U.S. patent number 4,671,298 [Application Number 06/674,941] was granted by the patent office on 1987-06-09 for isothermal rebreathing apparatus and method.
This patent grant is currently assigned to Meridian Medical Corporation. Invention is credited to Albert L. Babb, Michael P. Hlastala.
United States Patent |
4,671,298 |
Babb , et al. |
June 9, 1987 |
Isothermal rebreathing apparatus and method
Abstract
A isothermal rebreathing apparatus and method for collecting
human breath samples for chemical analysis of the ethyl alcohol
content wherein the breath samples are obtained from a subject
repetitively exhaling into the inhaling from an enclosed, flexible,
variable volume, bag-like collection receptacle which is heated to
maintain the breath sample enclosed therein at a prescribed
temperature, preferably at or near the subject's body temperature,
before extracting the breath sample for subsequent chemical
analysis. The collection receptacle may be enclosed by an airtight
chamber including heaters therein to warm the air around the
collection receptacle in order to regulate the temperature of the
breath sample therein. A bellows section in fluid communication
with the heating chamber allows for inflation and deflation of the
flexible collection receptacle while located in an airtight
environment.
Inventors: |
Babb; Albert L. (Seattle,
WA), Hlastala; Michael P. (Seattle, WA) |
Assignee: |
Meridian Medical Corporation
(Bellevue, WA)
|
Family
ID: |
24708491 |
Appl.
No.: |
06/674,941 |
Filed: |
November 26, 1984 |
Current U.S.
Class: |
600/532;
128/200.13; 128/204.17; 422/108; 422/109; 422/84; 436/132; 436/900;
600/539; 600/540 |
Current CPC
Class: |
G01N
33/4972 (20130101); Y10T 436/204165 (20150115); Y10S
436/90 (20130101) |
Current International
Class: |
G01N
33/483 (20060101); G01N 33/497 (20060101); A61B
005/00 () |
Field of
Search: |
;436/132,900
;422/84,108,109 ;128/718,719,630,725,727,728,201.13,204.17 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
|
|
|
2818605 |
|
Nov 1978 |
|
DE |
|
1168529 |
|
Oct 1969 |
|
GB |
|
Other References
Wright, et al.: Breath Alcohol Analysis and the Blood: Breath Ratio
Medicine Science Law 15(3): 205-210, 1975. .
A. W. Jones: Determination of Liquid/Air Partition Coefficients for
Dilute Solutions of Ethanol in Water, Whole Blood, and Plasma,
Journal of Analytical Toxicology 7:193-197, 1983. .
Mason and Dubowski: Breath Alcohol Analysis: Uses, Methods, and
Some Forensic Problems-Review and Opinion, Journal of Forensic
Science, 33:9-41, 1976. .
A. W. Jones: How Breathing Technique Can Influence the Results of
Breath-Alcohol Analysis, Medical Science Law, 4:275-280, 1982.
.
Harger et al.: Estimation of the Level of Blood Alcohol from
Analysis of Breath II. Use of Rebreathed Air, Journal of Studies in
Alcohol, 17:1-18, 1956. .
A. W. Jones: Effects of Temperature and Humidity of Inhaled Air on
the Concentration of Ethanol in a Man's Exhaled Breath, Clinical
Science, 63:441-445, 1982. .
A. W. Jones: Role of Rebreathing in Determination of the Blood
Breath Ratio of Exhaled Ethanol, JAP: Respir Environ Exercise
Physiol 55:1237-1241, 1983. .
Russell and Jones: Breath Ethyl Alcohol Concentration and Analysis
in the Presence of Chronic Obstructive Pulmonary Disease, Clinical
Biochemistry 16:182-187, 1983. .
Schwartz, et al.: Ein nueues Verfahren zur Bestimmung des
Blutalkoholgehaltes uber die Atemluft bei Bewusstlosen,
Anaesthetist 31:177-180, 1982. .
A. Slemeyer: Analytical Model Describing the Exchange Processes of
Alcohol in the Respiratory System, Alcohol, Drugs and Traffic
Safety, ed. by L. Goldbert, Almqvist and Wiksell International,
Stockholm pp. 456-468, 1981. .
M. P. Hlastala: Multiple Inert Gas Elimination Technique, JAP:
Respir Environ Exercise Physiol 56(1): 1-7, 1984. .
Hlastala and Ralph: Interaction of Exhaled Gas with Airway Mucosa,
Proceedings XXIX, Congress of the International Union of
Physiological Sciences 15:304, 1983. .
Robertson et al.: Respiratory and Inert Gas Exchange During High
Frequency Ventilation, JAP: Respir Environ Exercise Physiol
51:683-689, 1982. .
McEvoy et al.: Pulmonary Gas Exchange During High-Frequency
Ventilation, JAP: Respir Environ Exercise Physiol 52:1278-1288,
1982. .
A. W. Jones: Quantitative Measurements of Alcohol Concentration and
the Temperature of Breath During a Prolonged Exhalation, ACTA,
Physiologica Scandinavia 114:407-412, 1982. .
McFadden et al.: Direct Recordings of the Temperature in the
Tracheobronchial Tree in Normal Man, Journal of Clinical
Investigation 69:700-705, 1982. .
E. R. McFadden: Respiratory Heat and Water Exchange: Physiological
and Clinical Implications, JAP: Respir Environ Exercise Physiol
54:331-336, 1983. .
K. W. Dubowski: Breath Analysis as a Technique in Clinical
Chemistry, Clinical Chemistry 20:966-972, 1982. .
Levett and Karras: Errors in Current Alcohol Breath Analysis,
Alcohol, Drugs and Traffic Safety, ed. by L. Goldberg, Almqvist and
Wiksell International, Stockholm, 1981, pp. 527-532. .
H. Rahn: A Concept of Mean Alveolar Air and the Ventilation-Blood
Flow Relationships During Pulmonary Gas Exchange, Journal of
Physiology, 153:21-30, 1949. .
West and Dollery: Distribution of Blood Flow and
Ventilation-Perfusion Ratio in the Lung, Measured with Radioactive
CO.sub.2, JAP: 15:405-418, 1960. .
L. E. Farhi: Elimation of Inert Gas by the Lung, Respiratory
Physiology 3:1-11, 1967. .
W. S. Fowler: Lung Function Studies, III. Uneven Pulmonary
Ventilation in Normal Subjects and in Patients with Pulmonary
Disease, JAP 1:283-299, 1949. .
Hlastala and Robertson: Inert Gas Elimination Characteristics of
the Normal Lung, JAP: Respir Environ Exercise Physiol 44:258-266,
1978..
|
Primary Examiner: Bashore; S. Leon
Assistant Examiner: Manoharan; V.
Attorney, Agent or Firm: Hughes & Cassidy
Claims
What is claimed is:
1. An isothermal rebreathing apparatus for collecting breath gases
from a subject, for analysis of selected chemical components
comprising, in combination:
a. an enclosed, sample bag having a maximum expanded volume which
is at least as great as the subject's output volume;
b. means for permitting a subject to rebreathe breath gases by
repetitively exhaling the breath gases into and then inhaling the
exhaled breath gases from said sample bag, said means including an
inlet connected with said sample bag for allowing passage of the
breath gases;
c. means for maintaining the temperature of breath gases in the
sample bag in substantial equilibrium with the subject's body
temperature, including means for sensing the temperature of the
breath gases in said sample bag; and
d. means for extracting a sample of the breath gases from said bag
when the sensed temperature of the breath gases are in substantial
equilibrium with the subject's body temperature.
2. An isothermal rebreathing apparatus as set forth in claim 1
further comprising an enclosed heating container, said sample bag
is positioned within said container, said means for permitting a
subject to repetitively exhale into and inhale from said sample bag
further including a mouthpiece connected with said sample bag
within said heating container.
3. An isothermal rebreathing apparatus as set forth in claim 1
wherein said maintaining means further include means for measuring
the subject's actual body temperature and for utilizing said said
actual measured body temperature to establish a reference
temperature, means for heating the breath gases within the
container during the subject's rebreathing, and control means,
responsive to the reference temperature and to the sensed
temperature, for controlling said heating means.
4. An isothermal rebreathing apparatus as set forth in claims 1 or
2 wherein said means for extracting breath gases from said sample
bag includes an evacuation conduit to connected with said sample
bag and means for lowering the pressure within said evacuation
conduit to about 200 mm Hg.
5. An isothermal rebreathing apparatus as set forth in claim 4
wherein said means for lowering the pressure within said evacuation
conduit comprises a vacuum pump.
6. An isothermal rebreathing apparatus as set forth in claim 2
wherein said heating container includes a first chamber for
enclosing said sample bag, a second chamber, and conduit means
interconnecting said first and second chamber for permitting fluid
communication therebetween as the volume of breath gases contained
within said sample bag is increased and decreased as the subject
exhales into and inhales from said sample bag.
