U.S. patent application number 09/803237 was filed with the patent office on 2001-12-06 for method and apparatus for in vivo measurement of carbon monoxide production rate.
Invention is credited to Stone, Robert T..
Application Number | 20010049477 09/803237 |
Document ID | / |
Family ID | 22695492 |
Filed Date | 2001-12-06 |
United States Patent
Application |
20010049477 |
Kind Code |
A1 |
Stone, Robert T. |
December 6, 2001 |
Method and apparatus for in vivo measurement of carbon monoxide
production rate
Abstract
An apparatus for in vivo measurement of carbon monoxide
production rate comprising a first gas detector for detecting the
concentration of a first selected gas in at least first and second
gas samples, the first gas detector being adapted to provide output
signals corresponding to the first selected gas concentration in
the first and second gas samples; a second gas detector adapted to
substantially simultaneously detect the concentration of at least
second and third selected gases in the first and second gas
samples, the second gas detector being further adapted to provide
output signals corresponding to the second and third selected gas
concentrations in the first and second gas samples; means for
providing the first and second gas samples to the first and second
gas detectors; and processing means for determining the rate of
carbon monoxide production in at least the second sample in
response to the first and second gas detectors output signals.
Inventors: |
Stone, Robert T.;
(Sunnyvale, CA) |
Correspondence
Address: |
FRANCIS LAW GROUP
1808 SANTA CLARA AVE.
ALAMEDA
CA
94501
US
|
Family ID: |
22695492 |
Appl. No.: |
09/803237 |
Filed: |
March 8, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60189002 |
Mar 13, 2000 |
|
|
|
Current U.S.
Class: |
600/532 ;
73/23.3 |
Current CPC
Class: |
G01N 33/004 20130101;
A61B 5/417 20130101; A61B 5/0836 20130101; A61B 5/083 20130101;
G01N 2033/4975 20130101; Y02A 50/20 20180101; Y02A 50/243
20180101 |
Class at
Publication: |
600/532 ;
73/23.3 |
International
Class: |
A61B 005/08 |
Claims
What is claimed is:
1. An apparatus for in vivo measurement of carbon monoxide
production rate in a subject comprising: a first gas detector for
detecting the concentration of a first selected gas in at least a
first and second gas sample, said first gas detector being adapted
to provide at least a first output signal indicative of said first
selected gas concentration in said first gas sample and a second
output signal indicative of said first selected gas concentration
in said second gas sample; a second gas detector in communication
with said first gas detector, said second gas detector being
adapted to substantially simultaneously detect the concentration of
at least a second and third selected gas in at least said first and
second gas samples, said second gas detector being further adapted
to provide at least a third output signal indicative of said second
selected gas concentration in said first gas sample, a fourth
output signal indicative of said second selected gas concentration
in said second gas sample, a fifth output signal indicative of said
third selected gas concentration in said second gas sample and a
sixth output signal indicative of said third selected gas
concentration in said second gas sample; means for providing said
first and second gas samples to said first and second gas
detectors; and processing means in communication with said first
and second gas detectors for determining the rate of carbon
monoxide production in at least said second sample in response to
said first, second, third, fourth, fifth and sixth output
signals.
2. The apparatus of claim 1, wherein said first selected gas
comprises carbon dioxide.
3. The apparatus of claim 1, wherein said second selected gas
comprises carbon monoxide.
4. The apparatus of claim 1, wherein said third selected gas
comprises hydrogen.
5. The apparatus of claim 1, wherein said first gas sample
substantially comprises room air.
6. The apparatus of claim 1, wherein said second gas sample
comprises an expired breath sample from said subject.
7. The apparatus of claim 1, wherein said means for providing said
first and second gas samples includes a flow regulator and flow
inducing means.
8. The apparatus of claim 7, wherein said flow inducing means
comprises a positive displacement pump.
9. The apparatus of claim 1, wherein said apparatus includes an
organic vapor filter disposed between said first and second gas
detectors.
10. The apparatus of claim 9, wherein said organic vapor filter
substantially comprises activated charcoal.
