U.S. patent number RE35,295 [Application Number 08/296,018] was granted by the patent office on 1996-07-16 for sleep apnea treatment apparatus.
This patent grant is currently assigned to Respironics, Inc.. Invention is credited to Janice M. Cattano, Mark C. Estes.
United States Patent |
RE35,295 |
Estes , et al. |
July 16, 1996 |
**Please see images for:
( Certificate of Correction ) ** |
Sleep apnea treatment apparatus
Abstract
Improved methodology and apparatus for the treatment of sleep
apnea through (1) application of alternating high and low level
positive airway pressure within the airway of the patient with the
high and low airway pressure being coordinated with the spontaneous
respiration of the patient, (2) usage of adjustably programmable
pressure ramp circuitry capable of producing multiple pressure ramp
cycles of predetermined duration and pattern whereby the ramp
cycles may be customized to accommodate the specific needs of an
individual sleep apnea patient so as to ease the patient's
transition from wakefulness to sleep, and (3) remote control
operation of the apparatus for assisting those patients whose
mobility or capacity for physical exertion is intrinsically
limited.
Inventors: |
Estes; Mark C. (Irwin, PA),
Cattano; Janice M. (Gibsonia, PA) |
Assignee: |
Respironics, Inc. (Murrysville,
PA)
|
Family
ID: |
27021243 |
Appl.
No.: |
08/296,018 |
Filed: |
August 24, 1994 |
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
411012 |
Sep 22, 1989 |
5148802 |
|
|
Reissue of: |
786269 |
Nov 1, 1991 |
05239995 |
Aug 31, 1993 |
|
|
Current U.S.
Class: |
128/204.23;
128/204.21; 128/201.18 |
Current CPC
Class: |
A61M
16/024 (20170801); A61M 16/0069 (20140204); A61M
16/204 (20140204); A61M 16/205 (20140204); A61M
16/00 (20130101); A61M 16/0066 (20130101); A61M
2016/0039 (20130101); A61M 2016/0036 (20130101); A61M
2205/3561 (20130101); A61M 2016/0021 (20130101) |
Current International
Class: |
A61M
16/00 (20060101); A61M 16/20 (20060101); A61M
016/00 (); A62B 007/00 (); F16K 031/02 () |
Field of
Search: |
;128/204.18,204.21,204.23,204.26,716,719 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Medtronic.RTM. Sullivan.TM. Nasal CPAP System brochure, .COPYRGT.
Medtronic, Inc., 1991. .
"A Quiet CPAP System . . . ", Lifecare.RTM. CPAP-100, Jul. 1991,
Form #544, Lafayette, CO, 80026-9341..
|
Primary Examiner: Asher; Kimberly L.
Attorney, Agent or Firm: Reed Smith Shaw & McClay
Parent Case Text
.[.CROSS REFERENCE TO RELATED APPLICATION
This application is a continuation-in-part of pending U.S. patent
application Ser. No. 07/411,012, filed Sep. 22, 1989, now U.S. Pat.
No. 5,148,802 Entitled METHOD FOR TREATMENT OF SLEEP APNEA AND
APPARATUS FOR PROVIDING SUCH TREATMENT..].
Claims
What is claimed is:
1. Apparatus for delivering pressurized gas to the airway of a
patient who is breathing in repeated breathing cycles each
including an inspiratory phase and an expiratory phase, said
apparatus comprising:
gas flow generator means for providing a flow of said gas;
means for delivery of said gas flow from said gas flow generator
means to the airway of the patient;
pressure controller means cooperable with said gas flow generator
means to provide said gas flow within said means for delivery and
within the airway of the patient at selectively variable
pressures;
detector means for continually detecting the rate of flow of said
gas between said gas flow generator means and the airway of the
patient;
processor means cooperable with said detector means for continually
providing flow rate information of said gas between said gas flow
generator means and the airway of the patient, said flow rate
information including a first indicia corresponding to the
instantaneous flow rate of said gas and a reference indicia
approximating the average flow rate of said gas;
decision means operable to utilize said first indicia and said
reference indicia to identify the occurrence of said inspiratory
and expiratory phases, said decision means being cooperable with
said pressure controller means to control variation of the pressure
of said gas flow in response to identification of the occurrence of
said inspiratory and expiratory phases; and
ramp control circuitry means operatively connected to said pressure
controller means for effecting (1) a first ramp cycle wherein said
gas flow from said pressure controller means is initially output at
a first pressure and raises with time to a second pressure, and (2)
at least one additional ramp cycle selectively activatable through
conscious action of the patient.
2. The apparatus of claim 1 wherein said decision means is operable
to adjust said pressure controller means for a higher pressure gas
flow within said means for delivery when said first indicia exceeds
said reference indicia, and for a lower pressure gas flow within
said means for delivery when said first indicia is less than said
reference indicia.
3. The apparatus of claim 2 wherein said processor means includes
processing elements operable to adjust an existing value of said
reference indicia to provide an adjusted value thereof.
4. The apparatus of claim 3 wherein said processing elements
include means for processing said first indicia to provide a time
average of the flow rate of gas within said means for delivery as a
first component of said reference indicia.
5. The apparatus of claim 4 wherein said processing elements
further include means for processing said first indicia and said
reference indicia to provide a measure of the flow of gas within
said means for delivery during a predeterminable time period as a
second component of said reference indicia.
6. The apparatus of claim 5 wherein said predeterminable time
period is a single complete breathing cycle of the patient
including one said inspiratory phase and one said expiratory phase
in sequence.
7. The apparatus of claim 6 wherein said processing elements
further include means for processing said first indicia and to
provide a measure of the value of said first indicia at the end of
any said complete breathing cycle by the patient as a third
component of said reference indicia.
8. The apparatus of claim 1 further comprising means associated
with said ramp control circuitry means for adjusting the magnitude
of said first pressure.
9. The apparatus of claim I further comprising means associated
with said ramp control circuitry means for adjusting the magnitude
of said second pressure.
10. The apparatus of claim 9 where said second pressure is a
prescription pressure unique to the patient.
11. The apparatus of claim 1 further comprising means associated
with said ramp control circuitry means for adjusting the duration
of said first ramp cycle.
12. The apparatus of claim 11 further comprising means associated
with said ramp control circuitry means for selecting a fraction of
an adjusted duration of said first ramp cycle as established by
said means for adjusting the duration of said first ramp cycle.
13. The apparatus of claim 12 wherein said means for selecting a
fraction of an adjusted duration of said first ramp cycle permits
selection of a fraction of said adjusted duration from zero up to
and including said adjusted duration.
14. The apparatus of claim 12 further comprising means associated
with said ramp control circuitry means for adjusting the duration
of said at least one additional ramp cycle.
15. The apparatus of claim 14 wherein said means for adjusting the
duration of said at least one additional ramp cycle permits
adjustment of the duration of said at least one additional ramp
cycle from substantially zero up to and including said adjusted
duration.
16. The apparatus of claim 1 further comprising means associated
with said ramp control circuitry means for establishing a
predetermined pattern of pressure output from said pressure
controller means during progression from said first pressure to
said second pressure.
17. The apparatus of claim 16 further comprising means associated
with said ramp control circuitry means for establishing a pattern
of pressure output from said pressure controller means different
than said predetermined pattern during said at least one additional
ramp cycle.
18. The apparatus of claim 1 further comprising remote control
means operable by the patient for selectively activating said
apparatus and said ramp control circuitry means.
19. The apparatus of claim 18 where said remote control means
includes a first actuator having a first configuration and adapted
to be operated by the patient to activate said apparatus and a
second actuator having a second configuration substantially
different than said first configuration and adapted to activate
said ramp control circuitry means, whereby the patient can reliably
identify and operate said first and second actuators by sense of
touch.
