U.S. patent application number 12/549118 was filed with the patent office on 2010-09-02 for macro-control of treatment for sleep disordered breathing.
Invention is credited to David John Bassin, Peter Edward Bateman, Michael BERTHON-JONES, Steven Paul Farrugia, Robert Henry Frater, Gordon Joseph Malouf.
Application Number | 20100222685 12/549118 |
Document ID | / |
Family ID | 34632980 |
Filed Date | 2010-09-02 |
United States Patent
Application |
20100222685 |
Kind Code |
A1 |
BERTHON-JONES; Michael ; et
al. |
September 2, 2010 |
MACRO-CONTROL OF TREATMENT FOR SLEEP DISORDERED BREATHING
Abstract
A method and apparatus for treating sleep disordered breathing.
An arousal index is determined for use in an outer loop of a
control algorithm, the arousal index being a measure of the
frequency of sleep arousals. The respiratory airflow signal in an
inner loop of the control algorithm is monitored to detect an
airway obstruction. If the arousal index is high, then the
sensitivity of obstruction detection and/or the aggressiveness of
the treatment is increased, and if the arousal index is low, then
the sensitivity of the obstruction detection and/or the
aggressiveness of the treatment is decreased
Inventors: |
BERTHON-JONES; Michael;
(Leonay, AU) ; Malouf; Gordon Joseph; (Elizabeth
Bay, AU) ; Bateman; Peter Edward; (Cherrybrook,
AU) ; Bassin; David John; (Coogee, AU) ;
Frater; Robert Henry; (Lindfield, AU) ; Farrugia;
Steven Paul; (Lugamo, AU) |
Correspondence
Address: |
GOTTLIEB RACKMAN & REISMAN PC
270 MADISON AVENUE, 8TH FLOOR
NEW YORK
NY
10016-0601
US
|
Family ID: |
34632980 |
Appl. No.: |
12/549118 |
Filed: |
August 27, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10595917 |
Jun 12, 2006 |
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PCT/AU04/01652 |
Nov 25, 2004 |
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12549118 |
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60525405 |
Nov 26, 2003 |
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Current U.S.
Class: |
600/484 |
Current CPC
Class: |
G16H 20/30 20180101;
A61M 16/0069 20140204; A61M 16/024 20170801; A61B 5/4818 20130101;
A61B 5/4809 20130101; A61M 2016/0039 20130101; A61B 5/087 20130101;
G16H 20/00 20180101; A61M 16/06 20130101 |
Class at
Publication: |
600/484 |
International
Class: |
A61B 5/0205 20060101
A61B005/0205 |
Claims
1-62. (canceled)
63. A method for evaluating changes in heart failure disease in a
patient comprising steps of: measuring airflow of the patient using
a sensor to determine occurrences of central apneas; calculating a
heart failure index from a count of the number of central apneas
that have occurred; and comparing a present heart failure index to
a previously calculated heart failure index to determine how the
patient's heart failure disease has changed.
64. The method of claim 63 wherein the occurrences of central
apneas are counted over a period ranging from one night to one
week.
65. The method of claim 64 further comprising a step of identifying
subsequent heart failure disease treatment based at least in part
upon said heart failure index.
66. The method of claim 63 further comprising a step of identifying
subsequent heart failure disease treatment based at least in part
upon said heart failure index.
67. A method for monitoring congestive heart failure in a patient
comprising steps of: measuring airflow of the patient using a
sensor to determine occurrences of central apneas; calculating a
congestive heart failure index from a count of the number of
central apneas that have occurred; and comparing a present
congestive heart failure index to a previously calculated
congestive heart failure index to determine how the patient's
congestive heart failure has changed.
68. The method of claim 67 wherein the occurrences of central
apneas are counted over a period ranging from one night to one
week.
69. The method of claim 68 further comprising a step of identifying
subsequent congestive heart failure treatment based at least in
part upon said congestive heart failure index.
70. The method of claim 68 further comprising a step of identifying
subsequent congestive heart failure treatment based at least in
part upon said congestive heart failure index.
71. A method for evaluating changes in heart failure disease in a
patient comprising steps of: measuring airflow of the patient using
a sensor to determine occurrences of central apneas; calculating a
heart failure index from a count of the number of central apneas
that have occurred; and determining how the patient's heart failure
disease has progressed from changes in the heart failure index.
72. The method of claim 71 wherein the occurrences of central
apneas are counted over a period ranging from one night to one
week.
73. The method of claim 72 further comprising a step of identifying
subsequent heart failure disease treatment based at least in part
upon said heart failure index.
74. The method of claim 71 further comprising a step of identifying
subsequent heart failure disease treatment based at least in part
upon said heart failure index.
75. A method for monitoring congestive heart failure in a patient
comprising steps of: measuring airflow of the patient using a
sensor to determine occurrences of central apneas; calculating a
congestive heart failure index from a count of the number of
central apneas that have occurred; and determining how the
patient's congestive heart failure has progressed from changes in
the heart failure index.
76. The method of claim 75 wherein the occurrences of central
apneas are counted over a period ranging from one night to one
week.
77. The method of claim 76 further comprising a step of identifying
subsequent congestive heart failure treatment based at least in
part upon said congestive heart failure index.
78. The method of claim 76 further comprising a step of identifying
subsequent congestive heart failure treatment based at least in
part upon said congestive heart failure index.
