U.S. patent application number 13/232673 was filed with the patent office on 2012-01-05 for system and method for improved treatment of sleeping disorders using therapeutic positive airway pressure.
This patent application is currently assigned to New York University. Invention is credited to David M. Rapoport.
Application Number | 20120000466 13/232673 |
Document ID | / |
Family ID | 33517221 |
Filed Date | 2012-01-05 |
United States Patent
Application |
20120000466 |
Kind Code |
A1 |
Rapoport; David M. |
January 5, 2012 |
System and Method for Improved Treatment of Sleeping Disorders
using Therapeutic Positive Airway Pressure
Abstract
Described is a method and system providing therapeutic positive
airway pressure to a particular area of patient's airways. The
system may include a flow generator and a processing arrangement.
The flow generator supplies an airflow to an airway of the patient.
The processing arrangement is connected to the flow generator to
control a supply pressure at which the airflow is generated by the
flow generator. The processing arrangement continuously adjusts the
supply pressure to maintain a pressure in a predetermined portion
of the patient's airway substantially constant. The predetermined
portion of the patient's airway includes a collapsible portion of
an upper airway of the patient. The processing arrangement also
controls the supply pressure to maintain the pressure in the
collapsible portion of the patient's airway at a value at least as
great as a tissue pressure below which the collapsible portion
collapses.
Inventors: |
Rapoport; David M.; (New
York, NY) |
Assignee: |
New York University
New York
NY
|
Family ID: |
33517221 |
Appl. No.: |
13/232673 |
Filed: |
September 14, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10464126 |
Jun 18, 2003 |
8020555 |
|
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13232673 |
|
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Current U.S.
Class: |
128/204.23 ;
128/204.21 |
Current CPC
Class: |
A61M 16/06 20130101;
A61M 2016/0021 20130101; A61M 2016/0039 20130101; A61M 16/024
20170801 |
Class at
Publication: |
128/204.23 ;
128/204.21 |
International
Class: |
A61M 16/00 20060101
A61M016/00 |
Claims
1-22. (canceled)
23. A device for treatment of a sleeping disorder, comprising: a
flow generator configured to supply air to an airway of a patient
at a predetermined pressure P.sub.A; a processing arrangement
operably connected to the flow generator to maintain a gas pressure
within a predetermined portion of the patient's airway within a
desired range by adjusting one or both of the rate of airflow and a
pressure supplied by the flow generator.
24. The device of claim 23, wherein the processing arrangement is
configured to maintain a substantially constant pressure C.sub.P
within the patient's airway, the pressure C.sub.P being selected to
prevent a collapse of the patient's airway.
25. The device of claim 24, further comprising a mask connected to
the tube and configured to connect the flow generator to the airway
of the patient.
26. The device of claim 25, further comprising a flow tube
extending from the flow generator to the airway of the patient, the
flow tube having a resistance R.sub.AB, wherein the value R.sub.AB
is measured when the flow generator is providing the airflow and
the mask is open to the atmosphere.
27. The device of claim 26, wherein the flow generator is
configured to provide the airflow at one of a constant and a
variable flow rate.
28. The device of claim 26, wherein the pressure P.sub.A may be
continuously adjusted according to the formula:
P.sub.A=C.sub.P+R.sub.AB*F.sub.S+R.sub.BC*Fp, wherein: R.sub.BC is
a resistance in the predetermined portion of the patient's airway;
F.sub.s is an instantaneous rate of flow of air flowing from the
flow generator to the patient; F.sub.p is an instantaneous rate of
flow of air via inhalation and exhalation of the patient; wherein
the values of F.sub.S and F.sub.P are negative during expiration
and positive during inspiration.
29. The device of claim 26, wherein the pressure P.sub.A is
continuously adjusted according to R.sub.AB and R.sub.BC, wherein
R.sub.BC is a resistance in the predetermined portion of the
patient's airway.
30. The device of claim 28, wherein the value of R.sub.BC may be
determined from one of (a) a resistance measured from the patient,
(b) a fixed standardized resistance, (c) a resistance based on a
rhinometric analysis of the patient and (d) an estimated resistance
based on a pathology of the patient's nose.