20. Apparatus for delivering pressurized gas to the airway of a
patient who is breathing in repeated breathing cycles each
including an inspiratory phase and an expiratory phase, said
apparatus comprising:
gas flow generator means for providing a flow of said gas;
means for delivery of said gas flow from said gas flow generator
means to the airway of the patient;
pressure controller means cooperable with said gas flow generator
means to provide said gas flow within said means for delivery and
within the airway of the patient at selectively variable
pressures;
detector means for continually detecting the rate of flow of said
gas between said gas flow generator means and the airway of the
patient;
processor means cooperable with said detector means for continually
providing flow rate information of said gas between said gas flow
generator means and the airway of the patient, said flow rate
information including a first indicia corresponding to the
instantaneous flow rate of said gas and a reference indicia
approximating the average flow rate of said gas;
decision means operable to utilize said first indicia and said
reference indicia to identify the occurrence of said inspiratory
and expiratory phases, said decision means being cooperable with
said pressure controller means to control variation of the pressure
of said gas flow in response to identification of the occurrence of
said inspiratory and expiratory phases;
ramp control circuitry means operatively connected to said pressure
controller means for effecting (1) a first ramp cycle wherein said
gas flow from said pressure controller means is initially output at
a first pressure and raises with time to a second pressure, and (2)
at least one additional selectively activatable ramp cycle;
means associated with said ramp control circuitry means for
adjusting the magnitude or said first pressure;
means associated with said ramp control circuitry means for
adjusting the magnitude of said second pressure;
means associated with said ramp control circuitry means for
adjusting the duration of said first ramp cycle;
means associated with said ramp control circuitry means for
selecting a fraction of an adjusted duration of said first ramp
cycle as established by said means for adjusting the duration of
said first ramp cycle;
means associated with said ramp control circuitry means for
adjusting the duration of said at least one additional ramp
cycle;
means associated with said ramp control circuitry means for
establishing a predetermined pattern of pressure output from said
pressure controller means during progression from said first
pressure to said second pressure; and
remote control means operable by the patient for selectively
activating said apparatus and said ramp control circuitry
means.
21. The apparatus of claim 20 further comprising means associated
with said ramp control circuitry means for establishing a pattern
of pressure output from said pressure controller means different
than said predetermined pattern during said at least one additional
ramp cycle.
22. Apparatus for delivering pressurized gas to the airway of a
patient, said apparatus comprising:
gas flow generator means for providing a flow of said gas;
conduit means for delivery of said gas flow to the airway of said
patient;
pressure controller means cooperable with said gas flow generator
means to provide for flow of said gas within said conduit means and
within the airway of said patient at selectively variable
pressures;
ramp control circuitry means operatively connected to said pressure
controller means for effecting (1) a first ramp cycle wherein said
gas flow from said pressure controller means is initially output at
a first pressure and raises with time to a second pressure, and (2)
at least one additional ramp cycle selectively activatable through
conscious action of said patient; and
means associated with said ramp control circuitry means for
adjusting the duration of said first ramp cycle; and
means associated with said ramp control circuitry means for
selecting a fraction of an adjusted duration of said first ramp
cycle as established by said means for adjusting the duration of
said first ramp cycle.
23. The apparatus of claim 22 further comprising means associated
with said ramp control circuitry means for adjusting the magnitude
of said first pressure.
24. The apparatus of claim 22 further comprising means associated
with said ramp control circuitry means for adjusting the magnitude
of said second pressure.
25. The apparatus of claim 24 wherein said second pressure is a
prescription pressure unique to the patient.
26. The apparatus of claim 22 wherein said means selecting a
fraction of an adjusted duration of said first ramp cycle permits
selection of a fraction of said adjusted duration from zero up to
and including said adjusted duration.
27. The apparatus of claim 22 further comprising means associated
with said ramp control circuitry means for adjusting the duration
of said at least one additional ramp cycle.
28. The apparatus of claim 27 wherein said means for adjusting the
duration of said at least one additional ramp cycle permits
adjustment of the duration of said at least one additional ramp
cycle from substantially zero up to and including said adjusted
duration.
29. The apparatus of claim 22 further comprising means associated
with said ramp control circuitry means for establishing a
predetermined pattern of pressure output from said pressure
controller means as said pressure progresses from said first
pressure to said second pressure.
30. The apparatus of claim 29 further comprising means associated
with said ramp control circuitry means for establishing a pattern
of pressure output from said pressure controller means different
than said predetermined pattern during said at least one additional
ramp cycle.
31. The apparatus of claim 22 further comprising remote control
means operable by the patient for selectively activating said
apparatus and said ramp control circuitry means.
32. The apparatus of claim .[.22.]. .Iadd.31 .Iaddend.wherein said
remote control means includes a first actuator having a first
configuration and adapted to be operated by the patient to activate
said apparatus and a second actuator having a second configuration
substantially different than said first configuration and adapted
to activate said ramp control circuitry means, whereby the patient
can reliably identify and operate said first and second actuators
by sense of touch.
33. Apparatus for delivering pressurized gas to the airway of a
patient, said apparatus comprising:
gas flow generator means for providing a flow of said gas;
conduit means for delivery of said gas flow to the airway of the
patient;
pressure controller means cooperable with said gas flow generator
means to provide for flow of said gas within said conduit means and
within the airway of the patient at selectively variable
pressures;
ramp control circuitry means operatively connected to said pressure
controller means for effecting (1) a first ramp cycle wherein said
gas flow from said pressure controller means is initially output at
a first pressure and raises with time to a second pressure, and (2)
at least one additional selectively activatable ramp cycle;
means associated with said ramp control circuitry means for
adjusting the magnitude of said first pressure;
means associated with said ramp control circuitry means for
adjusting the magnitude of said second pressure;
means associated with said ramp control circuitry means for
adjusting the duration of said first ramp cycle;
means associated with said ramp control circuitry means for
selecting a fraction of an adjusted duration of said first ramp
cycle as established by said means for adjusting the duration of
said first ramp cycle;
means associated with said ramp control circuitry mans for
adjusting the duration of said at least one additional ramp
cycle;
means associated with said ramp control circuitry means for
establishing a predetermined pattern of pressure output from said
pressure control means during progression from said first pressure
to said second pressure; and
remote control means operable by the patient for selectively
activating said apparatus and said ramp control circuitry
means.
34. The apparatus of claim 33 further comprising means associated
with said ramp control circuitry means for establishing a pattern
of pressure output from said pressure controller means different
than said predetermined pattern during said at least one additional
ramp cycle.
Description
FIELD OF THE INVENTION
The present invention relates generally to methodology and
apparatus for treatment to sleep apnea and, more particularly, to
mono-level, bi-level, or proportional assist ventilation (PAV)
continuous positive airway pressure (CPAP) apparatus including
circuitry for enabling a patient to selectively actuate one or more
pressure ramp cycles wherein, during each ramp cycle, available
airway pressure increases with time from a predetermined minimum
pressure value to a prescription pressure, thereby facilitating the
patient's transition from a waking to a sleeping state.
BACKGROUND OF THE INVENTION
The sleep apnea syndrome afflicts an estimated 1% to 3% of the
general population and is due to episodic upper airway obstruction
during sleep. Those afflicted with sleep apnea experience sleep
fragmentation and intermittent, complete or nearly complete
cessation of ventilation during sleep with potentially severe
degrees of oxyhemoglobin unsaturation. These features may be
translated clinically into debilitating daytime sleepiness, cardiac
dysrhythmias, pulmonary-artery hypertension, congestive heart
failure and cognitive dysfunction. Other sequelae of sleep apnea
include right ventricular dysfunction with cor pulmonale, carbon
dioxide retention during wakefulness as well as during sleep, and
continuous reduced arterial oxygen tension. Hypersomnolent sleep
apnea patients may be at risk for excessive mortality from these
factors as well as by an elevated risk for accidents while driving
and/or operating potentially dangerous equipment.
Although details of the pathogenesis of upper airway obstruction in
sleep apnea patients have not been fully defined, it is generally
accepted that the mechanism includes either anatomic or functional
abnormalities of the upper airway which result in increased air
flow resistance. Such abnormalities may include narrowing of the
upper airway due to suction forces evolved during inspiration, the
effect of gravity pulling the tongue back to appose the pharyngeal
wall, and/or insufficient muscle tone in the upper airway dilator
muscles. It has also been hypothesized that a mechanism responsible
for the known association between obesity and sleep apnea is
excessive soft tissue in the anterior and lateral neck which
applies sufficient pressure on internal structures to narrow the
airway.
The treatment of sleep apnea has included such surgical
interventions as uvulopalatopharyngoplasty, gastric surgery for
obesity, and maxillo-facial reconstruction. Another mode of
surgical intervention used in the treatment of sleep apnea is
tracheostomy. These treatments constitute major undertakings with
considerable risk of postoperative morbidity if not mortality.
Pharmacologic therapy has in general been disappointing, especially
in patients with more than mild sleep apnea. In addition, side
effects from the pharmacologic agents that have been used are
frequent. Thus, medical practitioners continue to seek non-invasive
modes of treatment for sleep apnea with high success rates and high
patient compliance including, for example in cases relating to
obesity, weight loss through a regimen of exercise and regulated
diet.