11. A method for measuring the carbon monoxide production rate of a
subject, comprising the steps of: introducing a room air sample to
first and second gas detectors during a first period of time;
detecting the concentration of carbon dioxide in said room air
sample (CO.sub.2) with said first gas detector during said first
period of time; substantially simultaneously detecting the
concentration of carbon monoxide in said room air sample (CO) and
the concentration of hydrogen in said ambient room air sample
(H.sub.2) with said second gas detector during said first period of
time; introducing a breath sample from said subject to said first
and second gas detectors during a second period of time; measuring
the concentration of carbon dioxide in said breath sample
(CO.sub.2') with said first gas detector during said second period
of time; substantially simultaneously measuring the concentration
of carbon monoxide in said breath sample (CO') and the
concentration of hydrogen in said breath sample (H.sub.2') with
said second gas detector during said second period of time;
comparing said CO.sub.2', CO', and H.sub.2' detected in said breath
sample to said CO.sub.2, CO and H.sub.2 detected in said room air
sample to derive corrected carbon dioxide (CO.sub.2"), carbon
monoxide (CO") and hydrogen (H.sub.2") values; and determining the
carbon monoxide production rate ({dot over (V)}CO) from the
following relationship: 3 V .degree. CO = t 1 t 0 CO " t where:
t.sub.1-t.sub.0=said second period of time
12. The method of claim 11, wherein said method includes the step
of determining the hydrogen production rate ({dot over (V)}H.sub.2)
from the following relationship: 4 V .degree. H 2 = t 1 t o H 2 "
t
13. The method of claim 11, wherein said first period of time is in
the range of approximately 30 to 75 sec.
14. The method claim 11, wherein said second period of time is in
the range of approximately 60 to 120 sec.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims benefit under 35 U.S.C. 119 (e) of
U.S. Provisional Application No. 60/189,002, filed Mar. 13,
2000.
FIELD OF THE INVENTION
[0002] This invention relates to methods and apparatus for in vivo
measurement of carbon monoxide concentration in the exhaled breath
of a patient. More particularly, the invention relates to a method
and apparatus for direct measurement of the carbon monoxide
production rate of a patient.
BACKGROUND OF THE INVENTION
[0003] It is known that hemoglobin, myoglobin, and a series of heme
enzymes, which reside principally in the liver, are the major
hemoproteins. It is also well known that the end products of the
catabolism of the heme moiety of these compounds are (1) iron,
which is conserved, (2) carbon monoxide (CO), which is normally
excreted in the breath, and (3) bilirubin, which is excreted by the
liver and chemically modified in the gastrointestinal tract to a
series of urobilins.
[0004] The principal source of CO and of bilirubin--each a
surrogate for the other--is from the catabolism of circulating red
cells at the end of their life span. A small portion of CO is also
derived from cytoplasmic hemoglobin released as a shroud during
enucleation of normoblasts and from aborted red blood cell
precursors that never reach the peripheral blood (i.e., ineffective
erythropiesis).
[0005] The rate of CO excretion (or production) is thus clinically
significant. For example, in patents with hemolytic anemias,
hematologists need a measure of the effectiveness of therapy.
Usually they rely principally on an increase in the hematocrit or a
decrease in the reticulocyte count. An increase in hematocrit is
comparatively slow, whereas a decrease in reticulocyte count is
more rapid.
[0006] It is likely that if treatment were effective very rapidly
(i.e., instantaneously) it would take 5 to 7 days for the
reticulocyte count to decrease to normal levels because of maturing
red cell precursors already in the formative-stage pipeline in the
bone marrow. Moreover, reticulocyte levels may be altered by
intercurrent conditions such as inflammation and infections.
[0007] By contrast, the rate of carbon monoxide excretion typically
decreases rapidly to normal levels within hours and will more
accurately reflect hemolytic rates, as would the plasma
unconjugated bilirubin concentration.
[0008] Carbon monoxide excretion has two (2) distinct components.
The first represents endogeneous production of CO. The second
accrues from exogeneous CO absorbed from the atmosphere, both in
smokers and non-smokers.
[0009] Various non-invasive methods (and apparatus) have been
employed to determine the concentration of carbon monoxide in the
breath. One method includes incrementally acquiring a sample of
"end-tidal" breath and analyzing the acquired sample by mass
spectroscopy or gas chromatography to determine the end-tidal
carbon monoxide concentration. The sample is obtained by extracting
from each of several successive breaths a portion of the apparent
end-tidal breath using a syringe. The end-tidal portion of breath
is determined by observing the chest movements of the infant. See,
e.g., Vreman et al., U.S. Pat. No. 4,831,024.
[0010] A major drawback with this method is that the results merely
provide an estimate of the carbon monoxide concentration, not the
rate of carbon monoxide production.
