Blood alcohol concentration measuring from respiratory air

A method and apparatus for measuring a blood alcohol content value by means of a breath alcohol concentration as well as for securing the reliability of this measured value. The apparatus comprises: sensor elements (1) for obtaining a measured alcohol concentration value from an incoming exhalation air stream; sensor elements (1) for obtaining a measured carbon dioxide concentration value from the same exhalation air stream (9); as well as first output elements (2) for producing, if necessary, a result proportional at least to a blood alcohol content. The apparatus further includes a first memory (M1) for storing a predetermined carbon dioxide lower threshold value or lower threshold values (R1, R2, R3 and/or Rf) and/or an upper threshold value or upper threshold values (R4, R5, R6 and/or Rg) and a first comparing element (C1) for comparing the measured carbon dioxide concentration value to said threshold values as well as a first logic element (L1) for producing outputs of a preset type depending on whether the measured carbon dioxide concentration fails to reach or exceeds the predetermined lower threshold values or upper threshold values.

BACKGROUND OF THE INVENTION 
The present invention relates to a method for confirming the reliability of 
a blood alcohol concentration value to be measured from respiratory air. 
In this method, the incoming exhalation air is sampled during exhalation, 
for at least one measured alcohol concentration value and, during the same 
respiratory stage, it is sampled for at least one measured carbon dioxide 
concentration value. A result is produced which is proportional to the 
blood alcohol concentration value and which is based on one or more 
measured alcohol concentration values obtained during exhalation from the 
lungs. 
The invention relates also to an apparatus for implementing such 
measurement, said apparatus comprising sensor elements for obtaining a 
measured alcohol concentration and carbon dioxide concentration value from 
the incoming exhalation air stream as well as output elements for 
producing, if necessary, a result which is proportional at least to the 
blood alcohol concentration. 
For quite some time, the detection of blood alcohol content has been 
effected by means of testing devices which measure the air stream exhaled 
by a subject for its alcohol concentration which, as known, is to a 
certain degree proportional to the blood alcohol content, provided that 
the measured exhalation air originates in the deep lungs, and thus 
consists of so-called alveolar gases. Hence, the measurements are based on 
the hypothesis that a given alcohol concentration value measured from 
exhalation air always corresponds to a given blood alcohol concentration 
value. However, an effort to determine blood alcohol concentration by 
means of the alcohol concentration in exhalation air involves several 
sources of error. The publication DE 2,928,433 pursues a solution to the 
problem that the alcohol concentration of exhalation air fluctuates in 
time with the heart rate, which of course is not the case with the 
concentration of blood alcohol. As a solution to this problem, the cited 
publication discloses a control device capable of logical functions and 
calculation. On the other hand, the publication U.S. Pat. No. 5,376,555 
describes an arrangement for eliminating the effect of possible, so-called 
mouth alcohol at the initial stage of sampling the respiratory air. The 
fact is, namely, that if alcohol has been ingested just prior to 
measuring, the alcohol contained in the mouth as a result thereof produces 
a relatively high concentration peak in the alcohol content measured at 
the start of a breath sample. The effect of this peak is eliminated as 
described in the cited publication by making use of the carbon dioxide 
concentration also measured at the early stage of exhalation. If this is 
not done, the result may be a high breath alcohol concentration and, on 
the basis of presumed correlation, a too high estimate for blood alcohol 
content that does not correspond to true blood alcohol content. Thus, an 
object of the cited publication is to eliminate the incorrectly excessive 
alcohol concentration caused by mouth alcohol. 
In addition to the above sources of error, there are other sources of error 
which produce too low an alcohol concentration measure with respect to 
true blood alcohol content. For example, if a subject takes a few or 
several very deep breaths to create a hyperventilation prior to measuring 
alcohol concentration from alveolar air, the alcohol concentration measure 
obtained thereafter will be lower than it would be had the subject 
breathed in a normal manner. As a result of this, the estimate of blood 
alcohol content made on the basis of the measured value is also too low. 
This is the case even if the air exhaled by a subject in actual alcohol 
measuring has a sufficient volume and comes from the deep lungs in a 
proper manner and, thus, consists of alveolar gases. This hyperventilation 
has been described e.g. in the book Z. Kalenda: MASTERING INFRARED 
CAPNOGRAPHY, 1989. 
An incorrect result is also obtained if a subject, during measuring, 
restricts the amount and/or duration of his or her exhalation. Also in 
this case the measured alcohol concentration will be lower than what it 
would be had the subject exhaled from the deep lungs in a normal manner 
and also the estimate of blood alcohol content made on the basis of the 
measured value will be too low. 
A solution to this latter problem has been pursued e.g. by training the 
measuring device operating personnel, whereby the measuring device 
operator aims to oversee that a subject being examined exhales properly 
into the measuring device. However, this procedure is highly unreliable 
and different persons have substantially different pulmonary capacities 
and, thus, there are no guarantees regarding a sufficient exhalation time 
and/or exhalation volume. 