Recent work in the treatment of sleep apnea has included the use of
continuous positive airway pressure (CPAP) to maintain the airway
of the patient in a continuously open state during sleep. For
example, U.S. Pat. No. 4,655,213 and Australian patent
AU-B-83901/82 both disclose sleep apnea treatments based on
continuous positive airway pressure applied within the airway of
the patient.
Also of interest is U.S. Pat. No. 4,773,411 which discloses a
method and apparatus for ventilatory treatment characterized as
airway pressure release ventilation and which provides a
substantially constant elevated airway pressure with periodic short
term reductions of the elevated airway pressure to a pressure
magnitude no less than ambient atmospheric pressure.
Published PCT Application No. WO 88/10108 describes a CPAP
apparatus which includes a feedback system for controlling the
output pressure of a variable pressure air source whereby output
pressure from the air source is increased in response to detection
of sound indicative of snoring. A pressure ramp cycle (i.e., a
gradual increase in output pressure) occurs upon initial activation
of the apparatus while other ramp cycles occur automatically
thereafter upon detection of snoring sounds from the patient.
Publications pertaining to the application of CPAP in treatment of
sleep apnea include the following:
1. Lindsay, DA, Issa FG, and Sullivan C. E. "Mechanisms of Sleep
Desaturation in Chronic Airflow Limitation Studied with Nasal
Continuous Positive Airway Pressure (CPAP), " Am Rev Respir Dis,
1982; 125: p. 112.
2. Sanders NH, Moore SE, Eveslage J. "CPAP via nasal mask: A
treatment for occlusive sleep apnea, Chest, 1983; 83: pp.
144-145.
3. Sullivan CE, Berthon-Jones M. Issa FG. "Remission severe
obesity-hypoventilation syndrome after short-term treatment during
sleep with continuous positive airway pressure, Am Rev Respir Dis,
1983; 128: pp. 177-181.
4. Sullivan CE, Issa FG, Berthon-Jones M., Eveslage J. "Reversal of
obstructive sleep apnea by continuous positive airway pressure
applied through the nares, Lancet, 1981; 1: pp. 862-865.
5. Sullivan CE, Berthon-Jones M. Issa FG "Treatment of obstructive
apnea with continuous positive airway pressure applied through the
nose. Am Rev Respir Dis, 1982; 125: p. 107. Annual Meeting
Abstracts.
6. Rapoport DM, Sorkin B, Garay SM, Goldring RN. "Reversal of the
`Pickwickian Syndrome` by long-term use of nocturnal nasal-airway
pressure," N Engl J. Med, 1982; 307: pp. 931-933.
7. Sanders MH, Holzer BC, Pennock BE, "The effect of nasal CPAP on
various sleep apnea patterns, Chest, 1983; 84: p. 336. Presented at
the Annual Meeting of the American College of Chest Physicians,
Chicago Ill., October 1983.
8. Sanders, MH. "Nasal CPAP Effect on Patterns of Sleep Apnea",
Chest, 1984; 86: 839-844.
Although CPAP has been found to be very effective and well
accepted, it suffers from some of the same limitations, although to
a lesser degree, as do the surgery options: specifically a
significant proportion of sleep apnea patients do not tolerate CPAP
well. Thus, development of other viable non-invasive therapies has
been a continuing objective in the art.
SUMMARY OF THE INVENTION
The present invention contemplates a novel and improved method for
treatment of sleep apnea as well as novel methodology and apparatus
for carrying out such improve treatment method. The invention
contemplates the treatment of sleep apnea through application of
pressure at variance with ambient atmospheric pressure within the
upper airway of the patient in a manner to promote dilation of the
airway to thereby relieve upper airway occlusion during sleep.
In a first embodiment of the invention, positive pressure is
applied at a substantially constant pressure within the airway of
the patient to maintain the requisite dilating force to sustain
respiration during sleep periods. This form of treatment is
commonly known as mono-level CPAP therapy.
In another embodiment of the invention, positive pressure is
applied alternately at relatively higher and lower pressure levels
within the airway of the patient so that the pressure-induced force
applied to dilate the patients airway is alternately a larger and a
smaller magnitude dilating force. The higher and lower magnitude
positive pressures are initiated by spontaneous patient respiration
with the higher magnitude pressure being applied during inspiration
and the lower magnitude pressure being applied during expiration.
This method of treatment may descriptively be referred to as
bi-level CPAP therapy.
The invention further contemplates a novel and improved apparatus
which is operable in accordance with a novel and improved method to
provide sleep apnea treatment. More specifically, a flow generator
and an adjustable pressure controller supply air flow at a
predetermined, adjustable pressure to the airway of a patient
through a flow transducer. The flow transducer generates an output
signal which is then conditioned to provide a signal proportional
to the instantaneous flow rate of air to the patient. The
instantaneous flow rate signal is fed to a low pass filter which
passes only a signal indicative of the average flow rate over time.
The average flow rate signal typically would be expected to be a
value representing a positive flow as the system is likely to have
at least minimal leakage from the patient circuit (e.g., small
leaks about the perimeter of the respiration mask worn by the
patient). The average flow signal is indicative of such leakage
because the summation of all other components of flow over time
must be essentially zero since inspiration flow must equal
expiration flow volume over time, that is, over a period of time
the volume of air breathed in equals the volume of the gases
breathed out.
Both the instantaneous flow signal and the average flow rate signal
are fed to an inspiration/ expiration decision module which is, in
its simplest form, a comparator that continually compares the input
signals and provides a corresponding drive signal to the pressure
controller. In general, when the instantaneous flow exceeds average
flow, the patient is inhaling and the drive signal supplied to the
pressure controller sets the pressure controller to deliver air, at
a preselected elevated pressure, to the airway of the patient.
Similarly, when the instantaneous flow rate is less than the
average flow rate, the patient is exhaling and the decision
circuitry thus provides a drive signal to set the pressure
controller to provide a relatively lower magnitude of pressure in
the airway of the patient. The patient's airway thus is maintained
open by alternating higher and lower magnitudes of pressure which
are applied during spontaneous inhalation and exhalation,
respectively.
As has been noted, some sleep apnea patients do not tolerate
standard CPAP therapy. Specifically, approximately 25% of patients
cannot tolerate CPAP due to the attendant discomfort. CPAP mandates
equal pressures during both inhalation and exhalation. The elevated
pressure during both phases of breathing may create difficulty in
exhaling and the sensation of an inflated chest. However, we have
determined that although both inspiratory and expiratory air flow
resistances in the airway are elevated during sleep preceding the
onset of apnea, the airway flow resistance may be less during
expiration than during inspiration. Thus it follows that the
bi-level CPAP therapy of our invention as characterized above may
be sufficient to maintain pharyngeal patency during expiration even
though the pressure applied during expiration is not as high as
that needed to maintain pharyngeal patency during inspiration. In
addition, some patients may have increased upper airway resistance
primarily during inspiration with resulting adverse physiologic
consequences. Thus, our invention also contemplates applying
elevated pressure only during inhalation thus eliminating the need
for global (inhalation and exhalation) increases in airway
pressure. The relatively lower pressure applied during expiration
may in some cases approach or equal ambient pressure. The lower
pressure applied in the airway during expiration enhances patient
tolerance by alleviating some of the uncomfortable sensations
normally associated with CPAP.
Under prior CPAP therapy, pressures as high as 15 cm H.sub.2 O have
been required, and some patients on nasal CPAP thus have been
needlessly exposed to unnecessarily high expiratory pressures with
the attendant discomfort and elevated mean airway pressure, and
theoretic risk of barotrauma. Our invention permits independent
application of a higher inspiratory airway pressure in conjunction
with a lower expiratory airway pressure in order to provide a
therapy which is better tolerated by the 25% of the patient
population which does net tolerate CPAP therapy, and which may be
safer in the other 75% of the patient population.
As has been noted hereinabove, the switch between higher and lower
pressure magnitudes can be controlled by spontaneous patient
respiration, and the patient thus is able to independently govern
respiration rate and volume. As has been also noted, the invention
contemplates automatic compensation for system leakage whereby
nasal mask fit and air flow system integrity are of less
consequence than in the prior art. In addition to the benefit of
automatic leak compensation, other important benefits of the
invention include lower mean airway pressures for the patient and
enhanced safety, comfort and tolerance.
