U.S. patent application number 16/678759 was filed with the patent office on 2020-10-01 for breath selection for analysis.
The applicant listed for this patent is Capnia, Inc.. Invention is credited to Anish BHATNAGAR, Scott J. GILBERT, Anthony D. WONDKA.
Application Number | 20200305729 16/678759 |
Document ID | / |
Family ID | 1000004896739 |
Filed Date | 2020-10-01 |
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United States Patent
Application |
20200305729 |
Kind Code |
A1 |
WONDKA; Anthony D. ; et
al. |
October 1, 2020 |
BREATH SELECTION FOR ANALYSIS
Abstract
Methods and systems are described to obtain and analyze a gas
sample from a desired section of the breath of a person, while
accounting for erratic, episodic or otherwise challenging breathing
patterns that may otherwise make the capturing of a gas sample from
the desired section of breath difficult. These techniques may
provide more reliable, accurate and adequate samples of gas such as
end-tidal gas, and ultimately an accurate analysis of the sample
captured.
Inventors: |
WONDKA; Anthony D.; (San
Ramon, CA) ; BHATNAGAR; Anish; (Redwood City, CA)
; GILBERT; Scott J.; (Menlo Park, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Capnia, Inc. |
Foster City |
CA |
US |
|
|
Family ID: |
1000004896739 |
Appl. No.: |
16/678759 |
Filed: |
November 8, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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14150625 |
Jan 8, 2014 |
10499819 |
|
|
16678759 |
|
|
|
|
61750305 |
Jan 8, 2013 |
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Current U.S.
Class: |
1/1 ; 600/531;
600/532 |
Current CPC
Class: |
A61B 5/7285 20130101;
A61B 5/091 20130101; A61B 5/0816 20130101; A61B 2560/0223 20130101;
G16H 40/63 20180101; A61B 5/02055 20130101; A61B 5/01 20130101;
G16H 50/20 20180101; A61B 5/087 20130101; A61B 5/082 20130101; A61B
5/7203 20130101; A61B 5/7221 20130101; G16H 10/40 20180101; A61B
5/7275 20130101 |
International
Class: |
A61B 5/0205 20060101
A61B005/0205; A61B 5/00 20060101 A61B005/00; A61B 5/08 20060101
A61B005/08; G16H 40/63 20060101 G16H040/63; G16H 50/20 20060101
G16H050/20; G16H 10/40 20060101 G16H010/40 |
Claims
1-18. (canceled)
19. An apparatus for breath selection comprising: a sensor that
measures a plurality of breathing parameters of a series of exhaled
breaths, wherein a plurality of predetermined criteria are based on
the plurality of breathing parameters; a processor that applies a
breath selection algorithm to the series of exhaled breaths and
identifies a first valid exhaled breath when the first exhaled
breath meets at least two or more of the plurality of predetermined
criteria, the at least two or more predetermined criteria
comprising a peak amplitude and a time-based value, and wherein the
breath selection algorithm further identifies a second valid
exhaled breath when the second valid exhaled breath meets a percent
comparison of the two or more predetermined criteria; a breath
sampling system that captures the second valid exhaled breath; and
a gas analyzer that measures an analyte in the second valid exhaled
breath.
20. The apparatus of claim 19, wherein the analyte comprises carbon
monoxide.
21. The apparatus of claim 19, wherein the time-based value is
selected from the group consisting of a time duration below the
peak amplitude value, a time duration below a baseline value, an
inspiratory time, a breath period time, an expiratory time, and
end-tidal time, a CO.sub.2 value over time, and an O.sub.2 value
over time.
22. The apparatus of claim 19, wherein the breath selection
algorithm further comprises identifying a second valid exhaled
breath based on a breath period between the first and second valid
exhaled breaths.
23. The apparatus of claim 22, wherein the breath period is based
on a breath rate.
24. The apparatus of claim 19, wherein the sensor comprises a
carbon monoxide sensor, a pressure sensor, or an infrared (IR)
sensor.
25. A method for selecting a valid exhaled breath for analysis
comprising: identifying a first valid exhaled breath based on the
first valid exhaled breath meeting at least two or more
predetermined criteria, the at least two or more predetermined
criteria comprising a peak amplitude and a time-based value;
identifying a second valid exhaled breath based on a percent
comparison of the at least two or more predetermined criteria;
capturing the second valid exhaled breath using a breath sampling
system; and measuring an analyte in the second valid exhaled
breath.
26. The method of claim 25, wherein the analyte comprises carbon
monoxide.
27. The method of claim 25, wherein the time-based value is
selected from the group consisting of a time duration below the
peak amplitude value, a time duration below a baseline value, an
inspiratory time, a breath period time, an expiratory time, and
end-tidal time, a CO.sub.2 value over time, and an O.sub.2 value
over time.
28. The method of claim 25, wherein identifying the second valid
exhaled breath is further based on a breath period between the
first and second valid exhaled breaths.
29. The method of claim 28, wherein the breath period is based on a
breath rate.
30. An apparatus for breath selection comprising: a sensor that
measures parameters of a first exhaled breath, a second exhaled
breath, and a third exhaled breath; a first processor that
determines if a first measurement of the first exhaled breath meets
a first predetermined criteria; a second processor that determines
if a second measurement of the second exhaled breath meets a second
predetermined criteria, wherein the second measurement is made when
the first measurement is determined to meet the first predetermined
criteria; a third processor that determines if a third measurement
of the third exhaled breath meets a third predetermined criteria,
wherein the third measurement is made when the second measurement
is determined to meet the second predetermined criteria; and a
breath sampling system that stores the third exhaled breath when
the third processor determines the third measured parameter meets
the third predetermined criteria.
31. The apparatus of claim 30, wherein the third predetermined
criteria is based upon a trend associated with a plurality of
breaths.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Application No. 61/750,305 filed on, Jan. 8, 2013, the disclosure
of which is hereby incorporated by reference in its entirety.
FIELD
[0002] Described herein are devices and methods for the analysis of
breath exhalant for diagnostic purposes. More specifically, devices
and methods are described for identifying a physiologically
relevant portion of a breathing cycle, which may be used to
correlate the analysis of the exhalant to an underlying physiologic
condition.
BACKGROUND
[0003] Certain metabolites and chemicals produced in or entering
the body and bloodstream are excreted in the breath. The level in
the body or blood stream may be determined by measuring it in the
breath. For example, breath CO levels may be measured to detect and
monitor underlying disorders such as hematological disorders and
conditions, metabolic disorders, and environmental and behavioral
problems. For example, end-tidal CO can be correlated to blood CO,
which can be indicative of hemolysis, smoking or inhalation
poisoning. In order to measure end-tidal CO, alveolar gas may be
collected non-invasively from the exhaled breath of a patient by
capturing the portion of the breath at the end of exhalation. The
captured end-tidal gas can then be analyzed for its CO
concentration thus completing the non-invasive diagnostic
measurement. Typically, a correlation exists between the level of
an analyte in the exhaled gas and the level of a metabolite or
chemical or other substance in the body or blood, for example a 1:1
ratio or some other ratio.
[0004] It has been discovered that proper and accurate correlation
of blood-to-breath analyte levels, such as CO gas, may be dependent
on the breathing pattern. Typically, breath samples are taken
without contemplating whether or not the patient's breathing
pattern is appropriate for the diagnostic analysis being taken.
When the level of a certain gas in the blood is being analyzed by
measuring it in the breath, in some situations, in order for the
correlation of blood-to-breath level to be accurate, the patient
may need to be breathing at their normal resting tidal volume or
minute volume breathing pattern in terms of frequency and depth of
breathing. In other situations, the blood-to-breath correlation may
be more accurate if the person performs a non-resting tidal volume
breath, such as a sigh breath or breath hold (for example when
attempting to diagnose a metabolic disorder), or deep breath (for
example when attempting to diagnose an infection).
[0005] In addition, it may be beneficial during a breath test, that
the end-tidal gas be collected automatically or semi-automatically
from a non-cooperative patient or a patient incapable of following
instructions. Or in some cases a patient that may be capable of
cooperating, but is influenced by the test, and inadvertently may
submit a sample when breathing abnormally. In these situations,
obtaining a pure and adequate sample of gas from the breath can be
challenging.
SUMMARY
[0006] To address the above deficiencies, the present disclosure
provides systems and methods that define, target, capture, and
analyze a physiologically appropriate breath or breaths for the
diagnostic test being undertaken, and may avoid the analysis of
physiologically inappropriate breaths that could lead to a false
diagnostic result.
[0007] Described herein are breath analyte analyzers and methods
that may reliably collect an accurate sample of exhalant analyte
such as end-tidal gas from a wide-range of breathing patterns and
may encompass a wide-range of patient types, environmental
conditions, and clinical circumstances. In a first variation, a
breathing pattern is measured for a period of time until a certain
type of breath occurs. The type of breath desired may be predefined
by establishing breath threshold criteria for which an accurate
sample may be obtained. The threshold criteria may be, for example,
detection of a complete and normal tidal volume breath of the
patient. Once a threshold criteria is met, a sample may be taken
from the appropriate portion of that corresponding breath. In a
second variation, a sample is collected from a breath that meets
one of two or more predefined types of breaths. For example a
breath with an expiratory period of at least 0.5 seconds may be
predefined, and an exhalation of a complete and normal tidal volume
breath may be predefined, and a sample will be collected from
whichever breath occurs first. In a third variation, an apparatus
may prompt or otherwise communicate with a user to interfere with
the patient's breathing pattern such that the patient will produce
a breath that meets a certain breath type. In a fourth variation,
an apparatus may take an input of a physiological signal against
which breath targeting thresholds may be set, in order to verify
that a physiologically representative breath is targeted for the
prevailing clinical conditions. In a fifth variation, an apparatus
may target a physiologically representative breath if and when
found, and if not found, will target a breath that is
non-representative but will then apply a correction factor to
normalize the result to a representative breath. In a sixth
variation, the apparatus may prompt or communicate to the user to
give the user the option of waiting for the pre-defined type of
breath to occur, or to cancel the test to avoid long wait periods.
