Note: Descriptions are shown in the official language in which they were submitted.
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TITLE -
SLEEP APNEA TREATMENT APPARATUS AND HUMIDIFIER
This is a divisional application of co-pending
application 2,196,918, filed June 6, 1996.
FIELD OF THE INVENThON
The present invention relates generally to
methodology and apparatus for treatment of sleep apnea
and, more particularly, to mono-level, bi-level and
variable positive airway pressure apparatus.
BACKGROUND OF THE INVENTION
The sleep apnea syndrome afflicts an estimated
1% to 5% 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 desaturation. These features may be
translated clinically into extreme daytime sleepiness,
cardiac arrhythmias, pulmonary-artery hypertension,
congestive heart failure and/or 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
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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
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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.
Patent 4,655,213 discloses sleep apnea treatments based on
continuous positive airway pressure applied within the
airway of the patient.
An early mono-level CPAP apparatus is disclosed
in U. S. Pat. No. 5,117,819 wherein the pressure is
measured at the outlet of the blower so as to detect
pressure changes caused by the patient's breathing. The
arrangement is such that the control motor is regulated by
the microprocessor to maintain the pressure at constant
level regardless of whether the patient is inhaling or
exhaling.
Also of interest is U. S. Patent 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.
U. S. Patent Nos. 5,245,995 5,199,424, and
5,335,654, and published PCT Application No. WO 88/10108
describes a CPAP apparatus which includes a feedback/
diagnostic 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. The apparatus disclosed in
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K ,
these documents further include means for reducing they
CPAP level to a minimum level to maintain unobstructed
breathing in the absence of breathing patterns indicative
of obstructed breathing, e.g., snoring.
Bi-level positive airway therapy for treatment
of sleep apnea and related disorders is taught in U. S.
Patent No. 5,148,802. In bi-level therapy, pressure is
applied alternately at relatively higher and lower
prescription pressure levels within the airway of the
patient so that the pressure-induced patent force applied
to the patients airway is alternately a larger and a
smaller magnitude force. The higher and lower magnitude
positive prescription pressure levels, which will be
hereinafter referred to by the acronyms IPAP (inspiratory
positive airway pressure) and EPAP (expiratory positive
airway pressure), may be initiated by spontaneous patient
respiration, apparatus preprogramming, or both, with the
higher magnitude pressure (IPAP) being applied during
inspiration and the lower magnitude pressure (EPAP) being
applied during expiration. This method of treatment may
descriptively be referred to as bi-level therapy. In
bi-level therapy, it is EPAP which has the greater impact
upon patient comfort. Hence, the treating physician must
be cognizant of maintaining EPAP as low as is reasonably
possible to maintain sufficient pharyngeal patency during
expiration, while optimizing user tolerance and efficiency
of the therapy.
Both inspiratory and expiratory air flow
resistances in the airway are elevated during sleep
preceding the onset of 'apnea, although the airway flow
resistance may be less during expiration than during
inspiration. Thus it follows that the bi-level therapy as
characterized above should be sufficient to maintain
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pharyngeal patency during expiration even though the
pressure applied dining expiration is generally 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, depending upon a particular patient's
breathing requirements, elevated pressure may be applied
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
mono-level CPAP.
Although mono-level, bi-level and variable
positive airway pressure therapy has been found to be very
effective and generally well accepted, they suffer 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
positive airway pressure well. Thus, development of other
viable non-invasive therapies and better versions of
existing therapies has been a continuing objective in the
art.
In this regard, even the more sophisticated CPAP
apparatus heretofore known in the art, including those
described in U. S. Patent Nos. 5,245,995 5,199,424, and
5,335,654, and published PCT Application No. WO 88/10108,
suffer from certain operational disadvantages which stem
from the structural relationships of their essential
components.
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More particularly, the CPAP apparatus disclosed
in U. S. Patent Nos. 5,245,995 5,199,424, and 5,335,654,
and published PCT Application No. WO 88/10108 provide
feedback/diagnostic systems including at least one sensor
(typically an audio transducer such as a microphone) in
communication with the patient's respiratory system. This
sensor is located on or is connected to means (such as a
breathing mask or nasal prongs) in sealed air
communication with a patient's respiratory system. The
sensor continuously senses the patient's breathing
patterns and transmits signals indicative of those
patterns to information processing means which control the
motor speed of a blower. The breathing pattern signals
can also be continuously monitored and/or recorded,
thereby imparting to the apparatus a diagnostic as well as
therapeutic capability.