There are also situations which can produce an excessive measured alcohol 
concentration value. Such a situation is for example hypoventilation which 
is a reverse situation to the above hyperventilation and in which a 
subject breaths less than normal. In a hypoventilation situation, the 
CO.sub.2 concentration and alcohol concentration of an alveolar gas are 
higher than which would be the values correctly corresponding to the 
concentrations in blood. Thus, the alcohol concentration determined from 
an alveolar gas in a hypoventilation situation is higher than the 
equilibrium alcohol content of the human body and blood. In 
hypoventilation, a subject can be falsely convicted of intoxicated driving 
if the hypoventilation is not detected. 
The publication U.S. Pat. No. 3,830,630 discloses a system, wherein a 
resistance bridge consisting of filaments is used for measuring both 
CO.sub.2 -content and alcohol content from exhalation air. These two 
content measurements are linked to each other such that, if the measured 
carbon dioxide content rises to a minimum value of 4.5%, the resulting 
alcohol measurement is found to be correct. The cited publication states 
further that the CO.sub.2 -content and alcohol content are in equilibrium 
with blood alcohol content when the carbon dioxide content is 5%-5.25%. As 
for the above-described error situations, this prior art system only 
eliminates those caused by hyperventilation and even that requires that it 
indeed be alveolar exhalation air which is being measured. The publication 
mentions nothing about the necessity of monitoring this, nor does it 
describe any means for securing this aspect. This system may cause further 
errors for the reason that various persons have individual differences in 
the carbon dioxide concentration of a normal alveolar gas, the fluctuation 
range being roughly 4.7%-5.5%. If, for example, the normal alveolar 
CO.sub.2 -content of a person is 5.5% and the person blows into an alcohol 
measuring device and stops exhalation before the exhalation air comes from 
the sufficiently deep lungs, the exhalation may have a maximum CO.sub.2 
-content of for example 4.6%. According to the cited publication, this 
result is acceptable. As a matter of fact, the alcohol content measured 
from this particular exhalation is too low. 
SUMMARY OF THE INVENTION 
Hence, an object of the invention is to provide a method and an apparatus, 
whereby it is possible to make sure that the alcohol concentration 
measured from exhalation air is as correct as possible and thus in a per 
se known manner as proportional as possible to the blood alcohol content 
of a subject being examined. A particular parallel object of the invention 
is to make sure that a subject being examined does not have a chance to 
exert a lowering effect on the measured alcohol concentration value by 
taking a few or several deep breaths prior to measuring and/or by 
restricting the duration and/or volume of his or her exhalation during 
measuring, i.e. by using hyperventilation. Likewise, a particular second 
parallel object of the invention is to try and prevent a subject being 
examined from involuntarily acting to increase the measured alcohol 
concentration value by restricting the duration and/or volume of his or 
her exhalation prior to measuring, i.e. from ending up in hypoventilation. 
A third object of the invention is to try and eliminate the effect of 
differences in carbon dioxide concentrations found in exhalation air 
between individuals on the measured result and its reliability. A fourth 
object of the invention is to provide the operator of an alcohol 
concentration measuring device with a clear indication about the 
reliability of each individual measurement and whether other, and which, 
further measures are needed. Thus, the object is to replace some of the 
supervision required of a measuring device operator with precise and exact 
information produced on the basis of the data measured by the measuring 
apparatus itself. 
The above-described drawbacks can be eliminated and the above-defined 
objects can be achieved by means of a method of the invention, which is 
characterized by what is defined in the claims and by means of an 
apparatus of the invention, which is characterized by what is defined in 
the claims. 
The most important benefit of the invention is that, when applying a method 
and using an apparatus in accordance therewith for measuring alcohol 
concentration from the exhalation air stream of a subject, it is clearly 
and reliably verifiable whether or not the measured alcohol concentration 
value is perfectly applicable or possibly whether or not the measured 
value is applicable to some extent. Thus, by means of the invention it is 
possible to verify or confirm the reliability of the level of blood 
alcohol content determined by means of the concentration of breath 
alcohol. In addition, when proceeding according to the invention, it is 
possible to detect whether a subject being examined affects intentionally 
and/or unintentionally the measuring result. Furthermore, in the most 
preferred embodiments, it is possible to make sure that the final measured 
values are obtained from real alveolar breath and the effects of 
differences in individual carbon dioxide concentrations existing in 
exhalation air can be eliminated.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In a method as defined by the invention, the exhalation air of a subject is 
first measured for its alcohol concentration either continuously or 
periodically by using some prior known method, such as infra-red 
absorption, as explained hereinbelow in reference to an apparatus. In 
addition to this and according to the invention, the exhalation air of a 
subject is measured for its carbon dioxide concentration either 
continuously or periodically in some prior known manner, such as infra-red 
absorption, explained hereinbelow in reference to an apparatus. 