In a seventh variation, the apparatus may require a targeted breath
to both satisfy a breath type criteria and a breathing pattern
stability criteria.
[0008] In an eight variation, an apparatus for analyzing a breath
gas includes a sensor, a breath sampling system, a processor, and a
gas analyzer. The sensor may measure a breathing pattern parameter.
The breath sampling system may include a gas collection conduit.
The processor may determine if an exhaled breath should be sampled
for analysis based on a comparison of a breathing parameter
threshold value to the measured breathing pattern parameter. The
threshold value may delineate between a physiologically
representative breath and a physiologically non-representative
breath. The gas analyzer may analyze the breath gas.
[0009] In a ninth variation, an apparatus for analyzing a gas in
exhaled breath includes a sensor, a breath sampling system, a
processor, and a gas analyzer. The sensor may measure a breathing
parameter including an expiratory signal. The breath sampling
system may include a gas collection conduit. The processor may
determine if an exhaled breath should be sampled for analysis based
on a comparison of a breathing parameter threshold value to the
measured expiratory breathing signal parameter, wherein the
threshold value is a duration of a part of the breathing parameter.
The gas analyzer may analyze the breath gas.
[0010] In a tenth variation, an apparatus for collection of and
analysis of a gas in exhaled breath includes a sensor, a breath
sampling system, a processor, and a gas analyzer. The sensor may
measure a breathing parameter including an expiratory signal. The
breath sampling system may include a gas collection conduit. The
first processor may compare a breathing pattern threshold value to
the measured breathing pattern parameter and determine if the
measured parameter meets the threshold value, wherein the threshold
value delineates between a physiologically representative breath
and a physiologically non-representative breath. The gas analyzer
may analyze the breath gas, wherein the gas analyzer comprises a
second processor having a first gas analysis algorithm and a second
gas analysis algorithm. The first gas analysis algorithm is used
for breaths determined to meet the threshold value. The second gas
analysis algorithm is used for breaths determined to not meet the
threshold value, wherein the second algorithm comprises a
correction factor to convert a non-representative result from a
non-representative breath to a representative result.
[0011] In an eleventh variation, an apparatus for collection of and
analysis of a gas in exhaled breath includes a sensor, a breath
sampling system, a processor, and a gas analyzer. The sensor may
measure a breathing parameter including an expiratory signal. The
breath sampling system may include a gas collection conduit. The
processor may include an input to receive a physiological signal,
wherein the processor compares a breathing pattern parameter
threshold value to the measured breathing pattern parameter and
determines if a breath meets the threshold value, wherein the
threshold value is defined based on the physiological signal, and
wherein the threshold value is defined to delineate between a
physiologically representative breath and a physiologically
non-representative breath. The gas analyzer may analyze the breath
gas.
[0012] In a twelfth variation, the threshold value in any one of
eighth through eleventh variations is selected to be representative
of a complete tidal volume breath.
[0013] In a thirteenth variation, the apparatus in any one of
eighth through twelfth variations includes a breath signal trending
algorithm, and wherein the threshold value is at least one selected
from the group consisting of: a peak amplitude value, a baseline
value, a time duration above the peak amplitude value, a time
duration below the baseline value, and a percent comparison of a
current breath to trending algorithm.
[0014] In a fourteenth variation, the threshold value in any one of
eighth through thirteenth variations is selected to be an amplitude
value and a baseline value, wherein the values are selected to
represent a complete tidal volume breath.
[0015] In a fifteenth variation, the breath parameter threshold
value of the tenth variation is a breath rate of less than or equal
to 60 breaths per minute.
[0016] In a sixteenth variation, the threshold value in any one of
eighth through fifteenth variations is based on at least one
selected from the group consisting of an expiratory time, a portion
of an expiratory time, an airway pressure, a CO.sub.2 value (over
time), an O.sub.2 value (over time), an airway temperature, a
breath flow rate, a breath rate, a depth of breath, a duration of
breath, an inspiratory time, a pre-end-tidal time, an end-tidal
time, a post-expiratory time, an inspiratory pause, a peak
inspiratory pressure, a peak expiratory pressure, a characteristic
waveform for sneeze, cough, stacked breath or non-full breath, an
inspiratory amplitude, an expiratory amplitude, and a historical
breath criteria.
[0017] In a seventeenth variation, the physiologic signal of the
tenth variation is representative of a physiological parameter of a
patient, wherein the physiological parameter is at least one
selected from the group consisting of a blood pressure, a heart
rate, chest impedance, a weight, a height, an age, a race, a sex, a
diagnosis, a respiratory rate, a tidal volume, a minute volume, an
inspiratory:expiratory ratio, a blood gas, a cardiac output, an end
tidal CO.sub.2 concentration, a pulmonary perfusion, a base excess,
an O.sub.2 sat, and a ventilation:perfusion ratio.
[0018] In an eighteenth variation, the processor in any one of
eighth through seventeenth variations further comprises a breath
type information algorithm to determine a breath for sampling,
wherein the algorithm is at least partly based upon determining the
breath is at least one selected from the group consisting of a
breath hold, a deep breath, a forced exhaled breath, an inspiratory
pause, an expiratory pause, a resting respiration, and a breath
pattern repetition.
[0019] In a nineteenth variation, a breath trending algorithm of
any one of eighth through eighteenth variations is at least partly
based upon a breath pattern and wherein the algorithm determines to
sample after a predetermined number of repetitive breaths.
[0020] In a twentieth variation, the predetermined number of
breaths of the nineteenth variation is between 1 and 5 breaths.
[0021] In a twenty-first variation, the predetermined number of
breaths of the nineteenth variation is between 2 and 4 breaths.
[0022] In a twenty-second variation, an apparatus for analyzing an
exhaled breath includes a sensor, a first processor, and a breath
sampling system. The sensor may measure a parameter of the exhaled
breath. The first processor may determine if the measured parameter
meets a predetermined criteria corresponding to a physiologically
representative breath. The breath sampling system may store the
exhaled breath when the first processor determines the measured
parameter meets the predetermined criteria.
[0023] In a twenty-third variation, the apparatus of the
twenty-second variation includes a gas analyzer to analyze the
stored breath. In a twenty-fourth variation, the gas analyzer of
the twenty-third variation includes a second processor that applies
a first gas analysis algorithm when the first processor determines
the measured parameter meets the predetermined criteria and applies
a second gas analysis algorithm when the first processor determines
the measured parameter does not meet the predetermined criteria,
wherein the second algorithm comprises a correction factor.
[0024] In a twenty-fifth variation, the apparatus of any of the
twenty-second through twenty-fourth variations includes a
physiologic sensor that monitors a physiological parameter of a
patient and wherein the breath sampling system does not store the
exhaled breath when a third processor determines the physiological
parameter does not meet a predetermined physiological criteria.
[0025] In a twenty-sixth variation, the physiologic parameter of
the twenty-fifth variation includes at least one selected from the
group consisting of a blood pressure, a heart rate, chest
impedance, a weight, a height, an age, a race, a sex, a diagnosis,
a respiratory rate, a tidal volume, a minute volume, an
inspiratory:expiratory ratio, a blood gas, a cardiac output, an end
tidal CO.sub.2 concentration, a pulmonary perfusion, a base excess,
an O.sub.2 sat, and a ventilation:perfusion ratio.
[0026] In a twenty-seventh variation, the predetermined criteria of
any of the twenty-second through twenty-sixth variations includes a
minimum duration.
[0027] In a twenty-eight variation, the predetermined criteria of
any of the twenty-second through twenty-seventh variations includes
at least one selected from the group consisting of: a peak
amplitude value, a baseline value, a time duration above the peak
amplitude value, a time duration below the baseline value, and a
percent comparison of a current breath to a trending algorithm.
[0028] In a twenty-ninth variation, the predetermined criteria of
any of the twenty-second through twenty-eighth variations includes
an amplitude value and a baseline value representing a complete
tidal volume breath
[0029] In a thirtieth variation, the predetermined criteria of any
of the twenty-second through twenty-ninth variations includes a
breath rate of less than or equal to 60 breaths per minute.
[0030] In a thirty-first variation, the predetermined criteria of
any of the twenty-second through thirtieth variations is based on
at least one selected from the group consisting of an expiratory
time, a portion of an expiratory time, an airway pressure, a
CO.sub.2 value over time, an O.sub.2 value over time, an airway
temperature, a breath flow rate, a breath rate, a depth of breath,
a duration of breath, an inspiratory time, a pre-end-tidal time, an
end-tidal time, a post-expiratory time, an inspiratory pause, a
peak inspiratory pressure, a peak expiratory pressure, a
characteristic waveform for sneeze, cough, stacked breath or
non-full breath, an inspiratory amplitude, an expiratory amplitude,
and a historical breath criteria.
[0031] In a thirty-second variation, the predetermined criteria of
any of the twenty-second through thirty-first variations is based
upon at least one selected from the group consisting of a breath
hold, a deep breath, a forced exhaled breath, an inspiratory pause,
an expiratory pause, a resting respiration, and a breath pattern
repetition.
[0032] In a thirty-third variation, the predetermined criteria of
any of the twenty-second through thirty-first variations is based
upon a predetermined number of repetitive breaths.
[0033] In a thirty-fourth variation, the number of repetitive
breaths of the thirty-third variation is between 1 and 5
breaths.