The blower delivers pressurized air to the
patient through a length of conduit and the breathing mask
or nasal prongs. When the sensor detects breathing
patterns indicative of obstructed breathing, e.g.,
snoring, it transmit signals corresponding to this
condition to the information processing means which causes
an increase in blower motor speed and, therefore, blower
pressure output, until unobstructed breathing is
eliminated. The system also includes logic whereby blower
motor speed (and blower pressure output) is gradually
decreased if unobstructed breathing patterns are detected
over a preselected period of time. The purpose of this
feature is to provide the patient with a pressure
minimally sufficient to maintain airway patency during
unobstructed breathing, thereby enhancing patient comfort ~...
and therapy compliance.
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Despite the general effectiveness of these
apparatus, however, the structural relationship of their
feedback/diagnostic system with respect to the patient's
breathing circuit (i.e., the blower, gas delivery conduit,
and breathing mask or nasal prongs) results in an
arrangement of lesser reliability than would otherwise be
desirable.
For example, certain feedback/diagnostic systems
utilize a breathing pattern sensor mounted on or connected
to the breathing mask or nasal prongs. Such an
arrangement requires a length of feedback conduit to be
added to the patient's breathing circuit. The feedback
conduit extends from the breathing patterns sensor at the
mask to the blower.
Such an added feedback conduit renders the
patient's breathing circuit cumbersome and increases the
risk of entanglement of the feedback circuit. The
arrangement also increases the risk of the feedback
conduit becoming kinked or having the conduit accidently
disconnected from the breathing mask, either of which
render the device inoperable. Such a feedback conduit
also requires frequent cleaning because it is in contact
with the patient's expired air.
An advantage exists, therefore, for an apparatus
for delivering pressurized air to the airway of a patient
which includes a feedback/diagnostic system of higher
reliability and increased ease of use, whereby diagnostic
accuracy and patient comfort and adherence to the therapy
administered by the apparatus are optimized.
A problem associated with positive airway
pressure devices is a lack of moisture in the air
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v
delivered-by these devices has a drying-effect on patient
airways which causes the patient. to have considerable
discomfort and difficulty sleeping.
Humidifiers have been developed for use with
CPAP devices to humidify the air supplied to the patient.
In the type of system according to the present invention
in which the sensor is situated generally at an end of the
breathing circuit remote from the patient any type of
accessory such as a humidifier may attenuate or absorb
snore sound.
Humidifiers for use with CPAP apparatus are
taught in U.S. Patent Nos. 4,807,616 and 5,231,979. Other
humidifiers of interest are manufactured by Respironics,
Inc. of Murrysville, Pennsylvania and Healthdyne
Technologies. However, these humidifiers are for use with
conventional CPAP apparatus and therefore are not
configured to acoustically tune snoring sound as required
for use with the unique sleep apnea treatment apparatus of
the present invention.
An advantage exists, therefore, for a humidifier
which is configured to acoustically tune the snoring sound
received from a patient in order to set the resonant
frequency of the snore sound.
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
improved treatment method. The invention contemplates the
treatment of sleep apnea through application of pressure
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at variance with ambient atmospheric pressure within the
upper airway of the patient in a manner to promote patency
of the airway to thereby relieve upper airway occlusion
during sleep.
According to the invention, positive pressure
may be applied at a substantially constant, "mono-level,"
patient-specific prescription pressure, at alternatively
higher (IPAP) and lower (EPAP) "bi-level" pressures, or at
variable pressures within the airway of the patient to
maintain the requisite patent or "splint" force to sustain
respiration during sleep periods.
In all embodiments considered to be within the
scope of the instant invention, the apparatus for
delivering pressurized breathing gas to the airway of a
patient comprises a breathing gas flow generator,
information processing means for controlling the output of
the gas flow generator, and a length of flexible conduit
connected at one end to the gas flow generator and at an
opposite end to a patient interface means such as a
breathing mask or nasal prongs. By controlling the output
of the gas flow generator, the information processing
means likewise controls the pressure of the breathing gas
delivered to the patient through the flexible conduit and
the patient interface means.
The apparatus further includes a novel feedback
system which may impart both therapeutic as well as
diagnostic capability to the apparatus. The feedback
system includes at least one sensor means, such as a
pressure or flow responsive transducer, located on, within
or closely adjacent to the gas flow generator. The sensor
means continuously senses the patient's breathing patterns
and transmits signals indicative of those patterns to the
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r,
information processing means. The apparatus may also
include means whereby these signals can also be
continuously monitored and/or recorded whereby the
patient's specific breathing disorder may be diagnosed as
well as treated by the apparatus.