31. The device of claim 29, wherein the value of R.sub.BC may be
determined from one of (a) a resistance measured from the patient,
(b) a fixed standardized resistance, (c) a resistance based on a
rhinometric analysis of the patient and (d) an estimated resistance
based on a pathology of the patient's nose.
32. The device of claim 24, wherein the pressure C.sub.P is
maintained substantially constant throughout one of an entire
inspiratory phase and a full respiratory cycle.
33. The device of claim 32, wherein the pressure C.sub.P applied
during the expiratory phase is lower than the pressure C.sub.P
applied during the inspiratory phase.
34. The device of claim 23, further comprising a venting
arrangement configured to prevent the patient from rebreathing
exhaled gases.
35. The device of claim 34, wherein the venting arrangement is one
of a leak port or a non-rebreathing valve.
36. The device of claim 34, wherein the venting arrangement vents
the exhaled gas to the atmosphere.
37. The device of claim 28, further comprising a first pressure
sensor coupled to the flow tube and configured to measure a
pressure within the flow tube and provide the measured data to the
processing arrangement.
38. The device of claim 37, further comprising a second pressure
sensor configured to measure a pressure in one of the mask and the
flow generator and provide the measured data to the processing
arrangement.
39. The device of claim 23, wherein the predetermined portion of
the patient's airway is a portion of the upper airway susceptible
to collapse.
40. A method for treating a sleeping disorder, comprising the steps
of: supplying an airflow to an airway of a patient at a
predetermined pressure P.sub.A; and maintaining a gas pressure
within a predetermined portion of the patient's airway within a
desired range by adjusting one or both of the rate of airflow and a
pressure supplied by the flow generator via a processing
arrangement operably connected to a flow generator.
41. The method according to claim 40, wherein the processing
arrangement is configured to maintain a substantially constant
pressure C.sub.P within the patient's airway, the pressure C.sub.P
being selected to prevent a collapse of the patient's airway.
42. The method according to claim 41, wherein the pressure C.sub.P
is maintained substantially constant in the predetermined portion
throughout one of an entire inspiratory phase and a full
respiratory cycle.
43. The method according to claim 41, further comprising the steps
of: generating the airflow using the flow generator, the flow
generator being coupled to the patient's airway by a flow tube; and
providing the airflow to a mask situated over at least one of a
nose and a mouth of the patient via the flow tube.
44. The method according to claim 40, further comprising the step
of: diverting, via a venting arrangement, gases exhaled by the
patient from an incoming airflow to prevent re-breathing of the
exhaled gases.
45. The method according to claim 43, further comprising the step
of: determining a supply pressure P.sub.A according to the
following formula: P.sub.A=C.sub.P+R.sub.AB*Fs+R.sub.BC*F.sub.P
wherein, P.sub.A is the supply pressure provided by the flow
generator; R.sub.AB is a resistance in the flow tube, wherein the
value R.sub.AB is measured when the flow generator is providing the
airflow and the mask is opened to the atmosphere; F.sub.s is an
instantaneous rate of flow of air flowing from the flow generator
to the patient; R.sub.BC is a resistance in the predetermined
portion of the patient's airway, wherein the value of R.sub.BC may
be determined from one of (a) a resistance measured from the
patient, (b) a fixed standardized resistance, (c) a resistance
based on a rhinometric analysis of the patient and (d) an estimated
resistance based on a pathology of the patient's nose; and F.sub.P
is an instantaneous rate of flow of air via inhalation and
exhalation of the patient, wherein the values of F.sub.S and
F.sub.P are negative during expiration and positive during
inspiration.
46. The method according to claim 45, further comprising the steps
of: measuring, via a first sensor, a first value of pressure in the
flow tube; and providing the measured data to the processing
arrangement.
47. The method according to claim 46, further comprising the steps
of: measuring, via a second sensor, a second value of pressure
within one of the flow generator and the mask; and providing the
measured data to the processing arrangement.
Description
BACKGROUND
[0001] Obstructive sleep apnea/hypopnea syndrome (OSAHS) is a well
recognized disorder which may affect as much as 1-5% of the adult
population. OSAHS is one of the most common causes of excessive
daytime somnolence. OSAHS is most frequent in obese males, and it
is the single most frequent reason for referral to sleep disorder
clinics.