7. An ieothermal rebreathing apparatus asset forth in claim 6
further including means for measuring a pressure drop across said
conduit to determine a tidal volume of breath exhaled by the
subject.
8. An isothermal rebreathing apparatus as set forth in claim 3
wherein said heating means comprises at least one incandescent
lamp.
9. An isothermal rebreathing apparatus as set forth in claim 2
wherein said mouthpiece and and said sample bag are connected by a
conduit having an internal diameter of one inch to minimize
internal system resistance to breath exhalations emanating from
subjects experiencing breathing impediments.
10. An isothermal rebreathing apparatus as set forth in claim 2
additionally comprising means, disposed within said mouthpiece for
preheating the breath gases.
11. An isothermal rebreathing apparatus as set forth in claim 10
wherein said breath preheating means includes a plurality of
electrical resistance heating elements formed in a honeycomb
pattern, the plane thereof perpendicular to the direction of flow
of the breath gases.
12. An isothermal rebreathing apparatus as set forth in claim 1
additionally comprising means for directing the subject to inhale
and exhale breath gases at a predetermined frequency.
13. A method of collecting breath gases from a human subject for
analysis of a chemical composition of the breath gases, comprising
the steps of:
a. causing the subject to rebreathe the breath gases by
repetitively exhaling the breath gases into and then inhaling the
exhaled breath gases from a sample bag;
b. sensing the temperature of the breath gases in the sample bag
during the subject's exhaling and inhaling;
c. selecting a reference temperature which is substantially equal
to the subject's body temperature;
d. controlling the temperature of the breath gases in the sample
bag so that the breath gases are brought into substantial
equilibrium with the reference temperature;
e. extracting the rebreathed gases exhaled into the sample bag by
the subject after the temperature sensed within the sample bag has
been brought into substantial equilibrium with the subject's body
temperature; and
f. analyzing the extracted length gases.
14. The method as set forth in claim 13 wherein the reference
temperature is selected by measuring the actual temperature of the
subject's body.
15. The method as set forth in claim 13 wherein the controlling
step includes the step of heating the breath gases in the sample
container to a temperature in substantial equilibrium with the
subject's body temperature.
16. The method as set forth in claim 13 wherein during the causing
step the subject is caused to inhale and exhale through a
mouthpiece connected with the sample container; and wherein the
mouthpiece is preheated to further maintain the breath gases in the
mouthpiece in substantial thermal equilibrium with the selected
reference temperature.
17. The method as set forth in claim 13 wherein the rebreathed
gases are extracted from the sample bag by applying a reduced
pressure thereto.
18. The method as set forth in claim 17 wherein the pressure is
reduced to about 200 mm Hg.
19. The method as set forth in claim 13 wherein a tidal volume of
the breath gases exhaled into the sample bag by the subject is
further measured to ensure that the rebreathed gases exhaled by the
subject contain a sample of alveolar gas originating in a deep
region of the subject's lungs.
20. A method of collecting a breath sample from a human subject for
analysis of the chemical content of the breath sample, comprising
the steps of:
a. causing the subject to repetitively rebreathe breath gases by
exhaling the breath gases into and inhaling the exhaled breath
gases from a sample container;
b. sensing the temperature of the breath gases in the sample
container during the subject's exhaling and inhaling, and
generating a first output of the sensed breath gas temperature;
c. selecting a reference temperature which is representative of the
subject's normal body temperature and generating a second output of
the selected body temperature;
d. maintaining, in response to the first and second outputs, the
breath gases in the sample container during the rebreathing at a
temperature which is in substantial equilibrium with the selected
reference temperature; and
e. continuing to repetitively exhale the breath gases into and
exhale the breath gases from the enclosed sample container to
establish an equilibrium between the temperature of the subject's
breath gases and the selected reference temperature.
21. An apparauts for obtaining breath gases from a subject for
analysis of selected chemical components of the breath gases,
comprising:
a. means for collecting the breath gases, said collecting means
including (i) a sample container, and (ii) an inlet connected to
said sample container, said collecting means being engaged by the
subject to repetitively rebreathe the breath gases through said
inlet, said sample container having a maximum expanded volume which
is at least as great as the output volume of the subject's breath
gases; and
b. means for maintaining the temperature of the breath gases in the
sample container in substantial equilibrium with a selected
reference temperature.
Description
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates generally to chemical analysis of
human breath samples; and, more particularly, to apparatus and
methods for collecting human breath samples for accurate analysis
of their chemical content, in particular their ethyl alcohol
content. The invention takes advantage of the fact that the ethyl
alcohol content of the air located deep in the lungs (alveolar air)
is found to be in equilibrium with the ethyl alcohol content of the
blood; and, by utilizing the known mathematical constant
relationship between the ethyl alcohol in the lungs and the blood
alcohol concentration under equilibrium conditions, a determination
of the exact blood alcohol content based on the content of ethyl
alcohol in the lungs can be made.
As the ensuing description proceeds, those skilled in the art will
appreciate that the present invention can be used in a wide variety
of diverse applications such as: (i) in law enforcement for the
analysis of blood alcohol in suspected drunk drivers; (ii) in
medicine for the chemical analysis of human breath for the
detection or treatment of disease; and (iii) in physiological
evaluation of pulmonary dysfunction.
The foregoing potential applications for use of the present
invention, however, are listed as representative only, and are not
limitative of the scope of the present invention as reflected in
the appended claims.
2. Background Art
In the law enforcement area, it is often necessary to determine the
blood alcohol concentration in units of percent weight by volume of
persons suspected of driving while intoxicated (DWI). Testing of
the blood alcohol content of suspected drunk drivers is not new;
however, the public attitude towards drunk driving has changed in
recent years from that of general apathy to an attitude of anger
and concern. The public has now realized a large percentage of
fatal automobile accidents are caused by drunk drivers. Groups such
as Mothers Against Drunk Drivers (MADD) have organized on a
national level to pressure individual states and the federal
government to adopt tougher drunk driver laws. The success of the
anti-drunk driving lobbies has been evidenced recently by the trend
of many states to raise the alcohol drinking age to twenty-one
years old. In addition, many states are requiring mandatory jail
sentences for individuals convicted of firsttime drunk driving
offenses. Newspapers and magazines are giving increased publicity
to the vehicular death and destruction caused by drunk drivers, and
to the recent legislation enacted to discourage drunk driving.
State governors are using tough anti-drunk driving stances as a
major campaign issue. Tough drunk driving laws have been enacted
and enforced in Europe, Japan, and other countries for years;
however, in the United States, this is a relatively recent
phenomena.
With the prospect of jail and/or large fines facing those charged
with drunk driving offenses, defendants are fighting back in court
with renewed vigor. Their attack is aimed at the cornerstone of the
DWI charge--viz., the accuracy of the blood alcohol test itself,
and the competency of the personnel administering these tests.
Obviously, the most accurate test that could be employed is
analysis of a blood sample per se; but, such a test is invasive
and, therefore, generally a test that cannot be utilized absent the
subjects "informed consent". Therefore, the blood alcohol test most
often used by law enforcement authorities involves a relatively
easy-to-use, low cost, non-invasive procedure--viz., the
"Breathalizer" which is based upon non-invasive analysis of a
breath sample to determine the content of ethyl alcohol in the
bloodstream. It is for this reason that the accuracy of the breath
test for alcohol content is coming under the heaviest attack from
defendants charged with driving while intoxicated.
The average human lung contains approximately 300 million small air
sacs called "alveoli" which are surrounded by blood vessels. The
alveoli of the lung are connected to the mouth by the trachea and a
tree-like array of airways which allow for the movement of air from
outside the subject's body to the alveoli in the lung. The major
function of the lung is to allow for the exchange of oxygen and
carbon dioxide between the blood and air within the lung. It has
generally been accepted that the air content of the lung is an
optimal point for measuring the amount of alcohol in the blood
because the membranes of the lung are thin enough to allow rapid
exchange of the alcohol between the blood and the air within the
lung gas. Therefore, even though it is impossible to measure the
amount of alcohol within the alveolar gas, the partial pressure of
alcohol within the lung is believed to be the same as that in the
blood under equilibrium conditions. Therefore a major assumption is
made that the alcohol concentration in the exhaled breath, after
the dead space is exhaled, is a constant value and equal to the
blood value. It is also assumed that the breath alcohol
concentration is equal to the lung air alcohol concentration.
The fact that the blood perfusion (flow) rate in the vessels
surrounding the alveoli may vary has been known for years
(References 18, 19). For most gases eliminated by the lung, the
variation in matching alveolar ventilation and perfusion results in
large variations of alveolar gas partial pressure (Reference 20).
