U.S. patent application number 13/751858 was filed with the patent office on 2013-12-12 for system and methods for wireless body fluid monitoring.
This patent application is currently assigned to Corventis, Inc.. The applicant listed for this patent is Corventis, Inc.. Invention is credited to Mark J. Bly, Imad Libbus.
Application Number | 20130331665 13/751858 |
Document ID | / |
Family ID | 40452537 |
Filed Date | 2013-12-12 |
United States Patent
Application |
20130331665 |
Kind Code |
A1 |
Libbus; Imad ; et
al. |
December 12, 2013 |
SYSTEM AND METHODS FOR WIRELESS BODY FLUID MONITORING
Abstract
An adherent device to monitor a tissue hydration of a patient
comprises an adhesive patch to adhere to a skin of the patient. At
least four electrodes are connected to the patch and capable of
electrically coupling to the patient. Impedance circuitry is
coupled to the at least four electrodes to measure a tissue
resistance of the patient, where the circuitry is configured to
determine the tissue hydration in response to tissue resistance.
The circuitry may comprise a processor system and the tissue
resistance may correspond to a change in patient body fluid. The
impedance circuitry is configured to measure the hydration signal
using at least one low measurement frequency, which may be in the
range of 0 to 10 kHz. Multiple measurement frequencies may be used
and the hydration signal may include a tissue reactance
measurement.
Inventors: |
Libbus; Imad; (Saint Paul,
MN) ; Bly; Mark J.; (Falcon Heights, MN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Corventis, Inc.; |
|
|
US |
|
|
Assignee: |
Corventis, Inc.
San Jose
CA
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Family ID: |
40452537 |
Appl. No.: |
13/751858 |
Filed: |
January 28, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12210078 |
Sep 12, 2008 |
8374688 |
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13751858 |
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61055666 |
May 23, 2008 |
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60972537 |
Sep 14, 2007 |
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60972512 |
Sep 14, 2007 |
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Current U.S.
Class: |
600/306 ;
600/509 |
Current CPC
Class: |
A61B 5/443 20130101;
A61B 5/0537 20130101; A61B 2562/0215 20170801; A61B 2562/043
20130101; G16H 40/67 20180101; A61B 2560/0412 20130101; A61B 5/0245
20130101; G16H 50/30 20180101; A61B 5/01 20130101; A61B 5/04087
20130101; A61B 5/6843 20130101; A61B 5/04085 20130101; A61B 5/6833
20130101 |
Class at
Publication: |
600/306 ;
600/509 |
International
Class: |
A61B 5/053 20060101
A61B005/053; A61B 5/0408 20060101 A61B005/0408 |
Claims
1-39. (canceled)
40. An adherent device to monitor a patient, the device comprising:
an adhesive patch to adhere to a skin of the patient; at least two
electrodes connected to the patch and capable of electrically
coupling to the patient; and circuitry coupled to the at least two
electrodes to measure a tissue resistance of the patient at a
plurality of frequencies greater than zero, wherein the circuitry
is configured to detect a low frequency droop in the tissue
resistance and to, when low frequency droop is detected,
temporarily suspend data collection or disregard some collected
data based at least in part on the fact that the low frequency
droop has been detected.
41. The adherent device of claim 40, wherein the circuitry
comprises a processor system configured to determine a tissue
hydration of the patient in response to the tissue resistance.
42. The adherent device of claim 41, wherein the circuitry is
further configured to determine the tissue hydration based on a
tissue resistance measured at a single frequency.
43. The adherent device of claim 40, wherein the circuitry is
further configured to measure a tissue reactance of the
patient.
44. The adherent device of claim 40, wherein the circuitry is
configured to measure the tissue resistance using at least one low
measurement frequency.
45. The adherent device of claim 44, wherein the at least one low
measurement frequency is in the range of 5 to 15 kHz.
46. The adherent device of claim 44, wherein the at least one low
measurement frequency comprises multiple measurement
frequencies.
47. The adherent device of claim 40, wherein the at least two
electrodes comprise two force electrodes and two sense
electrodes.
48. The adherent device of claim 47, wherein the circuitry measures
tissue impedance, and wherein the circuitry is configured to:
determine an amount of extracellular edema from the tissue
impedance; and calculate and report a patient risk of an adverse
cardiac event based on the amount of extracellular edema.
49. A method of monitoring a patient, the method comprising:
adhering an adhesive patch to a skin of the patient to couple at
least two electrodes to the skin of the patient to form a
skin-electrode interface; measuring a tissue resistance of the
patient at a plurality of frequencies greater than zero with
impedance circuitry coupled to the at least two electrodes;
detecting a low frequency droop in the tissue resistance
measurement; and temporarily suspending data collection or
disregarding some collected data based at least in part on the fact
that the low frequency droop has been detected.
50. The method of claim 49, further comprising determining a
hydration of the patient using the tissue resistance
measurement.
51. The method of claim 50, wherein the hydration of the patient is
determined from a measurement of the tissue resistance at a single
low measurement frequency less than 10 kHz.
52. The method of claim 49, further comprising measuring a tissue
reactance of the patient.
53. The method of claim 52, further comprising determining a
quality of the skin-electrode coupling from the tissue reactance
measurement.
54. The method of claim 53, further comprising identifying a poor
skin-electrode coupling when the tissue reactance is greater than a
threshold of about 10.OMEGA..
55. The method of claim 49, further comprising identifying an
irregular skin-electrode coupling when the tissue resistance droop
exceeds a threshold of 10% of a nominal value.
56. The method of claim 49, further comprising: measuring a tissue
reactance of the patient; determining a hydration signal of the
patient with impedance circuitry coupled to the at least two
electrodes, wherein the hydration signal comprises the tissue
resistance measurement and the tissue reactance measurement;
determining an amount of extracellular edema using the tissue
resistance measurement; and determining a quality of skin-electrode
coupling using the tissue reactance measurement and without using
the tissue resistance measurement.
57. The method of claim 56, further comprising indicating a
replacement status of the adhesive patch based on the quality of
the skin-electrode coupling.
58. An adherent device to monitor a patient, the device comprising:
an adhesive patch to adhere to a skin of the patient; at least two
electrodes connected to the patch and capable of electrically
coupling to the patient to form a skin-electrode interface; and
circuitry coupled to the at least two electrodes to measure an
electrocardiogram signal of the patient, wherein the circuitry is
configured to measure a characteristic of the electrocardiogram
signal and, on the basis of the measured characteristic, determine
a quality of the skin-electrode interface.
59. The adherent device of claim 58, wherein the measured
characteristic of the electrocardiogram signal includes a noise of
the electrocardiogram signal, and wherein the circuitry is
configured to determine a quality of the skin-electrode interface
based at least in part on the noise of the electrocardiogram
signal.
60. The adherent device of claim 58, wherein the measured
characteristic of the electrocardiogram signal includes a
signal-to-noise ratio of the electrocardiogram signal, and wherein
the circuitry is configured to determine a quality of the
skin-electrode interface based at least in part on the
signal-to-noise ratio of the electrocardiogram signal.
61. A method of monitoring a patient, the method comprising:
adhering an adhesive patch to a skin of the patient to couple at
least two electrodes to the skin of the patient to form a
skin-electrode interface; measuring an electrocardiogram signal of
the patient with electrocardiogram circuitry coupled to the at
least two electrodes; and determining a quality of the
skin-electrode interface based on a characteristic of the
electrocardiogram signal.
62. The method of claim 61, wherein the characteristic of the
electrocardiogram signal includes a noise of the electrocardiogram
signal, and wherein determining a quality of the skin-electrode
interface based on a characteristic of the electrocardiogram signal
comprises determining a quality of the skin-electrode interface
based at least in part on the noise of the electrocardiogram
signal.
63. The method of claim 61, wherein the characteristic of the
electrocardiogram signal includes a signal-to-noise ratio of the
electrocardiogram signal, and wherein determining a quality of the
skin-electrode interface based on a characteristic of the
electrocardiogram signal comprises determining a quality of the
skin-electrode interface based at least in part on the
signal-to-noise ratio of the electrocardiogram signal.
Description
CROSS-REFERENCES TO RELATED APPLICATIONS
[0001] The present application is a continuation of pending U.S.
patent application Ser. No. 12/210,078 filed Sep. 12, 2008 and
titled "System and Methods for Wireless Body Fluid Monitoring",
which claims the benefit under 35 USC 119(e) of U.S. Provisional
Application Nos. 60/972,512 and 60/972,537 both filed Sep. 14,
2007, and 61/055,666 filed May 23, 2008; the full disclosures of
which are incorporated herein by reference in their entirety.
