U.S. patent application number 10/136778 was filed with the patent office on 2003-10-30 for method and apparatus to detect and monitor the frequency of obstructive sleep apnea.
Invention is credited to Cho, Yong K., Condie, Catherine R., Jensen, Donald N..
Application Number | 20030204213 10/136778 |
Document ID | / |
Family ID | 29249662 |
Filed Date | 2003-10-30 |
United States Patent
Application |
20030204213 |
Kind Code |
A1 |
Jensen, Donald N. ; et
al. |
October 30, 2003 |
Method and apparatus to detect and monitor the frequency of
obstructive sleep apnea
Abstract
The present invention provides a method and apparatus for
detecting and monitoring obstructive sleep apnea. The apparatus
includes an intracardiac impedance sensor to measure intracardiac
impedance, a movement sensor to measure an amount of movement of a
patient, and a controller operatively coupled to said intracardiac
impedance sensor and said movement sensor, said controller adapted
to receive at least one of an intracardiac impedance and the amount
of movement of the patient and detect obstructive sleep apnea based
upon said intracardiac impedance and said movement.
Inventors: |
Jensen, Donald N.; (Derwood,
MD) ; Condie, Catherine R.; (Shoreview, MN) ;
Cho, Yong K.; (Maple Grove, MN) |
Correspondence
Address: |
MEDTRONIC, INC.
710 MEDTRONIC PARKWAY NE
MS-LC340
MINNEAPOLIS
MN
55432-5604
US
|
Family ID: |
29249662 |
Appl. No.: |
10/136778 |
Filed: |
April 30, 2002 |
Current U.S.
Class: |
607/17 |
Current CPC
Class: |
A61B 5/24 20210101; A61B
5/0538 20130101; A61B 5/4818 20130101; A61B 5/1118 20130101; A61B
5/0809 20130101 |
Class at
Publication: |
607/17 |
International
Class: |
A61N 001/365 |
Claims
What is claimed:
1. A method of detecting and monitoring obstructive sleep apnea,
comprising: measuring an intracardiac impedance to detect a change
in the intracardiac impedance; measuring an amount of movement of a
patient; and determining the presence of obstructive sleep apnea
based upon the change in the intracardiac impedance and the
movement of the patient.
2. A method of claim 1, wherein measuring the intracardiac
impedance further comprises measuring the intracardiac impedance
between an intracardiac atrial electrode and an intracardiac
ventricular electrode.
3. A method of claim 1, wherein measuring the intracardiac
impedance further comprises detecting a decrease in the
intracardiac impedance.
4. A method of claim 1, wherein measuring the amount of movement of
the patient further comprises detecting a low amount of movement of
the patient.
5. A method of detecting and monitoring obstructive sleep apnea,
comprising: measuring the intrathoracic impedance to detect a
change in the intrathoracic impedance; and determining the presence
of obstructive sleep apnea based upon the change in the
intrathoracic impedance.
6. A method of claim 5, wherein measuring the intrathoracic
impedance further comprises measuring the intrathoracic impedance
between an endocardial electrode and a pacemaker housing.
7. A method of claim 5, wherein measuring the intrathoracic
impedance further comprises detecting a decrease in the
intrathoracic impedance.
8. A method of detecting and monitoring obstructive sleep apnea,
comprising: measuring impedance minute ventilation to detect a
change in the impedance minute ventilation; measuring an amount of
movement of a patient; and determining the presence of obstructive
sleep apnea based upon the change in the impedance minute
ventilation and the movement of the patient.
9. A method of claim 8, wherein measuring impedance minute
ventilation further comprises detecting an increase in impedance
minute ventilation followed by a decrease in impedance minute
ventilation.
10. A method of claim 8, wherein measuring impedance minute
ventilation further comprises detecting an immediate increase in
impedance minute ventilation followed by a more gradual decrease in
impedance minute ventilation.
11. A method of claim 8, wherein measuring the amount of movement
of the patient further comprises detecting a low amount of movement
of the patient.
12. A method of detecting and monitoring obstructive sleep apnea,
comprising: detecting sinus tachycardia; measuring an
atrial-ventricular conduction to detect a change in the
atrial-ventricular conduction; and determining the presence of
obstructive sleep apnea based upon detecting sinus tachycardia and
the change in the atrial-ventricular conduction.
13. A method of claim 12, measuring the atrial-ventricular
conduction further comprises detecting an increase in the
atrial-ventricular conduction.
