BREATH DIFFERENCES: ASSESSMENT OF SUBJECT RELATED DIFFERENCES BETWEEN SUCCESSIVE BREATH ALCOHOL SAMPLES

P J Goran, Miss S I Weston, J R Louis and M D OsseltonCentral Research and Support Establishment, Home Office ForensicScience Service, Aldermaston, Reading, RG7 4PN, UK.

SUMMARY. Differences in concentration between successive breath alcohol samples measured a few minutes apart have been a problem in Great Britain since the introduction of evidential breath alcohol testing in 1983. A national survey in 1984 involving 41,565 drink/driving cases reported that in 1.6% of cases there were breath alcohol differences greater than 20%. Experiments were conducted with subjects having different lung capacities.

The results suggested that differences of greater than 20% in alcohol level between successive breath samples are likely to be due to random regurgitation or eructation and are not related to a subject's lung capacity or other normal respiratory performance.

INTRODUCTION. Evidential breath alcohol testing was introduced into Great Britain in 1983 and since that date over half a million tests have been carried out. In April 1984, a year after the introduction of Evidential Breath Alcohol Testing, public concern was expressed over the performance of the instruments used. This resulted in the initiation of a National Six Month Survey of all aspects of the Breath Alcohol Testing Programme [1], Breath alcohol differences of 20% or more were recorded between successive breath samples in 1.6% of the cases recorded in the Survey so it was decided to examine the possible causes for these differences and the work undertaken by the Home Office Central Research and Support Establishment (CRSE) is reported in this paper.

In Great Britain a complete Breath Test requires 2 successive breath samples to be taken a few minutes apart. The lower of the 2 results obtained may be used in evidence for a prosecution under the Road Traffic Act 1988. The prescribed alcohol levels in Great Britain under the Road Traffic Act 1988 are Blood 80mg/100ml, Urine 107mg/100ml and Breath 35ug/100ml. The 2 evidential breath alcohol testing instruments approved for police use in Great Britain at the present time are the Lion Intoximeter 3000 and the Camic Breath Analyser.

EXPERIMENTAL, RESULTS AND DISCUSSION; Subject Related Aspects.This study concentrated on the subject related aspects as follows:- (i) Variation in individual Lung Capacity (FVC), (ii) Variation in individual Breathing Technique, (iii) Variation in individual Breath Temperature and (iv) Effect of the mucous membrane of the Upper Respiratory Tract.

The experiments received Medical Ethics Approval and the volunteer subjects for the experiments were provided with a clearly documented "Briefing for Volunteers", which included a statement that they may withdraw from the experiment at any time without giving a reason.

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Subjects were tested on a Vitalograph Spirometer in order to measure their Force Vital Capacity (FVC) and their heights were recorded, since FVC is related to height. The Forced Vital Capacity (FVC litres) is the amount of air which can be expired from the lung following a deep inspiration and expiration of air. The FVC will give a measure of a subject's lung capacity and so an indication of an individual's ability to use the evidential breath testing instruments.

Fifty subjects were tested and from these 20 were selected (10 male and 10 female) on the basis of their FVC and height in order to give a wide spread of FVC values ranging from 7.5 litre to 2.9 litre. The 20 subjects were divided into groups, based on their FVC and height, and experiments were undertaken with small groups at any one time. The subjects assembled at approximately 9.00am following the consumption of a normal light breakfast.

Drinks were dispensed as 50ml quantities of a spirit of the subject's choice diluted with 50ml of a mixer, such as Tonic.

The total volume of spirit consumed, over a period of 1.5 hours, was 200ml or 250ml, based on a subject's weight and tolerance, and sufficient to produce an approximate breath alcohol level of 40-50ug/100ml.

The display on the Lion Intoximeter 3000 provides a visual indication of the force being used to provide a breath sample by showing a number of bars (1 to 5). The number of bars displayed is related to the force being provided. For example, a 2 bar indication or Gentle expiration is given at an average pressure of 1250 pascals and requires 12 seconds and for a 5 bar indication or Forced expiration an average pressure of 5750 pascals with a time of 6 seconds. The majority of the tests involved subjects providing either a Gentle or a Forced expiration. All the experiments were performed using the Lion Intoximeter 3000.

Variation in Individual Lung Capacity (FVC). Subjects performed two complete breath tests and were instructed to breath normally prior to giving a test. During the first test the subjects were instructed to provide 2 breath samples with a Forced expiration and for the second test, 2 breath samples with a Gentle expiration. The average value of the 2 breath samples was taken in each case. The object of this test was to observe any difference in the breath alcohol value between a Forced and Gentle expiration and any difference caused by the variation in a subject's FVC. The results are summarised in Table 1.