In all embodiments, the present invention makes use of "ramp"
circuitry operatively connected to pressure control means of the
CPAP apparatus and selectively activatable by the patient to effect
at least one pressure "ramp cycle" which is described in greater
detail below. The maximum duration of the ramp cycle, the shape of
the ramp curve and the prescription pressure are normally
established by a sleep study of the patient and this data can be
programmed into the CPAP apparatus of the instant invention. It is
also desirable that the CPAP apparatus be operable either by manual
controls located directly on the apparatus or via remote
control.
Approximately 25% of all patients who undergo CPAP therapy for
sleep apnea experience respiration discomfort and find it difficult
to fall asleep because of the therapy. The purpose of a ramp cycle
is to alleviate this discomfort. A ramp cycle is an automatic cycle
that, once activated, causes the CPAP apparatus to output a
predetermined minimum positive pressure at or above ambient
pressure which is gradually increased over a predetermined time
period known as "ramp time" during which the patient begins to fall
asleep. Upon expiration of the ramp time the patient typically has
fallen asleep and at such time the pressure produced by the
apparatus is that of the patient's CPAP therapy prescription
pressure whereupon the patient receives normal CPAP treatment as he
sleeps.
A particular advantage of the present invention is that the unique
ramp circuitry enables not only an initial ramp cycle to be
achieved for when one first attempts to sleep but such circuitry
also permits one or more additional cycles to be selectively
activated by the user at instances where the user awakens during an
extended rest period and again requires a ramp cycle to fall back
to sleep. Typically, during a sleeping period of several hours, the
time required to once again fall asleep after briefly being
awakened is generally less than the time spent initially falling
asleep. To accommodate this phenomenon, the ramp circuitry of the
instant invention allows the user to advantageously adjust the ramp
time of any additional ramp cycle to run for a selected fraction of
the initial ramp time, which itself is a patient-selected fraction
of a prescription pressure preset by a health care professional in
supervision of the patient's sleep apnea treatment.
The ramp circuitry enables a physician or other health care worker
to set the initial ramp time and prescription pressure.
Additionally, however, the novel ramp circuitry of the present
invention permits adjustment of the "shape" of the pressure ramp
curve, whereby the physician, health care worker or patient can
suitably manipulate appropriate controls associated with the ramp
circuitry to control the pressure output pattern of the ramp (as
represented as a function of pressure versus time) such that it may
assume virtually any configuration including, inter alia, linear,
stepped, or curvilinear slope, depending upon a patient's
particular needs as dictated by the results of the patient's sleep
study.
Additionally, sufferers of sleep apnea are sometimes afflicted by
other maladies which limit the degree to which they may safely
physically exert themselves. An advantage of the present invention
is that it enables a limited-mobility user, at his discretion, to
operate the CPAP apparatus either by manual controls located
directly on the apparatus or via remote control. Equally as
important, it provides any sleep apnea sufferer using the CPAP
apparatus with the peace of mind of knowing that the pressure can
be reduced at any time via the remote control. Further, the
preferred embodiment of the remote control contemplated for use in
the present invention is one which the user can operate easily and
reliably either in light or darkness to turn the apparatus on and
off as well as selectively activate the first or subsequent ramp
cycles.
Further, although the ramp circuitry discussed hereinbelow will be
described specifically in connection with mono-level and bi-level
CPAP apparatus, it will be understood that its utility and
applicability is not limited thereto. That is to say, within the
scope of the instant invention it is also contemplated that the
presently disclosed ramp circuitry may be incorporated into other
types of CPAP apparatus including, but not limited to, proportional
assist ventilation (PAV) devices which are similar to bi-level CPAP
devices but instead provide substantially continuous adjustment of
pressure in response to patent volume and flow instead of
alternating between two fixed pressures in response to flow.
Other details, objects and advantages of the present invention will
become apparent as the following description of the presently
preferred embodiments and presently preferred methods of practicing
the invention proceeds.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will become more readily apparent from the following
description of preferred embodiments thereof shown, by way of
example only, in the accompanying drawings, wherein:
FIG. 1 is a functional block diagram of an apparatus according to
the instant invention;
FIG. 2 is a functional block diagram showing an alternative
embodiment of the invention;
FIG. 3 is a functional block diagram of the Estimated Leak Computer
of FIG. 2;
FIG. 4 is a frontal elevation of a control panel for a first
embodiment of the apparatus of this invention;
FIG. 5 is a functional block diagram of a further embodiment of an
apparatus according to the instant invention;
FIG. 6 is a functional block diagram of a further embodiment of an
apparatus according to the instant invention;
FIG. 7A is a flow diagram of a first embodiment of programmable
ramp control circuitry of the instant invention suitable for use in
CPAP apparatus;
FIG. 7B is a flow diagram of a further embodiment of programmable
ramp control circuitry of the instant invention suitable for use in
CPAP apparatus; and
FIGS. 8A, 8B and 8C reveal three examples of typical ramp curve
shapes that may be achieved via the programmable ramp circuitry of
FIG. 7.
DETAILED DESCRIPTION OF THE INVENTION
There is generally indicated at 10 in FIG. 1 an apparatus according
to one presently preferred embodiment of the instant invention and
shown in the form of a functional block diagram. Apparatus 10 is
operable according to a novel process which is another aspect of
the instant invention for delivering breathing gas such as air
alternately at relatively higher and lower pressures (i.e., equal
to or above ambient atmospheric pressure) to a patient 12 for
treatment of the condition known as sleep apnea.
Apparatus 10 comprises a gas flow generator 14 (e.g., a blower)
which receives breathing gas from any suitable source, a
pressurized bottle 16 or the ambient atmosphere, for example. The
gas flow from flow generator 14 is passed via a delivery conduit 20
to a breathing appliance such as a mask 22 of any suitable known
construction which is worn by patient 12. The mask 22 may
preferably be a nasal mask or a full face mask 22 as shown. Other
breathing appliances which may be used in lieu of a mask include
nasal cannulae, an endotracheal tube, or any other suitable
appliance for interfacing between a source of breathing gas and a
patient.
The mask 22 includes a suitable exhaust port means, schematically
indicated at 24, for exhaust of breathing gases during expiration.
Exhaust port 24 preferably is a continuously open port which
imposes a suitable flow resistance upon exhaust gas flow to permit
a pressure controller 26, located in line with conduit 20 between
flow generator 14 and mask 22, to control the pressure of air flow
within conduit 20 and thus within the airway of the patient 12. For
example, exhaust port 24 may be of sufficient cross-sectional flow
area to sustain a continuous exhaust flow of approximately 15
liters per minute. The flow via exhaust port 24 is one component,
and typically the major component of the overall system leakage,
which is an important parameter of system operation. In an
alternative embodiment to be discussed hereinbelow, it has been
found that a non-rebreathing valve may be substituted for the
continuously open port 24.
The pressure controller 26 is operative to control the pressure of
breathing gas within the conduit 20 and thus within the airway of
the patient. Pressure controller 26 is located preferably, although
not necessarily, downstream of flow generator 14 and may take the
form of an adjustable valve which provides a flow path which is
open to the ambient atmosphere via a restricted opening, the valve
being adjustable to maintain a constant pressure drop across the
opening for all flow rates and thus a constant pressure within
conduit 20.
Also interposed in line with conduit 20, preferably downstream of
pressure controller 26, is a suitable flow transducer 28 which
generates an output signal that is fed as indicated at 29 to a flow
signal conditioning circuit 30 for derivation of a signal
proportional to the instantaneous flow rate of breathing gas within
conduit 20 to the patient.
It will be appreciated that flow generator 14 is not necessarily a
positive displacement device. It may be, for example, a blower
which creates a pressure head within conduit 20 and provides air
flow only to the extent required to maintain that pressure head in
the presence of patient breathing cycles, the exhaust opening 24,
and action of pressure controller 26 as above described.
Accordingly, when the patient is exhaling, peak exhalation flow
rates from the lungs may far exceed the flow capacity of exhaust
port 24. As a result, exhalation gas back flows within conduit 20
through flow transducer 28 and toward pressure controller 26, and
the instantaneous flow rate signal from transducer 28 thus will
vary widely within a range from relatively large positive (i.e.,
toward the patient) flow to relatively large negative (i.e., from
the patient) flow.
The instantaneous flow rate signal from flow signal conditioning
circuitry 30 is fed as indicated at 32 to a decision module 34, a
known comparator circuit for example, and is additionally fed as
indicated at 36 to a low pass filter 38. Low pass filter 38 has a
cutoff frequency low enough to remove from the instantaneous flow
rate input signal most variations in the signal which are due to
normal breathing. Low pass filter 38 also has a long enough time
constant to ensure that spurious signals, aberrant flow patterns
and peak instantaneous flow rate values will not dramatically
affect system average flow. That is, the time constant of low pass
filter 38 is selected to be long enough that it responds slowly to
the instantaneous flow rate signal input. Accordingly, most
instantaneous flow rate input signals which could have a large
impact on system average flow in the short term have a much smaller
impact over a longer term, largely because such instantaneous flow
rate signal components will tend to cancel over the longer term.