[0002] The subject matter of the present application is related to
the following applications: 60/972,329; 60/972,354; 60/972,616;
60/972,363; 60/972,343; 60/972,581; 60/972,629; 60/972,316;
60/972,333; 60/972,359; 60/972,336; and 60/972,340 all of which
were filed on Sep. 14, 2007; 61/046,196 filed Apr. 18, 2008;
61/047,875 filed Apr. 25, 2008; 61/055,645, 61/055,656, and
61/055,662 all filed May 23, 2008; and 61/079,746 filed Jul. 10,
2008.
[0003] The following applications are being filed concurrently with
the present application, on Sep. 12, 2008: Attorney Docket Nos.
026843-000110US entitled "Multi-Sensor Patient Monitor to Detect
Impending Cardiac Decompensation Prediction"; 026843-000220US
entitled "Adherent Device with Multiple Physiological Sensors";
026843-000410US entitled "Injectable Device for Physiological
Monitoring"; 026843-000510US entitled "Delivery System for
Injectable Physiological Monitoring System"; 026843-000620US
entitled "Adherent Device for Cardiac Rhythm Management";
026843-000710US entitled "Adherent Device for Respiratory
Monitoring"; 026843-000810US entitled "Adherent Athletic Monitor";
026843-000910US entitled "Adherent Emergency Monitor";
026843-001320US entitled "Adherent Device with Physiological
Sensors"; 026843-001410US entitled "Medical Device Automatic
Start-up upon Contact to Patient Tissue"; 026843-002010US entitled
"Adherent Cardiac Monitor with Advanced Sensing Capabilities";
026843-002410US entitled "Adherent Device for Sleep Disordered
Breathing"; 026843-002710US entitled "Dynamic Pairing of Patients
to Data Collection Gateways"; 026843-003010US entitled "Adherent
Multi-Sensor Device with Implantable Device Communications
Capabilities"; 026843-003110US entitled "Data Collection in a
Multi-Sensor Patient Monitor"; 026843-003210US entitled "Adherent
Multi-Sensor Device with Empathic Monitoring"; 026843-003310US
entitled "Energy Management for Adherent Patient Monitor"; and
026843-003410US entitled "Tracking and Security for Adherent
Patient Monitor."
BACKGROUND OF THE INVENTION
[0004] 1. Field of the Invention
[0005] The present invention relates to patient monitoring.
Although embodiments make specific reference to monitoring
impedance and electrocardiogram signals with an adherent patch, the
system methods and device described herein may be applicable to
many applications in which physiological monitoring is used, for
example wireless physiological monitoring for extended periods.
[0006] Patients are often treated for diseases and/or conditions
associated with a compromised status of the patient, for example a
compromised physiologic status. In some instances, a patient may
report symptoms that require diagnosis to determine the underlying
cause. For example, a patient may report fainting or dizziness that
requires diagnosis, in which long term monitoring of the patient
can provide useful information as to the physiologic status of the
patient. In some instances a patient may have suffered a heart
attack and require care and/or monitoring after release from the
hospital. One example of a device to provide long term monitoring
of a patient is the Holter monitor, or ambulatory
electrocardiography device.
[0007] In addition to measuring heart signals with
electrocardiograms, known physiologic measurements include
impedance measurements. For example, transthoracic impedance
measurements can be used to measure hydration and respiration.
Although transthoracic measurements can be useful, such
measurements may use electrodes that are positioned across the
midline of the patient, and may be somewhat uncomfortable and/or
cumbersome for the patient to wear.
[0008] Work in relation to embodiments of the present invention
suggests that known methods and apparatus for long term monitoring
of patients, for example in-home monitoring, may be less than
ideal. At least some of the known devices may not collect the right
kinds of data to treat patients optimally. For example, although
successful at detecting and storing electrocardiogram signals,
devices such as the Holter monitor can be somewhat bulky and may
not collect all of the kinds of data that would be ideal to
diagnose and/or treat a patient. In at least some instances,
devices that are worn by the patient may be somewhat larger than
ideal and may be uncomfortable, which may lead to patients not
wearing the devices and not complying with directions from the
health care provider, such that data collected may be less than
ideal. Further, in at least some instances the current devices may
have less than ideal performance when the patient resumes a normal
lifestyle and the device is exposed to environmental factors such
as humidity or water, for example, when the patient takes a shower.
Although implantable devices may be used in some instances, many of
these devices can be invasive and/or costly, and may suffer at
least some of the shortcomings of known wearable devices.
[0009] Current methodologies for measuring patient hydration with
impedance may be less than ideal for remote patient monitoring,
such as in-home monitoring for extended periods. At least some of
the current devices that determine hydration with impedance, for
example for hospital use, may use more current and may have more
complex and bulky circuitry than would be ideal for in-home
monitoring in at least some instances, for example where the
patient is active and moves about the home. As noted above, the
size and comfort of a remote patient monitor can affect the quality
of the data received from the patient.
[0010] Therefore, a need exists for improved patient monitoring,
for example improved in-home patient monitoring. Ideally, such
improved patient monitoring would avoid at least some of the
short-comings of the present methods and devices.
[0011] 2. Description of the Background Art
[0012] The following patents and publications may describe
background art relevant to the present application: U.S. Pat. No.
7,133,716 to Kraemer et al.; U.S. Pat. No. 6,906,530 to Geisel;
U.S. Pat. No. 6,442,422 to Duckert; U.S. Pat. No. 6,050,267 to
Nardella et al.; U.S. Pat. No. 5,935,079 to Swanson et al.; U.S.
Pat. No. 5,836,990 to Li; U.S. Pat. No. 5,788,643 to Feldman; U.S.
Pat. No. 5,738,107 to Martinsen et al.; U.S. Pat. No. 5,449,000 to
Libke et al.; U.S. Pat. No. 4,966,158 to Honma et al.; U.S. Pat.
No. 4,692,685 to Blaze; U.S. Patent App. Pub. No. 2007/0043301 to
Martinsen et al.; U.S. Patent App. Pub. No. 2006/0281981 to Jang et
al.; U.S. Patent App. Pub. No. 2006/0004300 to Kennedy; U.S. Patent
App. Pub. No. 2005/0203435 to Nakada; and U.S. Patent App. Pub. No.
2005/0192488 to Bryenton et al.
BRIEF SUMMARY OF THE INVENTION
[0013] The present invention relates to patient monitoring.
Although embodiments make specific reference to monitoring
impedance and electrocardiogram signals with an adherent patch, the
system methods and device described herein may be applicable to any
application in which physiological monitoring is used, for example
wireless physiological monitoring for extended periods. Embodiments
of the present invention use tissue resistance to determine patient
hydration, such that the size, complexity and power consumption of
the associated circuitry can be minimized. In many embodiments,
tissue resistance alone is measured at a single frequency to
determine patient hydration, such that the circuitry and battery
size and power consumption of the device can be further minimized.
In other embodiments, tissue resistance and tissue reactance are
measured at a single frequency. In some embodiments, the quality of
the coupling of the electrode to tissue can be determined, and such
that the integrity of the measured patient data can be verified.
The quality of the coupling of the electrodes to tissue can be
quantified in many ways, for example with at least one of tissue
resistance measured at an additional frequency, tissue reactance
measured at the same frequency as the resistance, tissue impedance
measured between any two electrodes, or a signal to noise ratio
from electrocardiogram measurements. In many embodiments, the
adherent device can be continuously worn by the patient for an
extended period, for example at least one week, and reliable
measurements obtained with the improved comfort and small size of
the device.
[0014] In a first aspect, embodiments of the present invention
provide an adherent device for heart failure patient monitoring.
The device comprises an adhesive patch and at least two electrodes
connected to the patch that are capable of electrically coupling to
the skin of a patient. Circuitry coupled to the at least two
electrodes measures a hydration signal of the patient. The
hydration signal comprises bioimpedance data, for example tissue
resistance, which is used to determine changes in patient body
fluid. The device may use low measurement frequencies to minimize
the capacitative effects and isolate the extracellular impedance.
This can be beneficial for the detection of some patient
conditions, for example heart failure decompensation, because the
intracellular fluid does not change significantly over short
periods of time, and the edema in heart failure may comprise
extracellular edema.
[0015] In some embodiments, a single measurement frequency is
used.
[0016] In some embodiments, multiple measurement frequencies are
used to observe frequency dependent changes in the measured
resistance. These observations may be used to determine the quality
of the measurements taken or of the skin-electrode interface.
[0017] In some embodiments, the measured hydration signal comprises
only tissue resistance.
[0018] In some embodiments, the measured hydration signal comprises
tissue resistance and tissue reactance.