Like the feedback/diagnostic systems known in
the art, when the sensor detects breathing patterns
indicative of obstructed breathing, it transmits signals
corresponding to this condition to the information
processing means. This means, which may be any suitable
microprocessor or central processing unit (CPU), then
causes the flow generator to increase its output which
increases the. air pressure delivered to the patient until
obstructed breathing is no longer detected. The system
also includes logic whereby the flow generator output is
gradually decreased if unobstructed breathing patterns are
detected over a preselected period of time. This feature
serves to provide the patient with a pressure minimally
sufficient to maintain airway patency during unobstructed
breathing, thus enhancing patient comfort and therapy
compliance.
Unlike other positive airway pressure apparatus
equipped with feedback/diagnostic systems including a
breathing patterns sensor located on or connected to the
patient interface, the apparatus according to the present
invention finds its breathing patterns sensor situated
generally at the end of the breathing circuit remote from
the patient. That is, the sensor is preferably located
within, on or is connected closely adjacent to the outlet
of the gas flow generator controller. Situating the
breathing patterns sensor at this region of the breathing
circuit realizes considerable improvements in apparatus
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performance characteristics and 'in particular sensor
reliability and ease of use.
More specifically, by distancing the breathing
patterns sensor from the patient interface (i.e., the
breathing mask or nasal prongs), that portion of the feedback conduit
along the patient's breathing circuit is eliminated, and
only a relatively shorter feedback conduit is required and
is provided. Consequently, the patient's breathing circuit
is rendered considerably less cumbersome, the risk of
entanglement is negatived, and any annoyance of the
patient is minimized. The length of the shorter feedback
conduit reduces, if not totally eliminates, the risk of
being kinked or accidently disconnected from the patient's
breathing circuit. Additionally, frequent cleaning of the
shorter feedback conduit is not required because it is not
in direct contact with the patient's expired air. The
shorter feedback conduit also reduces the materials cost
for the system.
Admittedly, placement of the breathing patterns
sensor substantially at or near the gas flow generator
reduces the responsiveness of the apparatus to the
patient's continually changing respiratory needs. However
the reduction in responsiveness of the breathing patterns
sensor is compensated for by resonant tuning of the
system. That is, the frequency response of the patient's
breathing circuit and internal tubing of the present
system is acoustically tuned to optimally transmit sounds
with frequency content which is known to be indicative of
upper airway obstructions. Thus the tuned resonance is
such that sounds (snores) with frequencies near the
resonant frequency are amplified, thus boosting the
signal-to-noise ratio (more accurately the ratio of snore
noise to gas flow generator noise) back to the level which
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a r
is comparable to that which has been obtained by sensing
at the patient interface. As illustration, a patient's
lack of demand or -~a reduced demand for inspiratory air
often precedes, frequently by several seconds, by the
S onset of an audible snore or other pronounced physical
manifestation indicative of obstructed breathing. The
breathing pattern sensors typically must detect such
salient occurrences before they register an obstructed
breathing event. In such case, the sensor would transmit
data to the CPU such that the CPU could step up the output
of the flow generator well in advance of not only an
apneic event but also prior to the characteristic audible
snore patterns which normally precede such an event.
Known breathing pattern sensors typically accomplish this
while being located on or connected to the patient
interface. The sensor of the present invention, on the
other hand, may be an equally responsive pressure or flow
transducer sensitive to pressure or flow variations of any
selected magnitude and/or frequency, but located within,
on or connected closely adjacent to the outlet of the gas
flow generator.
In order to prevent drying of the breathing
passage during the administration of pressurized air
delivered by the flow generator of the present invention,
it is desirable to use the present invention in
combination with a humidifier. A problem associated with
using a humidifier with the breathing pattern sensor of
the present invention is the humidifier may attenuate or
absorb snore sound. This and other problems have been
solved by the humidifier in the present invention which
includes a U-shaped accumulation chamber which is
configured to acoustically tune the snoring sound received
from a patient.
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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:
Figure 1 is a functional block diagram of a
prior art CPAP apparatus including a patient feedback/
diagnostic system;
Figure 2 is a functional block diagram showing a
preferred embodiment of the present invention;
Figure 3 is a functional block diagram of a
further preferred embodiment of the present invention;
Figure 4 is a view schematically illustrating a
preferred embodiment of the present invention;
Figure 5 is a view schematically illustrating
the sleep apnea treatment apparatus of the present
invention in use with a humidifier of the present
invention;
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f~.