Thus, from the exhalation air is extracted at least one measured alcohol 
concentration value Ra and during the same respiratory cycle at least one 
measured carbon dioxide concentration value Rb. In the context of this 
invention, the same respiratory cycle means that between each measurement 
of alcohol concentration and each measurement of carbon dioxide 
concentration there is a time difference Td which is small in relation to 
a total exhalation time Tm or the time difference Td is zero, i.e. there 
is no time difference at all. The asterisks shown in FIG. 3B represent 
certain possible, periodically effected, separate alcohol and carbon 
dioxide concentration measurements. On the other hand, the graphs shown in 
the figures represent results from continuously effected measurements. 
Generally speaking this indicates that, if the alcohol concentration Ra is 
measured for example over an initial stage F1 or a rising stage F2 of 
exhalation, the carbon dioxide concentration must also be measured over 
the initial stage F1 or rising stage F2 of exhalation, this being the 
procedure in the cited publication U.S. Pat. No. 5,376,555 for detecting 
mouth alcohol. 
Generally, the exhalation air stream comprises sequences or stages F1-F4 
illustrated in FIG. 3A. Right at the beginning of exhalation there is an 
initial stage F1, the air representative thereof coming from an 
anatomically inactive part of the body, in other words, from the mouth and 
upper respiratory tracts, as well as including a "dead" gas which comes 
from the initial volume of a measuring apparatus and in which the 
proportion of air coming from the lungs increases as exhalation continues. 
This is followed by a plateau stage F3, wherein the gas comprises nothing 
but a deep lung, so-called alveolar gas. At the end of this stage there is 
obtained an end-tidal measuring value. Over a final stage F4, the 
concentration values fall down rapidly. 
According to the present invention, the measuring is effected on alcohol 
concentrations and carbon dioxide concentrations occurring particularly in 
the latter stage of exhalation, the measuring of both of these being 
targeted at the deep lung, so-called alveolar exhalation gas, which occurs 
or should occur over the plateau stage F3 of alcohol concentration and the 
detected carbon dioxide concentration. Thus, the invention is based on the 
unexpected discovery that, unlike in the beginning of exhalation, there is 
a parallel correlation between alcohol concentration Ra and carbon dioxide 
concentration Rb at the later stage of exhalation. In order that the 
alcohol concentration measured from alveolar air be as highly 
representative as possible of the real blood alcohol content, the output 
is produced by using the breath alcohol concentration measured at quite a 
late stage of exhalation for obtaining it as surely as possible from the 
deep lung alveolar gas. 
According to the invention, the carbon dioxide concentration of exhalation 
air is also measured for an output from an essentially equally late stage 
of exhalation in order to obtain also the carbon dioxide content as surely 
as possible from the deep lung alveolar gas. 
Normally, it is desirable to measure both concentrations over the plateau 
stage F3 of exhalation, provided that one exists in the exhalation. In 
order to make use of this phenomenon in a measuring of the invention, the 
measurement of alcohol concentration and that of carbon dioxide 
concentration are carried out over the same exhalation stage F3 and 
typically the time difference Td between each alcohol concentration 
measurement and a corresponding carbon dioxide concentration measurement 
is no more than 30% of the total exhalation time Tm. The smaller the time 
difference Td between the alcohol concentration measurement and the carbon 
dioxide concentration measurement, the more reliably these concentrations 
have been measured during the same respiratory stage. If carbon dioxide 
and alcohol are both measured continuously, the time difference Td is very 
small. 
According to the invention, if one or more carbon dioxide concentration 
values measured from exhalation air stream or all measured values Rb are 
lower than a predetermined lower threshold value R1 and/or R2 and/or R3 
and/or Rf, special actions are taken for delivering this information in a 
suitable form to the operator. In exactly the same way, according to a 
second principle of the invention, if one or more values of carbon dioxide 
concentration measured from an exhalation air stream or all measured 
values Rb are higher than a predetermined upper threshold value R4 and/or 
R5 and/or R6 and/or Rg, special actions are taken to deliver this 
information in a suitable form to the operator. Normally, when a person 
exhales and especially when he or she exhales from the deep lungs, i.e. an 
alveolar gas, the latter has a carbon dioxide concentration which is quite 
accurately within the range of 4.7-5.5% CO.sub.2. Generally, the 
exhalation air coming from the lungs has a carbon dioxide concentration 
value which is close to 5% CO.sub.2. In case the air exhaled by a person 
has a CO.sub.2 concentration which departs from the range of 4.7-5.5%, 
there is some special reason for this, as explained in the work Z. 
Kalenda: MASTERING INFRARED CAPNOGRAPHY, 1989. 