[0019] In another aspect, embodiments of the present invention
provide a method of monitoring a patient for heart failure. An
adhesive patch is adhered to a skin of the patient so as to couple
at least two electrodes to the skin of the patient. Circuitry
coupled to the at least two electrodes measures bioimpedance to
determine changes in patient body fluid.
[0020] In another aspect, embodiments of the present invention
provide an adherent device to monitor a tissue hydration of a
patient. The device includes an adhesive patch that adheres to the
skin of the patient and at least four electrodes connected to the
patch and capable of electrically coupling to the patient.
Circuitry is coupled to the at least four electrodes to measure a
tissue resistance of the patient and is configured to determine the
tissue hydration in response to the tissue resistance.
[0021] In some embodiments, the circuitry includes a processor
system that is configured to determine the hydration of the patient
in response to the tissue resistance.
[0022] In some embodiments, the impedance circuitry is configured
to measure the tissue resistance at a single frequency without
tissue reactance. The processor system is configured to determine
the tissue hydration in response to the tissue resistance measured
at the single frequency.
[0023] In some embodiments, the tissue resistance corresponds to a
change in patient body fluid. A processor may be coupled to the
impedance circuitry, such that the processor is configured to
determine an amount of extracellular edema from the change in
patient body fluid.
[0024] In some embodiments, the hydration signal of the patient
comprises a measurement of extracellular fluid.
[0025] In some embodiments, the impedance circuitry is configured
to measure the hydration signal using at least one low measurement
frequency. The at least one low measurement frequency may be in the
range of 5 to 15 kHz. The at least one low measurement frequency
may comprise a single measurement frequency, which may be in the
range of 0 to 10 kHz.
[0026] In other embodiments the at least one low measurement
frequency may comprise multiple measurement frequencies. The
hydration signal may comprise a tissue reactance measurement.
[0027] In another aspect, embodiments of the present invention
provide an adherent device to monitor a patient. The device
includes an adhesive patch to adhere to a skin of the patient and
at least four electrodes connected to the patch and capable of
electrically coupling to the patient at a skin-electrode interface.
Impedance circuitry is coupled to the at least four electrodes to
measure a hydration signal of the patient. The impedance circuitry
is configured to measure multiple frequencies.
[0028] In some embodiments, the hydration signal comprises a tissue
resistance measurement and a tissue reactance measurement.
[0029] In some embodiments, the device includes a processor coupled
to the impedance circuitry, where the processor is configured to
determine a quality of the skin-electrode interface from at least
one of an ECG signal-to-noise ratio, a tissue reactance, tissue
impedance measured between any two electrodes, or a second
measurement frequency. The processor may be configured to determine
the quality of the skin-electrode interface from a second
measurement frequency and may be configured to measure a droop in
the tissue resistance.
[0030] In another aspect, embodiments of the present invention
provide a method of monitoring a patient. The method includes
adhering an adhesive patch to a skin of the patient to couple at
least four electrodes to the skin of the patient to form a
skin-electrode interface and measuring a hydration signal of the
patient with impedance circuitry that is coupled to the at least
four electrodes. The hydration signal comprises a tissue resistance
measurement.
[0031] In some embodiments, the tissue resistance measurement
corresponds to a change in patient body fluid. The method may also
include determining an amount of extracellular edema from the
change in patient body fluid with a processor coupled to the
impedance circuitry.
[0032] In some embodiments, the hydration signal is measured with
at least one low measurement frequency. The at least one low
measurement frequency may be between 0 and 10 kHz. The at least one
low measurement frequency may comprise a single measurement
frequency or multiple measurement frequencies.
[0033] In some embodiments, the hydration signal also includes a
tissue reactance measurement. The method may also include
determining a quality of the skin-electrode coupling from the
tissue reactance measurement. The quality of the skin-electrode
coupling may be determined by at least one of determining an ECG
signal-to-noise ratio, determining a tissue reactance, measuring a
tissue impedance between any two electrodes, or measuring
resistance at a second measurement frequency.
[0034] In another aspect, embodiments of the present invention
provide a method of monitoring a patient, where the method includes
adhering an adhesive patch to the skin of the patient to couple at
least four electrodes to the skin of the patient to form a
skin-electrode interface. A hydration signal of the patient is
measured with impedance circuitry coupled to the at least four
electrodes, where the hydration signal comprises a tissue
resistance measurement and a tissue reactance measurement. An
amount of extracellular edema is determined from the tissue
resistance measurement and a quality of skin-electrode coupling is
determined from the tissue reactance measurement.
[0035] In some embodiments, the method also includes indicating a
replacement status of the adhesive patch based on the quality of
the skin-electrode coupling.
[0036] In another aspect, embodiments of the present invention
provide an adherent device to monitor a patient. The device
includes an adhesive patch to adhere to a skin of the patient and
at least four electrodes mechanically coupled to the patch and
capable of electrically coupling to the patient. The at least four
electrodes comprise at least two force electrodes and at least two
sense electrodes. Impedance circuitry is electrically coupled to
the at least two force electrodes to force an electrical current
and is coupled to the at least two sense electrodes to measure a
hydration signal of the patient, where the hydration signal
comprises a tissue resistance measurement. A processor system is
coupled to the impedance circuitry and configured to determine an
amount of extracellular edema from the hydration signal.
[0037] In some embodiments, the processor system is configured to
calculate and report a patient risk of an adverse cardiac event to
at least one of a remote center or a physician based on the amount
of extracellular edema.
[0038] In another aspect, embodiments of the present invention
provide a method of monitoring a patient. The method includes
adhering an adhesive patch to the skin of the patient so as to
couple at least four electrodes to the skin of the patient. The at
least four electrodes comprise at least two force electrodes and at
least two sense electrodes. A tissue resistance of the patient is
measured with impedance circuitry electrically coupled to the at
least two force electrodes and to the at least two sense
electrodes, such that the force electrodes force an electrical
current between the at least two force electrodes, wherein the
impedance circuitry generates a hydration signal. An amount of
extracellular edema is determined from the hydration signal.
[0039] In some embodiments, the electrical current is a low
frequency current. The low frequency current may have a frequency
from 0 to 10 kHz.
[0040] In some embodiments, the electrical current has a single
measurement frequency.
BRIEF DESCRIPTION OF THE DRAWINGS
[0041] FIG. 1A shows a patient and a monitoring system comprising
an adherent device, according to embodiments of the present
invention;
[0042] FIG. 1B shows a bottom view of the adherent device as in
FIG. 1A comprising an adherent patch;
[0043] FIG. 1C shows a top view of the adherent patch, as in FIG.
1B;
[0044] FIG. 1D shows a printed circuit boards and electronic
components over the adherent patch, as in FIG. 1C;
[0045] FIG. 1D-1 shows an equivalent circuit that can be used to
determine optimal frequencies for determining patient hydration,
according to embodiments of the present invention;
[0046] FIG. 1E shows batteries positioned over the printed circuit
board and electronic components as in FIG. 1D;
[0047] FIG. 1F shows a top view of an electronics housing and a
breathable cover over the batteries, electronic components and
printed circuit board as in FIG. 1E;
[0048] FIG. 1G shows a side view of the adherent device as in FIGS.
1A to 1F;
[0049] FIG. 1H shown a bottom isometric view of the adherent device
as in FIGS. 1A to 1G;
[0050] FIGS. 1I and 1J show a side cross-sectional view and an
exploded view, respectively, of the adherent device as in FIGS. 1A
to 1H;
[0051] FIG. 1K shows at least one electrode configured to
electrically couple to a skin of the patient through a breathable
tape, according to embodiments of the present invention;
[0052] FIGS. 2A to 2C show a system to monitor a patient for an
extended period comprising a reusable electronic component and a
plurality of disposable patch components, according to embodiments
of the present invention;
[0053] FIG. 2D shows a method of using the system as in FIGS. 2A to
2C;
[0054] FIGS. 3A to 3D show a method of monitoring a patient for an
extended period with an adherent patch with adherent patches
alternatively adhered to the right side or the left side of the
patient;
[0055] FIG. 4A shows an adherent device to measure an impedance
signal and an electrocardiogram signal, according to embodiments of
the present invention; and
[0056] FIG. 4B shows a method of measuring the impedance signal and
the electrocardiogram signal, according to embodiments of the
present invention.
[0057] FIG. 5A shows a method for monitoring a patient and
responding to a signal event.
[0058] FIGS. 5B, 5C and 5D show methods for monitoring body fluid
of a patient.
[0059] FIG. 6A shows a graph of measurements of tissue resistance
over a range of measurement frequencies, in accordance with
embodiments of the present invention, and FIG. 6B shows a portion
of the graph of FIG. 6A enlarged.