However, for a gas with a very high partition coefficient, such as
ethyl alcohol, the variation in alveolar partial pressure due to
differences in alveolar ventilation and perfusion matching is
virtually eliminated (Reference 22). Therefore the expected single
breath partial pressure profile for ethyl alcohol is essentially
flat.
There is a difference, however, in the actual concentration of
alcohol molecules within the gas contained in the lung (hereinafter
referred to as "alveolar gas") compared to the concentration of
alcohol molecules in the bloodstream. This difference is described
by a mathematical relationship called the "partition coefficient"
which is defined as the concentration of alcohol in the bloodstream
divided by the concentration of alcohol in the air of the lungs at
a prescribed temperature. Therefore, if a breath sample in
equilibrium with the blood in the lungs is obtained, the blood
alcohol concentration may be derived from the breath alcohol
content by multiplying the breath alcohol concentration by the
partition coefficient.
The exact value of the partition coefficient, although vital to an
accurate determination of the blood alcohol content, has been open
to dispute. See, for example, B. M. Wright, Breath Alcohol Analysis
And The Blood/Breath Ratio, MEDICAL SCIENCE LAW, Vol. 15, No. 3,
pp. 20-207 (1975); and M. F. Mason and K. M. Dubowski,
Breath-Alcohol Analysis: Uses, Methods, and Some Forensic
Problems--Review and Opinion, JOURNAL OF FORENSIC SCIENCE, Vol. 33,
pp. 9-41 (1976). The most accurate determination of the partition
coefficient, however, was found to be 1,756 at 37.degree. C. See,
A. W. Jones, Determination of Liquid/Air Partition Coefficient for
Dilute Solutions of Ethanol in Water, Whole Blood and Plasma,
JOURNAL OF ANALYTICAL TOXICOLOGY, Vol. 7, July/August, pp. 193-197
(1983). Therefore, the partition coefficient of 2100 currently used
in most breath tests results in calculated blood alcohol
concentrations that are erroneously high by about twenty percent
(20%).
Various techniques have been used in the past to determine blood
alcohol content based upon the breath alcohol content including
chemical processing, gas chromatography and infrared absorption
techniques. Briefly, infrared absorption involves passing infrared
waves of two discrete wavelengths within a discrete frequency band
through a breath sample wherein the energy at each wavelength is
measured after exiting the breath sample to determine the amount of
energy absorbed at each wavelength by the molecules in the breath
sample. These absorption values are then compared to known values
for the absorption of ethanol and other gases at various
concentrations to allow determination of the amount of ethyl
alcohol in the sample tested. U.S. Pat. No. 4,268,751--Fritzlen et
al discusses the use of two wavelengths of infrared energy at 3.48
microns and 3.3 microns to determine the presence of both ethanol
and acetone in a breath sample. Previously, a single wavelength of
3.39 microns was utilized; but, both ethanol and acetone absorb
infrared energy at this wavelength. However, since their absorption
amounts differ relatively at discrete wavelengths 3.39 microns and
3.48 microns, the presence of both ethanol and acetone in the
sample may be detected based upon the relative absorption of the
infrared energy at these two frequencies.
For further clarification, additional descriptions of the apparatus
and procedures used in infrared analysis are discussed in Harte,
U.S. Pat. No. 3,792,272 and Adrian, U.S. Pat. No. 4,057,724.
A further listing of work carried out in the area of breath alcohol
analysis is provided as follows:
1. R. N. Harger, R. B Forney and R. S. Baker, Estimation of the
Level of Blood Alcohol from Analysis of Breath II, Use of
Rebreathed Air, JOURNAL OF STUDIES IN ALCOHOL, Vol. 17, pp. 1-18
(1956);
2. A. W. Jones, How Breathing Technique Can Influence the Results
or Breath--Alcohol Analysis, MEDICAL SCIENCE LAW, Vol. 4, No. 4,
pp. 275-280 (1982);
3. A. W. Jones, Effects of Temperature and Humidity of Inhaled Air
on the Concentration of Ethanol in a Man's Exhaled Breath, CLINICAL
SCIENCE, Vol. 63, pp. 441-445 (1982);
4. A. W. Jones, Role of Rebreathing in Determination of the
Blood-Breath Ratio of Exhaled Ethanol, JOURNAL OF APPLIED
PHYSIOLOGY: RESPIRATION, ENVIRONMENTAL AND EXERCISE PHYSIOLOGY,
Vol. 55, pp. 1237-1241 (1983);
5. J. C. Russell and R. L. Jones, Breath Ethyl Alcohol
Concentration and Analysis in the Presence of Chronic Obstructive
Pulmonary Disease, CLINICAL BIOCHEMISTRY, Vol. 16, No. 3, pp.
182-187 (1983);
6. J. Schwartz, C. Pinkward and A. Slemeyer, Ein nueues Verfahren
zur Bestimmung des Blutalkoholgehaltes uber die Atemluft bei
Bewusstlosen, (A New Method to Estimate Blood Alcohol Concentration
From the Breath of Unconscious Subjects), ANAESTHETIST, Vol. 31,
pp. 177-180 (1982);
7. A. Slemeyer, Analytical Model Describing the Exchange Processes
of Alcohol in the Respiratory System, ALCOHOL, DRUGS AND TRAFFIC
SAFETY, ed. by L. Goldberg, Almqvist and Wiksell International,
Stockholm, pp. 456-468 (1981);
8. M. P. Hlastala, Multiple Inert Gas Elimination Technique,
JOURNAL OF APPLIED PHYSIOLOGY: RESPIRATION, ENVIRONMENTAL AND
EXERCISE PHYSIOLOGY, Vol. 56, No. 1, pp. 1-7 (1984);
9. M. P. Hlastala and D. D. Ralph, Inter-action of Exhaled Gas with
Airway Mucosa, PROCEEDINGS XXIX CONGRESS OF THE INTERNATIONAL UNION
OF PHYSIOLOGICAL SCIENCES, Vol. 15, p. 304 (1983);
10. H. T. Robertson, R. L. Coffey, T. A. Standaert and W.E. Truog,
Respiration and Inert Gas Exchange During High Frequency
Ventilation, JOURNAL OF APPLIED PHYSIOLOGY: RESPIRATION,
ENVIRONMENTAL AND EXERCISE PHYSIOLOGY, Vol. 51, pp. 683-689
(1982);
11. R. D. McEvoy, N. J. H. Davies, F. L. Mannino, R. J. Prutow, P.
T. Schumaker, R. D. Wagner and J. B. West, Pulmonary Gas Exchange
During High-Frequency Ventilation, JOURNAL OF APPLIED PHYSIOLOGY:
RESPIRATION, ENVIRONMENTAL AND EXERCISE PHYSIOLOGY, Vol. 52, pp.
1278-1288 (1982);
12. A. W. Jones, Quantitative Measurements of the Alcohol
Concentration and the Temperature or Breath During a Prolonged
Exhalation, ACTA. PHYSIOLOGICA SCANDINAVICA, Vol. 114, pp. 407-412
(1982);
13. E. R. McFadden, D. M Denison, J. F. Walker, B. Assoufi, A.
Peacock, and T. Sopwith, Direct Recordings of the Temperature in
the Tracheobronchial Tree in Normal Man, JOURNAL OF CLINICAL
INVESTIGATION, Vol. 69, pp. 700-705 (1982);
14. E. R. McFadden, Respiratory Heat and Water Exchange:
Physiological and Clinical Implications, JOURNAL OF APPLIED
PHYSIOLOGY: RESPIRATION, ENVIRONMENTAL AND EXERCISE PHYSIOLOGY,
Vol. 54, pp. 331-336 (1983);
15. K. M. Dubowski, Breath Analysis As A Technique In Clinical
Chemistry, CLINICAL CHEMISTRY, Vol. 20, pp. 966-972, 1982.