Description
FIELD OF THE INVENTION
[0001] This invention relates to methods and apparatus for treating
sleep disordered breathing. In particular, the invention relates to
automatic adjustment of control parameters for apparatus used in
the treatment of sleep disordered breathing.
BACKGROUND OF THE INVENTION
[0002] Sullivan invented the treatment of Obstructive Sleep Apnea
(OSA) with nasal Continuous Positive Airway Pressure (CPAP). (See
U.S. Pat. No. 4,944,310.) Diagnosis of OSA typically requires two
nights in a sleep clinic. During a first night, the patient is
monitored to see whether the patient has OSA. During the second
night, a range of nasal mask pressures are tested to determine an
appropriate pressure setting for a CPAP device to keep the
patient's airway open. Once a pressure setting is determined, the
patient is prescribed a CPAP device set to that pressure for
subsequent home treatment. Because of limited places in sleep
clinics, a patient can wait up to two years before he has the
opportunity to be diagnosed. More recently, automatic devices have
been developed which can diagnose and treat patients in their own
homes, reducing the delay. Some automatic devices also can increase
and decrease the treatment pressure during the night in accordance
with patient need.
[0003] U.S. Pat. No. 5,199,424 (Sullivan and Lynch) describes a
device for monitoring breathing during sleep and control of CPAP
treatment that is patient controlled. In particular, the patent
describes a CPAP apparatus including a controllable
variable-pressure air source; a nose piece for sealed air
communication with a patient's respiratory system; an air
communication line from the air source to the nose piece; a sound
transducer adapted to be in sound communication with the patient's
respiratory system; and a feedback system controlling the output
pressure of the air source in response to an output from the
transducer so as to increase the pressure of the air source, in
response to detection of sound indicative of snoring, in accordance
with a predefined procedure. The sound transducer, in its most
general form, comprises a pressure transducer which, in addition to
detecting snoring sounds, can detect other respiratory parameters
such as the rate of breathing, inhaled air flow volume, and inhaled
air flow rate. The output air pressure of the air source is
increased in response to one or more of these parameters in
accordance with a pre-defined procedure.
[0004] U.S. Pat. No. 5,134,995 (Gruenke et al.) is said to describe
an apparatus and method for facilitating the respiration of a
patient for treating mixed and obstructive sleep apnea and certain
cardiovascular conditions, among others, by increasing nasal air
pressure delivered to the patient's respiratory passages just prior
to inhalation and by subsequently decreasing the pressure to ease
exhalation effort. The preferred apparatus includes a
patient-coupled air delivery device for pressurizing the patient's
nasal passages at a controllable pressure, and a controller coupled
with the delivery device having a pressure transducer for
monitoring the nasal pressure and a micro-controller for
selectively controlling the nasal pressure. In operation, the
controller determines a point in the patient's breathing cycle just
prior to inhalation and initiates an increase in nasal pressure at
that point in order to stimulate normal inhalation, and
subsequently lowers the nasal pressure to ease exhalation
efforts.
[0005] U.S. Pat. No. 5,203,343 (Axe et al.) is said to describe a
method and device for controlling sleep disordered breathing
utilizing variable pressure. A compressor supplies air at a
relatively low pressure to the user's air passages while the user
is asleep. A pressure transducer monitors the pressure and converts
the pressure to an electrical signal. The electrical signal is
filtered and compared with the characteristics of waveforms that
exist during snoring. If the envelope of the waveform exceeds an
average threshold value in duration and in area, then a
microprocessor treats the envelope as possibly being associated
with a snore. If a selected number of envelopes of this nature
occur within a selected time period, then the microprocessor
considers snoring to exist and increases the pressure of the
compressor. If snoring is not detected within a certain time
period, then the microprocessor lowers the level gradually.
[0006] U.S. Pat. No. 5,335,654 (Rapoport) is said to describe, in
the treatment of obstructive sleep apnea, a CPAP flow generator
employed to direct air to a nasal mask fitted to a patient. The
airflow from the generator is monitored, and the flow and/or
pressure is increased when the waveform of the airflow exhibits
characteristics corresponding to flow limitation. The generator may
be controlled to repetitively test for waveform variations, in
order to adjust the CPAP flow to the minimum level that does not
produce flow limitation.
[0007] U.S. Pat. No. 5,704,345 (Berthon-Jones) describes a method
and apparatus for detection of apnea and obstruction of the airway
in the respiratory system. Methods and apparatus for determining
the occurrence of an apnea, patency and/or partial obstruction of
the airway are disclosed. Respiratory air flow from a patient is
measured to provide an air flow signal. The determination of an
apnea is performed by calculating the variance of the air flow
signal over a moving time window and comparing the variance with a
threshold value. One determination of partial obstruction of the
airway is performed by detecting the inspiratory part of the air
flow signal, scaling it to unity duration and area, and calculating
an index value of the amplitude of the scaled signal over a
mid-portion. Alternatively, the index value is a measure of the
flatness of the air flow signal over the mid-portion. One
determination of patency of the airway is performed by applying an
oscillatory pressure waveform of known frequency to a patient's
airway, calculating the magnitude of the component of the air flow
signal at the known frequency induced by the oscillatory pressure
waveform, and comparing the calculated magnitude with a threshold
value. Alternatively, the air flow signal is analyzed to detect the
presence of a component due to cardiogenic activity.
