be corrected taking the dilution into account, providing an estimated value of its actual breath concentration. The determination according to  FIG. 2   a ) can be performed in a few seconds, and by forced ventilation of the measuring volume, the apparatus is rapidly ready for a new test, without the need to physically replace any items.  FIG. 2   a ) thus represents a typical screening situation. 
     In the case of an undefined outcome of the screening performed according to  FIG. 2   a ), the same piece of equipment can be used for a more accurate determination according to  FIG. 2   b ). By undefined outcome is meant that the result is within the tolerance interval of a certain concentration limit. By performing another measurement at higher accuracy (smaller tolerance) it is possible to resolve the undefined situation. In this mode of operation, tight connection between the test subject&#39;s respiratory organs and the sensing unit  2  is secured e.g. by applying a tubular receptor  4   b , and the test person is instructed to provide forced and prolonged expiration through it, in order to ensure proper emptying of the expiratory air. Since the receptor  5  is tightly fitting to the test person&#39;s mouth opening, no dilution of the sample takes place, and correction with CO 2  is unnecessary. A prolonged expiration is however required to ensure minimum influence from the physiological dead-space on the measuring result. 
       FIG. 3  schematically shows the signal patterns when performing breath tests according to the procedures described above, in relation to  FIGS. 2   a ) and  b ). For the screening case  FIG. 3   a ) graphically shows the variation of the measured concentration of CO 2  and the substance of primary interest, in this case ethanol (EtOH) as a function of time during a breath test. A third graph represents the pressure measured at the inlet of the sensing unit  2  by the sensor  16 . 
     All three signals in  FIG. 3   a ) are basically zero at start, and grow to a maximum during the expiratory phase, and then return to zero as the sensing unit is ventilated. When the CO 2  concentration reaches its maximum, the algorithm will assume a dilution ratio of CO 2alv /CO 2meas , and multiply it with the measured ethanol concentration at that time in order to obtain the estimated undiluted EtOH concentration. 
     The entire course of  FIG. 3   a ) has a duration of only a few seconds, which is due to the fact that the test person is instructed to terminate the expiration when a certain threshold value of CO 2  has been reached, typically 2 kPa, corresponding to a dilution ratio of approximately 2.4. 
     The pressure signal from the sensor  16  exhibits a minor peak coinciding with the maximum flow. Its magnitude is typically less than 10 Pa (N/m 2 ). 
       FIG. 3   b ) shows the corresponding signal pattern with a tight-fitting receptor  4   b . The CO 2  concentration is increasing fast in the beginning and is then leveling out. When it exceeds a certain value, e.g. the normal alveolar concentration, the sample may be considered undiluted. The duration is longer in this case than in  FIG. 3   a ), typically 5 seconds. The concentration of ethanol follows the same pattern as CO 2  with minor deviation, such as an earlier up-rise, and a flatter plateau. 
     The pressure signal in  FIG. 3   b ) exhibits a considerably higher peak value than in  FIG. 3   a ). This is due to the fact that the respiratory organs of the test person generate a significant driving force, especially in the initial phase. The magnitude recorded by the pressure sensor  16  is also depending on the flow resistance of the particle filter  12 . The CO 2  or the pressure signal is used to determine whether the sample is considered diluted or undiluted. If the pressure in the initial phase exceeds a certain threshold, e.g. 100 Pa, then the connection between the test subject and the sensing unit  2  is considered tight. Then the CO 2alv /CO 2meas  ratio is automatically omitted from the calculation of the substance concentration. 
     A flow chart of the calculations is shown in  FIG. 4 . The calculation process for obtaining a concentration value for the substance of interest, e.g. ethanol, is initiated when a threshold of measured CO 2  concentration is exceeded, e.g. 2% (v/v). Then, if the peak differential pressure of the pressure sensor  16  does not exceed its threshold, e.g. 100 Pa, or if the CO 2  concentration does not exceed the alveolar concentration, then the measured substance concentration is multiplied by CO 2alv /CO 2meas , to obtain the estimated concentration which is displayed. If the pressure peak exceeds 100 Pa, or the CO 2  signal exceeds the alveolar concentration, then multiplication by CO 2alv /CO 2meas  is omitted.