16. M. F. Mason and K. M. Dubowski, Breath-Alcohol Analysis: Uses,
Methods, and Some Forensic Problems--Review and Opinion, JOURNAL OF
FORENSIC SCIENCE, Vol. 33, pp. 9-41 (1976);
17. J. Levett and L. Karras, Errors in Current Alcohol Breath
Analysis, ALCOHOL, DRUGS AND TRAFFIC SAFETY, ed. by L. Goldberg,
Almqvist and Wiksell International, Stockholm, pp. 527-532
(1981);
18. H. Rahn, A Concept of Mean Alveolar Air and the
Ventilation-Blood Flow Relationships During Pulmonary Gas Exchange,
JOURNAL OF PHYSIOLOGY Vol. 153, pp. 21-30 (1949);
19. J. B. West and C. T. Dollery, Distribution of Blood Flow and
Ventilation-Perfusion Ratio in the Lung, Measured With Radioactive
CO.sub.2, JOURNAL OF APPLIED PHYSIOLOGY, Vol. 15, pp. 405-418
(1960);
20. L. E. Farhi, Elimination of Inert Gas by the Lung, RESPIRATION
PHYSIOLOGY, Vol. 3, pp. 1-11 (1967);
21. W. S. Fowler, Lung Function Studies III. Uneven Pulmonary
Ventilation in Normal Subjects and in Patients With Pulmonary
Disease, JOURNAL OF APPLIED PHYSIOLOGY, Vol. 1, pp. 283-299 (1949);
and,
22. M. P. Hlastala and H. T. Robertson, Inert Gas Elimination
Characteristics of the Normal Lung, JOURNAL OF APPLIED PHYSIOLOGY:
RESPIRATION, ENVIRONMENTAL AND EXERCISE PHYSIOLOGY, Vol. 44, pp.
258-266 (1978).
In most current breath-testing apparatus, the subject is required
to breathe directly into a gas analyzer, such as an infrared
analyzer described previously, which utilizes a sample from the end
of the breath for analysis, hereinafter referred to as the
"end-expired breath method". This method allows for the exhalation
of a sufficient amount of breath gases to eliminate any air in the
mouth and trachea which are assumed to have little or no alcohol
content--that is, so-called "dead space gas"--such that the sample
of alveolar gas is taken from the latter part of the exhaled
breath. The end-expired breath method assumes that the alcohol
concentration of the exhaled breath after elimination of the dead
space gas is a constant value and proportional to the blood alcohol
content.
Recently, however, it has been shown that the alcohol concentration
in the breath is not constant but, rather, changes continuously as
the subject exhales. See, e.g., Reference Nos. 1 through 7, supra.
In the majority of studies, in fact, the alcohol concentration was
found to increase as the subject exhaled. To explain this
phenomenon, recent observations have found that highly soluble
gases interact with the subject's airways during inhalation and
exhalation. See, e.g., Reference Nos. 9 through 11 supra. During
inhalation, as the inhaled cooler air from the outside is brought
into the lungs, it is warmed by the transfer of heat from the
tissues of the subject's airways. See, e.g., Reference Nos. 12
through 14, supra. The heat transfer between the subject's airways
and the inhaled/exhaled breath results in partial condensation of
alcohol over the tissues of the airway, changing the concentration
of ethyl alcohol in the breath.
Early studies of the end-expired breath method of breath analysis
have produced data which bear reasonable correlation to the
concentrations of ethyl alcohol obtained through blood sample
tests. Because of changing breath alcohol concentrations, however,
random breath samples yielded average values which correlated to
the blood sample concentration even though variations as much as
fifty percent (50%) occurred in individual measurements. See, e.g.,
Reference Nos. 16 and 17, supra. These measurements were made,
however, by instruments which ignored the interaction of breath
alcohol with the tissue of the subject's airway.
The article by A. W. Jones entitled "The Role of Rebreating in
Determination of the Blood/Breath Ratio of Expired Ethanol"
(Reference No. 4), discloses that temperature gradients between the
subject's lungs and mouth result in the exchange of water-soluble
agents such as ethyl alcohol with the (37.degree.of the subject's
airways resulting in inaccurate measurements when the end of the
expired breath was analyzed. Jones indicates, however, that the
concentration of ethyl alcohol in end-expired air will be less than
that found in the alveolar gas. Jones utilized a rebreathing
procedure to reduce the temperature gradient across the airways and
trachea in an attempt to achieve a steady state breath temperature
of approximately 35.2.degree. C., which then was mathematically
adjusted to 37.degree. C., in an attempt to provide a more accurate
estimation of the alveolar level of ethyl alcohol. This
mathematical adjustment was based upon a supposed linear
relationship between expired breath temperature and the
blood/breath partition coefficient. Jones' mathematical adjustment
to 37.degree. C. is inaccurate however, because the airways and
trachea comprise a dynamic system where equilibrium conditions do
not exist. Jones' rebreathing technique required the subject to
breathe into a heated polyethylene bag one to five times, with the
final exhalation made into a separate breath analyzing instrument
which recorded the breath temperature, exhaled volume and breath
alcohol concentration.
In addition to the foregoing problems, those skilled in the art
have experienced many other significant problems when attempting to
collect breath samples for chemical analysis. Due to the high vapor
content of typical breath samples collected, there is a substantial
likelihood of condensation of such vapor onto the walls of the
sample collecting receptable resulting in additional
inaccuracies.
In the aforementioned article by R. N. Harger et al entitled
"Estimation of the Level of Blood Alcohol From Analysis of
Breath--Use of Rebreathed Air" (Reference No. 1), a polyethylene
bag was utilized for a rebreathing procedure. In an attempt to
eliminate any moisture condensation within the sample bag, the bag
was initially placed inside an incubator sack heated to
45.degree.-50.degree. C., remaining inside until the sample bag
reache a temperature of approximately 45.degree. C. The bag was
then removed from the incubator sack; the subject rebreathed five
times into the bag; the bag was then returned to the incubator sack
and evacuated to a sampling ampule tube. A disadvantage with
Harger's method of preventing condensation is that the temperature
of the breath sample inside the bag is neither measured nor
controlled when the sample bag is outside the incubator sack.
Therefore the temperature of the breath sample may fall below the
dew point temperature causing condensation within the sample
bag.
Additional problems occurring when using conventional breath
collection methods and apparatus include the resistance offered by
a narrow breathing tube to the flow of exhaled air therethrough, a
so-called "back pressure". This back pressure increases the
alveolar pressure making it difficult for people with lung diseases
or defects to provide a breath sample of sufficient volume to
include air from the deep lung area. The problem is further
exacerbated by the fact that the increased alveolar pressure causes
an alteration in the pattern of emptying the lungs resulting in
differences in alcohol concentration in the breath sample.
Although it has been recognized that temperature gradients within
the mouth, trachea and airways introduce errors into the
determination of blood alcohol content from breath sample analysis,
conventional methods and apparatus as described in the aforesaid
references have failed to achieve a solution for eliminating the
problems induced by such temperature gradients. Nor have such
conventional systems provided solutions for the aforesaid
condensation and back pressure problems. Therefore, prior to the
advent of the present invention, there has remained an urgent need
for improved methods and apparatus for determining the blood
alcohol content from a breath sample which can be collected and
analyzed at the proper temperature and which overcomes the problems
associated with condensation and resistance to the subject's
exhaled breath.
SUMMARY OF THE INVENTION
Accordingly, it is a general aim of the present invention to
provide an improved apparatus and method for collecting breath
samples for chemical analysis of their ethyl alcohol content, an
apparatus and method which is characterized by its improved
accuracy, ease of use, and decreased breathing resistance, and
which overcomes all the foregoing disadvantages inherent in
conventional apparatus and methods.
In one of its more detailed aspects, it is an object of the present
invention to provide an improved apparatus and method for
collecting breath samples under isothermal rebreathing conditions
resulting in thermal equilibrium between the breath sample and the
subject's airway tissues, characterized in that the breath samples
are collected in an enclosed, flexible, variable volume, bag-like
receptacle which includes means, such as for example, a mouthpiece
in communication with the interior space of the sample bag, to
permit a human subject to repetitively exhale into and inhale from
the sample bag while the breath sample within the bag is maintained
at or near the subject's body temperature. Suitable means for
maintaining the sample bag at a temperature in substantial
equilibrium with the subject's body temperature includes a closed,
airtight heating chamber enclosing the sample bag and including
therein means, such as a heating coil or incandescent light, for
heating the inside of the container and the sample bag contained
therein. Sensing means, such as a temperature probe, are utilized
to determine the temperature of the breath sample and in the sample
bag and to relay the temperature information to an automatic
electronic controller, such as a software controlled microcomputer,
or human operator, to compare the temperature information relayed
from the probe to a reference level established by either a
software program, input from a human operator, or measurement of
the subject's body temperature, in order to regulate the output of
the heating means within the heating container. The optimum breath
sample for accurately determining blood alcohol content is obtained
when the temperature of the rebreathed breath sample is at or near
the temperature of the subject's airway passages, normally
98.6.degree. F. or 37.degree. C. Sensing means are positioned in
close proximity to the sample bag inlet to obtain the most accurate
breath temperature information. Means for extracting the breath
sample from the sample bag for subsequent chemical analysis of the
ethyl alcohol content utilize an extraction conduit in fluid
communication with the sample bag; the pressure inside the
evacuation conduit is reduced to about 200 mm Hg by a vacuum or
parastoltic pump wherein the breath sample is evacuated to a sample
gas analyzer which uses conventional analysis methods such as
infrared analysis to determine the ethyl alcohol content.