For example, peak instantaneous flow rate values will tend to be
alternating relatively large positive and negative flow values
corresponding to peak inhalation and exhalation flow achieved by
the patient during normal spontaneous breathing. The output of low
pass filter 38 thus is a signal which is proportional to the
average flow in the system, and this is typically a positive flow
which corresponds to average system leakage (including flow from
exhaust 24) since, as noted, inhalation and exhalation flow cancel
for all practical purposes.
The average flow signal output from the low pass filter 38 is fed
as indicated at 40 to decision circuitry 34 where the instantaneous
flow rate signal is continually compared to the system average flow
signal. The output of the decision circuitry 34 is fed as a drive
signal indicated at 42 to control the pressure controller 26. The
pressure magnitude of breathing gas within conduit 20 thus is
coordinated With the spontaneous breathing effort of the patient
12, as follows.
When the patient begins to inhale, the instantaneous flow rate
signal goes to a positive value above the positive average flow
signal value. Detection of this increase in decision circuitry 34
is sensed at the start of patient inhalation. The output signal
from decision circuitry 34 is fed to pressure controller 26 which,
in response, provides higher pressure gas flow within conduit 20
and thus higher pressure within the airway of the patient 12. This
is the higher magnitude pressure value of our bi-level CPAP system
and is referred to hereinbelow as IPAP (inhalation positive airway
pressure). During inhalation, the flow rate within conduit 20 will
increase to a maximum and then decrease as inhalation comes to an
end.
At the start of exhalation, air flow into the patient's lungs is
nil and as a result the instantaneous flow rate signal will be less
than the average flow rate signal which, as noted is a relatively
constant positive flow value. The decision circuitry 34 senses this
condition at the start of exhalation and provides a drive signal to
pressure controller 26 which, in response, provides gas flow within
conduit 20 at a lower pressure which is the lower magnitude
pressure value of the bi-level CPAP system, referred to hereinbelow
as EPAP (exhalation positive airway pressure). As has been noted
hereinabove the range of EPAP pressures may include ambient
atmospheric pressure. When the patient again begins spontaneous
inhalation, the instantaneous flow rate signal again increases over
the average flow rate signal, and the decision circuitry once again
feeds a drive signal to pressure controller 26 to reinstitute the
IPAP pressure.
System operation as above specified requires at least periodic
comparison of the input signals 32 and 40 by decision circuitry 34.
Where this or other operations are described herein as continual,
the scope of meaning to be ascribed includes both continuous (i.e.,
uninterrupted) or periodic (I.e., at discrete intervals).
As has been noted, the system 10 has a built-in controlled leakage
via exhaust port 24 thus assuring that the average flow signal will
be at least a small positive flow. During inhalation, the flow
sensed by the flow transducer will be the sum of exhaust flow via
port 24 and all other system leakage downstream of transducer 28,
and inhalation flow within the airway of the patient 12.
Accordingly, during inhalation the instantaneous flow rate signal
as conditioned by conditioning module 30, will reliably and
consistently reflect inhalation flow exceeding the average flow
rate signal. During exhalation, the flow within conduit 20 reverses
as exhalation flow from the lungs of the patient far exceeds the
flow capacity of exhaust port 24. Accordingly, exhalation air
backflows within conduit 20 past transducer 28 and toward pressure
controller 26. Since pressure controller 26 is operable to maintain
set pressure, it will act in response to flow coming from both the
patient and the flow generator to open an outlet port sufficiently
to accommodate the additional flow volume and thereby maintain the
specified set pressure as determined by action of decision
circuitry 34.
In both the inhalation and exhalation cycle phases, the pressure of
the gas within conduit 20 exerts a pressure within the airway of
the patient to maintain an open airway and thereby alleviate airway
constriction.
In practice, it may be desirable to provide a slight offset in the
switching level within decision circuitry 34 with respect to the
average flow rate signal, so that the system does not prematurely
switch from the low pressure exhalation mode to the higher pressure
inhalation mode. That is, a switching setpoint offset in the
positive direction from system average flow may be provided such
that the system will not switch to the IPAP mode until the patient
actually exerts a significant spontaneous inspiratory effort of a
minimum predetermined magnitude. This will ensure that the
initiation of inhalation is completely spontaneous and not forced
by an artificial increase in airway pressure. A similar switching
setpoint offset may be provided when in the IPAP mode to ensure the
transition to the lower pressure EPAP mode will occur before the
flow rate of air into the lungs of the patient reaches zero (i.e.,
the switch to EPAP occurs slightly before the patient ceases
inhalation.) This will ensure that the patient will encounter no
undue initial resistance to spontaneous exhalation.
From the above description, it will be seen that a novel method of
treating sleep apnea is proposed according to which the airway
pressure of the patient is maintained at a higher positive pressure
during inspiration and a relatively lower pressure during
expiration, all without interference with the spontaneous breathing
of the patient. The described apparatus is operable to provide such
treatment for sleep apnea patients by providing a flow of breathing
gas to the patient at positive pressure, and varying the pressure
of the air flow to provide alternately high and low pressure within
the airway of the patient coordinated with the patient's
spontaneous inhalation and exhalation.
To provide pressure control, the flow rate of breathing gas to the
patient is detected and processed to continually provide a signal
which is proportional to the instantaneous breathing gas flow rate
in the system. The instantaneous flow rate signal to further
processed to eliminate variations attributable to normal patient
respiration and other causes thus generating a signal which is
proportional to the average or steady state system gas flow. The
average flow signal is continually compared with the instantaneous
flow signal as a means to detect the state of the patient's
spontaneous breathing versus average system flow. When
instantaneous flow exceeds the average flow, the patient is
inhaling, and in response the pressure of gas flowing to the
patient is set at a selected positive pressure, to provide a
corresponding positive pressure within the airway of the patient.
When comparison of the instantaneous flow rate signal with the
average flow signal indicates the patient is exhaling, as for
example when the instantaneous flow signal indicates flow equal to
or less than the average flow, the pressure of breathing gas to the
patient is adjusted to a selected lower pressure to provide a
corresponding lower pressure within the airway of the patient.
In an alternative embodiment of the invention as shown in FIGS. 2
and 3, the low pass filter 38 is replaced by an estimated leak
computer which includes a low pass filter as well as other
functional elements as shown in FIG. 3. The remainder of the system
as shown in FIG. 2 is similar in most respects to the system shown
in FIG. 1. Accordingly, like elements are identified by like
numbers, and the description hereinabove of FIG. 1 embodiment also
applies generally to FIG. 2.
By using the operative capability of the estimated leak computer
50, as described hereinbelow, it is possible to adjust the
reference signal which is fed to decision circuitry 34 on a breath
by breath basis rather than merely relying on long term average
system flow. To distinguish this new reference signal from average
system flow it will be referred to hereinbelow as the estimated
leak flow rate signal or just the estimated leak signal.
As was noted hereinabove, the average system flow rate reference
signal changes very slowly due to the long time constant of the low
pass filter 38. This operative feature was intentionally
incorporated to avoid disturbance of the reference signal by
aberrant instantaneous flow rate signal inputs such as erratic
breathing patterns. While it was possible to minimize the impact of
such aberrations on the average flow rate reference signal, the
average flow signal did nevertheless change, although by small
increments and only very slowly in response to disturbances. Due to
the long time constant of the low pass filter, such changes in the
reference signal even if transitory could last for a long time.
Additionally, even a small change in the reference signal could
produce a very significant effect on system triggering. For
example, since the objective is to trigger the system to the IPAP
mode when inhalation flow just begins to go positive, small changes
in the reference signal could result in relatively large changes in
the breathing effort needed to trigger the system to IPAP mode. In
some instances the change in reference signal could be so great
that with normal breathing effort the patient would be unable to
trigger the system. For example, if the system were turned on
before placement of the mask an the face of the patient, the
initial free flow of air from the unattached mask could result in a
very large magnitude positive value for initial average system
flow. If such value were to exceed the maximum inspiratory flow
rate achieved in spontaneous respiration by the patient, the system
would never trigger between the IPAP and EPAP modes because the
decision circuitry would never see an instantaneous flow rate
signal greater than the average flow rate signal, at least not
until a sufficient number of normal breathing cycles after
application of the mask to the patient to bring the reference
signal down to a value more closely commensurate with the actual
system leak in operation. As has been noted, with the low pass
filter this could take a rather long time, during which time the
patient would be breathing spontaneously against a uniform positive
pressure. This would be tantamount to conventional CPAP and not at
all in keeping with the present invention.
