AU706520B2

AU706520B2 - Method for the determination of the concentration of alcohol in exhaled air

Info

Publication number: AU706520B2
Application number: AU39178/95A
Authority: AU
Inventors: Uwe Kuhn
Original assignee: Draegerwerk AG and Co KGaA
Current assignee: Draegerwerk AG and Co KGaA
Priority date: 1994-12-03
Filing date: 1995-11-30
Publication date: 1999-06-17
Anticipated expiration: 2015-11-30
Also published as: FR2727760A1; GB2295679A; GB9524122D0; DE4443142A1; DE4443142C2; FR2727760B1; AU3917895A; GB2295679B

Description

Description Dragerwerk Aktiengesellschaft Moislinger Allee 53.55, 23542 Lbeck, DE Method for the determination of the concentration of alcohol in exhaled air.

The invention relates to a method for the determination of the concentration of alcohol in exhaled air, in which during an exhalation a gas sample is passed into a measuring chamber of a detecting device and a measuring curve proportional to the alcohol concentration is produced.

DE 39 04 994 Al discloses an apparatus for conveying a 15 gaseous sample into the measuring chamber of a detecting device in order to determine the proportion of alcohol in the gas sample. With the aid of a piston-cylinder unit the gas sample is pumped out of the exhaled air into the measuring chamber of the detecting apparatus. The detecting apparatus consists of an electrochemical measuring cell which includes a membrane permeable to alcohol molecules.

During the sampling stroke the gas sample is guided along a roundabout path over a large part of the membrane surface, so that a rapid reaction of the alcohol molecules in the 25 electrochemical measuring cell is achieved. Through the roundabout path a short response time of the measuring cell is obtained, since the largest part of the sample of gas being measured is already evaluated during the short suction stroke. After the reaction of the alcohol molecules the piston performs an exhaust stroke in order to remove the evaluated sample gas from the measuring chamber again.

This known apparatus performs the sampling stroke at a time at which any portions of the breath alcohol coming from the oral cavity have been breathed out, since these could falsify the result of measurement in the direction of a too high indication. But even if the sampling is undertaken at a later time during the exhalation, if oral alcohol is present there is no assurance that only the portion of the alcohol in the alveolar air is measured.

In the case of other principles of measurement for the determination of the alcohol concentration, e.g. those which operate according to the infra-red absorption principle, it is possible to measure the alcohol concentration with sufficient accuracy practically without delay, so that the presence of oral alcohol can be recognised from the shape of the concentration curve. However, such measuring methods require a higher outlay on apparatus. An apparatus operating according to the infrared absorption principle is shown in DE 26 10 578 B2.

It is an object of the invention to provide, for a detecting device which, because of its time constant, does not enable a direct determination of the variation in concentration to be made, a method of recognising the 15 presence of oral alcohol in the breath sample.

This is achieved by the steps of delivering a first gas sample into the measuring chamber at a first time at the start of the exhalation and recording a first measuring curve, delivering a second gas sample into the measuring S 20 chamber at a second time during the same exhalation, at which the breath from the mouth has been eliminated, and determining a second measuring curve, determining predetermined first parameters from the first measuring curve and predetermined second parameters from the second measuring curve, and comparing the first and second parameters of an exhalation with one another.

The object can also be achieved by delivering a first gas sample at a first time at the start of the exhalation into a first detecting device and recording a first measuring curve, and at a second time during the same exhalation, at which the breath from the mouth has been eliminated, delivering a second gas sample into a second detecting device and determining a second measuring curve, determining predetermined first parameters from the first measuring curve and predetermined second parameters from the second measuring curve, and comparing the first and second parameters of an exhalation with one another.

The advantage of the invention consists essentially in that during an exhalation two samples of gas to be measured are analysed, namely a first sample at the beginning of the exhalation, when the gas breathed out comes predominantly from the oral cavity, and a second sample at a later point in time when the breath from the mouth has largely been eliminated. The two samples can either be evaluated one after the other through a double sampling stroke with one detecting device, or by the use of two detecting devices.

The measuring curves obtained from the two samples are compared with one another, and from the measuring curves parameters characteristic of the shape of the measuring curves are determined which are used for the detection of the oral alcohol. With the method according to the 15 invention it is possible to indicate the presence of oral alcohol in the case of those detecting devices which do not allow a direct determination of concentration, e.g. slow IR sensors or semiconductor sensors. Electrochemical sensors can be used with particular advantage.