The improved apparatus and methods of the present invention
facilitate collection of a breath sample which provides for a more
accurate representation of the subject's blood alcohol content
wherein the heating chamber is interconnected and in fluid
communication with a second variable volume or bellows-like chamber
such that the volume of the bellows chamber increases as the sample
bag inflates and decreases as the sample deflates to permit the
sample bag to inflate and deflate inside an enclosed, airtight
container thereby maintaining improved temperature constancy around
the sample bag. Stated another way, the heating chamber includes a
first chamber portion for enclosing the sample bag, a second
variable volume change portion, and conduit means interconnecting
the first and second chamber portions for permitting fluid
communication therebetween as the volume of breath gases contained
within the sample bag is cyclically increased and decreased as the
subject exhales into and inhales from the sample bag.
Further improvements in temperature constancy are obtained
utilizing means, located upstream of the sample bag, for preheating
the breath sample to the desired temperature wherein the preheater
means comprise a number of electrical resistance heating elements
located in a conduit interconnecting the mouthpiece with the sample
bag, the heating elements forming a grid-like pattern across the
conduit passageway. An electronic sensor located on the heating
grid relays the temperature of the breath sample to a central
controller to regulate the temperature of the heating grid.
It is a further and more detailed object of the present invention
to minimize any internal breathing resistance of the isothermal
breathing apparatus in order to facilitate obtaining breath samples
of sufficient volume from subjects experiencing breathing
impediments wherein the conduit interconnecting the mouthpiece to
the sample bag has an internal diameter of approximately one
inch.
DESCRIPTION OF THE DRAWINGS
These and other objects and advantages of the present invention
will become more readily apparent upon reading the following
detailed description and upon reference to the attached drawings,
in which:
FIG. 1 is a graphical representation of breath alcohol
concentration as a function of the expired volume of breath;
FIG. 2 is a graphical representation of the breath alcohol
concentration as a function of time wherein there is compared
breath samples obtained from (i) first inhaling cool air
(20.degree. C.), (ii) first inhaling three breaths of warmed air
(35.degree. C.), and (iii) rebreathing warmed air (37.degree. C.);
and wherein time zero for sample runs at 20.degree. C. and
35.degree. C. commenced after the initial breath cycles of cool air
or warm air were completed;
FIG. 3 is a highly diagrammatic perspective view of an isothermal
rebreathing system embodying features of the present invention,
here illustrating the breath sample bag, heating container, suction
pump and motor, gas analyzer, and electrical power outlet;
FIG. 4 is a front cross-sectional view taken substantially along
the line 4--4 in FIG. 3, here depicting details of the heating
container and breath sample bag;
FIG. 5 is a perspective view of one embodiment of the present
invention comprising a bellows section in operable communication
with the heating container and sample bag receptacle;
FIG. 6 is a front cross-sectional view taken substantially along
the line 6--6 in FIG. 5 here depicting an embodiment comprising the
bellows section illustrated in FIG. 5; and,
FIG. 7 is a perspective view of one embodiment of the present
invention illustrating in phantom the breath preheating grid within
the breathing mouthpiece.
While the present invention is susceptible of various modifications
and alternative forms, specific embodiments thereof have been shown
by way of example in the drawings and will herein be described in
detail. It should be understood, however, that it is not intended
to limit the invention to the particular forms disclosed, but, on
the contrary, the intention is to cover all modifications,
equivalents and alternatives falling with the spirit and scope of
the invention as expressed in the appended claims.
DETAILED DESCRIPTION
As indicated previously, various studies have been conducted which
indicate that when utilizing a breath sample taken at the end of
the subject's exhaled breath, errors due to the interaction of heat
and alveolar gases with the tissues of the subject's airways
results. To confirm these findings, the following experiment was
performed.
EXAMPLE I
Five human subjects drank a sufficient quantity of Scotch Whiskey
to bring their blood alcohol level to between 0.06 and 0.14 gram
percent as documented by the blood samples analyzed by either the
clinical chemistry laboratory at Harborview Medical Center
(Washington State Toxicologists Lab) or the University of
Washington Hospital in Seattle. After waiting for at least 60
minutes after ingesting the alcohol, the subjects breathed into a
standard mouthpiece from room air at 20.degree. C., at an
exhalation flow rate of approximately 0.5 liters per second; the
subjects making one complete exhalation in accordance with the
standard method practiced by law enforcement personnel for
"Breathalizer" testing. The mouthpiece was connected to a wedge
spirometer, manufactured by Med-Science Company, St. Louis, Mo.,
which read out the volume of air exhaled and flow rate of exhaled
air to an 8-channel recorder made by Hewlett-Packard, Waltham,
Mass. The signals to the recorder were processed with a Sanborn
preamplifier and analog low-pass filters having a roll-off
frequency of 10 Hz to remove radio frequency interference. The
concentrations of ethyl alcohol and carbon dioxide were recorded
continuously on separate channels of the recorder. There was no
interference from acetone. Using a Model QMG 511 quadrupole mass
spectrometer manufactured by Balzers Corporation, Balzers,
Liechtenstein, measurements of the breath alcohol content were made
continuously during the entire duration of the exhaled breaths. The
mass spectrometer was controlled by a Model PDP 11/34 digital
computer manufactured by Digital Equipment, Maynard, Mass. Over the
past three years, it has been shown that for all gases measured,
Balzers' mass spectrometer is accurate to within two percent (2%)
of the actual concentration of the gas in the blood. The mass
spectrometer was calibrated to provide the calculated blood alcohol
concentrations by extracting a portion of the blood sample with a
syringe, allowing the sample to equilibrate at 37.degree. C. for 45
minutes, separating the liquid and gas phases, analyzing the gas
phase using the mass spectrometer, and analyzing the blood portion
for use as a reference value using a gas chromatograph. The results
of the tests from the five subjects were as follows:
______________________________________ Calculated Measured Blood
Alcohol Blood Cumulative Concentration Alcohol Volume of Based on
Mass Concentration Exhaled Air Spectrometer Subject (gm %) (ml)
Readout (gm %) ______________________________________ 1 .126 500
.033 1000 .082 1500 .104 2000 .116 2500 .128 3000 .140 3500 .153
4000 .165 4500 .177 5000 .189 2 .060 500 .007 1000 .050 1500 .057
2000 .065 2500 .070 3000 .074 3500 .077 4000 .082 3 .139 500 .080
1000 .111 1500 .130 2000 .148 2500 .161 3000 .173 4 .113 500 .015
1000 .075 1500 .109 2000 .124 2500 .137 3000 .151 3500 .155 5 .106
500 .021 1000 .079 1500 .098 2000 .109 2500 .117 3000 .122 3500
.127 4000 .133 ______________________________________
A curve representative of the above data graphically illustrated in
FIG. 1 indicates that the breath alcohol concentration is not
constant during exhalation. Rather, the data confirm the fact that
as the subject exhales, the alcohol concentration gradually
increases until a maximum value is reached near the end of the
exhaled breath. The end-exhaled breath sample contains a
concentration of alcohol sixty percent (60%) higher than that
determined by blood sample analysis. This is in contrast to the
initial portion of the exhaled breath which is up to fifty percent
(50%) below the concentration determined by the blood sample
analysis. As mentioned previously, it has been shown that the
highly soluble breath gases interact with the tissues in the
subject's airways during inhalation and exhalation. During
inhalation, as the inspired air from outside is brought into the
lung, it is warmed by the exchange of heat with the airways. The
gas from the alveoli are cooled slightly during exhalation from a
temperature of 37.degree. C. in the lung to a temperature of
34.degree. C. at the mouth. See, Reference No. 15.
Although not wishing to be bound by theory, it is believed that the
subject's inhaled breath is warmed by the tissues of the airway,
resulting in heat transfer thereto and a resultant cooling of the
airway walls. Therefore, during the initial portion of exhalation,
alveolar gas containing alcohol passes through the cooler airways,
resulting in some cooling of the alveolar gas and subsequent
condensation of the ethyl alcohol contained therein onto the
surface of the airways. As exhalation continues, the airways begin
to warm up, revaporizing this condensed alcohol, and increasing the
concentration of alcohol in the exhaled gas.