Figure 6 is a perspective view of a humidifier
of a first embodiment of the present invention showing a
humidifier top and a humidifier base in assembled
condition; and
Figure 7 is a plan view of a humidifier top of a
presently preferred second embodiment viewed from the
bottom.
DETAILED DESCRIPTION OF THE IN~IENTION
There is generally indicated at 10 in Figure 1,
in the form of a functional block diagram, a mono-level
CPAP apparatus including a patient feedback/diagnostic
system generally and schematically representative of the
apparatus disclosed in U. S. Patent Nos. 5,245,995
5,199,424, and 5,335,654, and published PCT Application
No. WO 88/10108.
Apparatus 10 includes a blower 12 driven by an
electric blower motor 14. The speed of motor 14 and thus
the output of the blower 12 is controlled by an
information processing means or central processing unit
(CPU) 16. The output of the blower is connected by a
suitable length of flexible gas delivery conduit means 18
to a patient interface means 20 such as, for example,
nasal prongs or, as illustrated, a breathing mask which is
in sealed air communication with the airway of a patient
22. If constructed as a breathing mask the patient
interface means 20 may include suitable exhaust port
means, schematically indicated at 24, for exhaust of.~
breathing gas during expiration. Exhaust port means 24
may be a conventional non-rebreathing valve or one or more
continuously open ports which impose a predetermined flow
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resistance against exhaust gas flow. Apparatus 10 also
includes a suitable pressure transducer 26 located on or
connected to the patient interface means 20. Typically,
the pressure transducer 26 is an audio transducer or
microphone. When, for example, snoring sounds occur the
pressure transducer detects the sounds and feeds
corresponding electrical signals to the CPU 16 which, in
turn, generates a flow generator motor control signal.
Such signal increases the speed of the flow generator
motor, thereby increasing output pressure supplied to the
patient by the blower 12 through conduit means 18 and the
patient interface means 20. The system may include
suitable data storage and retrieval means (not
illustrated) which may be connected to CPU 16 to enable
medical personnel to monitor and/or record the patient's
breathing patterns and thereby diagnose the patient's
particular respiratory disorder and breathing
requirements.
As snoring is caused by vibration of the soft
palate, it is therefore indicative of an unstable airway
and is a warning signal of the imminence of upper airway
occlusion in patients that suffer obstructive sleep apnea.
Snoring is itself undesirable not only as it is a
disturbance to others but it is strongly believed to be
connected with hypertension. If the resultant increase in
system output pressure is sufficient to completely
stabilize the airway, snoring will cease. If a further
snoring sound is detected, the pressure is again
incrementally increased. This process is repeated until
the upper airway is stabilized and snoring ceases. Hence,
the occurrence of obstructive apnea can be eliminated by
application of minimum appropriate pressure at the time of
use.
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The feedback circuit also includes means toy
gradually decrease the output pressure if an extended
period of snore-free breathing occurs in order to ensure
that the pressure is maintained at a level as low as
practicable to prevent the onset of apnea. This effect
can be achieved, for example, by the CPU 16 which, in the
absence of an electronic signal from the pressure
transducer 26 indicative of snoring, continuously and
gradually reduces the flow generator speed and output
l0 pressure over a period of time. If, however, a snore is
detected by the first pressure transducer, the CPU will
again act to incrementally increase the output of the flow
generator. The feedback circuit of the present invention
as will be discussed hereinafter in connection with Figure
2 preferably includes similar means.
In use, a patient using apparatus 10 may connect
himself to the apparatus and go to sleep. The output
pressure is initially at a minimum operating value of, for
example, approximately 3 cm H20 gauge pressure so as not
to cause the previously mentioned operational problems of
higher initial pressures. Not until some time after going
to sleep, the patient's body relaxes, will the airway
start to become unstable and the patient begin to snore.
The pressure transducer 26 will then respond to a snore,
or snore pattern, and via the CPU 16 increase the blower
motor speed such that output pressure increases, for
instance, by 1 cm H20 for each snore detected. The
pressure can be increased relatively rapidly, if the
patient's condition so requires, to a working pressure of
the order of 8-20 cm, which is a typical requirement.
Additionally, for ease of monitoring the variation over
time a parameter such as pressure output can be recorded
in some convenient retrievable form and medium (such as
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the aforesaid data storage and retrieval means) for
periodic study by medical personnel.