[0008] U.S. Pat. No. 6,367,474 (Berthon-Jones and Farrugia)
describes CPAP treatment apparatus having a controllable flow
generator operable to produce breathable air to a patient at a
treatment pressure elevated above atmosphere by a delivery tube
coupled to a mask having a connection with a patient's airway. A
sensor generates a signal representative of patient respiratory
flow that is provided to a controller. The controller is operable
to determine the occurrence of an apnea from a reduction in
respiratory airflow below a threshold and, if an apnea has
occurred, to determine the duration of the apnea and to cause the
flow generator to increase the treatment pressure by an amount
which is an increasing function of the duration of the apnea, and a
decreasing function of the treatment pressure immediately before
the apnea.
[0009] In general, these types of techniques of control of the
administration of CPAP treatment can be regarded as "micro-control"
algorithms. That is, they monitor the condition of the patient at
any given moment. A variety of techniques for monitoring the
patient's condition may be used, including detecting flattening of
the inspiratory flow-time curve, detecting a reduction in patient
ventilation, and detecting snoring. If there is an indication of
sleep disordered breathing, the response is to increase the
treatment pressure. Absent the indication of sleep disordered
breathing, treatment pressure may be decreased. A question of
interest is how effective such algorithms are in treating OSA.
[0010] The Apnea-Hypopnea Index (AHI) provides a measure of the
number of apneas and hypopneas which a patient experiences during
sleep. The AHI is sometimes used to assist in diagnosis of OSA. The
AHI may also be used as an indication of the effectiveness of the
nasal CPAP treatment. Hence, at least one automatic CPAP device,
the AUTOSET T.TM., manufactured by ResMed Limited, reports the AHI,
among other things, after a night's treatment. A problem with such
an approach is that if the AHI indicates that therapy has been
ineffective, the device may not be able to respond to such a result
without being adjusted by a technician or clinician.
BRIEF DESCRIPTION OF THE INVENTION
[0011] In accordance with a first aspect of the invention a method
and apparatus for treating sleep disordered breathing is provided
that automatically adjusts its sensitivity to indications of sleep
disordered breathing.
[0012] In accordance with another aspect of the invention, a method
and apparatus for treating sleep disordered breathing is provided
that monitors a patient's sleep arousal and in accordance with a
measure of sleep arousal automatically adjusts how aggressively it
responds to indications of sleep disordered breathing.
[0013] In accordance with another aspect of the invention, a method
and apparatus for treating sleep disordered breathing is provided
in which the effectiveness of therapy is continuously monitored.
Where there is an indication that therapy has not been effective,
treatment pressure changes are accelerated. Where there is an
indication that therapy has been effective, treatment pressure
changes are decelerated.
[0014] In accordance with another aspect of the invention, in
methods and apparatus providing micro-control of sleep disordered
breathing, a macro-control algorithm is provided that monitors its
effectiveness and adjusts its operational parameters if they prove
ineffective. Thus, a first detection control loop detects the
effectiveness of a second detection control loop by examining the
changing condition of the patient, and then the first detection
control loop adjusts the second detection control loop to improve
performance of the first control loop.
[0015] In accordance with another aspect of the invention, in
methods and apparatus for providing treatment of sleep disordered
breathing, an arousal index is determined for use in an outer loop
of a control algorithm, the arousal index being a measure of the
frequency of sleep arousals. A respiratory airflow signal of the
patient is monitored in an inner loop of the control algorithm to
detect obstructions. If the arousal index is high, then the
sensitivity of obstruction detection and/or the aggressiveness of
the treatment is increased, and if the arousal index is low, then
the sensitivity of the obstruction detection and/or the
aggressiveness of the treatment is decreased.
[0016] In accordance with another aspect of the invention there are
provided methods and apparatus for treating sleep disordered
breathing having an inner control loop and an outer control loop
wherein the inner loop is adapted to provide at least two treatment
modes and the outer loop is adapted to monitor the effectiveness of
therapy provided by the inner loop and change modes if
necessary.
[0017] In accordance with another aspect of the invention there is
provided a controller for a device for treating sleep disordered
breathing, the controller programmed to provide a set of
alternative treatment algorithms and programmed to select the most
appropriate member of the set in accordance with indications of
sleep disordered breathing.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 shows an apparatus in accordance with the
invention.
[0019] FIG. 2 shows a "macro-control" algorithm in accordance with
an embodiment of the invention.
[0020] FIG. 3 shows a "micro-control" algorithm in accordance with
an embodiment of the invention.
[0021] FIG. 4 is a graph of a flow versus time curve illustrating
an event of sleep arousal.
[0022] FIG. 5 is a chart of information flow in one embodiment of a
device for adjusting settings of a pressure delivery device in
accordance with a function of sleep or respiratory arousal.
[0023] FIG. 6 illustrates one embodiment of the input of a
controller for adjusting treatment pressure based on a sleep
arousal index.
[0024] FIG. 7 depicts a function for adjusting the aggressiveness
of reductions in treatment pressure in accordance the measure of
sleep arousal.
[0025] FIG. 8 depicts a function for adjusting the aggressiveness
of increases in treatment pressure in accordance the measure of
sleep arousal.
[0026] FIG. 9 depicts a function for adjusting the sensitivity of
flow limitation detection in accordance with the measure of sleep
arousal.
[0027] FIG. 10 illustrates another function for adjusting the
sensitivity of flow limitation detection in accordance with the
measure of sleep arousal.