It was noted that in all cases there was a decrease in the breath alcohol value from a Forced to a Gentle expiration. The actual difference varied between 2ug/100ml and 7ug/100ml and the percentage difference varied between 4% and 24%. The ability of subjects with a large FVC to provide a large breath sample did not always influence the differences observed between breath samples given with a Forced or Gentle expiration.

Variation in Individual Breathing Techniques. As recorded by several workers such as Wright [3] and Jones [4], breathing techniques can produce differences in breath alcohol values. The obvious techniques such as Hyperventilation and Hypoventilation were not pursued since these have been seen to produce a decrease and increase respectively in the breath alcohol value. Instead differences in breathing technique, which would appear to be normal to a police

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officer conducting a breath alcohol test, were considered. The techniques examined were as follows: (a) breathing through the Mouth or the Nose only, prior to providing a breath sample and (b) varying the way in which the sample was given, eg. Forced or Gentle and (c) any combination of these techniques.

All of the possible combinations were investigated but only the extreme condition results are presented since they are the ones most likely to produce a significant difference in alcohol level between successive breath samples.For these experiments the number of volunteers was 6: 3 male from the higher FVC groups and 3 female from the lower FVC groups.

Large differences were noted when subjects breathed through their Nose or their Mouth prior to giving a breath sample with either a Forced or Gentle expiration but the largest and most consistent differences were given by subjects breathing through their Nose followed by a Forced expiration, and through their

Mouth followed by a Gentle expiration. The results are given in Table 2.These results were confirmed with another group of 8 subjects with different Lung Capacities who were tested repeating the same experimental procedure.

The maximum difference observed during all these experiments involving variation in breathing technique was 24% between two successive breath samples and an actual difference of 14ug/100ml at a breath alcohol level of 58ug/100ml produced by a male subject with an FVC of 6.3 litres.

Variation in Individual Breath Temperature. When conducting the study into breathing techniques with the 6 subjects the variation of individual breath temperature was also examined.

Other workers [4, 5, 6, 7, 8] have already considered this and established that sequential breathing through the Nose or Mouth will produce significant breath temperature differences of up to l'C. Our approach was to look at possible breath temperature differences which would arise through providing breath samples with a Gentle or Forced expiration.

The breath temperature was measured using a Digitherm Ltd, UK, fast response probe located in one arm of a 'T' piece 10mm from the tip which was attached to the conventional Intoximeter mouthpiece. The other arm of the 'T' piece was attached to the breath sampling tube of the breath testing instrument. Differences in breath temperature up to 0.6'C were recorded.

The variation found between successive breath alcohol samples from the previous experiments involving variation in breathing technique could not be wholly explained from the differences in breath temperature found in our experiments or reported by other workers. We therefore decided to consider the effect of the Mucous Membrane of the Upper Respiratory Tract, which has been previously described by Jones [4].

Effect of the Mucous Membrane of the Upper Respiratory Tract.

The Upper Respiratory Tract comprises the nose, mouth, nasal passages,nasopharynx, larynx, trachea and bronchi. This is covered with a MucousMembrane which is approximately 98% water [9], This membrane conditions theinspired air by warming and wetting it in order to assist with the gaseous

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exchanges which take place in the alveoli. The ethanol in a breath sample will dissolve to some extent in the surface of the Mucous Membrane of the Upper Respiratory Tract and equilibrate with the inspired and expired air. The most likely factors to effect this equilibrium are changes in the temperature of the inspired air or an extreme breathing technique used by a subject.

When a breath test is carried out in a stable normal room temperature of around 22'C, differences in breath temperature will only be likely to contribute a small effect. Differences between successive breath samples caused by breathing through the Nose or Mouth combined with Gentle or Forced expiration can produce large differences as has been shown. The different breathing techniques appear to have a pronounced disrupting effect on the equilibrium between the ethanol vapour and the Mucous Membrane of the Upper Respiratory Tract.

To test this observation we constructed a simple model of the nose, mouth and nasal passages of the Upper Respiratory Tract.