14. A medical device for detecting and monitoring obstructive sleep
apnea, comprising: means for measuring an intracardiac impedance to
detect a change in the intracardiac impedance; means for measuring
an amount of movement of a patient; and means for determining the
presence of obstructive sleep apnea based upon the change in the
intracardiac impedance and the movement of the patient.
15. A medical device for detecting and monitoring obstructive sleep
apnea, comprising: means for measuring the intrathoracic impedance
to detect a change in the intrathoracic impedance; and means for
determining the presence of obstructive sleep apnea based upon the
change in the intrathoracic impedance.
16. A medical device for detecting and monitoring obstructive sleep
apnea, comprising: means for measuring impedance minute ventilation
to detect a change in the impedance minute ventilation; means for
measuring an amount of movement of a patient; and means for
determining the presence of obstructive sleep apnea based upon the
change in the impedance minute ventilation and the movement of the
patient.
17. A medical device for detecting and monitoring obstructive sleep
apnea, comprising: means for detecting sinus tachycardia; means for
measuring an atrial-ventricular conduction to detect a change in
the atrial-ventricular conduction; means for determining the
presence of obstructive sleep apnea based upon detecting sinus
tachycardia and the change in the atrial-ventricular
conduction.
18. A medical device for detecting and monitoring obstructive sleep
apnea, comprising: an intracardiac impedance sensor to measure an
intracardiac impedance; a movement sensor to measure an amount of
movement of a patient; and a controller operatively coupled to said
intracardiac impedance sensor and said movement sensor, said
controller adapted to receive at least one of an intracardiac
impedance and the amount of movement of the patient and detect
obstructive sleep apnea based upon said intracardiac impedance and
said movement.
19. The medical device of claim 18, wherein the movement sensor
further comprises a piezo crystal.
20. The medical device of claim 18, wherein the movement sensor
further comprises an accelerometer.
21. The medical device of claim 18, further comprising an
intrathoracic impedance sensor operatively coupled to said
controller to measure an intrathoracic impedance, said controller
adapted to receive the intrathoracic impedance and to detect said
obstructive sleep apnea based upon said intrathoraic impedance.
22. The medical device of claim 18, further comprising an
electrical sensor operatively coupled to said controller to measure
electrical activity in a heart, said controller adapted to receive
the electrical activity and to detect said obstructive sleep apnea
based upon said electrical activity.
23. The medical device of claim 22, wherein the electrical sensor
detects cardiac depolarizations.
24. The medical device of claim 22, wherein the electrical sensor
comprises an electrical sensing amplifier and at least one of a
cardiac electrode and a subcutaneous electrode.
25. The medical device of claim 22, wherein at least one of the
intracardiac impedance sensor, the intrathoracic impedance sensor,
the movement sensor, and the electrical sensor is implantable.
26. The medical device of claim 18, further comprising a telemetry
interface adapted to facilitate real-time access to the data on the
controller.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates generally to implantable medical
devices, and more particularly, to a method and apparatus to
automatically detect and monitor the frequency of obstructive sleep
apnea.
[0003] 2. Description of the Related Art
[0004] Although the function of sleep is not well understood, one
consequence of an inadequate quantity or poor quality of sleep is
an inability to maintain adequate wakefulness. The amount of sleep
an individual needs is thought to be neurologically determined and
is generally stable over time. Among other factors, an insufficient
amount of sleep (i.e., quantity of sleep) or a disruption of sleep
continuity (i.e., quality of sleep) will result in increased
daytime sleepiness. Increased sleepiness in a person may cause a
plethora of problems to that person as well as others. Increased
sleepiness is a major cause of accidents because people who are
sleepy are generally not fully aware of their surroundings.
Additionally, because of this decreased awareness, a person who
does not receive the adequate quantity and quality of sleep at
night may also be prone to decreased efficiency at home and at
work. A sleepy person may also require frequent naps during the day
to recuperate, thereby reducing productivity in the office as well
as in the chores of daily life. As a result, it is important for
people generally to receive a good night's rest. However, many
people have medical conditions that prevent them from receiving a
good night's rest. One such condition is sleep apnea.