[0028] FIG. 11 depicts a function for adjusting the sensitivity of
flow limitation detection in accordance with the measure of
treatment pressure.
DETAILED DESCRIPTION OF THE INVENTION
[0029] Apparatus suitable for performing the invention is shown in
FIG. 1. An impeller 1 is coupled to an electric motor 2 which is
connected to a servo 3 and directed by a controller 4. The
controller 4 includes a microprocessor, data storage, and memory
programmed with algorithms in accordance with the invention. Thus,
the controller or processor is configured and adapted to implement
the methodology described in more detail herein and may include
integrated chips, a memory and/or other instruction or data storage
medium. Programmed instructions either may be coded on integrated
chips in the memory of the device or may be loaded as software.
[0030] The impeller, motor and controller assembly form the blower.
A mask 5 is connected to the blower via a flexible conduit 6.
Various switches 7 and displays 8 are provided on the housing of
the blower. A number of sensors are provided within the blower to
monitor, among other things, flow 10, pressure 11, snore 12, motor
speed 13 and motor current 14. Various devices are known in the art
that can serve as these types of sensors. A communications
interface 15 is provided which allows data to be transferred
between the apparatus and an external device, such as a computer or
controller. While in a preferred form of the invention a nasal mask
5 is shown, other forms of patient interface such as a nose and
mouth mask or full-face mask may be used. Furthermore, while a
variable speed motor is preferred, other means for providing a
supply of breathable gas at positive pressure may be used, such as
a constant speed motor with variable venting or a stepped-down
piped pressure supply.
[0031] In accordance with the methods described in U.S. Pat. No.
5,704,345 (Berthon-Jones), the entire contents of which are hereby
incorporated by cross-reference, indications of sleep disordered
breathing, or airway obstruction in the patient, are monitored by
the device. For example, flow, pressure and snore sensors 10, 11,
12 provide information on the shape of the inspiratory flow-time
curve, patient ventilation and snore. A generally flattened
inspiratory flow-time curve is taken as an indication of partial
obstruction, as is the presence of snoring.
I. Obstruction Indicators
(a) Shape Factors
[0032] In one form, the shape of the flow-time curve is monitored
as follows. The digitized flow signal is filtered to remove any
leak component. Inspiratory and expiratory portions of each breath
are then identified by a zero-crossing detector. A number of evenly
spaced points (typically sixty-five), representing points in time,
are interpolated by an interpolator (in software) along the
inspiratory flow-time curve for each breath. The curve described by
the points is then scaled by a scaler to have unity length
(duration/period) and unity area to remove the effects of changing
respiratory rate and depth.
[0033] Conveniently, the scaled breaths are compared in a
comparator (in software) with a prestored template representing a
normal unobstructed breath. The template is very similar to the
curve for a normal inspiratory event. Breaths deviating from this
template by more than a specified threshold (typically 1 scaled
unit) at any time during the inspiratory event, such as those due
to coughs, sighs, swallows and hiccups, as determined by a test
element, are rejected.
[0034] For data not rejected by this test, a moving average of the
first such scaled point is calculated by an arithmetic processor
for the preceding several inspiratory events. This is repeated over
the same inspiratory events for the second such point, and so on.
Thus, sixty-five scaled data points are generated by the arithmetic
processor, and represent a moving average of the preceding several
inspiratory events. The moving average of continuously updated
values of the sixty-five points are hereinafter called the "scaled
flow". Similarly, a single inspiratory event can be utilized rather
than a moving average.
[0035] From the scaled flow two shape factors that directly relate
to the determination of partial obstruction are calculated. Each
shape factor equates to the Obstruction Index discussed above.
[0036] The first shape factor is the ratio of the mean of the
middle thirty-two scaled flow points to the mean overall sixty-five
scaled flow points. This is thus a determination of the reduction
of the magnitude (depression) of the mid-portion of the scaled
inspiratory event(s). Since the mean for all sixty-five points is
unity, the division need not actually be performed.
[0037] For a normal inspiratory event this ratio will have an
average value in excess of unity, because a normal inspiratory
event is of higher flow in the middle than elsewhere. Conversely,
for a severely flow-limited breath, the ratio will be unity or
less, because flow limitation occurs particularly during the middle
half of the breath when the upper airway suction collapsing
pressure is maximal. A ratio of 1.17 is typically taken as the
threshold value between partially obstructed and unobstructed
breathing, and equates to a degree of obstruction that would permit
maintenance of adequate oxygenation in a typical user.
[0038] In other embodiments the number of sampled points, number of
breaths and number of middle points can be varied, and still
achieve a meaningful determination of whether partial obstruction
is occurring. The threshold value similarly can be a value other
than 1.17. Decreasing the threshold makes the device less sensitive
to detecting obstruction. Increasing the threshold makes the device
more sensitive to detecting obstruction.
[0039] Alternatively, the second shape factor is calculated as the
RMS deviation from unit scaled flow, taken over the middle
thirty-two points. This is essentially a measure of the flatness of
the midportion of the scaled respiratory event(s). For a totally
flow-limited breath, the flow amplitude versus time curve would be
a square wave and the RMS deviation would be zero. For a normal
breath, the RMS deviation is approximately 0.2 units, and this
deviation decreases as the flow limitation becomes more severe. A
threshold value of 0.15 units is typically used. Decreasing the
threshold makes the device less sensitive to detecting obstruction.