[0002] OSAHS is associated with all conditions in which there is
anatomic or functional narrowing of the patient's upper airway, and
is characterized by an intermittent obstruction of the upper airway
occurring during sleep. The obstruction results in a spectrum of
respiratory disturbances ranging from the total absence of airflow
(apnea) to significant obstruction with or without reduced airflow
(hypopnea, episodes of elevated upper airway resistance and
snoring), despite continued respiratory efforts. The morbidity of
the syndrome arises from hypoxemia, hypercapnia, bradycardia and
sleep disruption associated with the respiratory obstruction event
and arousals from sleep.
[0003] The pathophysiology of OSAHS is not fully worked out.
However, it is now well recognized that obstruction of the upper
airway during sleep is in part due to the collapsible behavior of
the supraglottic segment of the respiratory airway during the
negative intraluminal pressure generated by inspiratory effort.
Thus, the human upper airway during sleep behaves as a Starling
resistor, which is defined by the property that the flow is limited
to a fixed value irrespective of the driving (inspiratory)
pressure. Partial or complete airway collapse can then occur
associated with the loss of airway tone which is characteristic of
the onset of sleep and which may be exaggerated in OSAHS.
[0004] Since 1981, positive airway pressure (PAP) applied by a
tight fitting nasal mask worn during sleep has evolved as the most
effective treatment for this disorder, and is now the standard of
care. The availability of this non-invasive form of therapy has
resulted in extensive publicity for sleep apnea/hypopnea and the
appearance of large numbers of patients who previously may have
avoided the medical establishment because of the fear of
tracheostomy. Increasing the comfort of the system (e.g., by
minimizing the applied nasal pressure) has been a major goal of
research aimed at improving patient compliance with therapy.
[0005] PAP therapy has become the mainstay of treatment in
Obstructive Sleep Disordered Breathing (OSDB), which includes
Obstructive Sleep Apnea/Hypopnea, Upper Airway Resistance Syndrome,
Snoring, exaggerations of sleep induced rises in collapsibility of
the upper airway and all conditions in which inappropriate
collapsing of a segment of the upper airway causes significant
un-physiologic obstruction to airflow. This collapse generally
occurs whenever pressure in the collapsible portion of the airway
becomes sub-atmospheric (or more accurately lower than a "tissue
pressure" in the surrounding wall at a critical location in the
upper airway of the patient). PAP therapy is directed to
maintaining pressure in the collapsible portion of the airway at or
above the critical "tissue pressure" at all times. In conventional
CPAP, this is achieved by raising the airway pressure in the entire
respiratory system to a level higher than this critical
pressure.
[0006] Conventional implementations of PAP therapies have either
provided a single continuous pressure at the nose or a combination
of such a continuous pressure with a lowering of pressure when the
pressure is not thought to be needed (e.g., during expiration).
Continuous PAP ("CPAP") generally provides a constant pressure at
least as large as the largest pressure necessary to prevent airway
collapse. Some PAP therapies have provided and modified pressure
profiles in an attempt to achieve the lowest (and presumably most
comfortable) pressure which produces the desired therapeutic
results.
[0007] For example, a procedure known as Bi-Level PAP is a known
modification to CPAP. In Bi-Level PAP, a first constant pressure is
set as an inspiratory pressure and a second lower constant pressure
is set to be applied during expiration. The choice of the second
pressure was originally based on the assumption that collapse of
the upper airway occurs primarily during inspiration and that
little or no collapsing force is generated absent the negative
airway pressure generated during inspiration. However, Bi-level PAP
has been shown to have little benefit in obstructive sleep apnea as
the second expiratory pressure needs to be set at or near the level
that would have been chosen for single pressure CPAP in order to
prevent airway collapse. Bi-Level PAP is now generally restricted
to patients who benefit from an unintended side effect of this mode
of positive pressure (i.e., assisted ventilation that may arise
when the difference between inspiration and expiration pressures
are significant). However, as will be discussed below, patients who
do not need assistance in breathing may find it difficult to draw
the amount of air they desire as these systems react to their
breathing by changing inhalation and exhalation pressures, and thus
may not deliver the necessary pressure at the beginning of
inspiration predictably.