FIG. 3A illustrates carbon dioxide and alcohol concentrations appearing in 
normal exhalation coming from the deep lungs, wherein the passages of 
concentration graphs Ra and Rb over a plateau stage F3 represent alveolar 
concentrations. Thus, the carbon dioxide concentration Rb has a final 
value Rbe which rises roughly to the value of 5% CO.sub.2, the alcohol 
concentration having a corresponding final value Rae (a so-called 
end-tidal value) which is correct and good for disclosing a value 
proportional to the blood alcohol content or a blood alcohol concentration 
value calculated therefrom. Thus, the resulting blood alcohol content 
value is highly equivalent to the true value. 
FIG. 3A also includes possible carbon dioxide concentration lower threshold 
values R1-R3, whereby a carbon dioxide concentration value above the 
uppermost R1 thereof indicates the usefulness of an exhalation and, as far 
as the latter is concerned, a possibility of producing a useful alcohol 
concentration value. This application employs graded lower threshold 
values R1, R2 and R3 but it is possible to employ just a single lower 
threshold value R1 or two lower threshold values R1 and R2 or possibly a 
larger number of lower threshold values than the above three or a variable 
lower threshold value Rf to be described hereinbelow. 
According to the invention, the lower threshold values are generally set 
lower than or equal to 4.7% CO.sub.2, although it is conceivable to set 
some lower threshold value within the range of 4.5-5.0% CO.sub.2. Thus, a 
single employed lower threshold value R1 can be set e.g. within the range 
of 4-4.7% CO.sub.2 or within the range of 3.5-4% CO.sub.2 or at a value 
lower than this, depending on the desired accuracy and reliability of the 
result. In case two lower threshold values R1 and R2 are employed, the 
former can be set e.g. within the range of 4-4.7% CO.sub.2 and the other 
within the range of 3.5-4% CO.sub.2 or R1 can be set within the range of 
3.5-4.7% CO.sub.2 and R2 at a value lower than 3.5% CO.sub.2. If three 
lower threshold values R1, R2 and R3 are employed, these can be set e.g. 
within the ranges of 4-5.5% CO.sub.2, 3.5-4% CO.sub.2 and 3.0-3.5% 
CO.sub.2, respectively, or in some other manner. The variable lower 
threshold value Rf, or a function resulting in variable lower threshold 
values, is designed such that the above principles are carried out. 
In a similar manner, FIG. 3C also includes possible upper threshold values 
R4-R6 for carbon dioxide concentration, the carbon dioxide concentration 
value setting below the lowermost R4 of these indicating the acceptability 
of exhalation and, in that respect, a possibility of obtaining a useful 
alcohol concentration value. This situation involves the use of graded 
upper threshold values R4, R5 and R6 but it is possible to employ just one 
upper threshold value R4 or two upper threshold values R4 and R5 or 
possibly more numerous upper threshold values than said three or a 
variable upper threshold value Rg to be described hereinbelow. 
According to the invention, the upper threshold values are generally set to 
be higher than or equal to 5.5% CO.sub.2, although it is conceivable to 
set some upper threshold value within the range of 5.3-6.0% CO.sub.2. 
Thus, one employed upper threshold value R4 can be set e.g. within the 
range of 5.5-6% CO.sub.2 or within the range of 6-6.5% CO.sub.2 or at a 
value higher than this, depending on the desired accuracy and reliability 
of the result. In case two upper threshold values R4 and R5 are used, the 
first can be set e.g. within the range of 5.5-6% CO.sub.2 and the second 
within the range of 6-6.5% CO.sub.2 or R4 can be set within the range of 
6-6.5% CO.sub.2 and R5 at a value higher than 6.5% CO.sub.2. If three 
upper threshold values R4, R5 and R6 are employed, these can be set e.g. 
within the range of 5.5-6% CO.sub.2, 6-6.5% CO.sub.2 and 6.5-7% CO.sub.2 
or in some other way. A function producing the variable upper threshold 
value Rg or variable upper threshold values is designed so as to fulfill 
the above-described principles. 
The previous paragraph has mainly dealt with fixed predetermined threshold 
values but, according to the invention, it is also possible to employ a 
predetermined variable threshold value or threshold values Rf and/or Rg. 
Such a variable threshold value Rf and Rg is determined in accordance with 
some predetermined function separately at each measurement on the basis of 
carbon dioxide concentration and/or alcohol concentration measuring 
results yielded by that particular measurement. Hence, the threshold value 
Rf is a continuous function and different for each measurement but, as the 
function setting the threshold value Rf is predetermined, all results 
calculated by means of the function are also predetermined since each 
starting value or combination of starting values is matched by an 
unequivocally corresponding threshold value Rf. In addition to the 
measured carbon dioxide concentration and/or alcohol concentration, the 
function can be adapted to account for other factors contributing to the 
reliability of measuring. Naturally, it is possible to employ a single 
variable threshold value or several variable threshold values or variable 
and fixed threshold values together. Also the subsequently described 
operating principles apply to variable threshold values. 