DETAILED DESCRIPTION OF THE INVENTION
[0060] Embodiments of the present invention relate to patient
monitoring. Although embodiments make specific reference to
monitoring impedance and electrocardiogram signals with an adherent
patch, the system methods and device described herein may be
applicable to any application in which physiological monitoring is
used, for example wireless physiological monitoring for extended
periods.
[0061] Decompensation is failure of the heart to maintain adequate
blood circulation. Although the heart can maintain at least some
pumping of blood, the quantity is inadequate to maintain healthy
tissues. Several symptoms can result from decompensation including
pulmonary congestion, breathlessness, faintness, cardiac
palpitation, edema of the extremities, and enlargement of the
liver. Cardiac decompensation can result in slow or sudden death.
Sudden Cardiac Arrest (hereinafter "SCA"), also referred to as
sudden cardiac death, is an abrupt loss of cardiac pumping function
that can be caused by a ventricular arrhythmia, for example
ventricular tachycardia and/or ventricular fibrillation. Although
decompensation and SCA can be related in that patients with
decompensation are also at an increased risk for SCA,
decompensation is primarily a mechanical dysfunction caused by
inadequate blood flow, and SCA is primarily an electrical
dysfunction caused by inadequate and/or inappropriate electrical
signals of the heart.
[0062] Embodiments may use bioimpedance to measure changes in
patient body fluid to aid in heart failure patient monitoring, for
example changes in resistance to detect an impending
decompensation. Because intracellular fluid does not change
significantly over short periods of time, and edema in heart
failure comprises extracellular edema, the device can use low
measurement frequencies, for example 0-10 kHz, to minimize
capacitive effects and isolate extracellular impedance.
[0063] Although some embodiments may use a single measurement
frequency, multiple measurement frequencies may also be used.
Frequency-dependent changes in measured resistance may be used to
determine the quality of the measurement and of the skin-electrode
interface, such as with adherent and/or wearable embodiments. For
example, wetting during showering can cause a low frequency droop
in measured resistance, which may indicate that data collection
should be temporarily suspended.
[0064] Bioimpedance comprises two components, tissue resistance and
tissue reactance, and change in body fluid can be closely
correlated with change in the tissue resistance. In many
embodiments, tissue resistance is measured and tracked, such that
it may not be necessary to measure the reactance. For example,
relative body fluid change can be determined in a computationally
efficient manner in response to the measured resistance, such that
the relative change in body fluid can be determined without
measurement of reactance and without a determination of absolute
body fluid.
[0065] Although the quality of the skin electrode interface can be
determined in many ways, in many embodiments, tissue reactance may
be used to measure the quality of the skin-electrode coupling. For
example, resistance may be used to track changes in body fluid, and
reactance used to determine the quality of the skin-electrode
interface. An increase in reactance may indicate a degradation of
skin-electrode contact, and can be used as a replacement
indicator.
[0066] In at least some embodiments, resistance at low frequencies,
for example less than 10 kHz, can be used to determine the quality
of impedance measurements. For example, when a shower is taken the
resistance may decrease, or droop, at lower frequencies but remain
consistent at higher frequencies, which indicates that the adherent
device and/or patient are exposed to water. FIGS. 6A and 6B,
described more fully herein below, illustrate the low frequency
droop effect on the measured resistance.
[0067] In many embodiments, the adherent devices described herein
may be used for 90 day monitoring, or more, and may comprise
completely disposable components and/or reusable components, and
can provide reliable data acquisition and transfer. In many
embodiments, the patch is configured for patient comfort, such that
the adherent patch can be worn and/or tolerated by the patient for
extended periods, for example 90 days or more. The patch may be
worn continuously for at least seven days, for example 14 days, and
then replaced with another patch. Adherent devices with comfortable
patches that can be worn for extended periods and in which patches
can be replaced and the electronics modules reused are described in
U.S. Pat. App. Nos. 60/972,537, entitled "Adherent Device with
Multiple Physiological Sensors"; and 60/972,629, entitled "Adherent
Device with Multiple Physiological Sensors", both filed on Sep. 14,
2007, the full disclosures of which have been previously
incorporated herein by reference. In many embodiments, the adherent
patch comprises a tape, which comprises a material, preferably
breathable, with an adhesive, such that trauma to the patient skin
can be minimized while the patch is worn for the extended period.
The printed circuit board may comprise a flex printed circuit board
that can flex with the patient to provide improved patient
comfort.
[0068] FIG. 1A shows a patient P and a monitoring system 10.
Patient P comprises a midline M, a first side S1, for example a
right side, and a second side S2, for example a left side.
Monitoring system 10 comprises an adherent device 100. Adherent
device 100 can be adhered to a patient P at many locations, for
example thorax T of patient P. In many embodiments, the adherent
device may adhere to one side of the patient, from which side data
can be collected. Work in relation with embodiments of the present
invention suggests that location on a side of the patient can
provide comfort for the patient while the device is adhered to the
patient.
[0069] Monitoring system 10 includes components to transmit data to
a remote center 106. Remote center 106 can be located in a
different building from the patient, for example in the same town
as the patient, and can be located as far from the patient as a
separate continent from the patient, for example the patient
located on a first continent and the remote center located on a
second continent. Adherent device 100 can communicate wirelessly to
an intermediate device 102, for example with a single wireless hop
from the adherent device on the patient to the intermediate device.
Intermediate device 102 can communicate with remote center 106 in
many ways, for example with an internet connection and/or with a
cellular connection. In many embodiments, monitoring system 10
comprises a distributed processing system with at least one
processor comprising a tangible medium of device 100, at least one
processor 102P of intermediate device 102, and at least one
processor 106P at remote center 106, each of which processors can
be in electronic communication with the other processors. At least
one processor 102P comprises a tangible medium 102T, and at least
one processor 106P comprises a tangible medium 106T. Remote
processor 106P may comprise a backend server located at the remote
center. Remote center 106 can be in communication with a health
care provider 108A with a communication system 107A, such as the
Internet, an intranet, phone lines, wireless and/or satellite
phone. Health care provider 108A, for example a family member, can
be in communication with patient P with a communication, for
example with a two way communication system, as indicated by arrow
109A, for example by cell phone, email, landline. Remote center 106
can be in communication with a health care professional, for
example a physician 108B, with a communication system 107B, such as
the Internet, an intranet, phone lines, wireless and/or satellite
phone. Physician 108B can be in communication with patient P with a
communication, for example with a two way communication system, as
indicated by arrow 109B, for example by cell phone, email,
landline. Remote center 106 can be in communication with an
emergency responder 108C, for example a 911 operator and/or
paramedic, with a communication system 107C, such as the Internet,
an intranet, phone lines, wireless and/or satellite phone.
Emergency responder 108C can travel to the patient as indicated by
arrow 109C. Thus, in many embodiments, monitoring system 10
comprises a closed loop system in which patient care can be
monitored and implemented from the remote center in response to
signals from the adherent device.
[0070] In many embodiments, the adherent device may continuously
monitor physiological parameters, communicate wirelessly with a
remote center, and provide alerts when necessary. The system may
comprise an adherent patch, which attaches to the patient's thorax
and contains sensing electrodes, battery, memory, logic, and
wireless communication capabilities. In some embodiments, the patch
can communicate with the remote center, via the intermediate device
in the patient's home. In some embodiments, remote center 106
receives the patient data and applies a patient evaluation
algorithm, for example the prediction algorithm to predict cardiac
decompensation. In some embodiments, the algorithm may comprise an
algorithm to predict impending cardiac decompensation is described
in U.S. Pat. App. No. 60/972,512, the full disclosure of which has
been previously incorporated herein by reference. When a flag is
raised, the center may communicate with the patient, hospital,
nurse, and/or physician to allow for therapeutic intervention, for
example to prevent decompensation.
[0071] The adherent device may be affixed and/or adhered to the
body in many ways. For example, with at least one of the following
an adhesive tape, a constant-force spring, suspenders around
shoulders, a screw-in microneedle electrode, a pre-shaped
electronics module to shape fabric to a thorax, a pinch onto roll
of skin, or transcutaneous anchoring. Patch and/or device
replacement may occur with a keyed patch (e.g. two-part patch), an
outline or anatomical mark, a low-adhesive guide (place
guide|remove old patch|place new patch|remove guide), or a keyed
attachment for chatter reduction. The patch and/or device may
comprise an adhesiveless embodiment (e.g. chest strap), and/or a
low-irritation adhesive for sensitive skin. The adherent patch
and/or device can comprise many shapes, for example at least one of
a dogbone, an hourglass, an oblong, a circular or an oval
shape.