If for example in the early stages of sleep some
lesser output pressure will suffice, apparatus 10 will not
increase the pressure until needed, that is, unless the
airway becomes unstable and snoring commences, no increase
in airway pressure is made. By continuously decreasing
the output pressure at a rate of, for example, 1 cm H20
each 15 minutes in the absence of snoring, the pressure is
never substantially greater than that required to prevent
apnea.
The feedback circuit of Figure 1 provides a
system which adjusts apparatus output pressure according
to variations in a patient's breathing requirements
throughout an entire sleep period. Further, apparatus 10
will likewise accommodate variable output pressure
requirements owing to general improvements or
deteriorations in a patient's general physical condition
as may occur over an extended period of time.
Despite the general effectiveness of apparatus
10, however, the structural relationship of its
feedback/diagnostic system with respect to the patient's
breathing circuit (i.e., the blower, gas delivery conduit,
and breathing mask) results in an arrangement which can be
cumbersome to use, inconvenient to maintain, and of lesser
reliability.
The present invention overcomes deficiencies of
cur_~ently available positive airway pressure apFaratus
such as apparatus 10 by proposing a novel
feedback/diagnostic system which is adapted for use in
mono-level, bi-level and variable output positive airway
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pressure apparatus. Although for brevity the invention
will be described in detail as it may be adapted to
mono-level positive airway pressure apparatus, it is
further contemplated that the particulars of the present
invention may also be gainfully adapted to equally
preferred embodiments including bi-level and variable
positive airway pressure apparatus, the general
characteristics and functions of which are well known in
the art. However, the particulars of the "bi-level" and
"variable" positive airway pressure apparatus embodiments
of the present invention will not be described at length.
Consequently, it will nevertheless be understood that the
presently proposed arrangement and operation of the
feedback/diagnostic system components with respect to the
breathing circuit will be substantially the same for a
"bi-level" and "variable" positive airway pressure
apparatus as those discussed hereinafter in connection
with the "mono-level" embodiment of the invention.
Referring to Figure 2, there is illustrated in
the form of a functional block diagram, an apparatus 110
representing perhaps the simplest of the presently
preferred embodiments of the invention contemplated by
applicants. Apparatus 110 includes a gas flow generator
114 (e.g., a blower) which receives breathing gas from any
suitable source such as a pressurized bottle or the
ambient atmosphere.
Located substantially at, i.e., within, on or
connected closely adjacent to, the outlet of the gas flow
generator 114 is a sensor means 126 in fluid communication
with a flexible gas delivery conduit means 118. One end ~
of conduit 118 is connected to the outlet of the gas flow
generator 114. The conduit 118 communicates the output of
the gas flow generator 114 to a patient interface means or
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breathing appliance 120 that is connected to the opposite
end of the conduit 118. The patient interface means 120
may be a mask of any suitable known construction which is
worn by patient 122 and is in sealed communication with
the patient's airway. The patient interface means 120 may
preferably be a nasal mask or a full face mask as
illustrated and hereinafter referred. Other breathing
appliances which may be used in lieu of a mask may include
nasal cannulae, an endotracheal tube, or any other
suitable appliance for interfacing between a source of
breathing gas and a patient.
The mask 120 includes suitable exhaust port
means, schematically indicated at 124, for exhaust of
breathing gases during expiration. Exhaust port means 124
preferably is a continuously open port provided in the
mask 120 or a non-rebreathing valve (NRV) situated closely
adjacent the mask in conduit 118. The exhaust port means
imposes a suitable flow resistance upon exhaust gas flow
to permit an information processing means or central
processing unit (CPU) 130, which receives signals
generated by sensor means 126 as indicated at 128, to
control the output of the gas flow generator in a manner
to be described at greater length hereinafter.
The exhaust port means 124 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 means 124 is one component, and typically the
major component of the overall system leakage, which is an
important parameter of system operation.
Sensor means 126 preferably comprises at least
one suitable pressure or flow transducer which
continuously detects pressure or flow discharge
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substantially at the outlet of the-gas flow generator,'-
which pressure or flow reflects the patient's breathing
patterns. Concurrently, the sensor means 126 generates
output signals 128 corresponding to the continuously
detected gas pressure or flow from the gas flow generator
114 and transmits these signals to a pressure or flow
signal conditioning circuit of the CPU 130 for derivation
of a signal proportional to the instantaneous pressure or
flow rate of breathing gas within conduit 118. Such flow
or pressure signal conditioning circuit may for example be
of the type described in U. S. Patent No. 5,148,802.