In addition to the embodiment based on a reference signal derived
from estimated leak flow rate on a breath by breath basis which is
controlled totally by spontaneous patient breathing, two further
modes of operation also are envisioned, one being spontaneous/timed
operation in which the system automatically triggers to the IPAP
mode for just long enough to initiate patient inspiration if the
system does not sense inspiratory effort within a selected time
after exhalation begins. To accomplish this, a timer is provided
which is reset at the beginning of each patient inspiration whether
the inspiratory cycle was triggered spontaneously or by the timer
itself. Thus, only the start of inspiration is initiated by the
timer. The rest of the operating cycle in this mode is controlled
by spontaneous patient breathing and the circuitry of the system to
be described.
A further mode of operation is based purely on timed operation of
the system rather than on spontaneous patient breathing effort, but
with the timed cycles coordinated to spontaneous patient
breathing.
Referring to FIG. 3, the estimated leak computer 50 includes the
low pass filter 38 as well as other circuits which are operative to
make corrections the estimated leak flow rate signal based on
ongoing analysis of each patient breath. A further circuit is
provided which is operative to adjust the estimated leak flow rate
signal quickly after major changes in system flow such as when the
blower has been running prior to the time when the mask is first
put on the patient, or after a major leak the system has either
started or has been shut off.
The low pass filter 38 also includes a data storage capability
whose function will be described hereinbelow.
The low pass filter 38 operates substantially as described above
with reference to FIG. 1 in that it provides a long term average of
system flow which is commensurate with steady state system leakage
including the flow capacity of the exhaust port 24. This long term
average is operative in the FIG. 3 embodiment to adjust the
estimated leak flow rate reference signal only when system flow
conditions are changing very slowly.
To provide breath by breath analysis and adjustment of the
reference signal, a differential amplifier 52 receives the
instantaneous flow rate signal as indicated at 54, and the
estimated leak signal output from low pass filter 38 as indicated
at 56.
The output of differential amplifier 52 is the difference between
instantaneous flow rate and estimated leak flow rate, or in other
words estimated instantaneous patient flow rate. This will be clear
upon considering that instantaneous flow is the sum of patient flow
plus actual system leakage. The estimated patient flow signal
output from differential amplifier 52 is provided as indicated at
58 to a flow integrator 60 which integrates estimated patient flow
breath by breath beginning and ending with the trigger to IPAP.
Accordingly, an additional input to the flow integrator 60 is the
IPAP/EPAP state signal as indicated at 62. The IPAP/EPAP state
signal is the same as the drive signal provided to pressure
controller 26; that is, it is a signal indicative of the pressure
state, as between IPAP and EPAP, of the system. The state signal
thus may be used to mark the beginning and end of each breath for
purposes of breath by breath integration by integrator 60.
If the estimated leak flow rate signal from low pass filter 38' is
equal to the true system leak flow rate, and if the patient's
inhaled and exhaled volumes are identical for a given breath (i.e.,
total positive patient flow equals total negative patient flow for
a given breath), then the integral calculated by integrator 60 will
be zero and no adjustment of estimated leak flow rate will result.
When the integral calculated by integrator 60 is nonzero, the
integral value in the form of an output signal from integrator 60
is provided as indicated at 64 to a sample and hold module 66. Of
course, even with a zero value integral, an output signal may be
provided to module 66, but the ultimate result will be no
adjustment of the estimated leak flow rate signal.
A nonzero integral value provided to module 66 is further provided
to module 38' as indicated at 68 with each patient breath by
operative action of the IPAP/EPAP state signal upon module 66 as
indicated at 70 The effect of a nonzero integral value provided to
module 38' is an adjustment of the estimated leak flow rate signal
proportional to the integral value and in the direction which would
reduce the integral value towards zero on the next breath if all
other conditions remain the same.
With this system, if the patient's net breathing cycle volume is
zero, and if the system leak flow rate changes, the integrator
circuit will compensate for the change in leak flow rate by
incremental adjustments to the estimated leak flow rate within
about ten patient breaths.
The integrator circuit 60 also will adjust the estimated leak flow
rate signal in response to nonzero net volume in a patient
breathing cycle. It is not unusual for a patient's breathing volume
to be nonzero. For example, a patient may inhale slightly more on
each breath than he exhales over several breathing cycles, and then
follow with a deeper or fuller exhalation. In this case, the
integrator circuit would adjust the estimated leak flow rate signal
as if the actual system leak rate had changed; however, since the
reference signal correction is only about one tenth as large as
would be required to make the total correction in one breath, the
reference signal wild not change appreciably over just one or two
breaths. Thus, the integrator circuit accommodates both changes in
system leakage and normal variations in patient breathing patterns.
The integrator circuit normally would be active, for example,
during rapid patient breathing.
An end exhalation module 74 is operative to calculate another data
component for use in estimating the system leak flow rate as
follows. The module 74 monitors the slope of the instantaneous flow
rate wave form. When the slope value is near zero during exhalation
(as indicated by the state signal input 76) the indication is that
the flow rate is not changing. If the slope of the instantaneous
flow rate signal wave form remains small after more than one second
into the respiratory phase, the indication is that exhalation has
ended and that the net flow rate at this point thus is the leak
flow rate. However, if estimated patient flow rate is nonzero at
the same time, one component of the instantaneous flow rate signal
must be patient flow.
When these conditions are met, the circuit adjusts the estimated
leak flow rate slowly in a direction to move estimated patient flow
rate toward zero to conform to instantaneous patient flow
conditions expected at the end of exhalation. The adjustment to
estimated leak flow rate is provided as an output from module 74 to
low pass filter 38' as indicated at 80. When this control mechanism
takes effect, it disables the breath by breath volume correction
capability of integrator circuit 60 for that breath only.
The output of module 74 is a time constant control signal which is
provided to low pass filter 38' to temporarily shorten the time
constant thereof for a sufficient period to allow the estimated
leak flow rate to approach the instantaneous flop rate signal at
that specific instant. It will be noted that shortening the low
pass filter time constant increases the rapidity with which the low
pass filter output (a system average) can adjust toward the
instantaneous flow rate signal input.
Another component of estimated leak flow rate control is a gross
error detector 82 which acts when the estimated patient flow rate,
provided thereto as indicated at 84, is away from zero for more
than about 5 seconds. Such a condition may normally occur, for
example, when the Flow generator 14 is running before mask 22 is
applied to the patient. This part of the control system is
operative to stabilize operation quickly after major changes in the
leak rate occur.
In accordance with the above description, it will be seen that low
pass filter 38' acts on the instantaneous flow rate signal to
provide an output corresponding to average system flow, which is
system leakage since patient inspiration and expiration over time
constitutes a net positive flow of zero. With other enhancements,
as described, the system average flow can be viewed as an estimate
of leakage flow rate.
The differential amplifier 52 processes the instantaneous flow rate
signal and the estimated leak flow rate signal to provide an
estimated patient flow rate signal which is integrated and nonzero
values of the integral are fed back to module 38' to adjust the
estimated leak flow rate signal on a breath by breath basis. The
integrator 60 is reset by the IPAP/EPAP state signal via connection
62.
Two circuits are provided which can override the integrator
circuit, including end exhalation detector 74 which provides an
output to adjust the time constant of low pass Filter 38' and which
also is provided as indicated at 86 to reset integrator 60. Gross
error detector 82 is also provided to process estimated patient
flow rate and to provide an adjustment to estimated leak flow rate
under conditions as specified. The output of module 82 also is
utilized as an integrator reset signal as indicated at 86. It will
be noted that the integrator 60 is reset with each breath of the
patient if, during that breath, it is ultimately overridden by
module 74 or 82. Accordingly, the multiple reset capabilities for
integrator 60 as described are required.
In operation, the system may be utilized in a spontaneous
triggering mode, a spontaneous/timed mode or a purely timed mode of
operation. In spontaneous operation, decision circuitry 34
continuously compares the instantaneous flow rate with estimated
leak flow rate. If the system is in the EPAP state or mode, it
remains there until instantaneous flow rate exceeds estimated leak
flow rate by approximately 40 cc per second. When this transition
occurs, decision circuitry 34 triggers the system into the IPAP
mode for 150 milliseconds. The system will then normally remain in
the IPAP mode as the instantaneous flow rate to the patient will
continue to increase during inhalation due to spontaneous patient
effort and the assistance of the increased IPAP pressure
After the transition to the IPAP mode in each breath, a temporary
offset is added to the estimated leak flow rate reference signal.