[0011] A further problem with this method is that accurate
assessment of the concentration difference in carbon monoxide
requires obtaining good samples of end-tidal patient breath. This
essentially requires that the patient have a regular, predictable
breathing cycle. Thus, it can be difficult to obtain a good sample
by watching chest wall movement, particularly for a newborn and for
patients having irregular breathing cycles.
[0012] In U.S. Pat. No. 5,293,875 further methods and apparatus are
disclosed for measuring the end-tidal carbon monoxide concentration
in a patient's breath. The method comprises measuring the room
carbon monoxide concentration, end-tidal carbon dioxide
concentration (ETCO.sub.2), the average carbon dioxide
concentration, and the average carbon monoxide concentration in the
patient's breath. From this data, the apparatus computes the
end-tidal carbon monoxide "concentration" corrected for room air
and the index of CO/CO.sub.2.
[0013] A major drawback of the '875 method is that the index of
CO/CO.sub.2 is a derived parameter, which, according to the
invention, "may" relate the rate of carbon monoxide production to
the degree of hemolysis. The apparatus is thus incapable of
providing a direct measure of the carbon monoxide production
rate.
[0014] Further, the apparatus employs a conventional
electrochemical sensor. Such sensors are sensitive to many other
gases such as hydrogen (H.sub.2), and are therefore susceptible to
error.
[0015] It is well known that hydrogen is a waste product, emanating
from the gastrointestinal system, which is also normally excreted
in the breath. The hydrogen typically evolves from various
digestive abnormalities, such as lactose intolerance, or the
inability to thoroughly digest the carbohydrates and/or
disaccharides contained in the system. When this occurs, bacteria
will digest the noted substances and give off hydrogen as a
bi-product.
[0016] Another problem with conventional sensors is that the
measurement dynamics of the sample gas transport through the gas
permeable membrane and oxidation-reduction in the electrochemical
cell results in a relatively slow response time such that discrete
samples of the end-tidal breath must be obtained and analyzed to
determine the end-tidal carbon monoxide concentration.
[0017] It is therefore an object of the present invention to
provide an improved method and apparatus for the in vivo
measurement of carbon monoxide production rate.
[0018] It is another object of the invention to provide a method
and apparatus for "direct", rapid, real-time assessment of the
level of hemolysis in the blood.
[0019] It is yet another object of the invention to provide a
method and apparatus for assessment of carbon monoxide production
rate that substantially reduces the errors associated with the
H.sub.2 excretion.
SUMMARY OF THE INVENTION
[0020] In accordance with the above objects and those that will be
mentioned and will become apparent below, the apparatus for in vivo
measurement of carbon monoxide production rate in accordance with
this invention comprises a first gas detector for detecting the
concentration of a first selected gas in at least first and second
gas samples, the first gas detector being adapted to provide output
signals corresponding to the first selected gas concentration in
the first and second gas samples; a second gas detector adapted to
substantially simultaneously detect the concentration of at least
second and third selected gases in the first and second gas
samples, the second gas detector being further adapted to provide
output signals corresponding to the second and third selected gas
concentrations in the first and second gas samples; means for
providing the first and second gas samples to the first and second
gas detectors; and processing means for determining the rate of
carbon monoxide production in at least the second sample in
response to the first and second gas detectors output signals.
[0021] The method of determining the carbon monoxide production
rate in a subject in accordance with the invention comprises the
steps of (a) introducing a room air sample to first and second gas
detectors during a first period of time; (b) detecting the
concentration of carbon dioxide in the room air sample (CO.sub.2)
during the first period of time; (c) substantially simultaneously
detecting the concentration of carbon monoxide in the room air
sample (CO) and the concentration of hydrogen in the room air
sample (H.sub.2) during the first period of time; (d) introducing a
breath sample from the subject to the first and second gas
detectors during a second period of time; (e) measuring the
concentration of carbon dioxide in the breath sample (CO.sub.2')
during the second period of time; (f) substantially simultaneously
measuring the concentration of carbon monoxide in the breath sample
(CO') and the concentration of hydrogen in the breath sample
(H.sub.2') during the second period of time; (g) comparing the
CO.sub.2', CO', and H.sub.2' detected in the breath sample to the
CO.sub.2, CO and H.sub.2 detected in the room air sample to derive
corrected carbon dioxide (CO.sub.2"), carbon monoxide (CO") and
hydrogen (H.sub.2") values; and (h) determining the carbon monoxide
production rate ({dot over (V)}CO) from the following relationship:
1 VCO = t 1 t 0 CO " t
[0022] where:
[0023] t.sub.1-t.sub.0=the second period of time
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] Further features and advantages will become apparent from
the following and more particular description of the preferred
embodiments of the invention, as illustrated in the accompanying
drawings, and in which like referenced characters generally refer
to the same parts or elements throughout the views, and in
which:
[0025] FIG. 1 is a schematic illustration of the heme
oxygenase-dependent production of CO;
[0026] FIG. 2 is a schematic illustration of one embodiment of the
apparatus for in vivo measurement of carbon monoxide production
rate according to the invention; and
[0027] FIG. 3 is an illustration of a test hood incorporating the
apparatus of the invention shown in FIG. 2.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0028] The present invention substantially reduces or eliminates
the drawbacks and disadvantages associated with prior art carbon
monoxide testing methods and apparatus. As discussed in detail
below, in contrast to prior art methods and apparatus which merely
provide an assessment of the carbon monoxide "concentration" in a
patient's breath, the method and apparatus of the invention
provides a rapid, in vivo assessment of the carbon monoxide
"production rate" in a patient.