[0005] Sleep apnea is generally defined as the cessation of
breathing during sleep. One type of a sleep apnea, obstructive
sleep apnea ("OSA"), is caused by repetitive upper airway
obstruction during sleep as a result of narrowing of the
respiratory passages. Partial obstruction of the passageways may
simply lead to hypopnea. Prolonged obstruction of the passageways,
however, may lead to nocturnal arousals.
[0006] OSA is generally characterized by a sleep-related withdrawal
of upper airway inspiratory muscle tone superimposed on a narrow,
highly compliant pharynx. As a result, the pharynx may during
sleep, leading to obstructive apnea.
[0007] The cause of OSA is thought to be a combination of anatomic
characteristics of the upper airway and abnormalities in the
neuromuscular control of the muscles in the throat. Sleep apnea is
more common in individuals with large tonsils, palate, and tongue,
and with a short thick neck. This anatomy may predispose the throat
to easily collapse. A badly deviated nasal septum or other nasal
obstruction can also worsen OSA because it limits the ability to
breathe through the nose. Overweight individuals are also at high
risk for OSA. Not all individuals with these anatomic features will
have OSA, and OSA occasionally occurs in people with
normal-appearing throats.
[0008] OSA may cause a variety of medical and other problems among
patients. Cycles of sleep, snoring, obstruction, arousal, and sleep
may occur many times throughout the night. Although such nocturnal
arousals may last only a few seconds, they prevent a person from
reaching the deep stages of sleep, which the body generally needs
to rest and replenish its strength. As a result, patients with OSA
may not receive a restful sleep because of multiple nocturnal
arousals.
[0009] Furthermore, multiple arousals with sleep fragmentation are
likely to cause excessive daytime sleepiness and fatigue, cognitive
impairment, depression, headaches, chest pain, and diminished
sexual drive. OSA is generally associated with cardiovascular
morbidity, including systemic hypertension, pulmonary hypertension,
ischemic heart disease, stroke, and cardiac arrhythmias. OSA is
also usually associated with increased mortality by negatively
effecting the status, progression, and outcomes of previously
existing conditions, such as congestive heart failure ("CHF").
[0010] OSA is a disorder which is generally underdiagnosed and
undertreated. Because OSA may worsen the effects of a previously
existing condition, such as CHF, treatment of OSA may be beneficial
to reduce its negative on the previously existing condition. Once
OSA has been properly diagnosed, a variety of therapies may be
available. Common OSA therapies include non-surgical methods, such
as continuous positive airway pressure ("CPAP"), as well as
surgical methods, such as uvulopalatopharyngoplasty ("UPPP").
Effective therapy for OSA can often reverse or ameliorate the
problems associated with OSA.
[0011] One method of diagnosis for OSA is nocturnal
polysomnography. In nocturnal polysomnography, multiple
physiological parameters are measured while the patient sleeps in a
laboratory. Typical parameters in a nocturnal polysomnography
include eye movement observations (to determine whether a patient
has reached REM sleep), an electroencephalogram (to determine
arousals from sleep), chest wall monitors (to document respiratory
movements), nasal and oral air-flow measurements, and an
electrocardiogram, among other parameters. A combination of these
and other factors are used by doctors and other qualified sleep
specialists to determine whether a patient has OSA. However,
nocturnal polysomnography is generally expensive and
time-consuming. Furthermore, many patients experience the symptoms
of OSA (e.g., nocturnal arousals, snoring) while they are asleep,
and therefore, never recognize that they may have a sleeping
disorder. As a result, many patients with OSA may not seek proper
diagnosis or treatment of their sleeping disorder from a doctor or
other qualified sleep specialist. Even if a patient is diagnosed
with OSA, frequent laboratory monitoring of the patient is
generally not feasible due to the expense and time involved in a
nocturnal polysomnography.
[0012] The technology explosion in the implantable medical devices
industry has resulted in many new and innovative devices and
methods for analyzing and improving the health of a patient. The
class of implantable medical devices now includes pacemakers,
implantable cardioverters, defibrillators, neural stimulators, and
drug administering devices, among others. Today's state-of-the-art
implantable medical devices are vastly more sophisticated and
complex than early ones, capable of performing significantly more
complex tasks. The therapeutic benefits of such devices have been
well proven.