FIG. 3B depicts a condition in which even the highest carbon dioxide 
concentration Rb measured in a long and deep-lung exhalation is lower than 
in the above-described normal condition. Such a decreased carbon dioxide 
concentration develops e.g. in a hyperventilation condition, which a 
subject may intentionally create by taking several deep breaths. Thus, the 
alcohol concentration Ra measured during this deep lung exhalation will 
also be lower than what it is in a normal condition without preceding deep 
breaths, although the blood alcohol level is the same in both instances. 
Hence, if the blood alcohol content were reported on the basis of an 
alcohol measuring result over this plateau stage F3, the result would be a 
value which is lower than the true existing value which was correctly 
represented by the alcohol concentration value of FIG. 3A. In this case, 
the highest measured carbon dioxide concentration Rb sets below the second 
threshold value R2, which situation can be reported to the operator for 
example as a detected carbon dioxide concentration (e.g. 3.7% CO.sub.2) by 
a suitable alarm, by suitable further instructions to the measuring device 
operator or by failing to disclose the measured alcohol content or by some 
other means to be described hereinbelow. 
FIG. 3C depicts first of all with a solid line and a dashed line a 
condition in which neither the carbon dioxide concentration Rb nor alcohol 
concentration Ra of exhalation includes any actual plateau stage F3, which 
indicates that a subject has not exhaled from the deep lungs but has 
restricted his or her exhalation during measuring. Thus, the highest 
detected value of carbon dioxide concentration Rb is also lower than a 
normal value, being in this case lower than said third lower threshold 
value R3. Also in this case, the conclusions drawn on the basis of alcohol 
concentration Ra measured from exhalation air and regarding the blood 
alcohol content would be too low in reference to the true blood alcohol 
level, since the alcohol concentration curve Ra of FIG. 3C extends at a 
lower level than the alcohol concentration curve produced by normal 
effective exhalation in a similar situation, as shown in FIG. 3A. In 
addition to this, it can be detected that the exhalation time Tx or 
exhalation volume Vx produced by restricted or reduced exhalation are 
lower than the maximum values Tm and Vm established in normal exhalation, 
as depicted in FIGS. 3A and 3B. In this case as well, the situation can be 
reported to the operator for example as a detected carbon dioxide 
concentration (e.g. 3.1% CO.sub.2) by a suitable alarm, by suitable 
further instructions to the measuring device operator or by failing to 
disclose the measured alcohol concentration or by some other means to be 
described hereinbelow. 
Secondly, FIG. 3C depicts a condition in which the carbon dioxide 
concentration Rb measured at the time of exhalation from the deep lungs is 
higher than in the above-described normal condition. Such an increased 
carbon dioxide concentration develops e.g. in a hypoventilation situation, 
wherein a subject, perhaps due to a tense condition caused by the 
measuring situation, may have even for a rather long time quite a shallow 
breathing with a small amount of air. Then, as he or she is ordered in the 
measuring situation to exhale from the deep lungs, the alcohol 
concentration Ra measured during the emerging exhalation will be higher 
than what it would in a normal situation without preceding shallow 
breaths, even though the blood alcohol content is the same in both 
situations. In this situation, it is possible to detect at least some sort 
of plateau stage and, thus, on the basis of an alcohol measuring result, 
the outcome would be a value which is higher than the truly valid value, 
which was correctly represented by the alcohol concentration value of FIG. 
3A. In this case, however, the highest measured carbon dioxide 
concentration Rb is above the first upper threshold value R4, which 
situation can be reported to the operator for example as a detected carbon 
dioxide concentration (e.g. 6.2% CO.sub.2) by means of a suitable alarm, 
suitable further instructions to the measuring device operator or by not 
disclosing the measured alcohol content or by some other means to be 
explained hereinbelow. In this described hypoventilation situation, the 
exhalation time Tx and exhalation volume Vx are usually normal, as in 
FIGS. 3A and 3B. 
Thus, according to the above-described inventive principle, if the carbon 
dioxide concentration Rb measured from exhalation exceeds the above lower 
threshold value and/or is lower than the above-described upper threshold 
value, the alcohol concentration value Rae measured from the same 
exhalation over its plateau stage F3 or corresponding to the end of 
exhalation (end-tidal) will be accepted as being representative of blood 
alcohol content and, thus, will be reported normally to the operator. In a 
situation like this, the alcohol concentration measured from exhalation 
and the true blood alcohol level have a known reliable correlation. 