[0029] As will be appreciated by one having skill in the art, the
method and apparatus of the invention may thus be employed in a
hospital nursery, clinic, or physician's office to provide a rapid,
accurate assessment of the level of hemolysis, which, if abnormally
high, could lead to various adverse consequences, such as
hyperbilirubinemia and jaundice.
[0030] Referring first to FIG. 1, there is shown an illustration of
the heme oxygenase-dependant production of CO. The heme degradation
reaction mechanism generating CO and bilirubin is complex and
involves the integrated action of three enzymes: microsomal heme
oxygenase, microsomal nicotinamide-adenine dinucleotide phosphate
(NADPH)-cytochrome c (P-450) reductase, and cytosolic biliverdin
reductase.
[0031] In the first step of this integrated system, heme is
autocatalyzed at the boundary of the cytosol and the endoplasmic
reticulum. Ferric (Fe(III)) heme typically binds to heme oxygenase
in a 1:1 molar ratio. Heme is reduced to the ferrous (Fe(II)) state
by the transfer of reducing equivalents through interaction with
NADPH-cytochrome c (P-450) reductase. In the ferrous state, heme
binds molecular oxygen (O.sub.2) and is altered through a sequence
of steps involving several intermediates, leading to
autooxidation.
[0032] With reduction of the alpha-hydroxyheme intermediate, the
alpha methene bridge carbon is eliminated as CO. The Fe(II)
component is released from the enzyme complex during the final step
in the HO reaction mechanism, and generated biliverdin is
subsequently reduced to bilirubin by the cytosolic enzyme,
biliverdin reductase.
[0033] The complete heme degradation reaction with its microsomal
and cytosolic components results in the equimolar formation of CO
and bilirubin per mole of heme degraded. Because of this
relationship, in-vitro and in vivo measurements of CO have been
used both as an index of heme catabolism and bilirubin production.
However, as discussed above, the CO measured by conventional
methods and apparatus is typically limited to CO "concentration",
not the clinically significant CO "production rate."
[0034] Referring now to FIG. 2, there is shown a preferred
embodiment of the method and apparatus of the invention. The
apparatus 10 includes a carbon dioxide (CO.sub.2) detector 12, an
organic vapor filter 14, a flow regulator 16, a pump 18, a combined
carbon monoxide/hydrogen (CO/H.sub.2) detector 20, and a
microprocessor 22.
[0035] As illustrated in FIG. 2, the CO.sub.2 detector 12, organic
filter 14, flow regulator 16, pump 18 and CO/H.sub.2 detector 20
are in fluid communication via flow line or tubing 30. The CO.sub.2
detector 12, flow regulator 16, pump 18 and CO/H.sub.2 detector 20
are also in communication with the microprocessor 22 via lines
23a-23d.
[0036] In additional envisioned embodiments of the invention, the
apparatus 10 includes a hydrophobic filter (shown in phantom and
denoted HF) disposed between the flow regulator 16 and CO.sub.2
detector 12 and in communication therewith via flow line 30. As
will be appreciated by one having ordinary skill in the art, the
hydrophobic filter (HF) would substantially reduce or eliminate any
moisture in the gas or flow line 30 (e.g., condensate) which could
interfere with the detection of carbon dioxide (CO.sub.2).