To test the above theory, the following experiments were
conducted:
EXAMPLE II
Utilizing the procedures of Example the alcohol concentration of
the subjects' breath from a single inhalation was recorded as a
function of time wherein time zero marked the beginning of the
exhalation. Data which was obtained during the testing of one
subject and representative of data obtained from the group of
subjects is provided below:
______________________________________ Calculated Calculated
Calculated Alcohol Alcohol Alcohol Concen- Concen- Concen- Time
tration Time tration Time tration (sec) (gm %) (sec) (gm %) (sec)
(gm %) ______________________________________ 0 0 11 .087 22 .124 1
.005 12 .091 23 .126 2 .014 13 .096 24 .129 3 .026 14 .100 25 .132
4 .037 15 .103 26 .134 5 .048 16 .107 27 .136 6 .057 17 .110 28
.138 7 .065 18 .112 8 .072 19 .116 9 .077 20 .118 10 .082 21 .121
______________________________________
The above data graphically illustrated in FIG. 2 by a dashed-dotted
line indicates that the breath alcohol concentration is rapidly
increasing after 20 seconds of exhalation when 20.degree. C. air is
breathed.
EXAMPLE III
The procedure of Example I was followed except that the subjects
initially took three breaths of air warmed to approximately
35.degree. C. by a portable hair dryer. The alcohol concentration
of a single exhaled breath was recorded as a function of time with
time zero beginning after the three initial breath cycles of warmed
air were taken. Data which was obtained during the the testing of
pne subject and representative of data obtained from the group of
subjects is provided below:
______________________________________ Calculated Calculated
Calculated Alcohol Alcohol Alcohol Concen- Concen- Concen- Time
tration Time tration Time tration (sec) (gm %) (sec) (gm %) (sec)
(gm %) ______________________________________ 0 0 11 .093 22 .114 1
.005 12 .095 23 .115 2 .016 13 .098 24 .116 3 .032 14 .100 25 .117
4 .048 15 .102 26 .117 5 .059 16 .104 27 .118 6 .069 17 .106 28
.119 7 .076 18 .108 29 .120 8 .081 19 .109 9 .086 20 .111 10 .089
21 .112 ______________________________________
The above data graphically illustrated in FIG. 2 by a dashed line
indicates that the change in breath alcohol concentration after 20
seconds of rebreathing is reduced when warm (approximately
35.degree. C.) air is initially breathed.
As discussed previously, the basic premise for determining blood
alcohol content based on the concentration of alcohol in the
alveolar gases of the lung is the fact that the blood alcohol is in
equilibrium with the alveolar alcohol due to the rapid exchange of
the alcohol between the blood and the gases in the lungs (alveolar
gas) which occurs at the subject's body temperature. At
equilibrium, the relative quantity of alcohol molecules in the
blood at body temperature (normally 37.degree. C.), although much
greater than the quantity of alcohol molecules in the air, is a
constant value under the conditions of body temperature and
equilibrium--this relative quantity is termed the "partition
coefficient". As the temperature varies from 37.degree. C., such
as, for example, where it is normally 34.degree. C. at the mouth,
the partition coefficient is no longer valid because the
coefficient is based upon an equilibrium airway temperature of
37.degree. C. whereas the sample breath collected may be at
35.degree. C. or even lower. A mathematical correction of the
breath alcohol concentration measured at 35.degree. C. to the body
temperature of generally 37.degree. C. is not accurate because of
the disequilibrium present due to the interchange of alcohol with
airway tissues when the breath sample is not at body
temperature.
In accordance with one of the more important aspects of the present
invention, an isothermal rebreathing system is provided wherein
provision is made for insuring that inhaled air and exhaled breath
at all locations in the rebreathing system ranging from the deepest
regions of the subject's lungs, through the various internal human
airways and trachea to the mouth, and within the breath sample
collection bag, was brought to, and maintained at, temperature
equilibrium--generally at the subject's actual body temperature
which, in the case of normal temperature, is near 37.degree. C.
(98.6.degree. F.)--prior to actual collection of the end-expired
breath for analysis. In the present invention, body temperature
(which normally varies from 37.degree. C.) will be measured with a
probe placed sublingually (under the tongue). In the exemplary
system, this is accomplished by rebreathing air from an enclosed
air collection system which will not interact with ethyl alcohol
and which is heated to 37.degree. C. (or to the subject's actual
body temperature in those instances where the subject's body
temperature is other than normal). As a consequence of operation at
conditions of temperature equilibrium between the tissue
temperature in the subject's rebreathing system and the air being
inhaled/exhaled, there is no tendency for heat transfer between
tissue and air; and, consequently, alcohol in the alveolar gases
being exhaled does not condense out and/or revaporize during the
breathing cycle, and the alcohol concentration in the end-expired
breath remains in equilibrium with the blood alcohol
concentration.
Referring now to FIGS. 3 and 4, there has been diagrammatically
illustrated an isothermal rebreathing system broadly comprising a
heating container, generally indicated at 20, enclosing a bag-like
sample receptacle 22 for the collection of exhaled air from a human
subject through a mouthpiece 24 wherein bag 22 is held at a preset
constant temperature by means of an electronic controller 26
positioned atop heating container 20. Controller 26 serves to
activate suitable heating means 30, located inside heating
container 20 and mounted on the sides thereof. Controller 26
includes, but is not limited to, the following principal components
(not shown) for controlling heaters 30 and other parts of the
isothermal rebreathing system to be described hereinbelow: a
microprocessor, programmable read only memory (PROM), random access
memory (RAM) and input/output devices. It should be appreciated
that the operation of these components as well as the software
controlling their operation is within the scope of one having
ordinary skill in the art and will not be described further.
The breath sample is evacuated by a suction pump 32 via a conduit
35 interconnecting suction pump 32 and a sample collecting chamber
(not shown) inside a sample gas analyzer 36. A conduit 34
projecting from the lower portion of the sample bag 22 through the
lower portion of the heating container 20 conducts the breath
sample to sample gas analyzer 36 for analysis of the chemical
composition of the breath sample such as by infrared analysis.
In carrying out the present invention, the exemplary heating
container 20 depicted in the drawings includes upper and lower
walls 40, 42, sidewalls 44, 46, and an endwall 48, defining an
essentially closed airtight container having a hinged access door
50 at the end opposite endwall 48. To permit observation of the
interior or container 20, one or more of the walls 40, 42, 44, 46,
48 may be formed of transparent plastic material, glass, or the
like. To maintain a closed, sealed airtight chamber, a conventional
gasket (not shown) is preferably positioned at the interface
between door 50 and the proximal ends of walls 40, 42, 44, 46. The
sample bag 22, located inside heating container 20, preferably
comprises a cylindrical, flexible bag-like receptacle approximately
two liters in volume to accommodate the subject's lung capacity,
and made of a material which is nonreactive with ethyl alcohol,
which has good thermal conductivity, and which is relatively
inexpensive so as to allow disposal of the bag after a breath
sample has been collected, a material, such as, for example,
polyvinylchloride or polytetraflouroethylene. In the illustrative
form of the invention, the sample bag 22 includes an open neck 54
at the proximal end thereof for the receipt of a stem 56 integral
with the mouthpiece 24; while mouthpiece 24 includes a passageway
58 to permit flow of sampIe gases from the subject's lungs to the
interior of sample bag 22. In order to secure the mouthpiece 24 to
stem 56 and bag 22, a locking collar 60 is provided which
circumscribes neck 54 of bag 22 so as to securely secure neck 54 to
stem 56. Mouthpiece 24 may comprise any suitable inexpensive,
pliable plastic material which is non-reactive to ethyl alcohol,
which fits into the subject's mouth and which is disposable after
the breath sample has been collected.
In order to seal the contents of the sample bag 22 from the outside
atmosphere when the prescribed breath sample temperature has been
reached and the subject has finished supplying a breath sample and
removed his mouth from mouthpiece 24, a clamping means 61, such as,
for example, a spring clip, may be manually affixed about stem 56,
such as when stem 56 is made of a sufficiently pliable material,
for example rubber or the like, to close passageway 58 to the
atmosphere. If, however, it is desired to have the above clamping
operation proceed automatically, clamping means 61 may comprise an
electronically actuated relay (not shown) via controller 26 to open
and close a valve (not shown) located within passageway 58.
Mouthpiece 24, including a circumferential ridge 63 configured to
fit inside the subject's mouth between the subject's lips and gums
providing an airtight seal therebetween, is positioned proximate
the top of access door 50 such that the subject's eyes and nose are
above and clear of access door 50. In order to reduce the alveolar
pressure buildup caused by forcing large volumes of exhaled air
through passageway 58, passageway 58 is sized approximately one
inch in diameter so as to allow normal exhalation. In addition,
this allows those subjects with limited lung capacity due to
physical defects or disease to exhale a sufficient volume of breath
into sample bag 22 to obtain an accurate sample. To provide an
airtight seal with the door 50, the stem 56 is inserted through an
aperture 64 formed in the door 50 and is held in place by an O-ring
seal 66 positioned within the aperture 64 to form an airtight
friction fit. It should be appreciated that the mouthpiece 24 is
easily removed from both door 50 and sample bag 22, thereby
allowing disposal of mouthpiece 24 and sample bag 22 before
collecting a new breath sample from another subject. It should also
be apparent to those skilled in the art that the sample bag 22 and
heating container 20 may be formed of different sizes, shapes and
materials and still perform the broad objectives of the present
invention as long as certain features are included such, for
example, as: (i) the ability for heating container 20 to achieve
sufficient temperature levels to heat the contents of the sample
bag 22 to temperatures on the order of 37.degree. C.; (ii) the
provision of a sample bag 22 which is nonreactive with those gases
introduced therein; and (iii), the provision of a sample bag 22
having thermal conductivity characteristics sufficient to insure
adequate heating of the gases contained therein.