[0034] In a thirty-fifth variation, the number of repetitive
breaths of the thirty-fourth variation is between 2 and 4
breaths.
[0035] In a thirty-sixth variation, an apparatus for analyzing
breath gas includes a sensor, a first processor, a second
processor, a third processor, and a breath sampling system. The
sensor may measure parameters of a first exhaled breath, a second
exhaled breath, and a third exhaled breath. The first processor may
determine if a first measurement of the first exhaled breath meets
a first predetermined criteria. The second processor may determine
if a second measurement of the second exhaled breath meets a second
predetermined criteria, wherein the second measurement is made when
the first measurement is determined to meet the first predetermined
criteria. The third processor may determine if a third measurement
of the third exhaled breath meets a third predetermined criteria,
wherein the third measurement is made when the second measurement
is determined to meet the second predetermined criteria. The breath
sampling system may store the third exhaled breath when the third
processor determines the third measured parameter meets the third
predetermined criteria.
[0036] In a thirty-seventh variation, the third predetermined
criteria of the thirty-sixth variation is based upon a trend
associated with a plurality of breaths.
[0037] In a thirty-eight variation, a method for analyzing breath
gas includes: measuring parameters of a first exhaled breath, a
second exhaled breath, and a third exhaled breath; determining if a
first measurement of the first exhaled breath meets a first
predetermined criteria; determining if a second measurement of the
second exhaled breath meets a second predetermined criteria,
wherein the second measurement is made when the first measurement
is determined to meet the first predetermined criteria; determining
if a third measurement of the third exhaled breath meets a third
predetermined criteria, wherein the third measurement is made when
the second measurement is determined to meet the second
predetermined criteria; and storing the third exhaled breath when
the third measurement is determined to meet the third predetermined
criteria.
[0038] In a thirty-ninth variation, the third predetermined
criteria of the thirty-eight variation is based upon a trend
associated with a plurality of breaths.
BRIEF DESCRIPTION OF THE DRAWINGS
[0039] FIG. 1 describes schematically an overview of a breath
analyzer in accordance with one variation.
[0040] FIG. 1b schematically describes an optional overview of the
breath analyzer in which the analysis may be conducted in
substantially real time, in accordance with one variation.
[0041] FIG. 1c schematically describes an optional overview of the
breath analyzer in which the sample may be saved and the analysis
may be conducted at a later time, in accordance with one
variation.
[0042] FIG. 2 describes an exemplary control system for operating
the breath analyzer of FIG. 1, in accordance with one
variation.
[0043] FIG. 3 graphically describes a typical breath monitoring
waveform based on a carbon dioxide measurement which is taken on
gas being drawn from a breath, in accordance with one
variation.
[0044] FIG. 4 graphically describes a typical breath monitoring
waveform based on an airway pressure measurement taken at the
proximal airway, in accordance with one variation.
[0045] FIG. 5 is a timing diagram describing the sequence of
operation of capturing a gas sample based on capnometry, in
accordance with one variation.
[0046] FIG. 6 is a timing diagram describing the sequence of
operation of capturing the gas sample based on airway pressure
monitoring, in accordance with one variation.
[0047] FIG. 7 is a pneumatic schematic describing the capturing of
a sample from the series of breaths described in FIG. 8, in
accordance with one variation.
[0048] FIG. 8 graphically describes a capnometry signal versus time
for a sequence of breaths from which a sample is taken, in
accordance with one variation.
[0049] FIG. 9 is a graph of signal strength versus time, in
accordance with one variation.
[0050] FIG. 10 describes a flow chart of a variation of a breath
detection and monitoring method in which measured breath values are
compared against set thresholds, in accordance with one
variation.
[0051] FIG. 11 describes a flow chart of a variation of a breath
detection and monitoring method in which measured breath values are
compared against a second set of criteria if a first set is not
met, in accordance with one variation.
[0052] FIG. 12 describes a flow chart of one variation in which a
user can enter clinical information into the system so that the
system can delineate between representative and non-representative
breaths for the diagnostic test being undertaken, in accordance
with one variation.
[0053] FIG. 13 describes a flow chart of one variation in which a
user can enter breath type information into the system so that the
system can delineate between representative and non-representative
breaths for the diagnostic test being undertaken, in accordance
with one variation.
[0054] FIG. 14 describes a flow chart of one variation in which a
system receives a physiological signal input from a secondary
monitor so that the system can calibrate its algorithms to a
physiological parameter of the patient, in accordance with one
variation.
[0055] FIG. 15 describes a flow chart of a variation of a control
system in which a secondary Capture and Analysis Algorithm may be
used if the preferred breathing pattern threshold parameters are
not met, in accordance with one variation.
[0056] FIG. 16 describes an exemplary flow chart of a variation in
which a second subroutine is invoked if the breath rate is too
fast, in accordance with one variation.
[0057] FIG. 17 describes a breathing signal from a series of
breaths showing breaths that may be too fast for end-tidal capture
and analysis, or that may not be complete tidal volume breaths, as
well as breaths that may be desirable targets for end-tidal sample
capture and analysis, in accordance with one variation.
[0058] FIG. 18 describes a breathing signal from a series of
breaths showing breaths that may be too erratic or physiologically
non-representative for analysis, as well as breaths that may be
desirable targets for end-tidal sample capture and analysis, in
accordance with one variation.
[0059] FIG. 19 describes a timing diagram of an example of a
monitoring and capture system that searches for and captures the
end-tidal gas following a sigh breath, in accordance with one
variation.
[0060] FIG. 20 is a breathing signal graph versus time which shows
the use of an expiratory signal parameter to determine if the
breath is representative or not, in accordance with one
variation.
[0061] FIG. 21 is a flow diagram describing a multi-part algorithm
for selecting a breath, the algorithm including a first step to
classify a potentially physiologically representative breath, a
second step of classifying a subsequent breath as potentially
physiologically representative, and a third step of classifying the
subsequent breath as physiologically representative, in accordance
with one variation.
[0062] FIG. 22 graphically describes breathing pressure signals
used to identify different sections of exhalation corresponding to
gas from different sections of the lung being exhaled, in
accordance with one variation.
[0063] FIG. 23 shows a pneumatic schematic of the system shown in
FIG. 1 and in which the system is used to target, isolate and
measure an analyte from any portion of the breathing curve, as
described in FIG. 22.
DETAILED DESCRIPTION
[0064] Described here are devices and methods for measuring certain
breath waveform characteristics. The measured characteristics may
be used to discriminate between breaths that may produce an
accurate gas measurement and breaths that may not produce an
accurate gas measurement. In the variations shown, for exemplary
purposes, ETCO gas measurements are described, and the patient's
breath sample is shown to be drawn into the instrument from the
patient by application of vacuum. However the disclosure also
applies to measurement of other breath gases and to other methods
of collecting breath gas, such as patients breathing into an
instrument for example.
[0065] In some variations, one or more breathing parameters may be
measured to identify the different constituent portions of a breath
and the respective time periods, and a pneumatic system may be used
for capturing the portion of exhaled breath in a sampling tube
using the identified time period. In some variations, one or more
valves and/or flow control mechanisms, such as a vacuum pump for
example, may be used to regulate the flow rate of gas drawn into
the sampling tube. In some variations, the captured portion of
breath may be analyzed for indications of a patient's physiological
state.
[0066] Measured breathing parameters may include one or more of
carbon dioxide, oxygen, airway pressure, airway temperature, breath
flow rate, chest impedance, diaphragmatic movement or innervation,
breath sounds, and breath vibrations. Identifying the time period
of a portion of a breath may include identifying substantially the
start and termination of that time period.
[0067] A diagnostic gas sample may be taken from the end-tidal
period, for example when attempting to monitor a physiologic
condition in the blood stream, such as hemolysis. For explanatory
purposes, exemplary variations for sampling end-tidal gas for
end-tidal CO measurement are given below, however the principles
apply to other diagnostic purposes.
[0068] FIG. 1 describes schematically an overview of one variation
of a device for capturing exhaled breath, including a sampling
cannula 1 and a gas sample collection and analysis instrument 2, in
accordance with one variation. Gas may be drawn from the patient,
for example using a sampling cannula 1 and a flow generator 12. The
flow rate of the flow generator may be measured by a flow
transducer, for example a pressure sensor array, 26 and 28,
arranged like a pneumotach. The measured flow rate may be used as a
closed loop feedback control to control the flow generator flow
rate. A breath sensor, such as a capnometer 10 or a pressure sensor
26, is used to measure the breathing pattern in real time. Gas from
the desired portion of the breath is captured and isolated in the
storage collection compartment 18. Gas entering the storage
compartment is controlled by at least one valve V1, for example
with a common port c always open, and a second open port, either a
to collect gas or b to isolate the storage compartment. There may
be a valve V2 between V1 and the flow generator to participate with
V1 in isolating the storage compartment. Gas not being captured for
analysis is channeled away from the storage compartment via a
bypass conduit 20. The captured gas is sent from the storage
compartment through a gas composition analyzer 14, such as a CO
sensor. A control system 22 with a microprocessor 24 controls the
system with the associated algorithms. The flow generator for
example can be a vacuum or pressure pump, such as a diaphragm pump,
or another type of flow generating device such as a vacuum source,
a Venturi from a positive pressure source, or a syringe pump.
Valves to manage gas routing can be an arrangement of 3 way 2
position valves as shown, or can be an arrangement of 4-way
3-position valves. Capnometer 10, if used, measures the breathing
pattern instantaneously using infrared (IR). The gas composition
analyzer for example can be an electrochemical sensor with a
reaction time, or a gas chromatographer, or a mass spectrometer.