[0037] The CO.sub.2 detector 12 is employed to provide at least a
first signal corresponding to the sensed concentration of carbon
dioxide in the standard (i.e., room air) and at least a second
signal corresponding to the sensed concentration of carbon dioxide
in the analyte stream (or sample). As will be appreciated by one
having skill in the art, various carbon dioxide gas detectors
and/or analyzers may be employed within the scope of the invention,
such as the Servomex Model No. 1505 fast-response carbon dioxide
infrared transducer.
[0038] The organic vapor filter 14, which is preferably disposed
between the CO.sub.2 detector 12 and the pump 18, contains any
medium that will absorb organic vapors and reducing gases that
might interfere with detecting carbon monoxide. In a preferred
embodiment, filter 14 contains activated charcoal.
[0039] As illustrated in FIG. 2, the flow regulator 16 preferably
includes two (2) gas input lines; a first "standard" line 32 in
communication with the atmosphere (i.e., room air), and a second
"sample" line 34 in communication with the sampling chamber 42 (see
FIG. 3), discussed in detail below. According to the invention, the
flow regulator 16 is disposed proximate the hydrophobic filter 15
and is adapted to selectively direct a gas sample from the
atmosphere (i.e., standard), denoted by arrow A, or analyte stream
(i.e., breath sample) from the chamber 42, denoted by arrow B, to
filter 15. The flow regulator 16 also limits the flow rate of the
analyte gas stream and standard.
[0040] Disposed proximate the CO/H.sub.2 detector 20 is the flow
inducing means of the invention. In contrast to prior art methods
which assess the concentration of carbon monoxide in the end-tidal
portion of the breath and, hence, require a constant flow rate
(see, e.g., U.S. Pat. No. 5,293,875), the method of the present
invention does not require a constant flow rate of the analyte gas
stream. Thus, various flow inducing means may be employed within
the scope of the invention, such as a positive displacement pump
and a fan/flow sensor assembly.
[0041] In the embodiment of the invention shown in FIG. 2, the flow
inducing means comprises a positive displacement pump 18. According
to the invention, the pump 18 and regulator 16 are adjusted so that
flow through line 30 is maintained in the range of approximately 40
to 60 ml/min., more preferably, 45 to 55 ml/min. The pump 18 is
also adapted to expel the analyte flow stream out exhaust 36 and
into the atmosphere, denoted by arrow C.
[0042] A key component of the apparatus is the novel CO/H.sub.2
detector 20, which is adapted to substantially simultaneously
detect both CO and H.sub.2. In a preferred embodiment, the
CO/H.sub.2 is adapted to provide at least a first plurality of
signals C.sub.1-C.sub.N proportional to the concentration of CO in
the analyte stream and at least a second plurality of signals
C'.sub.1-C'.sub.N proportional to the concentration of H.sub.2 in
the sample; the signals C.sub.1-C.sub.N, C'.sub.1-C'.sub.N being
provided over a predetermined period of time, i.e., t.sub.1 through
t.sub.0.
[0043] Microprocessor 22 is employed to control the operation of
the apparatus 10. As illustrated in FIG. 2, the microprocessor 22
is connected to and, hence, in communication with the regulator 16,
CO.sub.2 detector 12, pump 18 and CO/H.sub.2 detector 20 to control
the noted components.
[0044] The microprocessor 22 is further adapted to receive and
respond to the output signals from the CO.sub.2 and CO/H.sub.2
detectors 12, 20 corresponding to the sensed CO.sub.2, CO and
H.sub.2 concentration. These signals are then processed according
to the algorithm discussed below to compute a value corresponding
to the rate of CO and H.sub.2 production. The computed values may
then be displayed on a display device 24, such as a liquid crystal
display (LED) device.
[0045] According to the invention, the display device 24 is adapted
to provide a display corresponding to at least the (i) CO.sub.2
concentration (CCO.sub.2) in the standard and the analyte stream,
(ii) the CO concentration in the standard, (iii) the H.sub.2
concentration in the standard, (iv) the rate of CO production ({dot
over (V)}CO) in the analyte stream, (v) and the rate of H.sub.2
production ({dot over (V)}H.sub.2) in the analyte stream.
Preferably, display 24 includes a display screen for alphanumeric
text, including the determined CCO.sub.2, {dot over (V)}CO and {dot
over (V)}H.sub.2, and instructions to the operator for operating
the apparatus 10 to acquire the appropriate gas samples.
[0046] In additional envisioned embodiments of the invention, the
display device includes a keyboard for operator input. The display
device 24 may also include a paper printer or have an associated
printer (not shown) for providing a printed copy of the parameters
determined and/or measured, in character text or graphic form.