On the other hand, if the carbon dioxide concentration value Rb measured 
from exhalation and especially if the highest carbon dioxide concentration 
Rb measured from exhalation, the latter being most often a value Rbe 
appearing at the end of exhalation (end-tidal), is lower than this lower 
threshold value R1 and/or R2 and/or R3 and/or respectively higher than 
said upper threshold value R4 and/or R5 and/or R6, at least this failure 
to reach and/or, respectively, the exceeding of the threshold value is 
output or reported to the operator or the result received on the basis of 
the alcohol concentration measurement is not disclosed at all or the 
operator is given a visual or audible alarm or the operator is supplied 
with instructions to carry out a new measurement after a given period of 
time or this obtained information is otherwise exploited. 
Generally speaking, all such measurements can be categorized as being below 
the carbon dioxide concentration lower threshold value of the invention 
wherein the highest detected carbon dioxide concentration Rb fails to 
reach any of the lower threshold values R1-R3, no matter which stage of 
exhalation the measured CO.sub.2 -result is received from since, according 
to the present knowledge, the carbon dioxide concentration of exhalation, 
unlike the alcohol concentration, does not include concentration peaks. 
As described above, the arrangement of the invention may employ either a 
single carbon dioxide concentration lower threshold value R1 or several 
lower threshold values R1-R2 or R1-R3 and/or either a single carbon 
dioxide concentration upper threshold value R4 or several upper threshold 
values R4-R5 or R4-R6, as described above. 
Special measures can be undertaken according to whichever threshold value 
has not been reached at any given time. Thus, for example, a failure to 
reach the threshold value R1 depicted in the figures could be reported by 
way of an alarm or otherwise to the operator but the detected alcohol 
concentration would be disclosed nonetheless. If the detected carbon 
dioxide concentration fails to reach the lower threshold value R2 or 
exceeds the upper threshold value R5, the apparatus provides e.g. a 
certain fixed period after which a renewed measurement can be effected. 
During the time lapse it is monitored that the subject in question 
breathes normally. If the detected carbon dioxide value fails to reach the 
lower threshold value R3, the measured alcohol content shall not be 
reported to the operator and, instead, the apparatus delivers an 
instruction to subject the person undergoing testing to a blood test. 
Thus, the further actions can be ordered according to how low or 
respectively how high a level the detected carbon dioxide concentration of 
exhalation falls to or respectively rises to, whereby at least a major 
failure would lead to more radical actions. 
However, there is nothing to exclude notifying the operator of the carbon 
dioxide concentration Rb even in the case that the latter is higher than 
said highest determined lower threshold value R1 or lower than the lowest 
determined upper threshold value R4, in other words, the carbon dioxide 
concentration can always be reported to the operator, if desired. 
In addition to the utilization of the above-described carbon dioxide 
measuring and the threshold values defined therefor, the reliability of 
alcohol measuring can be improved by one or more of the following 
procedures. The plateau sections F3 occurring in the exhalation carbon 
dioxide concentration and alcohol concentration can be detected by 
measuring either carbon dioxide concentration Rb or alcohol concentration 
Ra over an exhalation time Tm, either continuously or several times. Thus, 
the plateau section F3 is verifiable by comparing two or more successive 
measured values and differences .DELTA.Ra and/or .DELTA.Rb therebetween. 
In case .DELTA.Ra and/or .DELTA.Rb over a given time difference .DELTA.T 
or volume difference .DELTA.V is smaller than a predetermined value, it 
can be concluded that exhalation has reached the plateau section F3 and in 
this respect a reliable alcohol measurement could be effected. As another 
alternative, it is possible to measure an exhalation time Tx or an 
exhalation volume Vx and to compare these with sufficiently high but 
realistic maximum values Tm and Vm provided by normal exhalation and, if 
the former are to a sufficient degree lower than these maximum values Tm 
and Vm, it can be concluded that a subject has not taken a sufficiently 
clear breath from the deep lungs. The output of alcohol content is 
produced by using either the average or weighted average of alcohol 
concentration Ra calculated over the duration or some portion of the 
duration of the plateau section F3 or a value picked up at some point in 
the plateau section or the highest detected alcohol concentration value, 
which in most cases is the value Rae near the end of exhalation. 
The above-described detection of the plateau section F3 by means of the 
discrimination quantities .DELTA.Ra and/or .DELTA.Rb and/or by means of 
the exhalation time Tx or exhalation volume Vx is in the method of the 
invention intended for yielding secondary, i.e. just additional 
information and reliability. What is essential in view of producing a 
correct alcohol measuring result is that the carbon dioxide concentration 
of exhalation be sufficiently high yet not excessively high, whereby it is 
possible to draw correct conclusions very reliably regarding blood alcohol 
content on the basis of alcohol concentration Ra measured from exhalation 
over the same stage. The detection of the plateau stage F3 by any of the 
above procedures further adds to the reliability at which the measured 
alcohol concentration Ra is used for drawing conclusions regarding the 
blood alcohol content. 