Increasing the threshold makes the device more sensitive to
obstruction.
[0040] Optionally, the shape factor may be determined by weighting
certain portions of the flow signal as disclosed in U.S. patent
application Ser. No. 09/924,325, filed on Aug. 8, 2001, the entire
disclosure of which is hereby incorporated by reference.
[0041] Both shape factors discussed above can be utilized
independently in implementing the methodology carried out by the
apparatus, and result in the sensitive and reliable detection of
partially obstructed breathing. Better performance again is
obtained by implementing both shape factors executed by the
controller so that both shape parameters act together. In this
case, the second shape factor is preferred for use to detect all
but the most severe obstructions, and the first shape factor
therefore is preferred for detecting only the most severe
obstructions, achieved by reducing the critical threshold from 1.17
to 1.0.
[0042] The two shape factors may operate in concert. The scaled
flow signal is provided to a shape detector. The shape detector
generates both shape factors. The first shape factor is applied to
a decision block and compared against the threshold value of 1.0.
If the outcome of the comparison is "Yes", then it is determined
that there should be an increase in the CPAP pressure setting. The
second shape factor is provided to the decision block, and a
comparison made against a threshold value of 0.15. If the answer is
"Yes", then it also is appropriate for an increase in the CPAP
pressure.
[0043] In either case, if the result of the comparison is "No",
then those results are ANDed in an AND operation. That is, an
output will only be achieved if both threshold criteria are not
satisfied. In this case, there is no partial obstruction, or
partial obstruction has subsided, in which case it is appropriate
to decrease the CPAP pressure.
[0044] This arrangement avoids any peculiarities affecting either
algorithm. For example, the presence of an initial non-flow-limited
period early in a breath can permit an early sharp peak in the
flow-time curve. This means that the scaled flow during the middle
half of the breath may be below unity. For very severely obstructed
breaths, the RMS deviation from unity may therefore rise again, and
the second shape factor will fail to recognize such breaths. They
will, however, be correctly identified by the now desensitized
first shape factor. Some normal breaths can involve an inspiratory
flow-time waveform approximating a right triangle, where the mean
flow during the middle half of inspiration is close to unity. Such
a waveform correctly triggers neither shape factor. That is, the
instantaneous flow during the middle half of the inspiration is
only unity at a single point, and above or below unity elsewhere,
so the RMS deviation from unit scaled flow will be large.
[0045] In one form of the invention, a new shape factor is
calculated for the inspiratory portion of each breath. In another
form, a shape factor is calculated from the inspiratory portion of
two or more breaths. Changing the number of breaths used in the
calculation of a shape factor changes the sensitivity of the
device. Including fewer breaths makes the device more sensitive to
indications of partial obstruction.
[0046] Once a determination has been made that there is an
indication of partial obstruction, the treatment pressure may be
increased. For example, when the first shape factor is below 1.0,
the CPAP pressure is increased in proportion to the amount of the
ratio being below 1.0. The difference between the shape factor and
the threshold may be multiplied by some gain to derive the change
in pressure. In one form, an increase of 1 cm H.sub.2O per breath
per unit below a ratio of 1.0 is used. Conversely, if the ratio is
above 1.0, indicating an absence of partial obstruction, the CPAP
pressure is gradually reduced with a time constant of 20 minutes.
If the second shape factor is below 0.2, the CPAP pressure is
increased at a rate of 1 cm H.sub.2O per breath per unit below 0.2.
Conversely, if the shape factor is above 0.2 units, the pressure is
gradually lowered with a time constant of 20 minutes. The amount of
the increase or decrease in pressure in the presence or absence of
an indication of partial obstruction defines in part how
aggressively the algorithm adapts its treatment.
[0047] Those skilled in the art will recognize that other methods
for detecting flow limitation may be used, for example, by
comparing a roundness index and a threshold, which may also be
controlled to increase or decrease sensitivity in detection.
(b) Snore Detection
[0048] As previously mentioned, detecting snoring can be an
indicator of obstruction in the patient's airway. If a snore is
detected by a snore detector (such as that disclosed in U.S. Pat.
No. 5,245,995, the entire contents of which are incorporated by
reference), then the mask pressure is also increased. If the snore
index on the given breath exceeds a critical threshold value, the
pressure is increased by 1 cm H.sub.2O per unit above the threshold
value.
[0049] Increasing the amount by which the pressure is increased
makes the device treat more aggressively. The default threshold for
the snore index is 0.2 units, corresponding approximately to a
snore that can only just be reliably detected by a technician
standing at the bedside. Increasing the snore threshold makes the
device less sensitive. In one form of the invention, the rate of
rise in pressure is limited to a maximum of 0.2 cm H.sub.2O per
second, or 12 cm H.sub.2O per minute. Conversely, decreasing the
snore threshold makes the device more sensitive.
II. Index of Respiratory Effort Related Arousal or Sleep
Arousal
[0050] To monitor the effectiveness of the device in treating sleep
disordered breathing, an index of sleep arousal or a respiratory
effort related arousal is calculated. (As used in the claims at the
end of this description, the term arousal index refers to a measure
that is a function of the frequency of arousals, be they due to
sleep arousals or respiratory effort related arousals.) In one
form, the index is calculated from the size of a patient's breath.