Other variations may use different gas analyzers. The sample
storage compartment can be a small bore inner diameter tube or
conduit of considerable length in order to reduce the cross section
which reduces gas molecule interaction along the length of the
conduit. The sampling cannula may be constructed of any non-rigid
kink-resistant plastic, such as a thermoset plastic for example
silicone, urethane or urethane blends, or such as a thermoplastic
for example PVC, C-FLEX, or other materials. The cannula can have a
range of inner diameters, and in some variations the cannula has a
diameter of less than 0.080 inches in order for the breath gas to
conform to columnar behavior with boundaries between breath
sections where mixing across sections may be reduced.
[0069] Pressure sensor 16 is an additional pressure sensor that may
be used in tandem with 26 so that a flow rate can be determined, in
addition to using it for airway pressure measurement. Flow rate can
be used to adjust the pump speed in some variations that utilize a
variable flow rate. Pressure sensor 16 can also be utilized for
ambient information where the breathing curve is measured by
pressure instead of capnometry. In some variations, an
instantaneous carbon monoxide sensor may be used as the breath
sensor, in place of a capnometer or an airway pressure sensor.
Other instantaneous breath sensors may also be used.
[0070] The bypass tube 20 allows the gas being drawn from the
patient or from ambient to bypass the sample tube 18 during times
which the sample tube may be isolated from these gases. In this
arrangement, valve V1 may be closed at port a and valve V2 may be
open at port b to allow flow from b through c. A flow generator may
be used to draw the sampling gas through the bypass type. A push
tube 21 may be used to push the end-tidal sample in the sample tube
18 out of the sample tube to the sensor 14, at which time valves V1
and V3 are each open at port b and V2 is closed at port a. Valve V4
switches the source gas from patient gas to ambient gas by opening
port b, when it is desired to not contaminate the internal gas
pathways with patient gas or for purging the system.
[0071] In some variations, the pneumatic system shown in FIG. 1
above may include a removable sampling compartment 18' as shown by
the instrument 2c in FIG. 1c. For example, sample tube 18' may be
removable from the system. In this way, the pneumatic system may be
able to fill a sample tube with a desired gas, and the sample tube
may be analyzed at another location, or preserved for later
analysis. In other variations, the gas may be routed from the
sample tube to a removable sampling compartment. In this variation,
the compartment may replace the analyzer 14 or otherwise be
positioned so that it can be removed and/or replaced. In other
variations, exemplified in FIG. 1b, the analyte in question may be
measured by the instrument 2b in real time or substantially real
time by the sensor 14. In this case, the sensor 14 may be
responsible for measuring the breathing signal for the purposes of
breath selection and determination of the section of the selected
breath that should be measured, as well as for measuring the level
of the analyte in question. Or, optionally, the sensor 16 may be
responsible for breath selection and breath section targeting,
while the sensor 14 is responsible for measuring the level of the
analyte in question. In any case, the breath selection algorithms
and the breath section targeting algorithms described throughout
apply to all of the different types of instrument
configurations.
[0072] FIG. 2 describes an exemplary control system 22 for
operating the device of FIG. 1, in accordance with one variation.
One module or algorithm 200 performs the breath monitoring and
detection function. In this module, a determination is made if the
breathing pattern or individual breaths meet certain criteria, in
order to determine whether or not a breath will be captured for
analysis. In some variations, the criteria may be predefined, or
defined in real-time, or user-defined, automatically defined or
semi-automatically defined. For example, predefined criteria may be
absolute or relative threshold parameters stored in the device's
software. Or a user may enter certain information relative to the
specific test being performed, and the system may use that
information to define the criteria. Or the system can automatically
establish the criteria in real time based on the prevailing
conditions. Or a combination of the above techniques can be
employed. A subsequent control system, module, or algorithm 400
performs the breath sample capturing function, and another
subsequent control system, module, or algorithm 500 performs the
breath sample analysis. As shown by the dashed line in FIG. 2, an
alternative sequence of operation is contemplated in which the
breath sample capturing algorithm 400 is skipped for those
instrument configurations in which the sample analysis step 500 is
performed in real time or substantially real time.
[0073] FIGS. 3 and 4 describe a typical breathing signal pattern of
a breath based on CO.sub.2 and airway pressure respectively. FIG. 3
graphically describes a typical breathing pattern from the
perspective of a carbon dioxide (CO.sub.2) signal measured in
breath drawn from the person's airway, such as from their nose, as
a function of time, with time on the horizontal axis, and CO.sub.2
level on the vertical axis, in accordance with one variation.
During the expiratory phase E, CO.sub.2 is expelled, hence the
CO.sub.2 level increases. During the inspiratory phase I, ambient
air occupies the nose, hence the measured CO.sub.2 drops to
essentially zero. There may be a variety of shapes to a breath
CO.sub.2 curve, based on the person's breathing pattern, their age,
how they are breathing and any underlying acute or chronic medical
conditions. A curve may show the following sub-portions for the
expiratory phase: (1) a beginning portion or pre-end-tidal section
PET, comprising low CO.sub.2 because the gas may simply be gas from
the proximal airway devoid of CO.sub.2, (2) a middle portion
showing CO.sub.2 rapidly increasing from zero to the CO.sub.2 level
at the distal segments of the lungs, and (3) an end-tidal ET
portion showing a plateauing or leveling off of the CO.sub.2,
representing the CO.sub.2 coming from the alveoli for that exhaled
breath, and (4) potentially a constant peak level at the very end
of the expiratory period. However, there can be many other curves
different from this curve. Peak CO.sub.2 levels are typically 4-6%
during the end-tidal period and close to or equal to zero during
the inspiratory period.
[0074] In some variations, the level of CO.sub.2 in an exhaled
breath may be used to determine the duration of a period of a
breath, such as the pre-end-tidal time TPET, expiratory time TE,
end-tidal time TET, inspiratory time TI, or breath period time TBP.
In further variations, a duration of a period of breath may be
characterized by a start and a termination of that period. In some
variations, a CO.sub.2 level may be used to determine a start or a
termination of a period of a breath. In other variations, a first
time derivative of a CO.sub.2 level may be used to determine a
start or a termination of a period of a breath. In yet other
variations, a second time derivative of a CO.sub.2 level may be
used to determine a start or a termination of a period of a breath.
In some variations, a combination of CO.sub.2 levels and CO.sub.2
level time derivatives may be used to determine a start or a
termination of a period of a breath. In some variations, a start of
an end-tidal period may be determined by a change in the first time
derivative of a CO.sub.2 level of the exhaled breath, such as a
sudden decrease in the first time derivative of the CO.sub.2 level.
In some variations, a decrease in the first time derivate of the
CO.sub.2 level may be more than a 10% decrease. In some variations,
a decrease in the first time derivate of the CO.sub.2 level may be
more than a 25% decrease. In some variations, the derivative will
approach or become zero showing very little rate of change or a
peak plateau respectively. In other variations, the start of an
end-tidal period may be determined by a large second time
derivative of the CO.sub.2 level. In some variations, a termination
of an end-tidal period may be determined by a maximum CO.sub.2
level, which may be detected or confirmed by a change in the sign
of the first time derivative of the CO.sub.2 level as the
derivative becomes negative associated with a drop of the CO.sub.2
level from its peak value. In further variations, a start of a
beginning period may be determined by a sudden increase in the
first time derivative of the CO.sub.2 level. In other variations,
the start of a beginning period may be determined by an increase in
the CO.sub.2 level from zero CO.sub.2 level. In some variations, a
termination of a middle period may be determined by a change in the
first time derivative of a CO.sub.2 level of the exhaled breath,
such as a sudden decrease in the first time derivative of the
CO.sub.2 level. In some variations, a CO.sub.2 level, first time
derivative thereof, or second time derivative thereof may be used
to determine the start and termination of one or more periods.
Other breath-borne gases may be used in place of CO.sub.2 for
measuring the breathing curve. For example, oxygen can be measured
which would indicate a higher oxygen concentration during
inspiration than expiration. It is also contemplated that the
breathing pattern may be instantaneously or substantially
instantaneously measured by a fast-responding CO sensor. In this
case referring to FIG. 1, the sensor 10 may be a fast responding CO
sensor that depicts the breathing pattern and also measures the
end-tidal CO level. After application of the various breath
qualification and disqualification variations described
subsequently, the CO level of a qualified breath can be reported as
the result.
[0075] FIG. 4 graphically describes a typical breathing signal from
the perspective of measured airway pressure, showing a negative
pressure during inspiratory phase and a positive pressure during
expiratory phase, in accordance with one variation. Typically
during at rest breathing the peak expiratory pressure may
correspond to the middle of the expiratory phase and the start of
the end-tidal period. In FIGS. 3 and 4, TI, TE, TPET, TET, TPE
represent inspiratory time, expiratory time, pre-end-tidal time,
end-tidal time, and post expiratory time respectively. An
inspiratory pause may also be present (not shown), in which the
peak of lung muscle movement during inspiration is paused before
the expiratory period begins. Peak inspiratory pressure may be -1
to -4 cwp during restful breathing, and up to -15 cwp during
heavier breathing, and peak expiratory pressure may be +0.5 to +2.0
cwp during restful breathing and up to +10 cwp during heavier
breathing when measured at the entrance to the nostrils.
Representative pressures and gas concentrations may vary with
environmental conditions, for example airway pressures during cold
temperatures may be increased for the same unit of volume.
[0076] In some variations, airway pressure may be used to determine
a start or a termination of a period of a breath. In other
variations, a first time derivative of an airway pressure may be
used to determine a start or a termination of a period of a breath.