S 20 Advantageously the parameters used for the evaluation of the measuring curves are the maximum values of the measuring curves, a first maximum value being associated with the first measuring curve and a second maximum value being associated with the second measuring curve. Instead of the maximum values, integral values under the measuring curves can be formed as parameters and used as parameters for the evaluation.

Advantageously the first gas sample is delivered at a time shortly after the beginning of the exhalation, i.e.

within a second after the beginning of the exhalation, and the time of taking the second gas sample is selected so that about 50% of the volume of the exhalation has been breathed out.

Advantageously the first maximum value is compared with the second maximum value in one inhalation and the presence of oral alcohol is indicated in the event that the first maximum value is greater than the second maximum value. In

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the event that integral values are formed, these are compared with one another.

-By way of example, an embodiment of the invention is illustrated in the drawings and is described in more detail below. In the drawings: Figure 1 shows a measuring curve of a breath sample without oral alcohol, Figure 2 shows a measuring curve of a breath sample with oral alcohol, Figure 3 shows an apparatus in accordance with the invention with two measuring cells, SFigure 4 shows a measuring curve of a breath sample o* .without oral alcohol for the apparatus shown in Figure 3 and eo 15 Figure 5 shows a measuring curve of a breath sample with oral alcohol for the apparatus shown in :Figure 3.

Figure 1 shows a measuring curve of an electrochemical measuring cell (not shown in the Figure) o 20 which is exposed to two gas samples in succession. The .o0 measuring cell may, for example, be constructed in accordance with DE 39 04 994 Al. The time t is plotted on the abscissa of the coordinate system shown in Figure i, and the sensor current i(t) is plotted on the ordinate For simplicity, let it be assumed that the exhalation begins at the time t 0 and the reference line for the sensor current i(t) coincides with the abscissa Shortly after the beginning of the exhalation, at the time t ti, a first gas sample is delivered and supplied to the electrochemical measuring cell. The electrochemical reaction of the alcohol molecules results in a first measuring curve with a first maximum value which is reached at the time t t 2 At a time t when at least 50% of the exhalation has been breathed out, a second gas sample is delivered into the measuring cell, and a second measuring curve is obtained with a second maximum value i 2 at the time t t 4 After passing the second maximum value i2. the second measuring curve falls steeply and then approaches the abscissa (2) asymptotically. In the present case the exhaled air contains no oral alcohol, and the first maximum value iI is smaller than the second maximum value i 2 a. The different magnitudes of the maximum values and i, is due to the fact that at the time t t 3 when the second gas sample is delivered, the alcohol molecules of the first gas sample have still not reacted completely.

Figure 2 show a measuring curve (10) of an exhalation which contains oral alcohol. At the time t t, a first gas sample is delivered into the measuring cell, and then a first measuring curve (14) with a first maximum value i is o*:oo again recorded, and at the time t t 3 a second gas sample arrives in the measuring cell, the electrochemical reaction of the alcohol molecules of the second gas sample leading to a second measuring curve (15) with a second maximum value The times t 3 and t, of the measuring curve (1) correspond to the times t 2 t 3 and t 4 of the measuring curve The index stands for the exhalation with o*o 20 oral alcohol. In the case of the first measuring curve (14) the first maximum value iA is clearly greater than the second maximum value i 2 1 since at the time t t. the gas sample essentially comprises the alcohol molecules present in the oral cavity, while at the time t t 3 the alcohol concentration of the alveolar air portion predominates. The maximum values i 1, i 2 are fed to a comparator (not shown in the Figure), and in the event that i 1 is greater than i2 a display unit (likewise not shown in the Figures) is activated which indicates the presence of oral alcohol, so that the concentration measurement is rejected or only used with reservations.

Figure 3 shows an apparatus (20) with a sample collecting device for delivery of a first gas sample through a first line (21) into a first electrochemical measuring cell (22) and for delivery of a second gas sample through a second line (23) into a second electrochemical measuring cell The measuring cells (22, 24) are connected to an evaluation and control unit which initiates the sampling and registers and evaluates the measuring signals delivered from the measuring cells (22, 24). Also connected to the control unit (25) is a flow sensor (26) which registers the beginning of an exhalation, i.e. the time t 0 for the sampling.

