Note: Descriptions are shown in the official language in which they were submitted.
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The invention concerns an appratus for determining the
alcohol concentration of the blood, with an alcohol-measuring
apparatus that measures the alcohol concentration of the res-
piratory air and a C02-monitoring device that responds to the
C02-content of the resplratory air and has a threshold stage
which generates a signal representing the validity of the alcohol
measurement when the C02-content exceeds a preset value.
An apparatus Or this kind is known from U.S. Pat. Spec.
3,830,630. This apparatus makes use of the principle that the
alcohol concentration Or the blood bears a rixed relationship
to the alcohol concentration Or the respiratory air when the latter,
being red into the alcohol-measuring apparatus, is derived ~rom
the alveoli of the lungs. In order to be sure that this alr ls
alveolar air, the C02 content of the respiratory air is monitored,
since it has been round that when it consists Or alveolar alr the
respiratory air contains at least 4.5 % by vol. C02. The known
apparatus includes a bridge circuit which contains a C02-sensitlve
resistance in one Or its branches and an alcohol-sehsitive
resistance in one Or its other branches. The brldge is so di-
mensioned that the al¢ohol-sensitive resistance is errective
when the C02-sensitive resistance has previously received su~ficient
C02-laden respiratory air, in which case the C02-content Or the
respiratory alr ~ust have exceeded the arorementioned 4.5 % by
vol. A disadvantage of the known apparatus ls the fact that the
sub~ect must breath lnto it several times, e.g. 3 to 5 times,
before the alcohol measurement can be carried out.
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With the aid Or the known apparatus it is posslble to ensure
that the alcohol measurement is carrled out on alveolar air.
However, the correlation factor between the alcohol-concentratlon
of the blood and the alcohol concentration o~ the respiratory
air also depends on the diffusion conditions o~ the lungs. Thus
people whose blood-alcohol concentration is to be determined can
falsify the results of the measurement by manlpulatlng the breath. -
For example, the breath-alcohol concentration can be considerably
reduced by vigorous hyperventllation before a breath-alcohol test,
and thls holds true even if the alcohol measurem~ent is carried
out on alveolar alr. Hyperventilation here means rapid, successive
deep breathlng.
The purpose o~ the invention is to disclose a structural-
ly slmple method whereby previous hyperventilation by the test
subJect can be recognlzed during breath-alcohol measurements.
This problem is solved, proceeding from an apparatus as
described ln detall above, by having the C02-monltoring equipment
lnclude a control stage whlch responds at the start of exhalation
and continues to respond as long as a slgnal lndicatin~ the
lnvalldity Or the alcohol measurement i9 generated and until
the threshold-value stage emits the signal representing valldlty.
- Surprlsingly lt has been found that monitoring the C02-
content of the respiratory air will show not only whether the ex-
pired air originates from the alveoll, but also whether the test
subJect has previously hyperventilated. Unlike the apparatus known
from U.S. Pat. Spec. 3,830,630, however, the measurement of the
C02-content and the alcohol measurement must be carried out on one
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and the same respiratlon stroke. Thls ls guaranteed by the control
stage whlch responds to the start Or exhalatlon. In contrast,
in the case Or the apparatus known from U.S. Pat. Spec. 3,830,630
the sub~ect must breath out several times berore the alcohol
measurement can be carried out. l~lth several successlve resplra-
tlons there is even an increased ~danger Or hyperventilatlon.
Of baslc lmportance are embodlments ln whlch lt ls indi-
cated that hyperventilation has taken place prior to the measure-
ment. The criterion for this ls that the slgnal representlng _
invalidity of the measurement continues to be present even arter
conclusion Or the respiratory stroke determined by the controlstage, i.e. no signal representlng validity has been generated
prior to the end of this respiratory stroke. The end Or the
respiratory stroke can also be determined by the control stage
analogously to the beginning o~ exhalation; however a timing
circuit can also be provided whose tlme constant corresponds
to the mean d~ratlon Or a respiratory stroke and at the end
of which the end Or this stroke is assumed. The indicatlon
o~ the erroneous measurement caused by hyperventllatlon can take
place ln a separate error-lndicating apparatus, e.g. in an opti-
cal slgnalllng apparatus, or the llke. Embodlments are preferred
~ ln ~hich the indicating apparatuses givlng the test results areblocked or at least dimmed out in the case of hyperventilation,
so that the erroneous test value is not indicated at all.