FIGS. 1 and 2 illustrate equipment for carrying out the above-described 
method. First of all, the apparatus includes a conventional flow channel 
10 through which a subject being examined blows an exhalation air stream 9 
and the flow channel is provided with sensor elements 1 for measuring 
alcohol concentration Ra as well as carbon dioxide concentration Rb. 
Furthermore, the apparatus includes necessary first output elements 2 for 
delivering at least a measured alcohol concentration result to the 
operator, if necessary. For a display of carbon dioxide concentration 
according to the invention, an alarm or some other application, the 
apparatus of the invention also includes second output elements 7. 
The sensor elements 1 comprise an infrared radiation source 6 for radiating 
through the channel 10 and, thus, through the exhalation air stream 9. In 
addition, the sensor elements include either two optical infrared sensors 
3a and 3b, each of which is preceded by a band-pass filter 4a and 4b 
transmissive to the wavelength to be measured thereby, or alternatively a 
single optical infrared sensor 3c and two replaceable band-pass filters 4c 
and 4d located in front of the latter and transmissive to each wavelength 
to be measured. Hence, in the former case 1a, one filter-sensor unit 4a, 
3a measures alcohol concentration and the other filter-sensor unit 4b, 3b 
measures carbon dioxide concentration in the respiratory air stream 9. 
Thus, the measuring can be completely or nearly continuous. In the latter 
case 1b, in front of the infrared sensor 3c is alternately replaced the 
filter 4c for alcohol concentration and the filter 4d for carbon dioxide 
concentration in view of alternately measuring the alcohol concentration 
and carbon dioxide concentration of the respiratory air stream. This 
latter case further requires a control element 5 for carrying out 
concentration measurements at fixed intervals and to guide the measured 
alcohol concentration values and measured carbon dioxide concentration 
values to a correct location in the apparatus for further processing. A 
third alternative is to employ two sensors 3a and 3b and, in addition to 
this, two infrared radiation sources 6a and 6b, one being trained at the 
first sensor and the other at the second sensor. This enables a total or 
nearly continuous measurement of both alcohol and carbon dioxide. In this 
configuration, it is not absolutely necessary to have band-pass filters in 
front of the sensors provided that the infrared radiation sources are 
emitting over sufficiently narrow bands. 
According to the invention, the apparatus includes a first memory M1, in 
which the fixed lower threshold value R1, two fixed lower threshold values 
R1 and R2 or three fixed lower threshold values R1-R3 or the variable 
lower threshold value Rf or variable lower threshold values and/or, 
respectively, the upper threshold value R4, two fixed upper threshold 
values R4 and R5 or three fixed upper threshold values R4-R6 or the 
variable upper threshold value Rg or variable upper threshold values, 
described above in reference to the method, are previously stored before 
setting the apparatus in operation. In order to compare these threshold 
values stored in memory M1 and the carbon dioxide concentration measured 
from exhalation air stream 9, the apparatus includes a comparing element 
C1 whose output provides information about which one or which ones of 
these threshold values the carbon dioxide concentration Rb measured at any 
given time fails to reach or exceeds. This information is forwarded to a 
first logic element L1. To this first logic element L1 is also connected a 
second memory M2 in which are stored outputs of a previously set type. 
These previously set type of outputs are, as already described above in 
reference to the method: a) a visual or audible alarm; b) which one of the 
lower threshold values R1 or R2 or R3 or Rf is not reached or the upper 
threshold values R4 or R5 or R6 or Rg is exceeded, i.e. identification of 
seriousness of the failure or respectively that of the exceeding; c) the 
output of measured carbon dioxide concentration and/or a measured carbon 
dioxide concentration curve; d) omission to disclose the result obtained 
on the basis of measured alcohol concentration; e) the apparatus issues, 
according to the degree of seriousness of the failure or exceeding or at 
any time a failure or exceeding occurs, an instruction for carrying out a 
measurement after a given period of time, whereby this given period of 
time can be adapted to depend on how grave is the failure to reach or the 
exceeding of a threshold value in reference to the threshold value itself 
or to the highest lower threshold value R1 or in reference to the lowest 
upper threshold value R4. Just these several threshold values described 
above can be used as an indicator for the seriousness of 
failure/exceeding, such that the failure to reach the higher threshold 
value R1 and exceeding the lowest upper threshold value R4 is less serious 
and the failure to reach the lowest lower threshold value R3 is the most 
serious and the failure to reach the middle lower threshold value R2 lies 
therebetween and, respectively, exceeding the highest upper threshold 
value R6 is the gravest and exceeding the middle upper threshold value R5 
lies therebetween. It is also possible to use just one lower threshold 
value and upper threshold value and to estimate the failure to reach the 
threshold value from there downwards and, respectively, the exceeding of 
the threshold value from there upwards linearly or otherwise according to 
the degree of change. The procedure is similar to the above when using 
variable threshold values Rf. On the basis of this above-described 
information stored in the second memory M2, the first logic elements hence 
produce one or more of these previously set type of outputs regarding 
carbon dioxide by means of the second output elements 7 always according 
to whether the carbon dioxide concentration measured at a given time fails 
to reach or exceeds the predetermined threshold values. In addition to 
this, the first logic element L1 delivers this information to a second or 
third logic element L2 or L3 to be described hereinbelow. 