Figure 4 shows measuring curves 5) which were recorded with the apparatus (20) according to Figure 3 and belong to a breath sample without oral alcohol. For simplicity it is again assumed that the exhalation takes ."place at the time t 0. Shortly after the beginning of the exhalation, at the time t t 1 a first gas sample is *oodelivered through the first measuring cell which contains a delivery device, and is evaluated as first measuring curve in the control unit At the time t t when at least 50% of the exhalation has been breathed S9 out, a second gas sample is delivered through the second measuring cell (24) and evaluated as second measuring curve.

Since there is no influence due to oral alcohol, the maximum S 20 values i 2 of the two measuring curves 5) ought to be "the same. Since, however, at the start of the exhalation some of the alcohol molecules are absorbed by the oral 9*g* mucous membranes, the maximum value i. is smaller than the maximum value i 2 m. In Figure 4 this difference is exaggerated for clarity. The times t i to t 4 of Figures 4 and correspond to the times t. to t 4 of Figures 1 and 2. The measuring curves 5) of the measuring cells (22, 24) are shown in Figure 4 within a coordinate system. In the case of a breath sample with oral alcohol the curve shape shown in Figure 5 is obtained. At the time t t. the first gas sample is delivered through the first measuring cell (22) and a first measuring curve (14) with a first maximum value i, A is obtained. The second gas sample delivered at the time t t. into the second measuring cell (24) gives a second measuring curve (15) with a second maximum value i 2

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comparison of the maximum values and i 2 M in the control unit (25) shows that ii., is greater than which is indicated as the presence of oral alcohol.

too.*:* 0 *.00* #000 V4,06, THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS: 1. Method for the determination of the concentration of alcohol in exhaled breath, wherein during an exhalation a gas sample is passed into a measuring chamber of a detecting device and a measuring curve 5, 14, 15) proportional to the alcohol concentration is produced, characterised by the steps of: delivering a first gas sample into the measuring chamber at a first time t at the beginning of an exhalation, and recording a first measuring curve (4, 14); delivering a second gas sample into the measuring chamber at a second time t during the same exhalation, at which the breath from the mouth has been eliminated, and determining a second measuring curve determining predetermined first parameters ii., from the first measuring curve 14) and predetermined second parameters i 2 from the second measuring curve 15) and comparing the first and second parameters i, 2 of an exhalation with one another.

2. Method for the determination of the concentration of alcohol in exhaled breath, wherein during an exhalation a gas sample is passed into a measuring chamber of a detector device and a measuring curve 5, 14, 15) proportional to the alcohol concentration is produced, characterised by the steps of: delivering a first gas sample into a first detecting device (22) at a first time t at the beginning of an exhalation, and recording a first measuring curve 14);

Claims

3. Method according to claim 1 or claim 2, characterised in that the first parameter is a first maximum value or integral value i1m, ilmA of the first measuring curve 14) and the second parameter is a second maximum value or integral value i2m, i2mA of the second measuring curve o 4. Method according to one of claims 1 to 3, characterised in that the first time t tl lies in a time interval up to about one second after the beginning of the oo ago exhalation and that the second time t 3 is selected so that more than 50% of the oo volume of the exhalation has been breathed out. Method according to claim 3 or claim 4, characterised in that the first maximum value or integral value ilmA is compared with the second maximum value or integral value i2mA and in the event that the first maximum value or integral value i l mA is greater than the second maximum value or integral value i2mA it is indicated that oral alcohol is present.
6. Apparatus for carrying out the method according to one of claims 1 to characterised in that the length of the response time of the detection device is such that it is less than one second. DATED this 13 th day of April 1999 DRAGERWERK AG WATERMARK PATENT TRADEMARK ATTORNEYS 290 BURWOOD ROAD HAWTHORN VICTORIA 3122 AUSTRALIA IAS:JPF:VRH DOG 26 AU3917895.WPC Abstract Method for the determination of the concentration of alcohol in exhaled air. A method for the determination of the concentration of in exhaled breath is to be improved so that oral *...alcohol in the breath sample can be detected by a gas sensor which operates with a time resolution of a few seconds. 5 This object is achieved by the steps of delivering a first gas sample into the measuring cell at a first time t at the beginning of the exhalation and recording a first measuring curve delivering a second gas sample into ooo the measuring cell at a second time t t 3 during the same exhalation, at which the breath from the mouth has been .eliminated, and determining a second measuring curve determining a predetermined first parameter i, from the first measuring curve (14) and a predetermined second •SSO parameter i 2 from the second measuring curve and "comparing the parameters i and i 2 of an exhalation with one another. (Figure 2)