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So as to be able to determine the start of exhalation, the
control stage may include e.g. a flow meter which responds to a
preset minimum flow. However, this calls for additional sensors
in the test duct of the apparatus through which the respiratory
air flows, a feature that is in itself undesirable owing to the
fact that such sensors bring about fluctuations of respiratory air
pressure and lead to condensation of the breath alcohol and hence
to test errors. Better, therefore, are embodiments in which no
supplementary sensors are re~uired. In such an embodiment the
control stage possesses a second threshold value stage that re-
sponds to the CO2-content of the respiratory air and generates
a signal representing the start of exhalation when the CO2-content
exceeds a second predetermined value, the first predetermined
value being below the first predetermined value monitored by the
aforementioned threshold value stage~ This utilizes the principle
that the CO2-content of the surrounding air is usually low and
only starts to rise with the start of exhalatian.
In the presence of irregular breathing it may happen that
the CO2-content fluctuates, especially at the beginning of exhal-
ation. If the second threshold value is here exceeded by several
times in the same respiratory stroke, this will result in an un-
stable operation of the apparatus. This disadvantage will not
arise if a flip-flop circuit is coupled to the first and second
threshold value stages, and if this circuit is put by the signal
from t~e second threshold Yalue stage into a setting in which it
generates the signal representing invalidity of the measurement,
and w~ere the flip-flap can be returned by the signal of the first
threshold stage ta its other setting.
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The testing of the respiratory air for hyperventilation
is preferably carried out independently of the measurement of the
maximum alcohol concentration of the respiratory air. The alcohol
measuring apparatus measures the alcohol concentration of the
respiratory air preferably in a continuous manner and possesses a
storage unit for thema~mum value of the measured alcohol concen-
tration and indicating equipment for the value stored in said unit.
In such alcohol measuring apparatuses it has been found expedient
for the indicating apparatus then to indicate the test result only
when the measurement is considered valid. The test subject in
this case has no possibility of checking whether his manipulation
of the breath has falsified the test result. In the embodiment
heretofore described this goal is most easily achieved by having
the signal of the flip-flop representing invalidity of the measure-
ment block or dim out the indicating apparatus.
Expediently, the signal representing invalidity of the
measurement is shown, e.g. optically, on an error-indicating de-
vice. This expedient is of importance especially in the case of
dimming-out indicators.
In order to facilitate the handling of the equipment the
error indicator will preferahly not light up as soon as the signal
representing invalidity of the measurement is generated, but only
when this signal is present e.g. at the end af a respiratory
stroke. In a first embodiment making this possible, provision is
made for a timing circuit, that is settable by the signal from
the second threshold value stage, to be connected to that stage,
thé output signal of which tim$ng circuit is connected by an and-
gate to the flip-flop signal representing invalidity of the alcohol
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measurement, and sets the error-indicating device to indication of
error whenever the signal representing invalidity still continues
after the expiry of the time span determined by said timing cir-
cuit. The time span of the timing circuit is chosen such that
alveolar air will certainly have been exhaled, independently of
the vital lung capacity of the test subject.
The signal of the first threshold value stage can be linked
via another and-gate to the output signal of the timing circuit,
whereby the flip-flop is returned to the other position when the
signal from the first threshold value stage appears during the
time span established by the timing circuit. If the threshold
value that rules out hyperventilation is reached by the first
threshold value stage, e.g. owing to breath manipulation, only
after expiry of the time span of the timing circuit, then the
test-value indicating apparatus will nevertheless not be released
to indicate the alcohol concentration.