[0008] Another modification of PAP is described, e.g., in U.S. Pat.
No. 6,105,575. This PAP system provides to a patient a minimally
sufficient pressure during at least a portion of a breathing cycle
to perform at least one of the following functions at any given
moment: (1) reduce cardiac preload and afterload and (2) prevent
airway collapse. When operating to prevent airway collapse, the
minimally sufficient pressure is determined by a summation of a
pressure needed to prevent airway collapse and a pressure needed to
overcome respiratory effort. This requirement to overcome
respiratory pressure makes the system provide assisted ventilation,
which, like Bi-Level PAP, is not need to treat obstructive sleep
disordered breathing if there is no hypoventilation syndrome.
SUMMARY OF THE INVENTION
[0009] Described is a method and system providing therapeutic
positive airway pressure designed to be held constant at a
particular area of patient's airways. The system may include a flow
generator and a processing arrangement. The flow generator supplies
an airflow to an airway of the patient. The processing arrangement
is connected to the flow generator to control a supply pressure at
which the airflow is generated by the flow generator.
[0010] The processing arrangement continuously adjusts the supply
pressure to maintain a pressure in a predetermined portion of the
patient's airway substantially constant. The predetermined portion
of the patient's airway includes a collapsible portion of an upper
airway of the patient. The processing arrangement also controls the
supply pressure to maintain the pressure in the collapsible portion
of the patient's airway at a value at least as great as a tissue
pressure below which the collapsible portion collapses.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The accompanying drawings which are incorporated in and
constitute part of the specification, illustrate several
embodiments of the invention and, together with the description,
serve to explain examples of the present invention. In the
drawings:
[0012] FIG. 1 shows an exemplary embodiment of a system according
to present invention;
[0013] FIGS. 2a and 2b show a schematic airflow passage in the
system illustrated in FIG. 1;
[0014] FIG. 3a illustrates a graph of pressure gradients during a
positive airway pressure applied during inspiration;
[0015] FIG. 3b illustrates a graph of pressure gradients during a
positive airway pressure applied during expiration;
[0016] FIGS. 4a-4c illustrate graphs of airflow/pressure
relationship in plurality of airway segment during utilization of
the system according to the present invention; and
[0017] FIGS. 5a-5c illustrate graphs of airflow at particular
points of the airflow passage.
DETAILED DESCRIPTION
[0018] FIG. 1 shows an exemplary embodiment of a system 1 according
to the present invention. The system 1 may include a mask 20 which
is connected via a tube 21 to receive air from a flow generator 22.
The mask 20 may cover patient's nose and/or mouth. A conventional
flow and pressure sensor 23 is coupled to the tube 21 and detects
both the airflow and pressure in the tube 21. Signals corresponding
to the airflow and the pressure are provided to a processing
arrangement 24 for processing. The processing arrangement 24
outputs a signal to a conventional flow control device 25 to
control a pressure applied to the flow tube 21. Those skilled in
the art will understand that, for certain types of flow generators
which may by employed as the flow generator 22, the processing
arrangement 24 may directly control the flow generator 22, instead
of controlling airflow therefrom by manipulating the separate flow
control device 25.
[0019] The system 1 also includes a conventional venting
arrangement 28 which may be in the form of a leak port or a
non-re-breathing valve with a venting tube. The venting arrangement
28 allows for gases exhaled by the patient to be diverted from the
incoming air to prevent re-breathing of the exhaled gases.
[0020] FIG. 2a shows a schematic of the airflow passage in the
system 1 from the flow generator 22 to the lungs of the patient. In
particular, the airflow passage may be divided into four logical
segments AB, BC, CD and DE as illustrated in FIGS. 2a and 2b.
First, the segment AB of the airflow passage extends from the flow
generator 22 to the inlet of the patient's nose and include the
tube 21 and the mask 20. A pressure P.sub.A is applied by the flow
generator 22 to a front end of the segment AB.