[0072] In many embodiments, the adherent device may comprise a
reusable electronics module with replaceable patches, and each of
the replaceable patches may include a battery. The module may
collect cumulative data for approximately 90 days and/or the entire
adherent component (electronics+patch) may be disposable. In a
completely disposable embodiment, a "baton" mechanism may be used
for data transfer and retention, for example baton transfer may
include baseline information. In some embodiments, the device may
have a rechargeable module, and may use dual battery and/or
electronics modules, wherein one module 101A can be recharged using
a charging station 103 while the other module 101B is placed on the
adherent patch with connectors. In some embodiments, the
intermediate device 102 may comprise the charging module, data
transfer, storage and/or transmission, such that one of the
electronics modules can be placed in the intermediate device for
charging and/or data transfer while the other electronics module is
worn by the patient.
[0073] System 10 can perform the following functions: initiation,
programming, measuring, storing, analyzing, communicating,
predicting, and displaying. The adherent device may contain a
subset of the following physiological sensors: bioimpedance,
respiration, respiration rate variability, heart rate (ave, min,
max), heart rhythm, hear rate variability (HRV), heart rate
turbulence (HRT), heart sounds (e.g. S3), respiratory sounds, blood
pressure, activity, posture, wake/sleep, orthopnea,
temperature/heat flux, and weight. The activity sensor may comprise
one or more of the following: ball switch, accelerometer, minute
ventilation, HR, bioimpedance noise, skin temperature/heat flux,
BP, muscle noise, posture.
[0074] The adherent device can wirelessly communicate with remote
center 106. The communication may occur directly (via a cellular or
Wi-Fi network), or indirectly through intermediate device 102.
Intermediate device 102 may consist of multiple devices, which can
communicate wired or wirelessly to relay data to remote center
106.
[0075] In many embodiments, instructions are transmitted from
remote site 106 to a processor supported with the adherent patch on
the patient, and the processor supported with the patient can
receive updated instructions for the patient treatment and/or
monitoring, for example while worn by the patient.
[0076] FIG. 1B shows a bottom view of adherent device 100 as in
FIG. 1A comprising an adherent patch 110. Adherent patch 110
comprises a first side, or a lower side 110A, that is oriented
toward the skin of the patient when placed on the patient. In many
embodiments, adherent patch 110 comprises a tape 110T which is a
material, preferably breathable, with an adhesive 116A. Patient
side 110A comprises adhesive 116A to adhere the patch 110 and
adherent device 100 to patient P. Electrodes 112A, 112B, 112C and
112D are affixed to adherent patch 110. In many embodiments, at
least four electrodes are attached to the patch, for example six
electrodes. In some embodiments the patch comprises two electrodes,
for example two electrodes to measure the electrocardiogram (ECG)
of the patient. Gel 114A, gel 114B, gel 114C and gel 114D can each
be positioned over electrodes 112A, 112B, 112C and 112D,
respectively, to provide electrical conductivity between the
electrodes and the skin of the patient. In many embodiments, the
electrodes can be affixed to the patch 110, for example with known
methods and structures such as rivets, adhesive, stitches, etc. In
many embodiments, patch 110 comprises a breathable material to
permit air and/or vapor to flow to and from the surface of the
skin.
[0077] FIG. 1C shows a top view of the adherent patch 100, as in
FIG. 1B. Adherent patch 100 comprises a second side, or upper side
110B. In many embodiments, electrodes 112A, 112B, 112C and 112D
extend from lower side 110A through adherent patch 110 to upper
side 110B. An adhesive 116B can be applied to upper side 110B to
adhere structures, for example a breathable cover, to the patch
such that the patch can support the electronics and other
structures when the patch is adhered to the patient. The PCB may
comprise completely flex PCB, rigid PCB, rigid PCB combined flex
PCB and/or rigid PCB boards connected by cable.
[0078] FIG. 1D shows a printed circuit boards and electronic
components over adherent patch 110, as in FIG. 1A to 1C. In some
embodiments, a printed circuit board (PCB), for example flex
printed circuit board120, may be connected to electrodes 112A,
112B, 112C and 112D with connectors 122A, 122B, 122C and 122D. Flex
printed circuit board 120 can include traces 123A, 123B, 123C and
123D that extend to connectors 122A, 122B, 122C and 122D,
respectively, on the flex PCB. Connectors 122A, 122B, 122C and 122D
can be positioned on flex printed circuit board 120 in alignment
with electrodes 112A, 112B, 112C and 112D so as to electrically
couple the flex PCB with the electrodes. In some embodiments,
connectors 122A, 122B, 122C and 122D may comprise insulated wires
and/or a film with conductive ink that provide strain relief
between the PCB and the electrodes. For example, connectors 122A,
122B, 122C and 122D may comprise a flexible polyester film coated
with conductive silver ink. In some embodiments, additional PCB's,
for example rigid PCB's 120A, 120B, 120C and 120D, can be connected
to flex printed circuit board 120. Electronic components 130 can be
connected to flex printed circuit board 120 and/or mounted thereon.
In some embodiments, electronic components 130 can be mounted on
the additional PCB's.
[0079] Electronic components 130 comprise components to take
physiologic measurements, transmit data to remote center 106 and
receive commands from remote center 106. In many embodiments,
electronics components 130 may comprise known low power circuitry,
for example complementary metal oxide semiconductor (CMOS)
circuitry components. Electronics components 130 comprise an
activity sensor and activity circuitry 134, impedance circuitry 136
and electrocardiogram circuitry, for example ECG circuitry 136. In
some embodiments, electronics circuitry 130 may comprise a
microphone and microphone circuitry 142 to detect an audio signal
from within the patient, and the audio signal may comprise a heart
sound and/or a respiratory sound, for example an S3 heart sound and
a respiratory sound with rales and/or crackles.
[0080] Electronics circuitry 130 may comprise a temperature sensor,
for example a thermistor in contact with the skin of the patient,
and temperature sensor circuitry 144 to measure a temperature of
the patient, for example a temperature of the skin of the patient.
A temperature sensor may be used to determine the sleep and wake
state of the patient. The temperature of the patient can decrease
as the patient goes to sleep and increase when the patient wakes
up.
[0081] Work in relation to embodiments of the present invention
suggests that skin temperature may effect impedance and/or
hydration measurements, and that skin temperature measurements may
be used to correct impedance and/or hydration measurements. In some
embodiments, increase in skin temperature or heat flux can be
associated with increased vaso-dilation near the skin surface, such
that measured impedance measurement decreased, even through the
hydration of the patient in deeper tissues under the skin remains
substantially unchanged. Thus, use of the temperature sensor can
allow for correction of the hydration signals to more accurately
assess the hydration, for example extra cellular hydration, of
deeper tissues of the patient, for example deeper tissues in the
thorax.
[0082] Electronics circuitry 130 may comprise a processor 146.
Processor 146 comprises a tangible medium, for example read only
memory (ROM), electrically erasable programmable read only memory
(EEPROM) and/or random access memory (RAM). Electronic circuitry
130 may comprise real time clock and frequency generator circuitry
148. In some embodiments, processor 136 may comprise the frequency
generator and real time clock. The processor can be configured to
control a collection and transmission of data from the impedance
circuitry electrocardiogram circuitry and the accelerometer. In
many embodiments, device 100 comprise a distributed processor
system, for example with multiple processors on device 100.
[0083] In many embodiments, electronics components 130 comprise
wireless communications circuitry 132 to communicate with remote
center 106. The wireless communication circuitry can be coupled to
the impedance circuitry, the electrocardiogram circuitry and the
accelerometer to transmit to a remote center with a communication
protocol at least one of the hydration signal, the
electrocardiogram signal or the inclination signal. In specific
embodiments, wireless communication circuitry is configured to
transmit the hydration signal, the electrocardiogram signal and the
inclination signal to the remote center with a single wireless hop,
for example from wireless communication circuitry 132 to
intermediate device 102. The communication protocol comprises at
least one of Bluetooth, Zigbee, WiFi, WiMax, IR, amplitude
modulation or frequency modulation. In many embodiments, the
communications protocol comprises a two way protocol such that the
remote center is capable of issuing commands to control data
collection.
[0084] Intermediate device 102 may comprise a data collection
system to collect and store data from the wireless transmitter. The
data collection system can be configured to communicate
periodically with the remote center. The data collection system can
transmit data in response to commands from remote center 106 and/or
in response to commands from the adherent device.
[0085] Activity sensor and activity circuitry 134 can comprise many
known activity sensors and circuitry. In many embodiments, the
accelerometer comprises at least one of a piezoelectric
accelerometer, capacitive accelerometer or electromechanical
accelerometer. The accelerometer may comprises a 3-axis
accelerometer to measure at least one of an inclination, a
position, an orientation or acceleration of the patient in three
dimensions. Work in relation to embodiments of the present
invention suggests that three dimensional orientation of the
patient and associated positions, for example sitting, standing,
lying down, can be very useful when combined with data from other
sensors, for example ECG data and/or hydration data.