[0013] There are many implementations of implantable medical
devices that provide data acquisition of important physiological
data from a human body. Many implantable medical devices are used
for cardiac monitoring and therapy. Often these devices comprise
sensors that are placed in blood vessels and/or chambers of the
heart. Often these devices are operatively coupled with implantable
monitors and therapy delivery devices. For example, such cardiac
systems include implantable heart monitors and therapy delivery
devices, such as pacemakers, cardioverters, defibrillators, heart
pumps, cardiomyostimulators, ischemia treatment devices, drug
delivery devices, and other heart therapy devices. Most of these
cardiac systems include electrodes for sensing and gain amplifiers
for recording and/or driving sense event signals from the
inter-cardiac or remote electrogram ("EGM").
[0014] Many patients who use implantable medical devices may be at
risk for OSA.
[0015] However, patients are generally left with traditional forms
of diagnosis for OSA, such as nocturnal polysomnography. As
mentioned, nocturnal polysomnography may be an expensive and
time-consuming procedure. Furthermore, many patients may not
recognize that they have symptoms relating to OSA, such that they
would seek diagnosis and treatment for the disorder. Nocturnal
polysomnography is generally an infrequent procedure that does not
provide long term monitoring of the patient's condition after he
has been diagnosed. The present invention is directed to
overcoming, or at least reducing the effects of, one or more of the
problems set forth above.
SUMMARY OF THE INVENTION
[0016] In one aspect of the present invention, an apparatus is
provided for detecting and monitoring obstructive sleep apnea. The
apparatus includes an intracardiac impedance sensor to measure
intracardiac impedance, a movement sensor to measure an amount of
movement of a patient, and a controller operatively coupled to said
intracardiac impedance sensor and said movement sensor, said
controller adapted to receive at least one of an intracardiac
impedance and the amount of movement of the patient and detect
obstructive sleep apnea based upon said intracardiac impedance and
said movement.
[0017] In another aspect of the present invention, a method is
provided for detecting and monitoring obstructive sleep apnea. The
method includes measuring an intracardiac impedance to detect a
change in the intracardiac impedance, measuring an amount of
movement of a patient, and determining the presence of obstructive
sleep apnea based upon the change in the intracardiac impedance and
the movement of the patient.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] The invention may be understood by reference to the
following description taken in conjunction with the accompanying
drawings, in which like reference numerals identify like elements,
and in which:
[0019] FIG. 1 is a simplified diagram of an implementation of an
implantable medical device, in accordance with one illustrative
embodiment of the present invention;
[0020] FIG. 2 illustrates a simplified block diagram representation
of an implantable medical system in accordance with one
illustrative embodiment of the present invention;
[0021] FIG. 3 illustrates a more detailed block diagram
representation of the implantable medical device of FIGS. I and 2,
in accordance with one illustrative embodiment of the present
invention; and
[0022] FIG. 4 illustrates a more detailed block diagram
representation of a plurality of sensors and its associated data
interfaces of FIG. 3, in accordance with one illustrative
embodiment of the present invention.
[0023] While the invention is susceptible to various modifications
and alternative forms, specific embodiments thereof have been shown
by way of example in the drawings and are herein described in
detail. It should be understood, however, that the description
herein of specific embodiments is not intended to limit the
invention to the particular forms disclosed, but on the contrary,
the intention is to cover all modifications, equivalents, and
alternatives falling within the spirit and scope of the invention
as defined by the appended claims.
DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS
[0024] Illustrative embodiments of the invention are described
below. In the interest of clarity, not all features of an actual
implementation are described in this specification. It will of
course be appreciated that in the development of any such actual
embodiment, numerous implementation-specific decisions must be made
to achieve the developers' specific goals, such as compliance with
system-related and business-related constraints, which will vary
from one implementation to another. Moreover, it will be
appreciated that such a development effort might be complex and
time-consuming, but would nevertheless be a routine undertaking for
those of ordinary skill in the art having the benefit of this
disclosure.
[0025] There are many discrete processes involving the operation of
implantable medical devices (e.g., pacemakers, cardio
defibrillators, the like). The operation of an implantable medical
device includes collecting, storing, and analyzing physiological
data relating to a patient, and/or delivering therapy (e.g.,
cardiac therapy) to a portion of a patient's body. Often, these
tasks are performed by an implantable medical system, which
includes an implantable medical device. Based upon the analysis
performed by the implantable medical system, one or more therapies
may be delivered to a particular portion of a patient's body. One
example of such a therapy is a cardiac therapy, which is delivered
to a patient's heart.