The offset is proportional to the integral of estimated patient
flow rate beginning at initiation of the inspiratory breath so that
it gradually increases with time during inspiration at a rate
proportional to the patient's inspiratory flow rate. Accordingly,
the flow rate level above estimated leak flow needed to keep the
system in the IPAP mode during inhalation decreases with time from
the beginning of inhalation and in proportion to the inspiratory
flow rate. With this enhancement, the longer an inhalation cycle
continues, the larger is the reference signal below which
instantaneous flow would have to decrease in order to trigger the
EPAP mode. For example, if a patient inhales at constant 500 cc per
second until near the end of inspiration, a transition to EPAP will
occur when his flow rate drops to about 167 cc per second after one
second, or 333 cc per second after two seconds, or 500 cc per
second after three seconds, and so forth. For a patient inhaling a
constant 250 cc per second, the triggers would occur at 83, 167 and
250 cc per second at one, two and three seconds into IPAP,
respectively.
In this way, the EPAP trigger threshold comes up to meet the
inspiratory flow rate with the following benefits. First, it
becomes easier and easier to end the inspiration cycle with
increasing time into the cycle. Second, if a leak develops which
causes an increase in instantaneous flow sufficient to trigger the
system into the IPAP mode, this system will automatically trigger
back to the EPAP mode after about 3.0 seconds regardless of patient
breathing effort. This would allow the volume-based leak correction
circuit (i.e., integrator 60) to act as it is activated with each
transition to the IPAP mode. Thus, if a leak develops suddenly,
there will be a tendency toward automatic triggering rather than
spontaneous operation for a few breaths, but the circuit will not
be locked into the IPAP mode.
Upon switching back to the EPAP mode, the trigger threshold will
remain above the estimated leak flow rate approximately 500
milliseconds to allow the system to remain stable in the EPAP mode
without switching again while the respective flow rates are
changing.
After 500 milliseconds, the trigger threshold offset is reset to
zero to await the next inspiratory effort.
The normal state for the circuit is for it to remain in the EPAP
mode until an inspiratory effort is made by the patient. The
automatic corrections and adjustments to the reference signal are
effective to keep the system from locking up in the IPAP mode and
to prevent auto-triggering while at the same time providing a high
level of sensitivity to inspiratory effort and rapid adjustment for
changing leak conditions and breathing patterns.
In the spontaneous/timed mode of operation, the system per forms
exactly as above described with reference to spontaneous operation,
except that it allows selection of a minimum breathing rate to be
superimposed upon the spontaneous operating mode. If the patient
does not make an inspiratory effort within a predetermined time,
the system will automatically trigger to the IPAP mode for 200
milliseconds. The increased airway pressure for this 200
milliseconds will initiate patent inspiration and provide
sufficient time that spontaneous patient flow will exceed the
reference signal so that the rest of the cycle may continue in the
spontaneous mode as above described. The breaths per minute timer
is reset by each trigger to IPAP whether the transition was
triggered by the patient or by the timer itself.
In the timed operating mode, all triggering between IPAP and EPAP
modes is controlled by a timer with a breath per minute control
being used to select a desired breathing rate from, for example, 3
to 30 breaths per minute. If feasible, the selected breathing rate
is coordinated to the patients spontaneous breathing rate. The
percent IPAP control is used to set the fraction of each breathing
cycle to be spent in the IPAP mode. For example, if the breaths per
minute control is set to 10 breaths per minute (6 seconds per
breath) and the percent IPAP control is set to 33%, then the flow
generator will spend, in each breathing cycle, two seconds in IPAP
and four seconds in EPAP.
FIG. 4 illustrates control panel for controlling the system above
described and including a function selector switch which includes
function settings for the three operating modes of spontaneous,
spontaneous/timed, and timed as above described. The controls for
spontaneous mode operation include IPAP and EPAP pressure
adjustment controls 90 and 92, respectively. These are used for
setting the respective IPAP and EPAP pressure levels. In the
spontaneous/timed mode of operation, controls 90 and 92 are
utilized as before to set IPAP and EPAP pressure levels, and
breaths per minute control 94 additionally is used to set the
minimum desired breathing rate in breaths per minute. In the timed
mode of operation, controls 90, 92 and 94 are effective, and in
addition the percent IPAP control 96 is used to set the time
percentage of each breath to be spent in the IPAP mode,
Lighted indicators such as LED's 97, 98 and 100 are also provided
to indicate whether the system is in the IPAP or EPAP state, and to
indicate whether in the spontaneous/timed mode of operation the
instantaneous state of the system is spontaneous operation or timed
operation.
Additionally, it may be desirable to provide a flow compensation
signal to pressure controller 26 as indicated at 102 in FIG. 2 to
compensate for flow resistance inherent in the circuit; a
non-rebreathing valve may be utilized in lieu of exhaust port 24 at
mask 22, and the like.
Turning to FIG. 5, there is depicted a further embodiment of the
present invention, herein designated by reference numeral 10'. This
embodiment functions substantially as a mono-level CPAP apparatus
wherein the pressures of the breathing gas flow supplied to the
patients airway is substantially constant except when ramp control
circuitry means 104 or 104', described below in connection with
FIGS. 7A and 7B, is activated by the patient, through manipulation
of a suitable mechanical actuator such as a switch, a button, or
the like, provided on the housing of the apparatus 10' or on remote
control 106 to produce one or more output pressure "ramp
cycles."
The embodiment of the instant invention illustrated in FIG. 6
operates much like the embodiment revealed in FIG. 1, i.e., a
bi-level CPAP apparatus. Apparatus 10", however, like apparatus 10'
shown in FIG. 5, also includes remote control 106 and ramp control
circuitry means 104 or 104'.
According to the preferred embodiments, the ramp control circuitry
means 104 (FIG. 7A) or 104' (FIG. 7B) provides full prescription
pressure on apparatus activation or "start up" and controls the
parameters of magnitude, duration and pressure output pattern or
"shape" of both the initial ramp cycle and any additional ramp
cycles. Unlike other CPAP apparatus having ramp capability wherein
a ramp cycle automatically commences upon apparatus start up,
apparatus 10' or 10" incorporating ramp control circuiting means
104 or 104' outputs pressure at full prescription pressure (which
is preset by the patient's overseeing health care professional)
until conscious activation of the initial ramp cycle by the
patient. This allows the patient to check for system leaks
immediately following start up. Alternatively, ramp control
circuitry means 104 or 104' may be so configured such that it
automatically commences a ramp cycle upon apparatus startup. The
commonality to all embodiments of the ramp control circuitry means
being, however, that at least those ramp cycles subsequent to
initial ramp cycle be selectively activatable by the patient via
means to be described hereinbelow. As will be more fully
appreciated from the following, the apparatus 10' or 10" equipped
with ramp control circuitry means 104 or 104' permits the patient
to not only control the aforesaid parameters of the ramp cycles
(which, to provide optimum treatment effectiveness may need to be
adjusted daily) but the commencement times of the ramp cycles as
well.
Turning first to FIG. 7A the ramp cycles produced by the ramp
control circuitry means 104 are generated by using a clock 108 to
drive a counter 110. The counter 110 increments for each rising
edge of the clock 108 and the output of the counter, which is
influenced by a number of factors described hereinafter, is
transmitted to a digital to analog converter 112. Other suitable
means, however, such as a microprocessor may be used in place of
digital to analog convertor 112 if desired. The analog output of
the converter is added at juncture 114 to the minimum pressure
setting that is input via an adjustable minimum pressure setting
control 116 and thereafter transmitted to the pressure controller
26 to provide a pressure ramp cycle.