[0086] Impedance circuitry 136 can generate both hydration data and
respiration data. In many embodiments, impedance circuitry 136 is
electrically connected to electrodes 112A, 112B, 112C and 112D in a
four pole configuration, such that electrodes 112A and 112D
comprise outer electrodes that are driven with a current and
comprise force electrodes that force the current through the
tissue. The current delivered between electrodes 112A and 112D
generates a measurable voltage between electrodes 112B and 112C,
such that electrodes 112B and 112C comprise inner, sense,
electrodes that sense and/or measure the voltage in response to the
current from the force electrodes. In some embodiments, electrodes
112B and 112C may comprise force electrodes and electrodes 112A and
112B may comprise sense electrodes. The voltage measured by the
sense electrodes can be used to measure the impedance of the
patient and determine the respiration rate and/or hydration of the
patient.
[0087] FIG. 1D1 shows an equivalent circuit 152 that can be used to
determine optimal frequencies for measuring patient hydration. Work
in relation to embodiments of the present invention indicates that
the frequency of the current and/or voltage at the force electrodes
can be selected so as to provide impedance signals related to the
extracellular and/or intracellular hydration of the patient tissue.
Equivalent circuit 152 comprises an intracellular resistance 156,
or R(ICW) in series with a capacitor 154, and an extracellular
resistance 158, or R(ECW). Extracellular resistance 158 is in
parallel with intracellular resistance 156 and capacitor 154
related to capacitance of cell membranes. In many embodiments,
impedances can be measured and provide useful information over a
wide range of frequencies, for example from about 0.5 kHz to about
200 KHz. Work in relation to embodiments of the present invention
suggests that extracellular resistance 158 can be significantly
related extracellular fluid and to cardiac decompensation, and that
extracellular resistance 158 and extracellular fluid can be
effectively measured with frequencies in a range from about 0.5 kHz
to about 20 kHz, for example from about 1 kHz to about 10 kHz. In
some embodiments, a single frequency can be used to determine the
extracellular resistance and/or fluid. As sample frequencies
increase from about 10 kHz to about 20 kHz, capacitance related to
cell membranes decrease the impedance, such that the intracellular
fluid contributes to the impedance and/or hydration measurements.
Thus, many embodiments of the present invention measure hydration
with frequencies from about 0.5 kHz to about 20 kHz to determine
patient hydration.
[0088] In many embodiments, impedance circuitry 136 can be
configured to determine respiration of the patient. In specific
embodiments, the impedance circuitry can measure the hydration at
25 Hz intervals, for example at 25 Hz intervals using impedance
measurements with a frequency from about 0.5 kHz to about 20
kHz.
[0089] ECG circuitry 138 can generate electrocardiogram signals and
data from two or more of electrodes 112A, 112B, 112C and 112D in
many ways. In some embodiments, ECG circuitry 138 is connected to
inner electrodes 112B and 122C, which may comprise sense electrodes
of the impedance circuitry as described above. In some embodiments,
ECG circuitry 138 can be connected to electrodes 112A and 112D so
as to increase spacing of the electrodes. The inner electrodes may
be positioned near the outer electrodes to increase the voltage of
the ECG signal measured by ECG circuitry 138. In many embodiments,
the ECG circuitry may measure the ECG signal from electrodes 112A
and 112D when current is not passed through electrodes 112A and
112D, for example with switches as described in U.S. App. No.
60/972,527, the full disclosure of which has been previously
incorporated herein by reference.
[0090] FIG. 1E shows batteries 150 positioned over the flex printed
circuit board and electronic components as in FIG. 1D. Batteries
150 may comprise rechargeable batteries that can be removed and/or
recharged. In some embodiments, batteries 150 can be removed from
the adherent patch and recharged and/or replaced.
[0091] FIG. 1F shows a top view of a cover 162 over the batteries,
electronic components and flex printed circuit board as in FIGS. 1A
to 1E. In many embodiments, an electronics housing 160 may be
disposed under cover 162 to protect the electronic components, and
in some embodiments electronics housing 160 may comprise an
encapsulant over the electronic components and PCB. In some
embodiments, cover 162 can be adhered to adherent patch 110 with an
adhesive 164 on an underside of cover 162. In many embodiments,
electronics housing 160 may comprise a water proof material, for
example a sealant adhesive such as epoxy or silicone coated over
the electronics components and/or PCB. In some embodiments,
electronics housing 160 may comprise metal and/or plastic. Metal or
plastic may be potted with a material such as epoxy or
silicone.
[0092] Cover 162 may comprise many known biocompatible cover,
casing and/or housing materials, such as elastomers, for example
silicone. The elastomer may be fenestrated to improve
breathability. In some embodiments, cover 162 may comprise many
known breathable materials, for example polyester, polyamide,
and/or elastane (Spandex). The breathable fabric may be coated to
make it water resistant, waterproof, and/or to aid in wicking
moisture away from the patch.
[0093] FIG. 1G shows a side view of adherent device 100 as in FIGS.
1A to 1F. Adherent device 100 comprises a maximum dimension, for
example a length 170 from about 4 to 10 inches (from about 100 mm
to about 250 mm), for example from about 6 to 8 inches (from about
150 mm to about 200 mm). In some embodiments, length 170 may be no
more than about 6 inches (no more than about 150 mm). Adherent
device 100 comprises a thickness 172. Thickness 172 may comprise a
maximum thickness along a profile of the device. Thickness 172 can
be from about 0.2 inches to about 0.4 inches (from about 5 mm to
about 10 mm), for example about 0.3 inches (about 7.5 mm).
[0094] FIG. 1H shown a bottom isometric view of adherent device 100
as in FIGS. 1A to 1G. Adherent device 100 comprises a width 174,
for example a maximum width along a width profile of adherent
device 100. Width 174 can be from about 2 to about 4 inches (from
about 50 mm to 100 mm), for example about 3 inches (about 75
mm).
[0095] FIGS. 1I and 1J show a side cross-sectional view and an
exploded view, respectively, of adherent device 100 as in FIGS. 1A
to 1H. Device 100 comprises several layers. Gel 114A, or gel layer,
is positioned on electrode 112A to provide electrical conductivity
between the electrode and the skin. Electrode 112A may comprise an
electrode layer. Adherent patch 110 may comprise a layer of
breathable tape 110T, for example a known breathable tape, such as
tricot-knit polyester fabric. An adhesive 116A, for example a layer
of acrylate pressure sensitive adhesive, can be disposed on
underside 110A of adherent patch 110.
[0096] A gel cover 180, or gel cover layer, for example a
polyurethane non-woven tape, can be positioned over patch 110
comprising the breathable tape. A PCB layer, for example flex
printed circuit board 120, or flex PCB layer, can be positioned
over gel cover 180 with electronic components 130 connected and/or
mounted to flex printed circuit board 120, for example mounted on
flex PCB so as to comprise an electronics layer disposed on the
flex PCB layer. In many embodiments, the adherent device may
comprise a segmented inner component, for example the PCB may be
segmented to provide at least some flexibility. In many
embodiments, the electronics layer may be encapsulated in
electronics housing 160 which may comprise a waterproof material,
for example silicone or epoxy. In many embodiments, the electrodes
are connected to the PCB with a flex connection, for example trace
123A of flex printed circuit board 120, so as to provide strain
relive between the electrodes 112A, 112B, 112C and 112D and the
PCB.
[0097] Gel cover 180 can inhibit flow of gel 114A and liquid. In
many embodiments, gel cover 180 can inhibit gel 114A from seeping
through breathable tape 110T to maintain gel integrity over time.
Gel cover 180 can also keep external moisture, for example liquid
water, from penetrating though the gel cover into gel 114A while
allowing moisture vapor from the gel, for example moisture vapor
from the skin, to transmit through the gel cover.
[0098] In many embodiments, cover 162 can encase the flex PCB
and/or electronics and can be adhered to at least one of the
electronics, the flex PCB or adherent patch 110, so as to protect
at least the electronics components and the PCB. Cover 162 can
attach to adherent patch 110 with adhesive 116B. Cover 162 can
comprise many known biocompatible cover materials, for example
silicone. Cover 162 can comprise an outer polymer cover to provide
smooth contour without limiting flexibility. In many embodiments,
cover 162 may comprise a breathable fabric. Cover 162 may comprise
many known breathable fabrics, for example breathable fabrics as
described above. In some embodiments, the breathable cover may
comprise a breathable water resistant cover. In some embodiments,
the breathable fabric may comprise polyester, nylon, polyamide,
and/or elastane (Spandex) to allow the breathable fabric to stretch
with body movement. In some embodiments, the breathable tape may
contain and elute a pharmaceutical agent, such as an antibiotic,
anti-inflammatory or antifungal agent, when the adherent device is
placed on the patient.