[0026] Embodiments of the present invention may be utilized to
detect and monitor the common symptoms and conditions related to
patients with Obstructive Sleep Apnea (OSA). It should be
appreciated that the present invention may be included in an
implantable device capable of collecting data other than data used
to diagnose or monitor OSA. The data may be collected by sensors in
the implantable device and may be used by doctors and other sleep
experts to judge the severity of apneas and to determine the
efficacy of apnea therapy, without the use of nocturnal
polysomnography.
[0027] Turning now to FIG. 1, one embodiment of implementing an
implantable medical device into a human body is illustrated. A
sensor device 210 (e.g., devices attached to leads 114) placed upon
the heart 116 of the human body 105 is used to acquire and process
physiological data. In one embodiment, the sensor device 210 may
also be a therapy delivery device (described in greater detail
below). An implantable medical device 220 collects and processes a
plurality of data acquired from the human body 105. In one
embodiment, the implantable medical device 220 may be a cardiac
pacemaker or an implantable cardiovertor defibrillator ("ICD"). The
data acquired by the implantable medical device 220 can be
monitored by an external system, such as the access device 240
comprising a programming head 122, which remotely communicates with
the implantable medical device 220. The programming head 122 is
utilized in accordance with medical device programming systems
known to those skilled in the art having the benefit of the present
disclosure, for facilitating two-way communication between the
implantable medical device 220 and the access device 240.
[0028] In one embodiment, a plurality of access devices 240 can be
employed to collect a plurality of data, including OSA data,
processed by the implantable medical device 220 in accordance with
embodiments of the present invention. The implantable medical
device 220 is housed within a hermetically sealed, biologically
inert outer canister or housing 113, which may itself be conductive
so as to serve as an electrode in the implantable medical device
220 pacing/sensing circuit. One or more sensors/leads, collectively
identified with reference numeral 114 in FIG. 1, are electrically
coupled to the implantable medical device 220 and extended into the
patient's heart 116 via a vein 118. Disposed generally near a
distal end of the leads 114 are one or more exposed conductive
electrodes (i.e., sensor device 210) for receiving electrical
cardiac signals or delivering electrical pacing stimuli to the
heart 116. The leads 114 may be implanted with their distal end
situated in either the atrium or ventricle of the heart 116. In an
alternative embodiment, the sensor device 210, or the leads 114
associated with the sensor device 210, may be situated in a blood
vessel on the heart 116, such as a vein 118.
[0029] Turning now to FIG. 2, a system 200, in accordance with one
embodiment of the present invention, is illustrated. The system 200
comprises a plurality of sensor devices, collectively identified
with reference numeral 210 in FIG. 2, an implantable medical device
220, an access device 240, and an interface 230 that provides a
communication link between the implantable medical device 220 and
the access device 240. Embodiments of the present invention provide
a plurality of physiological data from the sensor devices 210,
which are then processed and stored in the implantable medical
device 220. In one embodiment, the sensor devices 210 may collect
data that is used to detect and monitor OSA in a patient.
[0030] As mentioned, based upon physiological data and other
factors, the implantable medical device 220 may deliver a therapy
to a portion of the patient's body, via the sensor devices 210. The
access device 240 can then be used to monitor and analyze the
organized data from the implantable medical device 220 via the
interface 230 and view results from delivered therapy. The access
device 240 can be used to monitor the efficiency of the therapy
delivered by the implantable medical device 220. The access device
240 can be used to determine, based upon data stored by the
implantable medical device 220, whether a therapy delivered was of
proper energy intensity.
[0031] Turning now to FIG. 3, a more detailed block diagram
depiction of one embodiment of the implantable medical device 220
is illustrated. The implantable medical device 220 comprises a
processor 310, a control logic 320, a memory unit 330, a data
acquisition controller 340, a telemetry interface 350, and a
plurality of data interfaces 360, 370, 380, 390. The plurality of
sensor devices 210 of FIG. 2 provide various physiological data to
the implantable medical device 220. The processor 310 controls the
operation of the implantable medical device 220. The processor 310
utilizes the control logic 320 to perform a plurality of
operations, including memory access and storage operations. The
processor 310 communicates with the control logic 320 and the data
acquisition controller 340 via a bus line 325. The control logic
320 sends control signals to the memory unit 330 for controlling
and installing the memory unit 330, and to the data acquisition
controller 340, which controls the acquisition of physiological
data and drives output signals to the telemetry interface 350.