In yet other variations, a second time derivative of an airway
pressure may be used to determine a start or a termination of a
period of a breath. In some variations, a combination of airway
pressures and airway pressure time derivatives may be used to
determine a start or a termination of a period of a breath. In some
variations, a start of an end-tidal period may be determined by
maximum airway pressure, that is, by a zero first time derivative
of the airway pressure. In some variations, a termination of an
end-tidal period may be determined by zero airway pressure. In some
variations, an airway pressure, first time derivative thereof, or
second time derivative thereof may be used to determine the start
and termination of one or more periods. Airway pressure may be
measured through a secondary lumen extending the length of the
cannula in parallel with the sampling lumen, or may be measured by
teeing into the sampling lumen, or by placing a sensing transducer
at the airway of the patient.
[0077] In some variations, a breath sensor monitors the person's
breathing over time, and trends the breathing pattern by
determining a continually updated value that is characteristic of
the breathing pattern. For example, peak positive values of a
breathing signal may be measured and updated for each breath. Peak
values may be compared with previous peak values. Peak values may
be averaged over a previous number of multiple breaths. Similarly,
time-related aspects of the breaths may be trended, such as the
expiratory time. Various breath-related events that are not normal
breaths may be identified and exception algorithms may exist in
order to not include these non-normal breath events inadvertently
in deterministic steps. For example, the characteristic waveform of
a sneeze, cough, stacked breath, or non-full breath may be defined
in advance or based on monitoring of a particular patient, and when
detected by the breathing sensor, excepted from the appropriate
deterministic algorithms.
[0078] FIG. 5 graphically describes a lag period between when the
gas sample exits a breath sensor and when the sample reaches the
sample tube, in accordance with one variation. The top tracing
shows the actual breath phases as a function of time for three
breaths, the middle tracing shows a capnometry signal versus time
for the sequence of breaths and the lag period between when the gas
sample exits the capnometer and reaches the sample tube input
valve. The travel time for gas to travel from the person to the
capnometer through the sampling cannula is represented by t.alpha..
Therefore the capnometry signal shows a beginning of exhalation
slightly after the true beginning of exhalation. The travel time
for the gas to exit the capnometer and begin to enter the sample
collection compartment is represented by t.beta.. Therefore, as
shown in the bottom tracing, the sample compartment isolation valve
V1 is open to position a at time t(1), t.beta. after detection of
the start of the end-tidal period by the capnometer, for the sample
collection time t(s).
[0079] FIG. 6 graphically describes an airway pressure signal
versus time for a sequence of breaths, in accordance with one
variation. The top tracing shows the actual breath phases, the
middle tracing shows the airway pressure signal and the lower
tracing shows the sample isolation tube valve V1 position. In
airway pressure tracing the lag period between the gas sample
leaving the patient's airway and reaching the sample tube input
valve is shown. The phase shift between the actual breath, and the
pressure is t4, approximately equal to the distance of travel
divided by the speed of sound, hence is relatively instantaneous.
The travel time for the gas to exit the person's airway and begin
to enter the sample collection compartment is represented by
t.delta., Therefore the valve V1 opens to position a at time t(1'),
t.delta. after detection of the start of the end-tidal period by
the capnometer, for the sample collection time t(s). Capnometry and
airway pressure signals are shown in FIGS. 5 and 6 for exemplary
reasons, and the breathing sensor may be of other times, such as
temperature or acoustic.
[0080] FIG. 8 graphically describes breath waveforms 800 versus
time for a series of breaths B(1), B(2) to B(n+1) being monitored
by the system 2, in accordance with one variation. In the example
shown, the breathing signal is a Capnometry signal, however it
could be any other breath sensor signal. Eventually the system 2
determines that a specific breath, or number of breaths, or the
breathing pattern meets the necessary criteria and a breath or a
number of breaths is/are targeted for capturing gas from the
end-tidal section of that breath or breaths. In the example shown,
the end-tidal sample ET(n) of breath B(n) is targeted for sample
acquisition and compositional measurement.
[0081] FIG. 7 describes the pneumatic system 700 and exemplary
operation of the system 2 shown in FIG. 1, in accordance with one
variation. In FIG. 7, a volume V(18) the end-tidal gas from breath
B(n) in FIG. 8 is transported by the system 700 into the sample
compartment 18 where it is captured and isolated from other gases,
prior to analysis by the sensor 15. The flow path of the patient
gas prior to capturing the sample is from the patient through V4,
the Capnometer 11, V1, the sample tube 18, V2, the pump 12, V3,
then out the exhaust 27. When the tail end of the end-tidal sample
reaches V1 or the entrance to the sample tube 18, the valves switch
such that the flow path is from the ambient inlet 25, through V4,
the Capnometer 11, the bypass tube 20, V2, the pump 12, then out
the exhaust 27. When the system is ready to send the sample from
the sample tube to the sensor 15, the valves are switched such that
the flow path is changed from the patient inlet 1 to the ambient
inlet 25, through V4, the Capnometer 11, the bypass tube 20, V2,
the pump 12, the push tube 21, the sample tube 18, V1, then through
the sensor 15 and out the sensor exhaust. The push tube is purged
of any patient gas prior to these maneuvers.
[0082] FIG. 9 shows a portion of a graph 900 of sensor signal
strength versus time, in accordance with one variation. The sensor
may include sensor 15, discussed above. In the example shown, the
signal 14' is a voltage or current response from a reaction taking
place in an electrochemical sensor. As the sample is sent through
the sensor, the sensor reacts accordingly by a signal rise. The
rise and duration are related to the amount of gas in the sample.
Integrating the sensor signal over time, or averaging the sensor
signal over time, will provide a correlation to the amount of gas
in the sample. In some variations, system calibration may improve
accuracy. It is contemplated by the invention that the timing and
location of the analysis of the analyte in question may be
performed a number of ways. For example, the analysis may be in
real time or substantially real time as the exhaled breath is being
drawn or obtained from the subject. Or, the analysis may be
performed at some later time by saving the captured sample. Or, as
shown in some of the embodiments for exemplary purposes, the
analysis may be performed a short time after sample acquisition by
the same instrument. In some of these cases, aspects of the
apparatus shown in FIG. 7 are not required, however the breath
selection algorithms required to measure a physiologically
representative breath, described throughout, still apply. For
example, a sample tube 18 to isolate and hold the sample may not be
required, and bypass tube 20 and push tube 21 may not be required.
Or the sensor 14 may not be required as the sensor 10 may measure
both the breathing signal for determining and selecting a
representative breath, as well as measures the level of the analyte
in question. In addition, some of the Valves V1 through V4 may not
be required. Or, for example, the breath sample acquisition
instrument may be coupled to another analyte measuring instrument,
such as a gas chromatograph or other analytical instrument, The
foregoing examples are offered for illustration purposes and should
not be construed to limit the disclosure.
[0083] FIG. 10 describes a flow diagram of a variation of a breath
monitoring and detection algorithm 200 in which measured breath
values, for example, gas concentration, are compared against set
thresholds, in accordance with one variation. In Step 202, the
breathing pattern monitoring in search of a desired breath is
initiated. In Step 204, threshold values or criteria are applied to
which the measured breathing signal will be compared. In Step 206 a
next breath is measured. In Step 208 the measured breath is
compared to the threshold values or criteria set in Step 204. In
Steps 210 and 212, a determination is made whether the thresholds
are not met or met respectively. If met, the system transitions to
the gas sampling algorithm 400. If not met, the system may reset
the threshold values or criteria in Step 214 and then measure a
next breath. At any time if the criteria are not being met, the
system may provide an option to cancel or opt out of the testing in
Step 216. In some variations, the thresholds may be factory
defaults, or selected from a menu of defaults corresponding to
different clinical situations. The thresholds may be determined by
the user, or by the system based on information related to the test
that is inputted by the user. In some variations, the thresholds
may be applied to an expiratory signal or an inspiratory signal,
and may include amplitude criteria, timing criteria, timing
criteria required to meet an amplitude criteria, amplitude criteria
required to meet a timing criteria, averaging criteria, percentage
criteria, and any combination thereof. As the system monitors the
patient's breathing pattern, the threshold values may be updated as
necessary. Once the threshold values are met, the system moves on
to the sampling and analysis algorithms 400 and 500
respectively.
[0084] FIG. 11 describes a flow chart of a variation of a breath
monitoring and detection algorithm 200 in which a measured breath
value can be compared against a second set of criteria if a first
set is not met, in accordance with one variation. For example,
after initiating the breathing monitoring in Step 202, in Step 204
a first criteria may be set and may be a simple criteria such as a
breath rate requirement, for example, 20-40 breaths per minute.
After measuring a breath in Step 206 and applying the criteria in
Step 218, if that criteria is met as determined in Step 222, the
system enters the gas sampling algorithm Step 400. If however that
first criteria is not met as determined in Step 224, the system
applies a second, more complex set of criteria in Step 220. This
second set of criteria might be multiple criteria, for example the
combination of an amplitude criteria, a timing criteria, and a
percentage of historical breath average criteria. Once the second
set of criteria are met, for example as determined in Step 226, the
system may enter the gas sampling algorithm Step 400. The gas
sampling algorithm and gas analysis algorithm may factor in which
of the first or second criteria was met. For example, one criteria
may indicate a more consistent sample than another, and the
algorithms may adjust accordingly. In some variations, third,
fourth, fifth, or any number of criteria may be used and the
sampling and analysis algorithms adjust according to the criteria
which was met by the sample. In some variations, as shown in Step
214, the first or second set of criteria may be adjusted, updated,
reset or changed, for example based on the prevailing
conditions.