[0099] The breathable cover 162 and adherent patch 110 comprise
breathable tape can be configured to couple continuously for at
least one week the at least one electrode to the skin so as to
measure breathing of the patient. The breathable tape may comprise
the stretchable breathable material with the adhesive and the
breathable cover may comprises a stretchable water resistant
material connected to the breathable tape, as described above, such
that both the adherent patch and cover can stretch with the skin of
the patient. Arrows 182 show stretching of adherent patch 110, and
the stretching of adherent patch can be at least two dimensional
along the surface of the skin of the patient. As noted above,
connectors 122A, 122B, 122C and 122D between PCB 130 and electrodes
112A, 112B, 112C and 112D may comprise insulated wires that provide
strain relief between the PCB and the electrodes, such that the
electrodes can move with the adherent patch as the adherent patch
comprising breathable tape stretches. Arrows 184 show stretching of
cover 162, and the stretching of the cover can be at least two
dimensional along the surface of the skin of the patient. Cover 162
can be attached to adherent patch 110 with adhesive 116B such that
cover 162 stretches and/or retracts when adherent patch 110
stretches and/or retracts with the skin of the patient. For
example, cover 162 and adherent patch 110 can stretch in two
dimensions along length 170 and width 174 with the skin of the
patient, and stretching along length 170 can increase spacing
between electrodes. Stretching of the cover and adherent patch 110,
for example in two dimensions, can extend the time the patch is
adhered to the skin as the patch can move with the skin such that
the patch remains adhered to the skin Electronics housing 160 can
be smooth and allow breathable cover 162 to slide over electronics
housing 160, such that motion and/or stretching of cover 162 is
slidably coupled with housing 160. The printed circuit board can be
slidably coupled with adherent patch 110 that comprises breathable
tape 110T, such that the breathable tape can stretch with the skin
of the patient when the breathable tape is adhered to the skin of
the patient, for example along two dimensions comprising length 170
and width 174. Electronics components 130 can be affixed to printed
circuit board 120, for example with solder, and the electronics
housing can be affixed over the PCB and electronics components, for
example with dip coating, such that electronics components 130,
printed circuit board 120 and electronics housing 160 are coupled
together. Electronics components 130, printed circuit board 120,
and electronics housing 160 are disposed between the stretchable
breathable material of adherent patch 110 and the stretchable water
resistant material of cover 160 so as to allow the adherent patch
110 and cover 160 to stretch together while electronics components
130, printed circuit board 120, and electronics housing 160 do not
stretch substantially, if at all. This decoupling of electronics
housing 160, printed circuit board 120 and electronic components
130 can allow the adherent patch 110 comprising breathable tape to
move with the skin of the patient, such that the adherent patch can
remain adhered to the skin for an extended time of at least one
week, for example two or more weeks.
[0100] An air gap 169 may extend from adherent patch 110 to the
electronics module and/or PCB, so as to provide patient comfort.
Air gap 169 allows adherent patch 110 and breathable tape 110T to
remain supple and move, for example bend, with the skin of the
patient with minimal flexing and/or bending of printed circuit
board 120 and electronic components 130, as indicated by arrows
186. Printed circuit board 120 and electronics components 130 that
are separated from the breathable tape 110T with air gap 169 can
allow the skin to release moisture as water vapor through the
breathable tape, gel cover, and breathable cover. This release of
moisture from the skin through the air gap can minimize, and even
avoid, excess moisture, for example when the patient sweats and/or
showers.
[0101] The breathable tape of adherent patch 110 may comprise a
first mesh with a first porosity and gel cover 180 may comprise a
breathable tape with a second porosity, in which the second
porosity is less than the first porosity to minimize, and even
inhibit, flow of the gel through the breathable tape. The gel cover
may comprise a polyurethane film with the second porosity.
[0102] In many embodiments, the adherent device comprises a patch
component and at least one electronics module. The patch component
may comprise adherent patch 110 comprising the breathable tape with
adhesive coating 116A, at least one electrode, for example
electrode 114A and gel 114. The at least one electronics module can
be separable from the patch component. In many embodiments, the at
least one electronics module comprises the flex printed circuit
board 120, electronic components 130, electronics housing 160 and
cover 162, such that the flex printed circuit board, electronic
components, electronics housing and cover are reusable and/or
removable for recharging and data transfer, for example as
described above. In many embodiments, adhesive 116B is coated on
upper side 110A of adherent patch 110B, such that the electronics
module can be adhered to and/or separated from the adhesive
component. In specific embodiments, the electronic module can be
adhered to the patch component with a releasable connection, for
example with Velcro.TM., a known hook and loop connection, and/or
snap directly to the electrodes. In many embodiments, two
electronics modules can be provided, such that one electronics
module can be worn by the patient while the other is charged, as
described above. Monitoring with multiple adherent patches for an
extended period is described in U.S. Pat. App. No. 60/972,537, the
full disclosure of which has been previously incorporated herein by
reference. Many patch components can be provided for monitoring
over the extended period. For example, about 12 patches can be used
to monitor the patient for at least 90 days with at least one
electronics module, for example with two reusable electronics
modules.
[0103] At least one electrode 112A can extend through at least one
aperture 180A in the breathable tape 110 and gel cover 180.
[0104] In some embodiments, the adhesive patch may comprise a
medicated patch that releases a medicament, such as antibiotic,
beta-blocker, ACE inhibitor, diuretic, or steroid to reduce skin
irritation. The adhesive patch may comprise a thin, flexible,
breathable patch with a polymer grid for stiffening. This grid may
be anisotropic, may use electronic components to act as a
stiffener, may use electronics-enhanced adhesive elution, and may
use an alternating elution of adhesive and steroid.
[0105] FIG. 1K shows at least one electrode 190 configured to
electrically couple to a skin of the patient through a breathable
tape 192. In many embodiments, at least one electrode 190 and
breathable tape 192 comprise electrodes and materials similar to
those described above. Electrode 190 and breathable tape 192 can be
incorporated into adherent devices as described above, so as to
provide electrical coupling between the skin an electrode through
the breathable tape, for example with the gel.
[0106] FIGS. 2A to 2C show a schematic illustration of a system 200
to monitor a patient for an extended period. FIG. 2A shows a
schematic illustration of system 200 comprising a reusable
electronics module 210 and a plurality of disposable patch
components comprising a first disposable patch component 220A, a
second disposable patch component 220B, a third disposable patch
component 220C and a fourth disposable patch component 220D.
Although four patch components a shown the plurality may comprise
as few as two patch component and as many as three or more patch
components, for example 25 patch components.
[0107] FIG. 2B shows a schematic illustration of a side
cross-sectional view of reusable electronics module 210. Reusable
electronics module 210 may comprises many of the structures
described above that may comprise the electronics module. In many
embodiments, reusable electronics module 210 comprises a PCB, for
example a flex PCB 212, electronics components 216, batteries 216,
and a cover 217, for example as described above. In some
embodiments, reusable electronics module 210 may comprise an
electronics housing over the electronics components and/or PCB as
described above. The electronics components may comprise circuitry
and/or sensors for measuring ECG signals, hydration impedance
signals, respiration impedance signals and accelerometer signals,
for example as described above. In many embodiments, reusable
electronics module 210 comprises a connector 219 adapted to connect
to each of the disposable patch components, sequentially, for
example one disposable patch component at a time. Connector 219 can
be formed in many ways, and may comprise known connectors as
described above, for example a snap. In some embodiments, the
connectors on the electronics module and adhesive component can be
disposed at several locations on the reusable electronics module
and disposable patch component, for example near each electrode,
such that each electrode can couple directly to a corresponding
location on the flex PCB of the reusable electronics component.
[0108] Alternatively or in combination with batteries 216, each of
the plurality of disposable patch components may comprise a
disposable battery. For example first disposable patch component
220A may comprise a disposable battery 214A; second disposable
patch component 220B may comprise a disposable battery 214B; third
disposable patch component 220C may comprise a disposable battery
214C; and a fourth disposable patch component 220D may comprise a
disposable battery 214D. Each of the disposable batteries, 214A,
214B, 214C and 214D may be affixed to each of disposable patches
220A, 220B, 220C and 220D, respectively, such that the batteries
are adhered to the disposable patch component before, during and
after the respective patch component is adhered to the patient.