The size of a patient's breath can be determined by monitoring the
flow rate of air with time and integrating to calculate volumes. If
a patient exhibits a run or sequence of breaths of a first size
followed by a larger breath, this is an indication that he is being
aroused from sleep because of inadequate treatment and that more
aggressive therapy may be required. For example, a run or sequence
of 8 small breaths followed by a large breath can be an indicator
that the patient is being aroused from sleep. In one form, a breath
would be considered "large" if it was more than twice as large as
previous breaths or small breaths. Breaths would be considered
"small" if they were less than the average minute ventilation.
While in a preferred form it is only necessary to monitor patient
respiration, other indices of sleep arousal may be used. For
example, sensors can be used that determine indications of
sympathetic nervous system activity such as sweating and heart
rate.
[0051] In an alternative embodiment, arousal from sleep may be
determined by detecting a post apnea sigh or yawn. This may be
accomplished by a CPAP apparatus. For example, respiratory airflow
is monitored to detect a breathing sequence including a degree of
flattening or obstruction in a breath followed by a large breath.
The flattening or obstruction may be, for example, a minor or
subtle degree of flattening that might not even be considered
sufficient to increase the CPAP pressure, and may be detected using
the shape factors previously described with a very sensitive
threshold. The "large" breath may be considered "large" if it is
absolutely a large breath of a predetermined quantity or more
simply if it is relatively larger than other breaths of the patient
such as one or more of those immediately preceding the large
breath, which may be determined from volume. For example, the
inspiratory portion or a respiratory airflow signal may be
integrated on a breath by breath basis. A detectable condition of
this type is illustrated in FIG. 4. In the figure, the detection of
sleep arousal may be based on the detection of breath n following
the flow limited breath n-1 or several such breaths n-1, n-2 and
n-3.
[0052] In one embodiment of the invention, the detection of a
respiratory effort related arousal may be estimated by examining
respiratory irregularities with a short term moving average measure
of ventilation from data or a signal from the flow sensor. Peaks or
other significant or relative increases in the measure are
indicative of arousal events. The short term moving average can be
determined by integrating a low pass filtered respiratory airflow
signal with a time constant chosen for this purpose.
III. Overall Control Based on Sleep Arousal Detection
[0053] An overall or "macro-control" algorithm in accordance with
the invention makes a determination of how aggressively to treat
the patient based on a determination of whether he is being
successfully treated, and then adjusts the parameter values of the
"micro-control" loop accordingly. The macro-control loop is shown
in FIG. 2 and the micro-control loop is shown in FIG. 3, where the
latter is part of the former, as indicated. (The functions of G and
K shown at the bottom of FIG. 3 are discussed in connection with
FIGS. 7 and 8 below.) Patients who are becoming aroused from sleep
are treated more aggressively. Patients who are not being aroused
from sleep are treated less aggressively. Similarly, based on the
assessment of the success of the treatment, the algorithm can
adjust the sensitivity of the obstruction detection routine to
increase sensitivity for less successful treatment.
[0054] In one form of the invention, the device starts treating the
patient using default settings for parameter values, for example, a
threshold value, but monitors sleep arousal during the course of
the night. At the end of the night's treatment, representative
parameter values are stored in a memory and on subsequent treatment
nights, the representative parameter values from the previous
treatment session are used at the beginning of treatment.
[0055] If a determination that the patient is being aroused from
sleep has been made, the number of breaths which are averaged to
determine a shape index is reduced. If that is insufficient to
achieve an improvement in the patient, then the threshold level
necessary to initiate an increase in treatment pressure is
adjusted, making the device more sensitive.
[0056] In another form, the time constant of decay of treatment
pressure is increased if treatment is determined to be ineffective
based on the arousal index. In this way, the pressure stays high
for a longer period of time following an increase which has
resulted from the detection of an indication of partial
obstruction.
[0057] Optionally, the apparatus may be configured to increase the
treatment pressure in response to the detection of an event of
sleep arousal or respiratory effort related arousal in accordance
with one of the previously described arousal indices. For example,
pressure may be increased by a certain unit of pressure for each
detected event of arousal up to a maximum pressure. Similarly, the
pressure may be reduced towards a minimum support pressure in the
absence of arousal events over a period of time, such as one hour.
As an alternative, data associated with one or more breathing
cycles immediately preceding the breath indicative of the sleep
arousal may be subsequently analyzed by the apparatus to determine
a proportional amount of treatment pressure change that would be
appropriate to compensate for the respiratory related event. Thus,
additional or supplemental analysis may be triggered by the
detection of the sleep arousal. For example, the prior breaths may
be re-analyzed by one of the shape factors or obstruction detectors
discussed above with thresholds of greater sensitivity than they
were previously subjected to as discussed herein. With the new
analysis, a calculated proportional amount of pressure change may
be generated based on the detection of the flow limitation if such
flow limitation had not previously been detected for the particular
breath. In this embodiment, flow signal related data from previous
breaths can be stored in memory for the re-analysis.
[0058] In one embodiment of the invention, the control methodology
defaults to keep the pressure low (4 cmH.sub.2O) while the patient
is awake but will increase pressure with sleep onset. Methods for
doing so are known in the art. The device then detects the presence
of respiratory related event arousals or sleep arousals preferably
after a period of time over which the patient may fall asleep. In
one form the device will then monitor flow to detect a short,
sudden period of flow limitation, terminated by a big breath, which
will be indicative of a respiratory arousal. If it detects such a
sleep arousal, it will become (1) more sensitive to detecting
obstructive or other SDB events, for example, by making adjustments
to detection thresholds, (2) more rapid or aggressive in its
pressure response to these events, for example, by increasing the
pressure gain used in response to each event, and (3) more
reluctant to again lower the pressure when arousal events have
stabilized or discontinue.