[0085] FIGS. 12 through 14 describe algorithms which calibrate the
system to look for and target physiologically representative
breaths that can yield desired results for the given clinical
situation. Once the system is calibrated with relevant input
parameters, the system searches for the appropriate type of breath
and may dismiss other breaths. Once the appropriate type of breath
is found, the system may capture and analyze the end-tidal portion
of that breath. The subsequent breath analysis step therefore will
provide an accurate correlation to the underlying disease. For
example, if ETCO is being measured, breaths during hyperventilation
may be categorized as non-representative breaths and may be
dismissed. Or breaths during deep forced breathing may likewise be
categorized as non-representative breaths and may be dismissed.
Without these algorithms, a non-representative breath may be
captured and analyzed, yielding a result that may not truly
correlate to the blood level or to the underlying disease.
[0086] FIG. 12 describes a flow diagram of one variation in which a
user can enter relevant clinical information into the system's user
interface 30 in Step 230, in accordance with one variation. The
input may be used by the system's control system 22 to calibrate
the breath monitoring and detection algorithms 200 in order to
delineate between clinically representative and non-representative
breaths relevant to the diagnostic test being undertaken. For
example, the information entered can be age, weight, height, BMI,
metabolic rate, sex, race, diagnosis, minute volume, tidal volume,
respiratory rate, resting respiratory rate, inspiratory time,
expiratory time, I:E ratio, heart rate, blood gases, or cardiac
output, or combinations thereof. For example, if the age and weight
of a neonate is entered, the breath detection algorithms may be
calibrated to look for breaths that meet a certain breath rate. For
example, if one day old and 7.5 lbs is entered, a breath rate of
55-65 may be assigned to the breath detection threshold parameters
such that a breath typical of that patient's normal resting tidal
volume breathing pattern is targeted, captured and analyzed.
[0087] FIG. 13 describes a flow diagram of one variation in which
the user can enter desired breath type information into the
system's user interface 30 in Step 244, in accordance with one
variation. This input may be used by the system's control system 22
to calibrate the breath monitoring and detection algorithms 200 in
order to delineate between representative and non-representative
breaths for the diagnostic test being undertaken. For example, the
breath type information entered can be a sigh breath, breath hold,
deep breath, forced exhaled breath, inspiratory pause, or
expiratory pause, breath rate or a breath frequency parameter, or
combinations thereof. For example, when diagnosing a metabolic
disorder, a qualitative analysis of the breath may be required to
determine the presence or absence of a chemical. In this case, a
deep breath and a breath hold maneuver may be an optimal breath for
the qualitative measurement. Or for example, the clinician may
determine the normal resting tidal volume breath rate of the
patient, and enter this breath rate into the system which
calibrates the breath monitoring and detection algorithms to this
breath rate. For example, the breath rate entered may be 32 bpm,
resulting in the algorithm thresholds to be set to 30-34 bpm,
causing the system to search for, capture and analyze the end-tidal
gas from a breath that meets that criteria. Alternatively, as shown
by Step 240, the user may enter into the system's user interface 30
the type of diagnostic test to be performed, and with that
information, and optionally in conjunction with the information
entered in Step 244, the control system sets or selects the
criteria for a desired breath to be used in the breath monitoring
and detection algorithm 200.
[0088] FIG. 14 describes a flow diagram of one variation in which
the system's control system 22 receives a physiological signal
input from a secondary monitor in Step 252, in accordance with one
variation. The input may be used by the system's control system to
calibrate its breath monitoring and detection algorithms 200 to a
physiological parameter of the patient, in order to delineate
between representative and non-representative breaths for the
diagnostic test being undertaken. For example the physiologic
parameter may be heart rate, respiratory rate, etCO.sub.2, blood
pressure, cardiac output, pulmonary perfusion, blood gases, base
excess, blood pressure, oxygen saturation, ventilation:perfusion
ratio, or combinations thereof. For example, when measuring a
certain chemical or analyte in the alveolar gas that diffuses from
the blood stream, the diffusion rate from the blood into the
alveoli may be dependent on the rate of pulmonary blood flow. The
higher the heart rate or cardiac output, the higher the rate of
diffusion and the higher concentration of the chemical in the
alveolar gas. Therefore, once the cardiac output or heart rate is
inputted into the system, the system can calibrate itself to those
parameters to normalize the alveolar gas measurement result against
the prevailing clinical conditions of the patient. In addition to
the input of a physiological parameter, as shown in Step 250 a user
may input into the user interface 30 a desired breath type to
sample, or a desired diagnostic test to be performed, or a
patient-related parameter, in order to complement the physiological
parameter input from Step 252 in the breath monitoring and
detection algorithm 200, so that the desired breath and or test is
sampled and performed.
[0089] FIG. 15 describes a flow diagram of a variation of a control
system 22 in which a secondary capture and analysis algorithm B,
392, may be used if the primary or preferred breathing pattern
threshold parameters are not met as determined in Step 212, in
accordance with one variation. For example, a primary set of
threshold parameters may be breath rate and expiratory time related
parameters. For example, the Algorithm A, 390, may target an
end-tidal section of gas from a breath that is physiologically
representative of the normal breathing pattern, or resting tidal
volume, or alternatively representative of the breath desired for
the diagnostic application. If the primary set of threshold
parameters are met as determined in Step 210, the system enters the
capturing and analysis algorithms 400 and 500 respectively and
determines a result accordingly. However, if these parameters are
not met as determined in Step 212, the system may enter a second
set of capture and analysis algorithms 401 and 501 respectively in
Algorithm B, 392. For example, if the respiratory rate is too high
and/or if the expiratory time is too short, the system's capture
and analysis algorithms may include breath frequency correction.
For example, the capturing subroutine 401 may result in a sample
tube that may be 90% filled with end-tidal gas and 10% filled with
pre-end-tidal gas, thus diluting the end-tidal sample. In this case
the analysis algorithms 501 may mathematically correct for this
dilution. Respiratory frequency and dilution are provided as one
example in which a second set of algorithms may be required,
however, it should be noted that there are other reasons that a
second set of capture and analysis algorithms may be required. For
example, Algorithm B may include receiving additional input from
the user or automatically in order to calibrate the breath
detection threshold parameters to the prevailing clinical
situation. For example, if the patient is hyperventilating, it may
be predetermined that the end-tidal gas measurement is for example
50% of a true measurement, and the system may capture, analyze and
adjust as necessary. Other potential input parameters may be a
heart parameter such as heart rate, cardiac output or blood flow, a
gas exchange parameter such as blood gases or pulse oximetry, other
respiratory parameters such as minute volume, or a patient type
parameter such as age, sex, height or disease state.
[0090] FIG. 16 describes a flow diagram of one variation of a
primary and secondary breath monitoring and detection subroutine
260 and 280 respectively, in accordance with one variation. In
Subroutine A 260, a counter is initiated in Step 262, for example a
breath counter or time counter, and a breathing pattern signal
begins to be measured, for example breath rate or end-tidal time.
In step 264, the breathing signal of the next breath is measured.
In Step 266, the breathing signal measurement is compared to
threshold values or criteria and a determination is made whether to
transition to the capturing algorithm 400, or to prompt the user or
to transition to the other Subroutine 280. In Subroutine A 260, if
the breath criteria are not met, the user may be prompted to verify
that the system is set up correctly, and the user may also be
prompted to wait, or make adjustments with the patient, for example
body position, or wait until the patient is not agitated. If the
breath criteria are still not met, the system may enter a second
subroutine, Subroutine B, in which an alternate type of breath is
searched for, for example a sigh breath. Once found, the end-tidal
section of the breath may be captured and analyzed, and correction
factors are applied to the result if needed. For example, if it is
determined that the criteria are not met in Step 266, in Step 268
the system commands the user interface 30 to prompt the user of the
breath detection status. For example, in Step 266, the criteria may
be breath rate less than 60 bpm and end-tidal time greater than 0.5
seconds. If not met, Subroutine B 280 may be eventually invoked.
However, before Subroutine B is invoked, Step 266 may command the
user interface to display messages in Step 270 such as "breath rate
too fast" or "slow patient's breath rate" or ask the user for
example if they want to "wait for breath type A?" or "invoke
algorithm B?". In Step 268, if various criteria are not met which
indicate a weak or missing signal, the system may command the user
interface to display messages in Step 268 such as "verify cannula
is attached", or "verify patient is breathing through cannulated
nostril."
[0091] In Subroutine B, 280, a counter is initiated in Step 282,
for example a breath or time counter, and a first breath is
measured. In Step 284 the counter is incremented. In Step 264 a
next breath is measured. In Step 286 the measured breath is
compared to Algorithm B's breath monitoring and detection criteria,
and if satisfied in Step 290 the breath is sampled in Step 400. For
example, in Step 286, the criteria may be looking for a sigh
breath. If the criteria are not satisfied as shown in Step 292,
another set of criteria are applied to the measured breath in Step
288, for example a certain expiratory time requirement. If met as
shown in Step 294 the breath is sampled in Step 400, however if not
met as shown in Step 296, the cycle continues on to measure the
next breath, and or the system prompts the user with the option to
opt out as shown in Step 216.
[0092] FIGS. 17 and 18 describe examples of valid and invalid
breaths with respect to whether or not the end-tidal portion of the
breath is representative of the alveolar gas concentrations.
Various breath signal criteria, including amplitude and frequency
criteria, are included in the breath detection and targeting
algorithms in order to disqualify "invalid" breaths and qualify
"valid" breaths. The criteria may include trending of breaths and
comparison of a current breath to the recent trend, and comparison
against default threshold values and alternatively against
customized threshold values based on the test's prevailing
circumstances. It may be beneficial to target a breath that meets a
complete normal tidal volume breath and also may be beneficial to
target a breath in the midst of steady state breathing after a
number of complete normal tidal volume breaths, to assure steady
state conditions of the gas composition in the breath has been
reached or re-established.