In another embodiment it is provided that two triggering
stages are connected to the second threshold value stage, the
first of which triggering stages responds to the change of signal
of the second threshold value stage that occurs ~hen the second
predetermined threshold value is exceeded, and puts the flip-flop
into its position corresponding to invalidity of the alcohol
measurement, and the second of which triggering stages responds
to the change of signal of the second threshold value stage in
the opposite direction, and it is provided that the output signal
of the second triggering stage is linked through an and-gate to
the flip-flop signal representing invalidity of the alcohol
measurement and sets the error-indicating instrument at error-
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indication. This embodiment has the advantage that it responds
to breath manipulations, e.g. short breathing. The first trigger-
ing stage determining the startof the exhalation process when the
C02-content rises above the threshold value of the second
threshold value stage, while the second triggering stage is re-
leased when the threashold value of the seonc threshold value
stage is exceeded again towards the end of the exhalation pro-
cess. The triggering stages can be monoflops which generate brief
triggering impoulses compared with the duration of the respira-
tion stroke when they are released by side parts of the output
signal of the second threshold value stage,
In what follows embodiments of the invention are explainedin greater detail with reference to drawings.
Fig. 1 shows the time curve of the C02-content of the emitted
air with and without previous hyperventilation, in a
schematic diagram;
Fig. 2 is a block circuit diagram of a first embGdiment of a
measuring apparatus that recognizes the previous hyper-
ventilation, and
!a Fig, 3 is a block circuit diagram of a secand embodiment.
In Fig. 1 the time curve of C02-concentration of the air
emitted by a test subject is denoted by 1. The breath-emission
process begins at the time t = 0 and ends at the time tl. The
C02-concentration increases after the start of breath emission
and exceeds a threshbld value Sl when air is emitted from the
alveoli of the lungs. It is known that the alcohol concentration
of the respiratory air stands in a constant ratio to the alcohol
concentrat~on of the blood when the alcohol concentration is
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measured in alveolar air. The concentration ratio changes,
however, when the test subject has hyperventilated vigorously
before the alcohol measurement. It has been found that the maxi-
mum value of the CO2-concentration attainable during exhalation
decreases considerably when there has been previous hyperventi-
lation. Curve 3 in Fig. 1 shows the variation of CO2-concentra-
tion with the time when there has been previous hyperventilation.
Curve 3 fails to reach the threshold value Sl. This criterion
can be utilized for the recognition of a previous hyperventila-
tion.
Fig. 2 shows a first embodiment of a ~reath-alcohol tester
which avoids measuring error~ caused by previous hyperventilation
of the test subject. The subject breathes out in the direction
of arrow 5 through a test duct 7, in which an alcohol-measuring
sensor 9 of a continuously measuring alcohol tester is located.
Through an analog-digital converter 11 a maximum-value storing
unit 13 is connected to alcohol sensor 9. This stores the maxi-
mum alcohol concentration value measured during the exh~lation
of the test subject. The CQntentS ofmaximu~value storage unit
13 are indicated in a dimming-out indicating instrument 15.
The test duct also contains a CO2-sensor 17 whose signa'l,
corresponding to the CO2-concentration of the respiratory air is
fed to two threshold value stages 19, 21. Threshold value stage
19 determines the start of exhalation and responds at a threshold ,
value S2 (Fig. 1~, which corresponds to a smaller CO2-concentra- '~
tion than the threshold value Sl (,Fig. 1) of threshold value
stage 21, Threshold value stage 19 triggers a timing circuit 23
to the Q-output of which a triggering stage 25, e.g. a monoflop,
is connected, which converts the ascending flank of the output
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signal of timing circuit 23 into a short, e.g. needle-shaped
triggering impulse. The triggering impulse fed to a setting input
S of a flip-flop 27, sets the latter. The indicating instrument
15 of the alcohol tester is connected to the Q-output of flip-flop
27 and remains dimmed out as long as flip-flop 27 remains set.