[0059] For subsequent sleep arousals (representing patients
intermediate between the stable and unstable ends of the spectrum),
the above process is repeated, so that after about two arousals or
some near number, the device will adjust itself to treat with
greatly increased rate of response, and once an optimal pressure is
found, to maintain that optimal pressure for an hour or so.
[0060] Preferably, if further respiratory arousals are detected
(representing the most unstable, arousable, currently poorly
treated extreme of the spectrum) the device remains indefinitely at
a therapeutic pressure. Thus, the device would have become
essentially a fixed CPAP device, with automatic detection of sleep
onset. Optionally, in the next day of treatment, the device can
revert either to its default behavior as previously described, or
it can resume to a larger or smaller degree the sensitivity of
detection, aggressiveness (more rapid) treatment pressure response,
or persistence in maintaining a higher pressure by using the
settings arrived at during the prior session.
[0061] A methodology/apparatus for sleep arousal-based control in
the treatment of SDB is illustrated in FIGS. 5 and 6. As shown in
FIG. 5, an obstruction and/or a snore detector derive an
obstruction index and/or a snore index from respiratory airflow.
(As used in the claims, the term obstruction detection embraces
detection of a high obstruction index, a high snore index, or
both.) A respiratory effort related arousal or sleep arousal
detector derives a sleep arousal index from an obstruction index or
snore index and respiratory airflow. The obstruction and/or snore
index and the sleep arousal index are then utilized in deriving a
pressure setting by a pressure determination device. FIG. 6 depicts
the pressure determination device of FIG. 5. As depicted in FIG. 6,
the respiratory effort related arousal/sleep arousal index is
applied to adjust the thresholds compared with the
obstruction/snore indices. The sleep arousal index is also applied
to adjust the gain to change the aggressiveness of pressure
increases. Finally, the sleep arousal index is also applied to
adjust the recovery time constant of the treatment pressure to
delay the pressure decay after an SDB event has subsided. In other
words, a higher respiratory arousal index renders a more sensitive
obstruction/snore detection, a more aggressive pressure increase in
response to detected events and a prolonged period of pressure
treatment to an SDB event.
(a) Sleep Arousal Based Gain Adjustment
[0062] As previously noted, in response to detected sleep
arousal(s), the pressure response made to detected SDB events may
be modified to generate more aggressive increases and/or less
aggressive decreases in pressure. Various functions can provide
these adjustments as a function of an index of detected sleep
arousals. For example, the aggressiveness of pressure withdrawal
(i.e., a less aggressive decrease) can be accomplished with the
following formula, which may serve as the pressure change when
there is no detected obstruction that would require an increase in
pressure.
.DELTA.P=-K(P-P.sub.min) when S>S.sub.T
[0063] where: [0064] .DELTA.P is the pressure adjustment or the
pressure change; [0065] K is a function of the detected sleep
arousal; [0066] P is the actual pressure being delivered to the
patient; [0067] P.sub.min is a desired minimum pressure level;
[0068] S is an obstruction index such as flow flattening or snore
index; [0069] S.sub.T is a threshold value for the obstruction
index.
[0070] Various functions of sleep arousal K may be devised. For
example, one such function may be based on the number of detected
sleep arousals with K decreasing with an increasing number of
detected events to a maximum. Such a function is illustrated in
FIG. 7. The selection of the number of arousals and maximum value
of K may be based on clinical experimentation and would be within
the skills of individuals in the field. As shown, the number of
arousals may be based on a function of time, for example, a per
hour basis using the number of events from the immediately
preceding hour. In an alternative embodiment, the function may be
based on the number of sleep arousals in a particular session with
the device, for example, during a single night. In the example
formula shown, as the pressure decreases after obstruction is no
longer found, pressure will decrease more slowly as the number of
sleep arousals detected approaches 15 events in the previous hour.
Thus, the decay in treatment pressure as a result of the above
function will tend to be exponential, approaching the minimum
pressure for few or no detected events but decaying less rapidly as
a greater number of events are detected. As shown, exceeding a
certain number of such detections can prevent the device from
withdrawing treatment as K approaches 0 near a chosen critical
number of sleep arousal events.
[0071] Conversely, when the shape detector/snore index indicates
that there is an SDB event that must be treated by comparing a
detected index to a threshold, the treatment pressure will be
increased as a function of some gain. In one embodiment of the
invention, the gain affecting the rate of the pressure increase is
a function of sleep arousal. One such gain may be utilized to
deliver treatment pressure in accordance with the following
formula:
.DELTA.P=G(S-S.sub.T) when S<S.sub.T
[0072] where [0073] .DELTA.P is the pressure adjustment or the
pressure change; [0074] G is a function of the detected sleep
arousal; [0075] S is an obstruction index such as flow flattening
or snore index; [0076] S.sub.T is a threshold value for the
obstruction index. For example, an exponential function for G may
be utilized to increase the gain as an increasing function of a
cumulative number of detected sleep arousal events. One such
function is illustrated in the graph of FIG. 8. In the graph shown,
if no events of sleep arousal are detected or if none are detected
after a certain period of time, for example, none in the
immediately preceding hour, the gain remains at a typical gain.