Depending upon the characteristics of the
conditioned flow or pressure signal, the CPU may generate
a command signal 132 to either increase or decrease the
output of the gas flow generator 114, e.g., to increase or
decrease the speed of an electric motor (not illustrated)
thereof. The gas flow generator 114, sensor means 126 and
CPU 130 thus comprise a feedback circuit or system capable
of continuously and automatically controlling the
breathing pressure supplied to the patient's airway
responsive to the patient's respiratory requirements as
dictated by the patient's breathing patterns.
Like the feedback/diagnostic systems known in
the art, when the sensor means 126 detects breathing
patterns indicative of obstructed breathing, it transmits
signals corresponding to this condition to the CPU 130.
The CPU then causes the gas flow generator 114 to increase
its output which increases the air pressure delivered to
the patient until obstructed breathing is no longer
detected. The system also includes means such as
appropriate logic programmed into the CPU whereby the gas
flow generator output is gradually decreased if
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unobstructed breathing patterns are detected over a
preselected period of time. This feature serves tc
provide the patient with a pressure minimally sufficient
to maintain airway patency during unobstructed breathing,
thus enhancing patient comfort and therapy compliance.
In many respects, therefore, the feedback
circuit of the present invention performs similarly to the
feedback circuits disclosed in previously discussed U. S.
Patent Nos. 5,245,995 and 5,199,424 and published PCT
Application No. WO 88/10108. However, by situating the
sensor means 126 proximate the outlet of the gas flow
generator rather than proximate the patient interface
means 120 many significant benefits in apparatus
performance are realized, which translate into increased
patient comfort and therapy compliance.
Admittedly, placement of the breathing patterns
sensor substantially at or near the gas flow generator
reduces the responsiveness of the apparatus to the
patient's continually changing respiratory needs. However
the reduction in responsiveness of the breathing patterns
sensor is compensated for by resonant tuning of the
system. That is, the frequency response of the patient's
breathing circuit and internal tubing of the present
system is acoustically tuned to optimally transmit sounds
with frequency content which is known to be indicative or
upper airway obstructions. Thus the tuned resonance is
such that sounds with frequencies near the resonant
frequency (snores) are amplified, thus boosting the
signal-to-noise ratio (more accurately the ratio of snore
noise to gas flow generator noise) back to the level which
is comparable to that which has been obtained by sensing
at the patient interface. As illustration, a patient's
lack of demand or a reduced demand for inspiratory air
CA 02357148 2001-09-05
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often precedes, frequently by several-seconds, the onset'
of an audible snore or other pronounced physical
manifestation indicative of obstructed breathing. In such
case, the sensor means would transmit data to the CPU 130
such that the CPU may step up the output of the gas flow
generator 114 well in advance of not only an apneic event
but also prior to the characteristic audible snore
patterns which normally precede such an event. Known
breathing pattern sensors typically accomplish this while
being located on or connected to the patient interface.
The sensor of the present invention, on the other hand,
may be an equally responsive pressure or flow transducer
sensitive to pressure or flow variations of any selected
magnitude and/or frequency, but located within, on or
connected closely adjacent to the outlet of the gas flow
generator.
In addition to its accurate and responsive
feedback capability, the feedback circuit of apparatus
110, by virtue of the strategic placement of sensor means
126, also affords medical personnel the opportunity to
monitor and/or record the patient's breathing activity
with high precision. With this capability, the medical
personnel may confidently diagnose the patient's
particular breathing disorder, prescribe the appropriate
therapy, and monitor the patient's progress while
undergoing treatment using apparatus 110. In this regard,
such monitoring and/or recording may be achieved by system
data storage and retrieval means 140.
System data storage and retrieval means 140 may
within the scope of the present invention comprise any ~-,
suitable computer memory into which information can be
written and from which information can be read.
Representative, although not limitative, embodiments of
CA 02357148 2001-09-05
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the system data storage and retrieval means may therefore
include a random access memory (RAM), magnetic tapes or
magnetic disks which may be incorporated into a
stand-alone personal computer, mainframe computer, or the
like (not illustrated).
System data storage and retrieval means 140 may
be configured to record output data from gas flow
generator 114 and/or, as indicated, it may compile data
from one or more data input lines 142 which communicate
data transmitted by other sensors or monitors (not shown)
which are operatively connected to other patients in a
manner known to those skilled in the art.