[0021] The segments BC and CD comprise the upper airway of the
patient extending between the patient's nose and a lower airway. In
particular, the segment BC extends from the nose of the patient to
the end of the area of the airway which has a boney support (i.e.,
extending through the nasopharynx to the end of the hard palate).
The segment CD extends from the beginning of the unsupported airway
(e.g., at or near the level of the soft palate) to the resumption
of the non-collapsible airway (i.e., the segment DE), such as an
entrance to the larynx. The segment BC is a non-collapsible segment
of the upper airway, while the segment CD is a collapsible segment
of the upper airway. Behavior of the segment CD is generally
believed to be responsible for OSAHS. Finally, the segment DE is
the lower airway of the patient and is located between the end of
the upper airway (i.e., the larynx) and the alveoli of the lungs of
the patient.
[0022] Unlike some conventional PAP system which adjust pressure to
provide assisted breathing (i.e., to overcome respiratory effort),
the system 1 is intended to maintain a substantially constant
pressure C.sub.P in the segment CD, as shown in FIGS. 4c and 5c, to
prevent as far as possible any assistance to or hindrance of the
patient's breathing. By properly selecting C.sub.?, airway collapse
can be prevented without additional effect on breathing effort. The
desired pressure in the segment CD is determined based on
conditions of a particular patient. To maintain the pressure
C.sub.P in the segment CD, the pressure P.sub.A (as shown in FIG.
5a) needs to be adjusted to compensate for dissipation of pressure
along the segments AB and BC which precede the segment CD because
they are upstream of the flow during inspiration and which add to
the pressure generated during expiration because they are
downstream of the flow. For example, the pressure P.sub.A might be
adjusted to compensate for pressure dissipation in the segment AB
during inspiration, as shown in FIG. 4a, due to the intrinsic
resistance of the tube 21 and/or the mask 20. For example, during
inspiration, the pressure P.sub.A is reduced by the time is reaches
the mask 20 (see FIG. 5b). The pressure P.sub.A may be further
adjusted to compensate for pressure dissipation in the segment BC,
as shown in FIG. 4b. No adjustments are needed for pressure
dissipation in the segment DE (see FIG. 4d).
[0023] A value of this pressure dissipation is determined by the
resistance and the flow through each segment. This value may be
either positive (e.g., during inspiration as shown in FIG. 3a) or
negative (e.g., during expiration as shown in FIG. 3b). The
pressure C, may be adjusted manually (e.g., by .a technician
performing a titration under laboratory monitoring) or
automatically (e.g., by an automated self-titrating technique).
[0024] The pressure P.sub.A may be continuously determined
according to the following exemplary formula:
P.sub.A=C.sub.P+R.sub.AB*F.sub.S+R.sub.BC*F.sub.P
wherein,
[0025] P.sub.A is a pressure applied by the flow generator 22;
[0026] C.sub.p is the constant pressure which is targeted as that
to be applied to the segment CD;
[0027] R.sub.AB is the resistance in the segment AB (which
determines the pressure dissipation in the segment AB at each rate
of airflow through the system);
[0028] R.sub.BC is a resistance in the segment BC (which determines
the pressure dissipation in the segment BC at each rate of airflow
in that segment);
[0029] F.sub.P is the instantaneous rate of flow of air by the
patient (i.e., the actual flow rate in and out of the nose at each
point of time of the patient's breathing (which is zero between
breaths, rises throughout inspiration, then falls to zero and
becomes negative during expiration) to which must be added any flow
that occurs due to the leaks through the patient's mouth; and
[0030] F.sub.S is an instantaneous rate of flow of air leaving the
pressure generator 22 and flowing through the tube 21 to the
patient (i.e., an actual flow rate at the inlet of the tube at each
point of time). This rate of flow is composed of the flow rate of
the patient's breathing (which is zero between breaths and rises
throughout inspiration, then falls to zero and becomes negative
during expiration), to which is added any amount of airflow leaking
continuously through the system (which is composed of the sum of
the flow of through the intentional leakport, any variable leaks
present where the mask 20 fits to the patient's face and any leak
though the patient's mouth).