[0032] The telemetry interface 350 can facilitate real-time access
of physiological data acquired by the data acquisition controller
340. Therefore, a physician can view physiological data on a real
time basis by accessing the data acquisition controller 340, via
the telemetry interface 350. The data acquisition controller 340
can prompt the data interfaces 360, 370, 380, 390 to retrieve
physiological data from the sensor device 210, process such data,
and deliver physiological data to the data acquisition controller
340. The data interfaces 360, 370, 380, 390 can perform a number of
analog-to-digital conversions and time-interval conversions, known
to those skilled in the art, upon the acquired physiological data.
The data interfaces 360, 370, 380, 390 can acquire, condition, and
process physiological data and forward them to the data acquisition
controller 340.
[0033] It should be appreciated that, in an alternate embodiment,
the functionality of the data interfaces 360, 370, 380, 390 may be
combined with the sensor devices 210, such that information
gathered by the sensor devices 210 may be readily utilized by the
implantable medical device 220 without further processing by
another device or interface. It should also be appreciated that,
although the sensor devices 210 are separated from the implantable
medical device 220 for illustrative purposes in FIGS. 2 and 3, the
implantable medical device 220 may further comprise the sensor
devices 210.
[0034] Turning now to FIG. 4, one embodiment of the sensor device
210 and the implantable medical device 220 of FIGS. 1, 2, and 3, in
accordance with the present invention, is shown. In the illustrated
embodiment of FIG. 4, four sensors are shown. However, it should be
appreciated that the implantable medical device 220 may comprise of
more or less sensors than the illustrated embodiment of FIG. 4,
such that OSA may be properly diagnosed on a patient. It should
also be appreciated that the functionality of each sensor described
below may be combined into one or more sensors, such that OSA may
be properly diagnosed on a patient.
[0035] The implantable medical device 220 comprises four sensors,
which individually and in combination may be used to detect OSA in
a patient. An intracardiac impedance sensor 210-1 measures
impedance between an intracardiac atrial electrode and an
intracardiac ventricular electrode. An intrathoracic impedance
sensor 210-2 measures impedance across the thorax. In one
embodiment, the intrathoracic impedance sensor 210-2 may include
pacemaker sensors, which measure impedance between a pacemaker and
an intracardiac electrode. The impedance between the pacemaker and
the intracardiac electrode may be used to estimate in minute
ventilation ("MV"). A movement sensor 210-3 detects movement in a
patient during sleep. The movement sensor 210-3, in one embodiment,
may be a piezo crystal or an accelerometer. An electrical sensor
210-4 detects cardiac depolarizations.
[0036] Using the four sensors 210-1, 210-2, 210-3, 210-4, a
plurality of information can be gathered to properly diagnosis OSA
on a patient. The information gathered by the sensors 210-1, 210-2,
210-3, and 210-4 is processed by an intracardiac data interface
360, an intrathoracic impedance data interface 370, a movement data
interface 380, and an electrical data interface 390, respectively,
before the information is forwarded to the data acquisition
controller 340. Although sensors can be used individually to
diagnose OSA, combinations of two or more sensors may form a basis
for diagnosis of OSA. For example, a large decrease in impedance
between atrial and ventricular electrodes (i.e., a decrease in the
intracardiac impedance sensor 210-1) occurring when a patient is
not exercising (i.e., a low reading from the movement sensor 210-3)
may be a factor towards diagnosis of OSA. As a patient attempts to
breath while his airway is obstructed, negative intrathoracic
pressure may increase, which overfills the right side of the heart.
This overfilling of the right side of the heart increases the
diameter of the atrium and the ventricle. Although the volume of
the heart does not change, the shape of the heart becomes shorter
and wider. As a result, a drop in atrial-to-ventricular impedance
may be observed during OSA because the wider blood pool will cause
a reduced impedance. The wider blood pool may also be a result
vigorous exercise from the patient. Therefore, the intracardiac
impedance sensor 210-1 may be read in conjunction with the movement
sensor 210-3. In one embodiment, a low reading from the movement
sensor 210-3 indicates the patient is not exercising or in some
other physical activity. A decrease in the intracardiac impedance
sensor 210-1 and a low reading from the movement sensor 210-3
indicates a possibility that the patient has OSA.