Figure 3 reveals, in the form of a functional
block diagram, an apparatus 210 for use in treatment of
sleep apnea and related disorders that is constructed in
accordance with a further preferred embodiment of the
present invention. For brevity, only those elements of
apparatus 210 which depart materially in structure and/or
function from their counterpart elements in Figure 2 will
be described in detail where such description is necessary
for a proper understanding of the invention. In other
words, except where otherwise indicated, gas flow
generator 214, conduit means 218, patient interface means
220, exhaust port means 224, sensor means 226, CPU 230 and
system data storage and retrieval means 240 of Figure 3
desirably are constructed as and function substantially
identically to gas flow generator 114, conduit 118,
patient interface means 120, exhaust port means 124,
sensor means 126, CPU 130 and system data storage and
retrieval means 140 discussed hereinabove in connection
with Figure 2.
CA 02357148 2001-09-05
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r
The primary distinction between apparatus 210
and apparatus 110 is the presence of-a pressure controller
216 which may be -controlled separately from and in
addition to the gas flow generator 214 by CPU 230.
The pressure controller 26 is thus operative to
regulate, at least in part, the pressure of breathing gas
within the conduit means 218 and thus within the airway of
the patient 222. Pressure controller 216 is located
preferably, although not necessarily, within or closely
downstream of flow generator 214 and may take the form of
an adjustable valve, the valve being adjustable to provide
a constant or variable pressure drop across the valve for
all flow rates and thus any desired pressure within
conduit means 218.
Interposed in line with conduit means 218,
downstream and substantially adjacent to pressure
controller 216, is a suitable sensor means 226 such as a
pressure or flow transducer which generates an output
signal that is fed as indicated at 228 to a pressure or
flow signal conditioning circuit of CPU 230 for
derivation of a signal proportional to the instantaneous
pressure or flow rate of breathing gas within conduit
means 218 to the patient.
Depending upon the instantaneous pressure or
flow condition detected by sensor means 226, which feeds a
signal 228 corresponding to that condition to the CPU 230,
the CPU may generate and transmit a command signal 232 to
increase or decrease the output of the gas flow generator
214 in the manner discussed above in connection with the
description of Figure 2. Alternatively, or in addition
to, command signal 232, the CPU may generate arid transmit
command signal 234 (shown in dashed line) to the pressure
CA 02357148 2001-09-05
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controller 216 to adjust the pressure drop produced
thereby. In this way particularly sophisticated
instantaneous pressure output patterns may be achieved to
satisfy the demands of the patient on a breath-to-breath
basis.
Furthermore, data storage and retrieval means
240 may be configured to compile input not only from the
gas flow generator 214 and from the patient 222 via input
lines 242, but also from the pressure controller 216 to
provide the overseeing medical personnel an even more
complete representation of the patient's respiratory
activity.
Figure 4 schematically illustrates an
arrangement wherein apparatus 310 includes a device 312
incorporating the flow generator 314, breathing
patterns sensor means 326, a CPU or central processing
unit 330 which includes a pressure controller (not
illustrated). The flow generator 314 presents a bellows
338 terminating in a circuit coupler 344 presented
externally of the device 312. A patient or first conduit
means 318 has one end connected to the circuit coupler 344
and an opposite end connected to the patient interface
means 320 which includes exhaust port means 324.
Unlike other positive airway pressure apparatus
equipped with feedback/diagnostic systems including a
breathing patterns sensor located on or connected to the
patient interface, the apparatus 310 according to the
present invention finds its breathing patterns sensor
means 326 situated generally at the end of the breathing
circuit remote from the patient 322. That is, the sensor
326 is preferably located within, on or is connected
closely adjacent to the outlet of the gas flow generator
CA 02357148 2001-09-05
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314. More specifically, the sensor means_326 comprises a
pressure transducer 346 operably connected to the CPU 330.
The sensor means 326 is in fluid communication with the
patient or first conduit means 318 by means of sensor or
second conduit 347. In accordance with the present
invention, the sensor or second conduit means 347
comprises a internal conduit portion 348 disposed
entirely within the device 312, and an external conduit
portion 350 disposed exteriorly of the device 312. The
sensor or second conduit means 347 has one end connected
to the pressure transducer 346 and an opposite end
connected to the patient or first conduit means 318
through the circuit coupler 344 and thus provide sound
pressure communication between the pressure transducer 346
and the patient or first conduit means 318 through the
circuit coupler 344. The arrangement is such that when
the transmitted sound wave is close to the resonant
frequency of the system, greatly amplified sound pressure
will be transmitted from the mask 320 through the patient
or first conduit means 318, the circuit coupler 344, and
the sensor or second conduit means 347 to the pressure
transducer 346. That is, the system responds like a
harmonic oscillator with one degree of freedom.