However, as the number of these detected events accumulates, the
gain will be increased, preferably as an exponential function
approaching some maximum or higher gain. Of course, as the number
of detected sleep arousal events decreases, the gain will be
reduced according to the chosen graph of the sleep arousal
function.
[0077] While an exponential function is shown, those skilled in the
art will recognize that other functions for increasing the gain as
a function of an increasing number of detected sleep arousal events
can be utilized, for example, a linear or other ramp function.
(b) Sleep Arousal Based Threshold Adjustment
[0078] As previously mentioned, an adjustment or change to the
sensitivity of the apparatus may be implemented by changing
obstruction response thresholds as a function of an index of sleep
arousals. Those skilled in the art will recognize that a change by
either an increase or decrease in the threshold amount may be
associated with either an increase or decrease in sensitivity. This
relationship is attributable to the nature of the particular
obstruction index and its threshold as described previously. Some
suitable functions relating to the methods disclosed herein are
illustrated in the graphs of FIGS. 9 and 10. In the illustrated
exemplary graph of FIG. 9, as the number of detected events
increases over a period of time, such as the immediately preceding
hour, the threshold will be a decreasing function, such as a ramp,
from a less sensitive to a more sensitive value. For example, for
adjustment to the snore threshold as discussed above, when no sleep
arousal events are detected, the snore threshold may remain at its
default of about 0.2 units. However, as the number of arousal
events increases, the threshold may be reduced according to a ramp
or linear function to a lower threshold, rendering the detection of
snoring related obstructive events more likely (increasing
sensitivity).
[0079] The sample graph of FIG. 10 may be utilized to adjust or
change the sensitivity of the shape factors discussed previously.
As illustrated, a default threshold may remain constant in the
absence of detected sleep arousal events. However, as the detected
number of sleep arousals increases, the shape factor threshold will
increase rendering the detection of obstructive events more likely
(more sensitive), which in turn will result in a greater likelihood
of an increase in pressure treatment to address the detected
obstruction events. Those skilled in the art will recognize that
other functions of the sleep arousal index may be utilized to
change the sensitivity of various obstruction thresholds.
[0080] Similarly, the threshold may also be a function of treatment
pressure. One such function is illustrated in FIG. 11 as it relates
to the second shape factor discussed previously. In the example,
the threshold is held at a default value of 0.15 until the
treatment pressure exceeds 10 cm H.sub.2O. The threshold then
decreases, approaching 0 as the treatment pressure approaches 20 cm
H.sub.2O.
[0081] In another form of the invention, apparatus for treating
sleep disordered breathing is provided with a controller programmed
to select the most appropriate therapy from a "toolbox" of
treatment algorithms. The controller has two parts.
[0082] A first part is programmed to provide different forms of
therapy, for example, basic CPAP, automatically adjusting CPAP
(such as described in U.S. Pat. No. 5,704,345), bi-level CPAP or
more complicated therapies such as for treatment of Cheyne-Stokes
(CS) respiration (see, for example, U.S. Pat. No. 6,532,959, the
contents of which are hereby expressly incorporated by
cross-reference).
[0083] The second part monitors the patient and the effectiveness
of the current treatment algorithm. Thus a device in accordance
with the invention includes an apnea monitor able to distinguish
central and obstructive apneas (see, for example, U.S. Pat. No.
5,704,345), an oximeter able to detect oxygen desaturation events,
and a snoring monitor. Indices are calculated. For example, the
controller determines the number of central apneas, obstructive
apneas, hypopneas, and desaturation events and determines
appropriate indices such as the Apnea Hypopnea Index (AHI), Central
apnea Index (CI) and desaturation index (DI). The intensity and
severity of snoring is also monitored, as is flow flattening.
[0084] The controller changes treatment modes when a particular
mode is indicated. In one form, the device defaults to basic CPAP
treatment at a pressure suitable for treating a range of conditions
such as 8-12 cmH.sub.2O, preferably 9 cmH.sub.2O. Snoring, flow
flattening and obstructive apneas indicate that the treatment level
may be insufficient and the device will switch to an automatic CPAP
treatment algorithm (see U.S. Pat. No. 5,704,345). However, an AHI
>5/hour is indicative that the sensitivity of the Automatic CPAP
algorithm needs to be increased, and the controller will then
attempt this. A CI>5/hour is indicative that a bi-level CPAP or
Cheyne-Stokes treatment algorithm is appropriate. If
AHI+CI>5/hour then bi-level or CS treatment is indicated.
Ongoing periodic desaturations (for example, 3%-4% desaturation
>10/hour) indicate bi-level CPAP.
[0085] In one form of the invention, a central apnea detector is
included. This can then be used to monitor the occurrence of
central apneas in Congestive Heart Failure (CHF). By monitoring
central apneas, progression of the disease can be monitored. An
alarm or device message could be used to alert a physician of
disease progression. Furthermore, inasmuch as a central apnea marks
the onset of decompensation, the invention can be used to provide a
warning of acute decompensation and the requirement of
hospitalization.
[0086] While the invention has been described with various
alternative embodiments and features, it is to be understood that
the embodiments and features are merely illustrative of the
principles of the invention. Those skilled in the art would
understand that other variations can be made without departing with
the spirit and scope of the invention.
* * * * *