[0037] Another possible indication that a patient has OSA may be
provided by the intrathoracic impedance sensor 210-2. In one
embodiment, the intrathoracic impedance sensor 210-2 may measure
impedance between an implantable device housing, such as a can
electrode, and an endocardial electrode, such as an atrial
electrode or a ventricular electrode. A decrease in intrathoracic
impedance during attempted inspiration may be a factor in
determining whether a patient has OSA. As a patient attempts to
breathe while his airway is obstructed, the circumference of his
thorax may expand. As the patient's thorax expands, the diaphragm
pushes the heart and lungs upward. As the lungs are pushed upward,
the lungs do not change volume, but instead become shorter and
wider. The shorter and wider shape of the lungs may reduce
intrathoracic impedance. In addition, as a patient attempts to
breath while his airway is obstructed, negative intrathoracic
pressure may increase, which overfills the right side of the heart.
As the right side of the heart overflows, a wider blood pathway
forms, thereby reducing intrathoracic impedance. Furthermore,
upward movement of the diaphragm pushes the heart closer to the
implantable medical device 220, thereby reducing impedance. A
decrease in the intrathoracic impedance sensor 210-2 indicates the
possibility that the patient has OSA.
[0038] Another possible indication that a patient has OSA comes
from a rapid increase in impedance minute ventilation ("MV")
followed by a slower decrease in impedance MV. A person who does
not have sleep apnea breathes normally during rest. A patient who
has OSA usually cannot breathe normally during rest because of an
obstruction in the airway. While the patient's heart is attempting
to pump blood into the lungs, the obstruction is preventing the
patient from breathing. As a result, the patient's heart begins to
pump faster to compensate for the lack of blood flow. After an
arousal event, the patient begins to breathe again, but because the
heart was pumping fast before the arousal event, the patient goes
through a hyperpneic phase, which is a period of abnormally rapid
or deep breathing. Studies have shown that during the hyperpneic
phase there may be an immediate rise in MV followed by a more
gradual drop in MV over a period of time.
[0039] An arousal event each time an obstruction is relieved may
cause brief periods of movement detectable by the movement sensor.
As mentioned, in one embodiment, the movement sensor may be a piezo
crystal or an accelerometer. During the hyperpneic phase following
the release of an obstruction, there is usually a brief arousal
which can cause body movement detectable by movement sensors. A
brief period of movement during sleep coinciding with the dramatic
increase in respiration (i.e., a rapid increase in impedance MV
followed by a slower decrease in impedance MV), as described above,
may indicate the patient has OSA. An immediate rise in MV followed
by a more gradual drop in MV, coupled with a brief of movement of
sleep, indicates the possibility that the patient has OSA.
[0040] Yet another possible indication that a patient has OSA may
be provided by the electrical sensor 210-4. OSA can cause
bradycardia during an obstruction. Bradycardia is an abnormally
slow or unsteady heart rhythm (usually less than 60 beats per
minute) that causes symptoms such as dizziness, fainting, fatigue,
and shortness of breath. Release of the obstruction is generally
accompanied by sinus tachycardia and possibly increased
atrial-ventricular conduction. Sinus tachycardia is a fast
heartbeat (usually more than 150 beats per minute) because of rapid
firing of the sinoatrial (i.e., sinus) node. Both sinus tachycardia
and increased atrial-ventricular conduction can be detected by
intracardiac electrodes and electrical sensing amplifiers or by
subcutaneous electrodes and electrical sensing amplifiers.
[0041] Referring back to FIG. 3, as the sensors 210-1, 210-2,
210-3, 210-4 collect data, the data interfaces 360, 370, 380, 390
process the data, in accordance with conventional practice, and
forwards the data to the data acquisition controller 340. The
processor 310 then utilizes the control logic 320 to provide the
data from the data acquisition controller to the memory unit 330.
In addition, a doctor or another qualified sleep professional may
use the telemetry interface 350 to facilitate real-time access to
the data on the data acquisition controller. The doctor or another
qualified sleep specialist may analyze the collected data to
determine whether the patient has OSA.
[0042] The particular embodiments disclosed above are illustrative
only, as the invention may be modified and practiced in different
but equivalent manners apparent to those skilled in the art having
the benefit of the teachings herein. Furthermore, no limitations
are intended to the details of construction or design herein shown,
other than as described in the claims below. It is therefore
evident that the particular embodiments disclosed above may be
altered or modified and all such variations are considered within
the scope and spirit of the invention. Accordingly, the protection
sought herein is as set forth in the claims below.
* * * * *