To permit routing of the breath sample contained within the sample
bag 22, a sample collecting needle 68 extends through a septum 70
in the lower portion of sample bag 22 and passes into the interior
thereof, as best illustrated in FIG. 2. The tip of a sample
collecting needle 68 is located in close proximity to passageway 58
to extract the breath samples at or near the prescribed
temperature. To this end, conduit 34 is coupled to sample
collecting needle 68; conduit 34 extending through an O-ring seal
72 formed in the lower panel 42 of the heating container 20, thus
maintaining an airtight fit therewith. Thus, the arrangement is
such that the breath sample contained within the bag 22 comprising
the equilibrated breath from the deepest regions of the subject's
lungs is withdrawn under vacuum created by pump 32 to a removable
sample collecting chamber (not shown) located within the sample gas
analyzer 36 (FIG. 3); the sample collecting chamber sealable from
the atmosphere in order to preserve the breath sample for later
analysis. The sample gas analyzer 36 may be any of the conventional
types commonly available in the marketplace such, for example, as
the nondispersive infrared gas analyzer marketed by Andros
Analyzers Inc., Berkeley, Calif., forms part of the present
invention. Since such equipment is completely conventional and well
known to persons skilled in the art, it will not be herein
described in detail.
In carrying out the invention, provision made for withdrawing the
sample gas contained in sample bag 22 utilizing a conventional
parastoltic pump or vacuum pump 32 driven by motor 78--for example,
the motor driven pump 32 may comprise a model PM 330 pump of the
type manufactured by Medical Special Inc., Philadelphia, Pa.--and
for routing the withdrawn sample to the sample collecting chamber
in the sample gas analyzer 36 via collection needle 68, conduit 34,
and a conventional pressure transducer 76 located downstream of
collection needle 68.
Suction pump 32 is normally operated by controller 26 to maintain a
pressure of approximately 200 mm Hg inside sample conduit 34
wherein the preset pressure established by controller 26 is
continuously compared with the pressure sensed by transducer 76 to
control the pressure drop created by pump 32. A pressure of 200 mm
Hg prevents condensation of a typical breath sample in sample line
34 above 15.degree. C. assuming the gas in sample bag 22 approaches
100% saturation at body temperature. It can be appreciated that any
condensation of the sample gas will affect the relative
concentration of ethyl alcohol delivered to the sample collecting
chamber in the analyzer 36, thereby resulting in an erroneous
analysis. At 200 mm Hg, the condensation temperature of water is
sufficiently below room temperature to reduce the likelihood of
accidental condensation. A heating blanket, not shown, comprising
an electrical resistance heating element embedded within a
thermally conductive, fire-resistant material may be placed around
conduit 34 to prevent condensation therein.
A major premise of the rebreathing procedure is that the
concentration of alcohol in the blood is directly related to the
alveolar concentrations of ethyl alcohol in equilibrium with the
ethyl alcohol in the blood. As discussed previously, there is a
mathematical constant, the partition coefficient, which expresses
the relationship between the ethyl alcohol content of the blood and
the ethyl alcohol content of the air in the lungs. Although the
blood flow (perfusion) rate in the blood vessels surrounding the
alveoli may vary, the partition coefficient is independent of this
perfusion rate. It should be appreciated, therefore, that a certain
minimum volume of air per exhalation is necessary to obtain a
breath sample which includes the alveolar gases and, therefore,
which accurately reflects the blood alcohol content.
In one embodiment of the present invention shown in FIGS. 5 and 6,
a bellows section, generally indicated at 82, comprising bellows
84, is mounted at the distal end of the heating container 20. A
flow measuring means generally indicated at 85, includes a conduit
86 located within and extending through endwall 48 of the heating
container 20 in communication with both the interior of heating
container 20 and bellows section 82. Conduit 86 includes a porous
screen 87 across the inside thereof to impede the flow of air
through tube 86, air which is dispelled from heating container 20
into bellows section 82 due to the expansion of sample bag 22 when
filled with exhaled air from the subject. A differential pressure
measuring means (not shown), such as for example a pressure
transducer, in operable communication with screen 87 measures the
pressure drop across screen 87 during the inhalation/exhalation
cycle; and, that pressure drop, when integrated over time by
controller 26, serves to permit calculation of the volume of air
exhaled per breath, hereinafter referred to as "tidal volume".
Utilization of bellows section 82 allows heating container 20 to
remain closed from the atmosphere during rebreathing to insure
sample bag 22 remains at the prescribed temperature. The values of
pressure and tidal volume are displayed in digital form at
controller 26. A minimum tidal volume required from the subject for
an accurate breath sample is approximately 500 milliliters. The
microprocessor controller 26 insures that the tidal volume is
sufficient to obtain a valid sample.
In order to regulate the frequency and length of the subject's
rebreathing cycles, indicator lights 89, 91 are mounted atop
heating container 20 on upper wall 40 within the subject's field of
vision. Indicators 89, 91 are lit for a predetermined length of
time and at a predetermined frequency to guide the subject during
the inhalation and exhalation portions of the rebreathing cycle,
such that light 89 remains lit for a period of time over which the
subject inhales, and light 91 remains lit for a period of time over
which the subject exhales. Indicator lights 89, 91 are operated by
controller 26 which is preprogrammed to activate lights 89, 91 at
the proper frequency. In order to verify that the subject is
breathing at the programmed rate, the rebreathing frequency of the
subject is calculated by controller 26 using an internal counter
(not shown) to count the number of times the breath flow pressure
across screen 87 drops to zero from a positive flow pressure over a
predetermined time interval. If the subject's rebreathing frequency
varies a predetermined amount from the preprogrammed frequency, a
message is displayed at LCD window 104 indicating an improper
breathing frequency. Indicator lights 89, 91 may be labelled and
color coded so that the subject is guided by the correct light in
the rebreathing cycle.
Referring again to FIGS. 3 and 4, a temperature probe 88 is
provided at the distal end of the sample bag 22 and serves to
pierce a septum 90 formed in the bag 22, thus maintaining an
airtight seal. Preferably, the tip of probe 88 is positioned in
close proximity to the mouthpiece 24 and the sample collection
needle 68 so as to enable continuous monitoring of the breath
sample temperature by the controller 26. A plurality of heating
means 30 (which may comprise resistance-type electrical heating
elements or merely light bulbs) are mounted on vertical supports 92
at opposite sides of heating container 20, and provide sufficient
thermal energy within heating container 20 to maintain a gas sample
within the sample bag 22 at a preselected temperature.
An oral thermometer 94, secured by holder 96 in a friction fit
therewith, is located atop heating container 20 and is provided for
measuring the subject's actual body temperature which is input to
the microprocessor controller 26. Thus, the thermometer 94, after
being placed in the subject's mouth prior to obtaining a breath
sample, provides the reference temperature--e.g., the subject's
body temperature--which is input to the controller 26 for
maintaining the temperature of the breath sample in the sample bag
22 in equilibrium with the subject's actual body tempeature.
In the illustrative embodiment of the present invention, the
heaters 30 comprise one or more electric lights which are secured
to vertical supports 92 and which are activated by controller 26.
Thus, when utilizing a sample bag 22 having a volumetric capacity
of approximately two liters, the heaters 30 serve to output at
least 100 watts of power to maintain a temperature of 37.degree.
C.--viz., normal body temperature--inside sample bag 22, or,
alternatively, to maintain temperature level in bag 22 which is
equal to the actual body temperature of the subject, whether
elevated above 98.6.degree. F. (37.degree. C.) or at a lower level.