Alternately, or in addition, audible sounds, visual indicators or
lights may be used to prompt the operator to perform the
appropriate act.
[0047] Referring now to FIG. 3, in a preferred embodiment of the
invention, the apparatus 10 is positioned on a test hood 40, having
a test chamber 42 disposed therein. As illustrated in FIG. 3, the
hood 40 is provided with an entrance port 43 to facilitate
placement of the infant's head 7 within the chamber 42.
[0048] As will be appreciated by one having ordinary skill in the
art, the hood 40 may comprise various shapes and sizes, to position
a patient's head (i.e., adult or infant) within a defined chamber
or position the entire body of the infant 5 therein.
[0049] According to a preferred embodiment of the present
invention, {dot over (V)}CO and {dot over (V)}H.sub.2 are
determined in the following manner. The patient (i.e., infant 5) is
positioned in test chamber 42.
[0050] Pump 18 is initiated and a "standard" of room air is drawn
through line 32 at a selected flow rate, e.g., 50 ml/min, for a
first period of time in the range of 30 to 75 sec. The "standard"
is directed to and through the CO.sub.2 and CO/H.sub.2 detectors
12, 20.
[0051] At the end of a first time period, the sensed concentration
of carbon dioxide (CO'.sub.2), carbon monoxide (CO') and hydrogen
(H'.sub.2) in the standard are obtained. A first signal from the
CO.sub.2 detector 12 corresponding to the sensed concentration
CO'.sub.2, and third and fourth signals from the CO/H.sub.2
detector 20 corresponding to the concentrations of CO' and
H'.sub.2, respectively, are communicated to the microprocessor 22
and stored in memory.
[0052] The microprocessor 22 then signals the regulator 16 to close
line 32 and draw a test sample (i.e., analyte stream) from the
chamber 42. The analyte stream is then directed to and through the
filters 15, 14, and CO.sub.2 and CO/H.sub.2 detectors 12, 20.
[0053] During a second period of time (i.e., t.sub.1-t.sub.0), the
sensed concentrations of carbon dioxide, carbon monoxide and
hydrogen in the analyte stream, CO.sub.2", CO" and H.sub.2",
respectively, are obtained. In a preferred embodiment of the
invention, the second period of time (t.sub.1-t.sub.0) is in the
range of 60 to 120 sec.
[0054] A second signal corresponding to CO.sub.2" and the plurality
of first and second signals C.sub.1-C.sub.N, C'.sub.1-C'.sub.N,
corresponding to values of CO" and H.sub.2" obtained over time
period t.sub.1 through t.sub.0, are communicated to the
microprocessor 22.
[0055] The noted values of CO.sub.2', CO.sub.2", CO', H.sub.2',
C.sub.1-C.sub.N, and C'.sub.1-C'.sub.N are evaluated as follows:
First, the values of the CO.sub.2, CO and H.sub.2 obtained from the
standard, i.e., CO'.sub.2, CO', H'.sub.2, are compared to the
values of the CO.sub.2, CO and H.sub.2 obtained from the analyte
stream, i.e., CO.sub.2", CO", H.sub.2". The values CO.sub.2", CO",
H.sub.2" are then adjusted, if necessary, to account for the
CO.sub.2', CO' and H.sub.2' detected in the standard.
[0056] The values {dot over (V)}CO and {dot over (V)}H.sub.2 are
then determined from the following relationships: 2 V CO = t 1 t o
CO c " t and ( 1 ) V .degree. H 2 = t 1 t o H 2 c " t ( 2 )
[0057] where:
[0058] t.sub.1-t.sub.0=desired analyte stream test cycle or time
interval;
[0059] CO".sub.c=corrected CO" value; and
[0060] H.sub.2".sub.c=corrected H" value.
[0061] As will be appreciated by one having ordinary skill in the
art, the method and apparatus of the invention provides several
distinct advantages over the prior art. In contrast to the noted
prior art methods that merely measure the concentration of CO in
the end-tidal breath, which is not truly indicative of the
physiological state of the patient, the method of the present
invention provides rapid, accurate, direct in vivo measurement of
VCO and VH.sub.2.
[0062] A further advantage is that the apparatus is compact,
lightweight and readily adaptable to virtually all-testing
environments.
[0063] Without departing from the spirit and scope of this
invention, one of ordinary skill can make various changes and
modifications to the invention to adapt it to various usages and
conditions. As such, these changes and modifications are properly,
equitably, and intended to be, within the full range of equivalence
of the following claims.
* * * * *