The measured alcohol value coming from the sensor elements 1 progresses 
first to a calculator D which, according to a predesigned programming, if 
there are several measured alcohol values, effects the calculation of an 
average or, in a predetermined manner, a weighted average of these or the 
selection of the highest of measured alcohol values received. This 
calculated information or several pieces of calculated information advance 
further to the second or third logic element L2 or L3. 
The embodiment of FIG. 1 is further provided with a third memory M3 which 
is supplied with alcohol concentration measuring values and/or carbon 
dioxide concentration measuring values measured during the same exhalation 
for being stored therein. This third memory M3 is further connected to a 
second comparing element C2, wherein the latest one of the above stored 
alcohol concentration measuring values and/or carbon dioxide concentration 
measuring values is compared to the preceding one or ones and the obtained 
difference value .DELTA.Ra and/or respectively .DELTA.Rb is forwarded to 
the second logic element L2. The second logic element L2 compares the 
difference value .DELTA.Ra and/or respectively .DELTA.Rb to the maximum 
values stored in a fourth memory M4 and, if this difference value or 
difference values are lower than the stored maximum values, the apparatus 
concludes that the measured results have been obtained from the plateau 
stage F3 of exhalation 9 and, thus, in this respect, the alcohol measuring 
output is possible by means of the elements 2 on the basis of a value 
received from the calculator D. However, this possible output is 
restricted by means of a restricting connection leading from the first 
logic element L1 to the second logic element L2 for preventing, if 
necessary, the second logic element L2 from producing an output of the 
measured alcohol in case the carbon dioxide concentration detected by the 
first logic element L1 is too low or too high. 
In the embodiment of FIG. 2, the channel 10 for exhalation air stream 9 is 
provided with an instrument 8, which can be e.g. a rotating blade wheel, a 
turbine or some other pressure-difference recognizing element for 
detecting the passage of exhalation air stream 9 through the channel 10. 
In one alternative, the apparatus further includes an element Kv measuring 
the volume Vx of this exhalation air stream 9, whereby the instrument 8 
must of course be of the type that delivers to the measuring element Kv a 
quantity which is proportional to the volume flow. In second alternative, 
the apparatus further includes, and instead of the element Kv, an element 
Kt measuring the time Tx of exhalation air stream 9, whereby the 
instrument 8 must only recognize the existence of the air stream 9. These 
required minimum values for exhalation volume Vx and exhalation time Tx 
are stored in a fifth memory M5. The third logic element L3 compares 
values received from the volume measuring element Kv and/or duration 
measuring element Kt with the values stored in the memory M5 and, in case 
the achieved values are higher than these preset values, the apparatus 
concludes that the measured results have been received from the plateau 
stage F3 and, thus, in this respect, the alcohol measuring output is 
possible by means of the elements 2 on the basis of a value received from 
the calculator D. However, this possible output is restricted by means of 
a restricting connection leading from the first logic element L1 to the 
second logic element L2 for preventing, if necessary, the second logic 
element L2 from producing an output of the measured alcohol in case the 
carbon dioxide concentration detected by the first logic element L1 is too 
low or too high. 
In case the apparatus of the invention is adapted to measure just one 
alcohol concentration value and just one carbon dioxide concentration 
value, said apparatus requires neither the third memory M3, fourth memory 
M4 nor the second comparing element C2. Thus, the calculator D is possibly 
also unnecessary as a single measured value cannot be subjected 
calculations. If the apparatus of the invention is adapted to operate 
without measuring the exhalation volume Vx and time Tx, said apparatus 
requires neither the instrument 8, measuring elements Kv or Kt nor the 
fifth memory M5. Even if stripped of these mentioned components, the 
apparatus of the invention operates as intended but, generally, it is 
preferred that some of these functions be included in the apparatus for 
enhanced reliability. It is obvious that, in practice, the apparatus can 
be designed by using a wide range of different components. 
The dotted lines in FIGS. 1 and 2 indicate a threshold value calculator E 
for calculating, according to a function stored therein, the variable 
threshold value Rf or variable threshold values on the basis of the 
measured alcohol concentration value Ra and/or measured carbon dioxide 
concentration value Rb. This threshold value information is transferred in 
this case just for the duration of a particular measurement into the first 
memory M1 for operation. The first memory M1 is wiped clean of the 
threshold value Rf and respectively Rg prior to storing a new threshold 
value to be calculated in connection with the next measurement. Of course, 
this threshold value calculator E is included in the apparatus only in the 
case that the measuring arrangement includes the use of a predetermined 
variable threshold value.