[0093] FIG. 17 is a timing diagram describing an erratic breathing
pattern, for example from a neonatal patient, in accordance with
one variation. The breathing parameter signal measurement is shown
on the vertical axis and may be for example a CO2 signal. The
breath monitoring and detection algorithms may set threshold
criteria for the CO2 signal to classify breaths as valid or invalid
for sampling purposes. The threshold criteria may be a signal's
peak amplitude 300 or amplitudes, a signal baseline level 302 or
levels, and various frequency or time related parameters such as
thresholds for the inspiratory time TI, the breath period time TBP,
the expiratory time TE and or the end-tidal time TET, 306, 304, 308
and 310 respectively. As shown in the graph, breaths b1-b11 may be
too short in duration for the system to realistically capture an
accurate end-tidal sample from these breaths. The average breath
rate of this series of breaths is 96 bpm, which would make the
exhalation portion of the waveform for these breaths approximately
0.313 seconds in duration. Given that the end-tidal section of
exhalation is the latter half of exhalation, only a fraction of the
0.313 second would be the appropriate section to target an
end-tidal sample, which may yield an unreliable sample. Breaths
this fast even for neonates may not be complete tidal volume
breaths; rather they may be partial breaths, or hyperventilation
breaths, or mostly deadspace breaths, in which case the end-tidal
gas, even if it could be accurately collected, will not be
representative of alveolar gas and will instead have more deadspace
gas. Therefore, it may be inaccurate and undesirable to perform an
end-tidal measurement on any of the breaths b1-b11. In order to
screen out such rapid and incomplete breaths, breath signal
amplitude thresholds can be set to define a complete tidal volume
breath, for example, reaching a certain peak during the expiratory
phase, and reaching a certain valley during inspiratory phase, as
well as staying above and below those thresholds respectively for
an appropriate period of time. Now turning to breaths b12-b16,
while breath b16 appears to meet both proposed thresholds, it is
preceded by erratic and inconsistent breathing, and while it may be
a complete tidal volume breath, the end-tidal gas in that breath
may not have reached steady-state gas composition levels. Now
turning to breaths b17-b19, three consecutive breaths meet the
tidal volume threshold requirements, and in this example it is
proposed that breath b19 has reached steady-state end-tidal gas
composition levels, and is a clinically representative breath to
target, acquire and measure.
[0094] FIG. 18 shows an additional example of a series of breaths
b1-b19, including physiologically representative breaths and
non-representative breaths, in accordance with one variation. An
example of breath signal noise is described between breaths b2 and
b3. This noise may for example be sensor noise, sensor noise
accompanied by an apneic period, patient movement, cannula
movement, noise from coughing or other high frequency breath
related noise, or cardiogenic noise. These waveforms may be
disqualified for sampling as they may not produce a valid alveolar
gas sample. Breath b3 meets the threshold criteria described
previously in FIG. 17, however, the gas composition of breath b3
may be out of balance because it followed the noise, so breath b3
may be disqualified by the breath targeting algorithms. Breaths
b4-b6 describe breath stacking where the next breath begins prior
to completion of the prior breath. The end-tidal gas in breaths
during breath stacking may not be representative of alveolar gas
and may be dismissed. Breath b7 and b8 following the breath
stacking may still be out of balance and may be dismissed as well.
Breath b9 is characteristic of an inspiratory breath hold, or an
inspiratory sigh, a post expiratory period, or an apneic period.
The exhaled gas from breath b9 may need to be disqualified,
depending on the diagnostic test being conducted, as the end-tidal
gas may contain a higher than normal alveolar gas concentration
since gas in the blood has had a longer time to diffuse into the
alveoli. Breath b10 may be dismissed by the targeting algorithm as
well because of the risk their gas compositions have not yet
returned to normal. Breath b11 is a partial incomplete breath,
smaller than the average normal breath, and is also dismissed by
the targeting algorithms, and breaths b12 and b13 may be dismissed
because of the risk they have not returned to their normal gas
compositions. Breath b14 is a larger than normal breath and may be
dismissed by the algorithms. Finally, there is a series of 3 or
more consecutive normal breaths that meet the threshold criteria,
and breath b18 can be targeted for sampling. Other permutations of
the above targeting and breath qualification algorithms may be used
as well. For example, the number of breaths before a sample is
taken may be varied.
[0095] In the foregoing descriptions, a sigh breath may be
disqualified because its end-tidal gas may not be representative of
the steady-state alveolar gas concentrations. However, in some
physiological states and clinical conditions it may actually be
beneficial to target a sigh breath. In these situations, the breath
may be a more accurate representation of alveolar gas, or in other
situations, the sigh breath may be the only type of breath that can
be realistically captured for analysis, and a correction factor may
be applied to convert the measured result to the true physiological
value. FIG. 19 describes a variation in which a system acquires an
end-tidal gas sample from an exhaled breath following a sigh
inspiration. As shown in the top tracing, the breathing pattern is
relatively erratic and the breath rate relatively fast between t0
and t1, as determined by measuring the breath rate, for example a
three breath running average as shown for the first three breath
periods bp1, bp2 and bp3. As a result, the end-tidal portion of the
breathing pattern is not pronounced or defined enough to reliably
capture a sample from the end-tidal period, and or to capture an
end-tidal sample volume that is sufficient enough in volume for
accurate analysis by the sensor. In the example shown in FIG. 19,
because the breath pattern is too erratic and or too rapid, a
criterion may be established to monitor for the occurrence of a
sigh breath. For example, the inspiratory times of the breaths are
measured and compared against a threshold time and if the threshold
is met or exceeded, the breath may be classified as a sigh breath.
The threshold time may be for example 250% of the average
historical inspiratory time. The threshold criteria used to
determine if a breath is a sigh breath may be, for example, an
inspiratory time value that is established based on historical
inspiratory times, for example 150% of the average inspiratory time
of the last 3 breaths. Alternatively it can be an inspiratory time
value that is predefined based on normal values. For example the
average inspiratory time of three sequential breaths, shown as ti1,
ti2 and ti3 may be used to establish an average to which a
potential sigh breath is compared. In the example shown the
inspiratory time ti9 displays a considerable increase over the
average of the three previously mentioned, and thus the exhalation
following ti9, should be considered a potential sigh breath
exhalation. Measuring its expiratory time, te9 will help in the
assessment of whether or not it is a sigh breath. Expiratory time
te9 can be compared to previous expiratory times. Or alternatively
a sigh can be determined by the amplitude of the inspiratory
signal, for example if an airway pressure signal is a larger
negative value than normal. Once the sigh breath occurs, the
following exhalation may be targeted for acquisition of a gas
sample from the end-tidal section.
[0096] The valves V1-V4 shown in the lower tracings in FIG. 19
control the various sequences of operation including monitoring of
the breathing pattern, acquiring the end-tidal sample into the
sample tube, and pushing the sample to the gas analyzer. As will be
readily understood by one of skill in the art, valves V1-V4 are
used for explanatory purposes and systems with more or less valves
could be used and the timing adjusted accordingly. The valves may
be 3 position valves as shown in FIGS. 1 and 7, with a common port
c always open, and with either port a or b open at any given time.
At time 326 an inspiratory time counter is initiated. At time 328
the inspiratory time counter is ended. At time 330 an expiratory
time counter is initiated. At time 332 the end of the expiratory
gas is detected exiting the breathing sensor, such as a Capnometer.
At time 334, the expiratory time counter is terminated. At time 336
a sample travel time counter is initiated, tracking the time of
travel of the gas sample from the breathing sensor to the sample
tube. At time 338, Tz seconds before time 340, a command is sent to
the appropriate valves to isolate the desired gas sample from other
gases in the system. At time 340, T' seconds after time 332, the
end of the end-tidal gas sample has reached the entrance to the
sample tube, or valve V2. At time 342 a command is sent to switch
the valve ports such that gas does not flow through the sample tube
18, and gas comes in from the ambient inlet (see FIGS. 1 and 7). At
time 344 all valves are switched to port b being open so that the
sample is pushed by ambient air to the sensor for compositional
analysis. The exhaled gas after a sigh inspiration may beneficially
provide a good source of gas for an ETCO measurement for a number
of reasons. First, the exhalation time and end-tidal time is likely
to be extended, making targeting the end-tidal portion relatively
easy and therefore potentially more accurate for certain diagnostic
tests. Second, the depth of inspiration during the sigh fills the
alveoli more than normal, thus providing more end-tidal volume in
the subsequent exhalation than an average end-tidal volume, thus
potentially providing a richer end-tidal sample for analysis.
Third, there is typically longer residence time of the gas in the
alveoli during a sigh inspiration, compared to a normal breath, and
this longer residence time allows for more gas exchange from the
blood stream into the alveoli, and therefore the ETCO measured in
the end-tidal gas may provide a more accurate representation of
blood CO then the ETCO measured in the end-tidal portion of a
normal breath. Fourth, sigh breaths have a tendency to recruit
areas of the lung that are atellectactic or not fully inflated.
Therefore, the end-tidal gas in exhalation after a sigh breath may
be more representative of the entire lung in certain clinical
situations, and therefore possibly more representative of the CO in
the blood stream.