This comprised a plastic tube of diameter 20mm and length of 300mm covered on the inner surface with a layer of chamois leather. The chamois leather surface was moistened and an ethanol vapour sample passed through the tube for about 20 minutes in order to allow the ethanol vapour to come into equilibrium with the surface of the chamois leather. A simulated breath test was carried out using an ethanol vapour sample of the same concentration. This test was followed by tests where the equilibrium between the ethanol vapour and inner chamois leather surface of the tube was disrupted by passing 1 to 5 litres of clean room air through the apparatus. The results showed differences of up to 8% with the 5 litre room air purge. The equilibrium between the ethanol vapour sample and the chamois leather surface of the apparatus had been disrupted and produced a similar difference in the ethanol vapour level to that which we had observed with human subjects when the Mucous Membrane of the Upper Respiratiry Tract was disrupted by varying breathing technique.

CONCLUSIONS. The following conclusions were reached from the results

(a) A subject with a large Forced Vital Capacity (FVC) may not necessarily be able to produce large breath differences between successive breath samples.

(b) A difference in breath temperature between successive breath samples will only make a small contribution when tests are conducted under normal conditions at room temperature.

(c) The largest differences were caused by differences in breathing technique. This, to some extent, may reflect differences in breath temperature but will mainly involve disruption of the equilibrium between the ethanol vapour and the Mucous Membrane of the Upper Respiratory Tract. The largest difference recorded between successive breath samples was 24%, however this would not account fully for all of the 1.6% cases giving differences of 20% or more noted in the National Six Month Survey [1] for differences of over 80% were recorded.

We suggest therefore, that many of the differences noted in the National Six

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Month Survey [1] may have been produced by some form of mouth alcohol which could be produced by regurgitation or eructation between breath samples or during the provision of a sample. As breath differences between successive samples are dependent on the subject's breath sample it would appear that a possible way of dealing with this problem would be to incorporate a mouth alcohol detector in future evidential breath alcohol testing instruments.

REFERENCES

1. Cobb, P.G.W. and Dabbs, M.D.G. (1985). Foreword by Professor Sir William Paton, FRS. Report on breath alcohol measuring instruments. HMSO Publication, ISBN 0 11 3408064.

2. NPL Report BCS 2 (1983). BCS scheme for evidential breath testing. HMSO Publication, ISBN 0143-7321.

3. Wright, B.M., Jones, T.P. and Jones, A.W. (1975). Breath alcohol analysis and the breath:blood ratio. Med Sei Law, 15, 205-210.

4. Mason, M.F. and Dubowski, K.M. (1976). Breath-alcohol analysis; uses, methods and some forensic problems - review and opinion. J For Sei, 21, 9-41.

5. Jones, A.W. (1982). How breathing technique can influence the results of breath-alcohol analysis. Med Sei Law, 22,275-280.

6. Jones, A.W. (1982). Quantitative measurements of the alcohol concentration and temperature of breath during a prolonged exhalation. Acta Physiol Scand, 114, 407-412.

7. Marcol, Z.S. and Arab, A. (1988). Increase in oral temperature by hyperemisation and its significance for the determination of breath alcohol content. Atemalkohol, 4.1-2, 55-59.

8. Schoknecht, G., Kophamel, B. and Barduhn, B. (1989).

Determination of temperature in breath-alcohol analysis Blutalkohol, 26, 137-147.

9. Kilburn, K. H. (1977). Clearance mechanisms in the respiratory tract.In D. H. K. Lee (Ed.), Section 9: Reactions to environmental agents, Handbook of Physiology (pp. 243-262).

Bethesda, Maryland, USA: American Physiology Society.

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FORCED AND GENTLE EXPIRATIONS (20 SUBJECTS)

TABLE 1

GROUP HEIGHT(m)

FVC(1)

DECREASE (yg/100ml)

DECREASE%

1* 1.88-1.78 7.5-6.4 5-2 16-52* 1.83-1.70 6.4-5.0 7-2 24-43# 1.79-1.57 4.6-4.1 6-3 24-84# 1.75-1.55 3.9-2.9 5-3 17-5

* 5 Males # 5 Females

TABLE 2BREATHING THROUGH NOSE OR MOUTH, NOSE FORCED AND

MOUTH GENTLE EXPIRATION (6 SUBJECTS)

SUBJECT HEIGHT(m)

FVC(1)

BREATH VALUE (yg/100ml)

NOSE FORCEDDECREASE (yg/l00ml)

DECREASE%

1* 1.80 6.4 45 8 182* 1. 87 5.4 36 8 22

3* 1.83 5.3 58 14 244# 1.79 4.1 58 12 21

5# 1.70 3.4 46 9 20

6# 1.55 2.9 46 8 17

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