Electric lights are desirable in some instances because they can
also provide an independent source of light which is useful when
collecting breath samples in low light areas or at night. Heating
coils may be utilized in place of electric lights when a more
efficient source of heat is desired and the availability of an
independent source of light is unimportant. Operation of heaters 30
is accomplished by controller 26 in conjunction with temperature
probe 88 and thermometer 94. Thus, the subject's body temperature
relayed from thermometer 94 is compared by controller 26 to the
temperature relayed from probe 88, resulting in activation of the
heaters 30 when the relayed temperature from probe 88 is below the
subject's body temperature. Heaters 30 may be operated in a
proportional mode wherein the current supplied to the heaters 30 is
proportional to the deviation of the sample bag temperature from
the subject's body temperature. As the amount of deviation
increases, a potentiometer (not shown) operated by controller 26
increases the flow of current to heaters 30, thereby increasing the
power output in the form of heat. In a second operating mode
utilizing two or more heaters 30 which have lower individual power
ratings than the heater described previously, constant current may
be delivered to the heaters 30 until a temperature of about
1.degree. C. or 2.degree. C. below body temperature is reached, at
which time the current is quickly terminated by controller 26 to
all but one of the heaters 30. To raise the temperature of sample
bag 22 to body temperature, the current of the remaining activated
heater 30 is regulated by the potentiometer/controller pair until
body temperature is reached, at which time the current is
terminated, thereby reducing the amount of overshoot above body
temperature due to the lower power output when using only one
heater.
A rotating fan blade 98 positioned in proximity to the center of
heating container 20 aids in the distribution of heated air about
the sample bag 22 to insure a uniform temperature is maintained
across the surface thereof. Fan blade 98 is mounted on the output
shaft 100 of a suitable electric motor 102. Baffles (not shown) may
be placed inside heating container 20 to assist fan 98 in
circulating dead air for better heat distribution.
Overall control of the various system components described
previously is maintained by controller 26, the microprocessor based
microcomputer subsystem which includes a digital display which may
be a liquid crystal display (LCD) or the like for displaying
various temperatures and/or pressures at window 104 located on the
face of controller 26. Controller 26 is responsible for receiving
the following data:
1. Body temperature of the human subject as measured by thermometer
94;
2. Temperature of gases within sample bag 22 as measured by probe
88;
3. Pressure of sample gases through conduit 34 as measured by
transducer 76;
4. Pressure differential of expelled air through conduit 86
measured by a pressure transducer;
5. Number of times breath flow pressure across screen 87 drops to
zero;
6. Signals from analyzer 36.
Controller 26 controls the following operations:
1. Flow of current to heaters 30 in response to the difference in
the subject's body temperature and the temperature of the breath
sample inside sample bag 22.
2. Pressure drop created by suction pump 32 in response to the
difference in pressure between the pressure set at the controller
26 and the pressure at transducer 76.
Controller 26 calculates and/or displays/prints out the following
information:
1. Body temperature of the human subject;
2. Flow rate of subject's exhaled breath;
3. Volume of air per exhaled breath;
4. Blood alcohol concentration;
5. Rebreathinq frequency;
6. Information to assess adequacy of procedures.
Controller 26 utilizes an 16-bit microprocessor such as a Motorola
68000. Controller 26 includes an internal printer (not shown) for
providing a hard copy of information through slot 107 located below
window 104.
Electrical power requirements for the isothermal breathing system
may be supplied from any 120 volt household supply or,
alternatively, from a 12 volt car battery utilizing the cigarette
lighter outlet inside the car. Electrical power is required for the
operation of heaters 30, fan motor 102, suction pump motor 78,
controller 26, pressure transducer 76, temperature probe 88 and the
bellows pressure transducer.
Referring again to FIG. 1, electrical power is supplied from a
power source illustrated as an outlet 106 connected to distribution
bus box 108 adjacent to controller 26. Current flow from bus 108 to
the fan motor 102, pump motor 78 and heaters 30 may be controlled
by conventional electronic components such as various electronic
filters to reduce any radio frequency interference (RFI); the
specifics for connecting controller 26 to the previously mentioned
components of the isothermal breathing system are well known to
persons of ordinary skill in the art and, therefore, need not be
further described herein.
In one embodiment of the present invention shown in FIG. 7, a
breath pre-heating means 120 is positioned across passageway 58
inside mouthpiece 24. The pre-heating means 120 comprises a
honeycomb heating grid -22 made up of individual electrical
resistance elements which when supplied with electrical current
from controller 26 heat the breath sample flowing through
passageway 58 nd across heating grid 122. A temperature detector
124, such as for example a thermocouple, attached near the center
of grid 122 transmits the grid temperature to controller 26 for
comparison with the reference temperature to maintain the proper
grid temperature.
Operation of the isothermal rebreathing system proceeds as follows
with reference to FIGS. 3 and 4: the system operator inserts the
stem 56 of a sanitary, disposable mouthpiece 24 through aperture 64
in door 50, forming a friction, airtight seal therewith. A
disposable sample bag 22 is mounted on stem 56 and held in place by
collar 60 to form an airtight seal between the mouthpiece 24 and
the sample bag 22. Door 50 is closed and latched shut. The system
is turned on at controller 26 which goes through a preprogrammed
self check of all components. Preprogrammed readouts (prompts)
appearing at LCD window 104 direct the operator to obtain the
subject's body temperature using thermometer 94. Body temperature
data is processed by controller 26 which activates heaters 30 and
fan motor 102 to warm the air inside sample bag 22 to a temperature
level in equilibrium with the subject's actual body
temperature--normally 37.degree. C. (98.6.degree. F.)--at which
time the temperature is displayed in window 104 to prompt the
operator to proceed with the sample collection The operator
acknowledges the LCD prompt by pressing a "continue" key 110 on the
controller 26, allowing the controller 26 to activate suction pump
motor 78, thus reducing the pressure in sample line 34 to a
predetermined value. The preset pressure is compared to the
pressure relayed from flow measuring means 85 (FIG. 6), and when
the two pressures match, the LCD window 104 displays the pressure
relayed from flow measuring means 85, thus prompting the operator
to proceed. The tidal volume of the subject's breathing is
continually monitored by flow measuring means 85 such that if the
tidal volume is less than the preset number, a prompt at LCD window
104 indicates an invalid sample. The subject is instructed to
exhale through the mouthpiece 24 when indicator light 91 is lit,
and then inhale through mouthpiece 24 when light 89 is lit; lights
89, 91 are activated so that the subject breathes at a frequency of
approximately 30 breaths per minute for approximately 20 seconds.
While the subject is breathing into sample bag 22, suction pump 32
is drawing the breath sample through conduit 34 to the sample
collection chamber in the analyzer 36. When the subject is finished
providing the breath sample, the operator presses the "continue"
key 110 which terminates electrical current to all components. The
operator then removes the mouthpiece 24 and the sample bag 22 and
discards them. The operator again presses the "continue" key 110
which provides current to suction pump motor 78 for a preprogrammed
length of time to purge conduit 34 of any remaining sample gases in
preparation for sampling the next subject's breath.
It should be appreciated that the foregoing operational description
is merely one manner of operating the isothermal rebreathing system
involving the interaction of a human operator and subject,
electrical and mechanical components, and computer software.
Depending upon the sophistication desired and number of data
sampling components included, the microcomputer system may be
programmed to reduce the involvement of the human operator to
merely turning on the system and insuring subject compliance with
the controller 26 prompts. On the other hand, the monitoring and
control of the various aforementioned temperatures and pressures
may be accomplished entirely by a human operator without the need
for microcomputer control. Therefore, the above functional
description merely constitutes one functional embodiment for
operating the system of the present invention.
EXAMPLE IV
The procedures of Example I were followed except that the subjects'
rebreathed into an isothermal rebreathing system comprising a
sample bag, made from polytetrafluoroethylene contained within a
first box made from Lucite, a registered trademark, which was
enclosed by a second Lucite box, the air around the second box
heated to a temperature of approximately 37.degree. C. The subjects
commenced rebreathing into the sample bag at a rate of 20 breaths
per minute. The alcohol concentration of the several cycles of the
subjects' exhaled breath was recorded as a function of time with
time zero beginning upon initial rebreathing into the sample bag.
Data which was obtained during the testing of one subject and
representative of data obtained from the group of subjects is
provided below:
______________________________________ Calculated Calculated
Calculated Alcohol Alcohol Alcohol Concen- Concen- Concen- Time
tration Time tration Time tration (sec) (gm %) (sec) (gm %) (sec)
(gm %) ______________________________________ 0 0 12 .101 24 .106 1
.013 13 .101 25 .106 2 .053 14 .102 26 .107 3 .069 15 .103 27 .107
4 .068 16 .104 28 .107 5 .071 17 .105 29 .106 6 .084 18 .105 30
.107 7 .090 19 .104 31 .107 8 .090 20 .104 32 .107 9 .092 21 .105
33 .106 10 .097 22 .106 34 .107 11 .100 23 .106 35 .107
______________________________________
The representative blood alcohol concentration as determined from
chemical analysis of the subjects' blood was 0.104 gm %.
* * * * *