[0031] The resistance (or rate of pressure dissipation) R.sub.AB
for any given airflow circuit may be determined based on a
measurement of the pressure P.sub.A which occurs when a particular
flow rate X is used to calibrate the system 1. This calibration may
be done with the distal end of the segment AB left open to the
atmosphere and a known (either constant or varying) flow applied by
the flow generator 22. Preferably, this applied flow should be
approximately equivalent to an amount of leakage that will occur
when the mask 20 is worn by the patient (e.g., 30 l/min). For
example, this relationship defining the resistance R.sub.AB may be
a substantially constant ratio of F.sub.S to P.sub.A. Those skilled
in the art will understand that the R.sub.AB may be different as
various tubes and masks are used as the tube 21 and the mask 20,
respectively. The determination of the R.sub.AB value may require a
calibration phase during which flow from the flow generator 22 is
systematically varied through a full range of possible flows (e.g.,
0-50 l/min), while no patient is attached to the segment AB.
Alternatively, the R.sub.AB value may be obtained from a table of
previously calculated data for the pressure/flow relationship for a
particular segment AB (e.g., a known tube/mask combination).
[0032] The R.sub.BC and the resultant correction value for a loss
of pressure within the segment BC of the patient's airway which is
upstream of the collapsible segment CD of the upper airway is more
difficult to determine directly from measurements external to the
patient. In normal patients, the resistance of the upper airway is
known from published data (using direct measurement by rhinometry)
to be about 0.1-0.2 cm H.sub.2O/liter/sec of flow.
[0033] In the absence of direct patient data, a fixed value of the
R.sub.BC (e.g., in the vicinity of 0.1 cm H.sub.2O/liter/sec) may
be assumed if the patient has no nasal disease. Higher values could
be assumed if there is, by clinical history or patient examination,
a known pathology of the nose expected to produce an increase in
nasal resistance. If rhinometry of the patient is performed prior
to use of the system 1, the value obtained may be used as the
pressure dissipation value R.sub.BC.
[0034] Once the R.sub.BC and R.sub.AB have been estimated or
determined, the values of R.sub.AB is multiplied by F.sub.S and
R.sub.BC is multiplied by F.sub.P and these values are summed. This
result is continuously updated to regularly compensate for the loss
or addition of pressure in the segments AB and BC. The value of
F.sub.S is the measured flow exiting the flow generator 22, and the
value of F.sub.P (the patient's instantaneous flow rate) plus any
leak through the patient's mouth may be determined by averaging a
value of flow of the flow measured exiting of the flow generator 22
over multiple respiratory cycles and subtracting this average value
from an instantaneous flow value from the flow generator 22. This
calculation results in the patient's instantaneous flow because the
patient's inhalation and exhalation volumes must be equal, and thus
the weighted time averages of the patient's flow rate over multiple
respiratory cycles must be zero. Thus, any non-zero value of the
average system flow from the flow generator 22 must be due to leaks
which are not part of the patient's respiration flow. If this
average system flow is subtracted from the total flow, what remains
is an instantaneous patient flow (which averages over time to
zero).
[0035] As stated above, the system 1 avoids the problems associated
with systems that intentionally or unintentionally assist the
breathing of patients by providing different pressures to the
patient's lungs during inhalation and exhalation. Specifically,
these systems may cause patients to inhale more air than they
require inducing a reaction whereby the patient draws less air in
subsequent breaths relying on the system assist to provide the
extra air required. The system may then react by changing the
inhalation and exhalation pressures and a series of system
adjustments and patient reactions may be begun which, in some
cases, is never stabilized. By maintaining the pressure in the
collapsible portion of the airway substantially constant, the
patient receives no breathing assistance and these problems are not
encountered. The only variations in pressure are above the
collapsible segment of the airway and do not extend below in such a
way as to reach the lung itself. Thus, at no time does the present
system deliver a pressure which would assist the patient's normal
breathing efforts or reduce his efforts below that which would be
present if he had no disease of his upper airway and were breathing
without the mask.
[0036] It will be apparent to those skilled in the art that various
modifications and variations can be made in the structure and the
methodology of the present invention, without departing from the
spirit or scope of the invention. Thus, it is intended that the
present invention cover the modifications and variations of this
invention provided they come within the scope of the appended
claims and their equivalents.
* * * * *