Flip-flop 27 is reset when the CO2-concentration exceeds threshold
value Sl of threshold value stage 21. The output signal of
threshold value stage 21, which is connected in an AND-gate 29 to
the output signal of the Q-output of timing circuit 23 is fed for
this purpose via an or-gate 31 to the reset input R of flip-flop
27. Flip-flop 27 i5 thus reset when the CO2-concentration exceeds
the threshold value Sl within the time span determined by the
timing circuit. With flip-flop 27 reset the dimming signal which
temporarily indicates invalidity of the alcohol-concentrat.ion
measurement is shut off and indicating instrument 15 shows the
alcohol-concentration value retained in maximum-value storage unit
13.
In order to be ahle to show the signal indicating invalid-
ity o~ the alcohol-concentration measurement even after expiry of
the time span of timing unit 23 in an optical indicating apparatus
33, an and-gate 35 connects the signal of the negated output Q'
of timing unit 23 with the signal of the output Q of flip-flop 27.
The setting input S of a flip-flop 37 is connected to the output
of the and-gate 35. The output Q' of flip-flop 37 controls indic-
ating instrument 33. Indicating instrument 33 shows an error,
i.e. invalidity o~ the alcohol-concentration measurement, when-
ever threshold value Sl of threshold value stage 21 is not reached
during the time span established by timing unit 23. The reset
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inputs R of flip-flops 27 and 37 are connected via a key 39 or the
like *o-a-source of operating voltage V , reset input R of flip-
flop 27 having its connection made through OR-gate 31. With the
aid of key 39 flip-flops 27 and 37 can be put to a defined switch-
ing position at the start o~ the measuring procedure.
The embodiment according to Fig. 3 differs from that
according to Fig. 2 basically only in the CO2-monitoring apparatus.
Wherever functionally similar parts are involved, these are de-
noted by the same reference numbers multiplied by 100. For
explanation of these parts see the description above.
The alcohol tester again contains a test duct 107, an
analog-digital converter 111, a maximum-value storage unit 113
and a dimmable indicating instrument 115.
The CO2-monitoring apparatus, like the embodiment accord-
ing to Fig. 2, includes a threshold value stage 119 for a smaller
threshold value S2 of the CO2-concentration and a threshold value
stage 121 for a larger threshold value Sl of the CO2-concentration.
To threshold value stage 19, unlike this embodiment, however, two
triggering stages 141 and 143 are connected which are released by
the flanks of the output signal of threshold value stage 119 and
then emit brief triggering impulses in both cases. The triggering
stages 141, 143 can be designed as monoflops. Triggering stage
141 determines the ascent o~ the output signal of threshold value
stage 119 when it exceeds the value S2 at the start of the exhal-
ation process. The triggering impulse of triggering stage 141
sets a flip-flop 145 corresponding to flip-flop 27 of Fig. 2, the
Q-output signal af which dims out indicating instrument 115. The
back-setting input R Q~ flip-~lop 145 i connected, through an
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or-gate 147 corresponding to or-gate 31 of Fig. 2, to the threshold
value stage 121, whereby flip-flop 145 is set back whenever
threshold value Sl is reached, and indicating instrument 115 is
released so as to show the value of the alcohol concentration that
has been stored in maximum-value storage unit 113.
Triggering stage 143 receives the flanks of the output
signal of threshold value stage 119 that occur when it falls below
the threshold value S2. Triggering stages 141, 143 thus respond
to flanks of opposite polarity. An or-gate 149 connects the Q-
output signal of flip-flop 145 to the output signal of triggering
stage 143 and sets a flip-flop 151, the output of which in turn
controls an error-indicating instrument 153 corresponding to the
indicating instrument 33 of Fig. 2. Error-indicating instrument
153 thus shows invalidity of the alcohol-concentration measure-
ment when the CO2-concentration threshold Sl is not exceeded
between the start and finish of the exhalation process determined
by triggering stages 141, 143. Reset inputs R of flip-flops 145,
151 are again connected through a key 155 to a source of operating
voltage V~, so that it is possible to switch flip-flops 145, 151
to a defined position at the start of the measurement.
Threshold value Sl s~ould lie approximately in the range
of 4 to 7% by volume CO2, preferably at approximately 5% by volume.
For thres~old value S2 values around 1% by volume CO2 are suit-
a~le,
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