By taking advantage of moving the sensor means
326 back to the device 312, the present invention provides
system that is acoustically tuned to optimally transmit
sounds in the frequency range of 20 to 120 Hz (the same
range of sounds that are indicative of upper airway
obstructions) .
In apparatus, such as that illustrated in -'°
Fig. 4, the volume and entrance characteristics of the
bellows 338, the blower 314, and the patient circuit 318
also affect the resonance properties in a complex manner.
CA 02357148 2001-09-05
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Therefore the optimum lengths of the-internal and external
conduit portions 348, 350 are best verified empirically.
This is achieved by placing a sound source at the patient
mask 320, sweeping through the range of frequencies of
interest, and measuring the output response of the
pressure transducer 346. The lengths of the internal and
external conduit portions 348, 350 are varied until the
desired frequency response is achieved.
In one operative embodiment of the apparatus of
Fig. 4, one-eighth inch inner diameter tubing is used as
the internal and external conduit portions 348, 350. A
length L of 40 inches of the internal and external conduit
portions 348, 350 was found to provide the desired
resonant frequency, w of 70 cycles per second. At that
resonant frequency, the apparatus 310 is acoustically
tuned to optimally transmit sounds in the target frequency
range of 20 to 120 Hz -- the primary frequency range of
sounds that are indicative of upper airway obstruction.
It should be understood, however, that the length L of the
internal and external conduits 348, 350 will change with
changes in the system elements. That is, the particular
type of patient circuit 318, blower 314, bellows 338,
circuit coupler 344, and pressure transducer 346 used in
the system do determine the length L of the internal and
external conduits 348, 350 that is required to produce the
desired resonant frequency of 70 cycles per second.
Likewise, it should be understood that the frequencies of
sounds associated with upper airway obstructions are known
to fall within a range of about 20 to 2,000 Hz.
Therefore, other operative embodiments of the apparatus
may be tuned by similar methods to resonant frequencies
other than 70 Hz.
CA 02357148 2001-09-05
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It should also be apparent that by distancing
the breathing patterns_sensor from the patient interface
(i.e., the breathing mask or nasal prongs), the patient
conduit means 318 is rendered considerably less
cumbersome, the risk of entanglement is negatived, and the
annoyance of the patient is minimized. The length of the
shorter feedback conduit reduces, if not totally
eliminates, the risk of being kinked or accidently
disconnected from the patient's breathing circuit.
Additionally, frequent cleaning of the shorter feedback
conduit is not required because it is not in direct
contact with the patient's expired air. The shorter
feedback conduit also reduces the materials cost for the
system.
Turning to Figures 5-7, a sleep apnea treatment
apparatus according to the present invention is
illustrated in combination with a humidifier of the
present invention. When the apparatus 310 according to
the present invention includes a humidifier 400 or 500,
the circuit coupler 344 detaches from the gas flow
generator device 312 and to an outlet 416 of the
humidifier 400 or 500. An inlet 415 is then connected to
the outlet of the gas flow generator device 312.
Referring to Figure 6, humidifier 400 has a U-shaped
chamber 427 having a first leg 428 which directs air from
the body of the humidifier and a second leg 429 which
directs air towards the outlet 416. The U-shaped chamber
427 acoustically tunes the snoring sound received from a
patient. In an alternative preferred embodiment
illustrated in Figure 7, humidifier 500 includes an inlet
516 and a U~~shaped chamber 527 having a chamber inlet 543,
a diameter transition portion 544 and a laterally
extending outlet 515. The configuration of the U-shaped
chamber 527 optimally transmits sound frequencies falling
CA 02357148 2001-09-05
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within a frequency range which is known to be associated
with upper airway obstructions by setting the resonant
frequency of the snore sound. The position of the
diameter transition portion 544 controls the resonant
frequency such that the resonant frequency of interest may
be selected. Further included is a dissipation hole 545
between chamber inlet 543 and the outlet portion 516 of
U-shaped chamber 427. Dissipation hole 545 in this
presently preferred embodiment is approximately 0.098
inches in diameter. Energy is stored in U-shaped chamber
42? during each oscillation cycle of snore sound.
Dissipation hole 545 helps dissipate some of that energy
to adjust the Q or quality factor (a measure of resonance)
of the circuit. Thus, dissipation hole 545 dissipates the
energy stored in each oscillation cycle of snore sound to
make the Q of the U-shaped chamber 427 comparable to that
of the CPAP device.
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.