[0097] FIG. 20 describes a graph of a breathing parameter signal
amplitude over a sequence of seven breaths b1 through b7, in
accordance with one variation. In FIG. 20, an end-tidal section of
gas is depicted as ET1 through ET7, an expiratory signal time
parameter is depicted as EST1 through EST7, and expiratory time is
depicted as TE. As can be seen in the graph, the breath period,
BP4, of the fourth breath, b4, appears to be equal to the breath
period of the three preceding breaths, and therefore breath four
may be deemed to be a representative breath from which a valid
end-tidal gas measurement can be taken. However, upon closer
inspection, breath four is actually non-representative of the
historical typical breaths, as indicated by an expiratory signal
parameter EST4. The shorter EST4 of breath b4, which corresponds to
a longer than average inspiratory time, for example an inspiratory
hold or pause, may result in an end-tidal concentration that is not
representative of the alveolar gas. Breath b7 which is preceded by
two apparently representative breaths likely consists of end-tidal
gas that has reached steady-state and is representative of alveolar
gas. In order to prevent inadvertent capturing of
non-representative breaths, and assure capturing of representative
breaths due to the above paradigm, some variations utilize an
expiratory time signal rather than or in addition to the breath
period in order to determine if the breath is a representative
target or not. The expiratory time signal may be the expiratory
duration, the duration of the rise of the signal, or other
frequency related parameters associated with the expiratory phase
of the breathing signal.
[0098] FIG. 21 describes breath selection algorithm 379, in
accordance with one variation. Algorithm 379 comprises at least two
stages. In the preliminary initialization steps, in Step 202 the
breath pattern monitoring is initiated, in Step 204 a set of
primary threshold values are applied or default values are used,
and in Step 206 a next breath is measured accordingly. The primary
threshold values may be amplitude and timing values, for example.
Steps 380 to 387 describe the first main stage of the algorithm
379. After initialization and during and after the measurement of a
first breath, in Step 380 the breath is compared to the set of
primary threshold values. In Steps 382 and 384 the determination is
made if the measured breath meets the threshold criteria or not,
respectively, and in steps 386 and 387 the measured breath is
classified as representative or non-representative respectively. If
non-representative, the algorithm returns to Step 206. If
representative, the algorithm moves on to the second Stage
beginning with Step 206' measuring a next breath. In Step 380', the
measured breath is compared to the primary threshold parameters.
The primary threshold parameters may be the same parameters as in
Step 380, or might be revised or updated between measurements. In
Steps 382' and 384' a determination is made whether the primary
threshold parameters are met or not respectively. In Steps 386' and
387', the breath is classified as potentially representative or
non-representative, respectively. Should the breath be classified
as non-representative, the algorithm returns to step 206, otherwise
the breath may move on to a third Stage of the algorithm. In the
third Stage, a set of secondary breathing signal threshold
parameters are established in Step 388 and in Step 206'' a next
breath is measured. The secondary threshold parameters may be for
example breath signal amplitude and or timing values that are
established based on the potentially representative breath
classified in Step 386. In Step 388 a comparison is then made
between the potentially representative breath which was classified
in Step 386' to the previous potentially representative breath
classified in Step 386. In Steps 390 and 391 a determination is
made if the breath measured in Step 206'' meets the secondary
threshold parameters, and if so, the breath is classified as
representative and is sent on for sampling and measurement,
otherwise, the algorithm returns to Step 206.
[0099] In the multi-stage algorithm 379 described in FIG. 21, for
example, the primary threshold values may be breath signal
amplitude and durations of portions of the breath signal, in order
to verify that a breath waveform is not an artifact and not an
abnormal breath such as a sigh breath, a partial breath, or a
breath hold breath. If a breath meets the threshold values, then
the next breath is likewise evaluated. If the next breath also
meets the threshold values, it can then be compared against the
first breath to verify that the breathing pattern is stable.
Therefore, the secondary threshold parameters may be that of a
comparison against the previous breath, assuming the previous
breath met the primary threshold values. The comparison can be for
example in signal amplitude indicative of breath depth, and or
signal duration indicative of breath period or breath rate. This
may reduce the risk of sampling a breath that is not a regular
tidal volume breath, or not of the breath type desired. Moreover,
the routine may help make sure that the breath ultimately sampled
was taken from a breath after another normal breath, thus
potentially avoiding the effect that an abnormal breath would have
on the composition of a subsequent normal breath. The comparison to
previous breaths in the example shown is a comparison to one
previous potentially representative breaths, but the comparison can
also be to more than on previous potentially representative
breaths, not necessarily in sequence. For example, a 10.sup.th
breath may be compared to a 3.sup.rd, 5.sup.th and 7.sup.th breath
which were each classified as potentially representative, and in
which case the other intervening breaths were deemed
non-representative based on the primary threshold parameters.
[0100] In addition, in situations in which the sample collected in
the sample tube is not a pure end-tidal sample and is diluted with
pre-end-tidal exhaled gas, the dilution can be corrected for using
an expiratory signal parameter such as EST4 shown in FIG. 20,
rather than using the breath rate based on the breath period BP4.
This dilution correction technique may beneficially increase the
accuracy of the correction since the sample tube dilution may be
more dependent on the expiratory duration than the breath period
duration.
[0101] As used herein, the term end-tidal can be understood to
refer to a section of an exhaled breath that is at or near the end
of the expiratory period, and may be after the deadspace has been
exhaled from the person. SuFurther, in addition to measuring gases
such as CO in the end-tidal gas exemplified throughout the
specification, it is also contemplated that non-gases such as
particulates and other chemicals may be measured in the same or
similar manner.
[0102] FIG. 22 graphically describes breathing pressure signals
used to identify different sections of exhalation corresponding to
gas from different sections of the lung being exhaled, in
accordance with one variation. In some cases in may be desired to
measure gas or other analytes stemming from different sections of
the lung besides the end-tidal section. For example, analytes from
the upper airway may be indicative of upper airway respiratory
problems like asthma or airway disorders and diseases. Analytes
from the middle airways between the upper airways and the lower
bronchioles may be indicative of for example forms of lung cancer
or analytes stemming from the stomach getting into the airways from
the esophagus, and analytes from lower airways may be indicative of
yet other syndromes like lung infections or potentially systemic
problems. Further, comparison of one compartment to another may be
useful in understanding an underlying disease or condition. In the
example shown the top tracing is a capnometry signal and the lower
tracing is an airway pressure signal, although the measurement can
be other types of signals such as oxygen, temperature, or acoustic.
Using one of, or a combination of the signals, the expiratory phase
E can be separated into various portions of exhalation, for example
exhalation of upper airway gases, middle airway gases, lower airway
gases and end-tidal gases, labeled EUA, EMA, ELA, and ET
respectively. For example the start of the exhalation of upper
airway gas can be discerned by a positive increase in airway
pressure, and the end of the upper airway gas exhalation can be
discerned by an increase in the exhaled CO2 level. The start of
exhalation of the middle airway gas EMA may be discerned by an
increase in the CO2 level and the end of exhalation of the middle
airway gas may be discerned by reaching a plateau in the airway
pressure signal. The start of exhalation of the lower airway gas
may be discerned by a decrease in the airway pressure signal and
the end of exhalation of the lower airway gas may be discerned by a
change in slope of the airway pressure signal or a certain rise in
the CO2 signal.
[0103] FIG. 23 shows a pneumatic schematic of the system shown in
FIG. 1 and in which the system is used to target, isolate and
measure an analyte from any portion of the breathing curve, as
described in FIG. 22. In the example shown, breath n is targeted by
the procedures and techniques explained in the forgoing
descriptions. In this case the desired diagnostic test is examining
the upper airway for an analyte indicative of an inflammatory
disease such as asthma. Expiratory gas from the upper airway from
breath n, EUAG(n) is isolated in the sample tube 18, and later
shuttled to the sensor 15 for compositional analysis. In this case
the analysis may be of NO gas, or other analytes related to
inflammatory response. In the schematic example shown, the
inspiratory gas IG(n) and other sections of the expiratory gas
EMAG(n), ELAG(n) from breath n, and end-tidal gas from the previous
breath ETG(n-1) are elsewhere in the system and isolated from the
gas sample in sample tube, so as to not disturb the homogeneity of
the targeted sample. While some diseases, conditions, gases or
analytes have been mentioned in conjunction with FIGS. 22 and 23 as
well as the preceding Figures, these have been mentioned as
examples only and the system, apparatus, algorithms and methods
described can be used to sample and measure any analyte of interest
for any disease or condition of interest.
[0104] As will be readily understood by those of ordinary skill in
the art, the devices described herein are offered by way of example
only and other devices could be used to implement the methods and
systems described herein. Moreover, although the device described
may be used to illustrate certain features of the disclosure, it
should be understood that the methods and systems disclosed here
are not limited to a specific device.
[0105] Although some variations are discussed by reference to
algorithms, it should be understood that the descriptions cover
corresponding methods and apparatuses that embody the
variations.
[0106] Further, although variations above may be discussed with
reference to identifying a portion of gas and then analyzing the
gas, it should be understood that some variations may not include
an analysis portion. In some variations, the gas is stored without
analysis, for example, the gas may be transported to a remote
location for analysis. A stored gas should be understood broadly
and includes at least storing prior to analysis and storing for
transport.
[0107] In the foregoing descriptions of variations of the
invention, it should be noted that it is also conceived that the
sequences of operation described in the Figures can be combined in
all possible permutations. In addition, while the examples describe
ETCO measurement they may apply to other gases, for example
hydrogen. Additionally, while some variations may apply to CO.sub.2
measurements, it should be understood that the apparatuses and
methods described herein could be applied to a direct CO sensor.
The examples provided throughout are illustrative of the principles
of the invention, and that various modifications, alterations, and
combinations can be made by those skilled in the art without
departing from the scope and spirit of the invention. Any of the
variations of the various breath measurement and sampling devices
disclosed herein can include features described by any other breath
measurement and sampling devices or combination of breath
measurement and sampling devices herein. Accordingly, it is not
intended that the invention be limited, except as by the appended
claims. For all of the variations described above, the steps of the
methods need not be performed sequentially.
* * * * *