A ramp actuator 118, typically a user-manipulable button, switch,
or the like, is operated to effect commencement of a ramp cycle,
whether such cycle be the initial or a subsequent cycle. One such
ramp actuator is desirably provided on both the apparatus 10' or
10" and the remote control 106. The same arrangement is also
preferred for the apparatus power "on/off" actuator. Whether
provided on the remote control or apparatus 10' or 10" it is
preferred that the power actuator (not shown) be substantially
different in physical configuration than that of the ramp actuator
such that a patient is provided visual and tactile feedback and can
readily and reliably identify and operate the actuators either by
sight or sense of touch. For purposes of illustration, both the
power actuator and ramp actuator will be understood to be
depressible buttons; however, their possible physical
manifestations are not intended nor should they be construed to be
limited exclusively thereto. Upon depression of the power actuator
button, a control logic means 120 selects the patient's
prescription pressure as determined by the patient's sleep study as
the start-up pressure. The prescription pressure is initially input
by the physician or other health care professional into the ramp
control circuitry means 104 via a prescription pressure setting
control 122 which permits establishment and subsequent adjustment
of the magnitude of the prescription pressure. A ramp time setting
control 124 such as, for example, a rotary switch or other suitable
control, is also provided (preferably internally of the apparatus
housing to prevent patient tampering) and it, too, is normally set
by the health care professional to establish the appropriate ramp
time of the first ramp cycle of the apparatus 10' or 10", i.e.,
that ramp cycle which is employed when a patient first seeks to
fall asleep, such as at bed time. The appropriate ramp time for the
first ramp cycle is also determined from data gathered in
connection with the patient's sleep study. A typical duration or
"ramp time" of the initial ramp cycle may be up to as high as 45
minutes or even more.
As the patient becomes gradually accustomed to using the CPAP
apparatus and/or realizes benefits from the CPAP therapy, it is
common for the patient to require less time to initially fall
asleep when using the apparatus than when the patient first began
CPAP treatment. Consequently, when using any CPAP apparatus
equipped with the ramp control circuitry means of the present
invention, a need occasionally arises for the initial ramp time
setting to be adjusted (typically to a lesser duration than that
initially set by the health care professional). Since it is
oftentimes inconvenient or impractical for the patient to meet with
his or her health care professional for necessary readjustments of
the ramp time setting control 124, the ramp control circuitry means
of the present invention further desirably comprises a percent ramp
time setting control 126 that is accessible by the patient and
adjustable to produce for the initial ramp cycle a modified initial
ramp time that is a fraction of the initial ramp time last
established by the health care professional via ramp time setting
control 124. Percent ramp time setting control 126, preferably a
rotary switch or the like, is adjustable to produce initial ramp
times ranging from a minimum of from about 0 to 20% up to and
including a maximum of 100% of the initial ramp time preset by the
health care professional.
Frequently, a patient awakens during a period of extended sleep for
any number of reasons. And, as is generally the case, the time
required for a patient to fall back to sleep once awakened is less
than that initially required. To accommodate this particular
phenomenon, the ramp control circuitry means 104 (and 104' of FIG.
7B) of the present invention preferably include an additional
ramp(s) time setting control 127 that is adjustable to produce in
ramp cycles subsequent to the initial ramp cycle (the duration of
which is established by the setting of control 124 as modified by
the setting of control 126) ramp times ranging from a minimum of
from about 0 to 20% of the initial ramp cycle time up to and
including a maximum of 100% of the initial ramp cycle time. The
ramp circuitry control means 104 and 104' are thus designed such
that upon activation of any ramp cycle subsequent to the initial
ramp cycle the apparatus 10' or 10" executes a ramp cycle lasting
for a duration established by the setting of the additional ramp(s)
time setting control 127. Hence, the patient is not only assisted
in falling back to sleep by the gradual increase in CPAP pressure
but also is more quickly treated by the beneficial prescription
pressure once he does again fall asleep due to the generally
shorter duration of the subsequent ramp cycle(s) relative to the
initial ramp cycle. The additional ramp(s) time setting control 127
is preferably readily accessible by the patient yet not in area
where it is likely to be inadvertently bumped or changed.
Looking to FIG. 7A, it is revealed that the ramp control circuitry
means 104 also preferably include an adjustable ramp pressure
output pattern control 128 for establishing a predetermined pattern
of pressure output from pressure controller 26 during progression
in a ramp cycle from the minimum ramp pressure set by minimum
pressure setting control 116 and the maximum ramp pressure
(prescription pressure) set by the prescription pressure setting
control 122. In FIG. 7B, the virtual structural and functional
equivalent of ramp pressure output pattern control 128 is the first
ramp pressure output pattern control 128'. Either of controls 128
or 128' are operable by the health care professional or the patient
to establish the selected pattern by which the pressure controller
26 outputs pressurized air during any ramp cycle in the case of
ramp control circuitry means 104 or during the first ramp cycle in
the case of ramp control circuitry means 104'. Thus, the controls
128 and 128' serve to establish the "shape" of the ramp curve as a
function of output pressure versus ramp time. Because of controls
128 and 128', essentially any desired pattern of ramp output
pressure may be selected, examples of which will be discussed later
by reference to FIGS. 8A, 8B and 8C. In further connection
therewith, ramp circuitry control means 104' of FIG. 7B is
distinguished from ramp circuitry control means 104 of FIG. 7A by
virtue of an adjustable component identified as additional ramp(s)
pressure output pattern control 130. The function of this
particular control is to enable an operator to form the pressure
output pattern of ramp cycles subsequent to the initial ramp cycle
into a pattern different therefrom. To illustrate, the initial ramp
pattern established by the first ramp pressure output control 128'
may be, for example, substantially linear in slope, whereas the
subsequent ramp pattern established by the additional ramp(s)
pressure output pattern control 130 may be, inter alia, curvilinear
or stepped in slope.
The operation of ramp circuitry control means 104 is essentially as
follows. Once the apparatus 10' or 10" within which means 104 is
incorporated is powered and discharging pressurized air at
prescription pressure, a first depression of ramp actuator button
118 results in transmission of a signal to control logic means 120
causing the control logic means to commence a first ramp cycle.
When activated, the first ramp cycle effects a drop in output
pressure to the minimum pressure setting determined by the position
of minimum pressure setting control 116 (typically approximately
2.5 cm H.sub.2 O) over a period of up to 5 seconds (normal
motor-blower run down). Upon reaching the minimum pressure, the
output pressure from pressure controller 26 begins to increase and
continues to increase for the period of time assigned by the ramp
time setting control 124 as modified by percent ramp control 126 in
accordance with the predetermined pattern dictated by the ramp
pressure output control 128 until the prescription pressure is
attained. Thereafter, the output pressure remains at the
prescription pressure in the mono-level CPAP apparatus 10' depicted
in FIG. 5, while in bi-level CPAP apparatus 10" shown in FIG. 6 the
IPAP pressure level remains at the prescription pressure except
where the prescription pressure is further modified by the IPAP
pressure adjustment control 90 (FIG. 4).
Upon a second or any subsequent depression of the ramp actuator
button 118 there is transmitted to the control logic means 120 a
signal directing same to commence another ramp cycle whose duration
is determined not only by the setting of the ramp time setting
control 124 and percent ramp time setting control 126 but also by
that of the additional ramp(s) time setting control 127, the
influence of such control 127 being selectively overridden by
control logic means 120 during the initial ramp cycle. It will be
appreciated that the pattern or shape of the pressure output curve
of any additional ramp cycle is determined by the setting of ramp
pressure output pattern control 128 except that such pattern will
be compressed in proportion to the fraction of the initial ramp
time chosen by the setting of the additional ramp(s) time setting
control 127.
The ramp control circuitry means 104' illustrated in 7B operates
essentially identically to its counterpart of FIG. 7A, the primary
difference being that ramp control circuitry means 104', via the
additional ramp(s) pressure output pattern control 130, enables the
pressure pattern of the second and any other additional ramp cycles
to differ from that of the initial ramp cycle. As an example, where
the first ramp pressure output pattern control 128' may be adjusted
so as to produce a substantially linear slope output pressure
pattern, the additional ramp(s) pressure output pattern control 130
may be selectively adjusted so as produce a stepped, curved or
still other pressure output pattern different from the
substantially linear slope of the first ramp cycle, as may be
desired or necessary.
FIG. 8A, 8B and 8C reveal exemplary shapes of pressure output
patterns which may be selected for the first 132 and subsequent 134
ramp cycles, namely, substantially linear slope in FIG. 8A,
curvilinear in FIG. 8B and stepped in FIG. 8C. It will be
appreciated that the pressure output patterns may assume virtually
any desired configuration to best suit a particular patient's
requirements and, as noted hereabove, the second and subsequent
ramp patterns may differ from their associated initial ramp
cycles.
Although the invention has been described in detail for the purpose
of illustration, it is to be understood that such detail is solely
for that purpose and that variations can be made therein by those
skilled in the art without departing from the spirit and scope of
the invention except as it may be limited by the claims.
* * * * *