Each of the disposable batteries, 214A, 214B, 214C and 214D may be
coupled to connectors 215A, 215B, 215C and 215D, respectively. Each
of connectors 215A, 215B, 215C and 215D can be configured to couple
to a connector of the reusable module 220, so as to power the
reusable module with the disposable battery coupled thereto. Each
of the disposable batteries, 214A, 214B, 214C and 214D may be
coupled to connectors 215A, 215B, 215C and 215D, respectively, such
that the batteries are not coupled to the electrodes of the
respective patch component, so as to minimize, and even avoid,
degradation of the electrodes and/or gel during storage when each
disposable battery is adhered to each respective disposable patch
component.
[0109] FIG. 2C shows a schematic illustration first disposable
patch component 220A of the plurality of disposable patch
components that is similar to the other disposable patch
components, for example second disposable patch component 220B,
third disposable patch component 220C and fourth disposable patch
component 220C. The disposable patch component comprises a
breathable tape 227A, an adhesive 226A on an underside of
breathable tape 227A to adhere to the skin of the patient, and at
least four electrodes 222A. The at least four electrodes 224A are
configured to couple to the skin of a patient, for example with a
gel 226A, in some embodiments the electrodes may extend through the
breathable tape to couple directly to the skin of the patient with
aid form the gel. In some embodiments, the at least four electrodes
may be indirectly coupled to the skin through a gel and/or the
breathable tape, for example as described above. A connector 229A
on the upper side of the disposable adhesive component can be
configured for attachment to connector 219 on reusable electronics
module 210 so as to electrically couple the electrodes with the
electronics module. The upper side of the disposable patch
component may comprise an adhesive 224A to adhere the disposable
patch component to the reusable electronics module. The reusable
electronics module can be adhered to the patch component with many
additional known ways to adhere components, for example with
Velcro.TM. comprising hooks and loops, snaps, a snap fit, a lock
and key mechanisms, magnets, detents and the like.
[0110] FIG. 2D shows a method 250 of using system 200, as in FIGS.
2A to 2C. A step 252 adheres electronics module 210 to first
disposable adherent patch component 220A of the plurality of
adherent patch components and adheres the first disposable patch
component to the skin of the patient, for example with the first
adherent patch component adhered to the reusable electronics
module. A step 254 removes the first disposable adherent patch from
the patient and separates first disposable adherent patch component
220A from reusable electronics module 210. A step 256 adheres
electronics module 210 to second disposable adherent patch
component 220B and adheres the second disposable patch component to
the skin of the patient, for example with the second adherent patch
component adhered to the reusable electronics module. A step 258
removes the second disposable adherent patch from the patient and
separates second disposable adherent patch component 220B from
reusable electronics module 210. A step 260 adheres electronics
module 210 to third disposable adherent patch component 220C and
adheres the third disposable patch component to the skin of the
patient, for example with the third adherent patch component
adhered to the reusable electronics module. A step 262 removes the
third disposable adherent patch from the patient and separates
third disposable adherent patch component 220C from reusable
electronics module 210. A step 264 adheres electronics module 210
to fourth disposable adherent patch component 220D and adheres the
fourth disposable patch component to the skin of the patient, for
example with the fourth adherent patch component adhered to the
reusable electronics module. A step 268 removes the fourth
disposable adherent patch from the patient and separates fourth
disposable adherent patch component 220D from reusable electronics
module 210.
[0111] In many embodiments, physiologic signals, for example ECG,
hydration impedance, respiration impedance and accelerometer
impedance are measured when the adherent patch component is adhered
to the patient, for example when any of the first, second, third or
fourth disposable adherent patches is adhered to the patient.
[0112] FIGS. 3A to 3D show a method 300 of monitoring a patient for
an extended period with adherent patches alternatively adhered to a
right side 302 and a left side 304 of the patient. Work in relation
to embodiments of the present invention suggests that repeated
positioning of a patch at the same location can irritate the skin
and may cause patient discomfort. This can be avoided by
alternating the patch placement between left and right sides of the
patient, often a front left and a front right side of the patient
where the patient can reach easily to replace the patch. In some
embodiments, the patch location can be alternated on the same side
of the patient, for example higher and/or lower on the same side of
the patient without substantial overlap to allow the skin to
recover and/or heal. In many embodiments, the patch can be
symmetrically positioned on an opposite side such that signals may
be similar to a previous position of the patch symmetrically
disposed on an opposite side of the patient. In many embodiments,
the duration between removal of one patch and placement of the
other patch can be short, such that any differences between the
signals may be assumed to be related to placement of the patch, and
these differences can be removed with signal processing.
[0113] In many embodiments each patch comprises at least four
electrodes configured to measure an ECG signal and impedance, for
example hydration and/or respiration impedance. In many
embodiments, the patient comprises a midline 304, with first side,
for example right side 302, and second side, for example left side
306, symmetrically disposed about the midline. A step 310 adheres a
first adherent patch 312 to at a first location 314 on a first side
302 of the patient for a first period of time, for example about 1
week. While the adherent patch 312 is position at first location
314 on the first side of the patient, the electrodes of the patch
are coupled to the skin of the patient to measure the ECG signal
and impedance signals.
[0114] A step 320 removes patch 312 and adheres a second adherent
patch 322 at a second location 324 on a second side 206 of the
patient for a second period of time, for example about 1 week. In
many embodiments, second location 324 can be symmetrically disposed
opposite first location 314 across midline 304, for example so as
to minimize changes in the sequential impedance signals measured
from the second side and first side. While adherent patch 322 is
position at second location 324 on the second side of the patient,
the electrodes of the patch are coupled to the skin of the patient
to measure the ECG signal and impedance signals. In many
embodiments, while adherent patch 322 is positioned at second
location 324, skin at first location 314 can heal and recover from
adherent coverage of the first patch. In many embodiments, second
location 324 is symmetrically disposed opposite first location 314
across midline 304, for example so as to minimize changes in the
impedance signals measured between the first side and second side.
In many embodiments, the duration between removal of one patch and
placement of the other patch can be short, such that any
differences between the signals may be assumed to be related to
placement of the patch, and these differences can be removed with
signal processing.
[0115] A step 330 removes second patch 322 and adheres a third
adherent patch 332 at a third location 334 on the first side, for
example right side 302, of the patient for a third period of time,
for example about 1 week. In many embodiments, third location 334
can be symmetrically disposed opposite second location 324 across
midline 304, for example so as to minimize changes in the
sequential impedance signals measured from the third side and
second side. In many embodiments, third location 334 substantially
overlaps with first location 314, so as to minimize differences in
measurements between the first adherent patch and third adherent
patch that may be due to patch location. While adherent patch 332
is positioned at third location 334 on the first side of the
patient, the electrodes of the patch are coupled to the skin of the
patient to measure the ECG signal and impedance signals. In many
embodiments, while adherent patch 332 is positioned at third
location 334, skin at second location 324 can heal and recover from
adherent coverage of the second patch. In many embodiments, the
duration between removal of one patch and placement of the other
patch can be short, such that any differences between the signals
may be assumed to be related to placement of the patch, and these
differences can be removed with signal processing.
[0116] A step 340 removes third patch 332 and adheres a fourth
adherent patch 342 at a fourth location 344 on the second side, for
example left side 306, of the patient for a fourth period of time,
for example about 1 week. In many embodiments, fourth location 344
can be symmetrically disposed opposite third location 334 across
midline 304, for example so as to minimize changes in the
sequential impedance signal measured from the fourth side and third
side. In many embodiments, fourth location 344 substantially
overlaps with second location 324, so as to minimize differences in
measurements between the second adherent patch and fourth adherent
patch that may be due to patch location. While adherent patch 342
is positioned at fourth location 344 on the second side of the
patient, the electrodes of the patch are coupled to the skin of the
patient to measure the ECG signal and impedance signals. In many
embodiments, while adherent patch 342 is positioned at fourth
location 324, skin at third location 334 can heal and recover from
adherent coverage of the third patch. In many embodiments, the
duration between removal of one patch and placement of the other
patch can be short, such that any differences between the signals
may be assumed to be related to placement of the patch, and these
differences can be removed with signal processing.
[0117] It should be appreciated that the specific steps illustrated
in FIGS. 3A to 3D provide a particular method of monitoring a
patient for an extended period, according to an embodiment of the
present invention. Other sequences of steps may also be performed
according to alternative embodiments. For example, alternative
embodiments of the present invention may perform the steps outlined
above in a different order. Moreover, the individual steps
illustrated in FIGS. 3A to 3D may include multiple sub-steps that
may be performed in various sequences as appropriate to the
individual step. Furthermore, additional steps may be added or
removed depending on the particular applications. One of ordinary
skill in the art would recognize many variations, modifications,
and alternatives.
[0118] FIG. 4A shows a monitoring system 400 comprising an adherent
device 410 to measure an impedance signal and an electrocardiogram
signal. Device 410 may comprise wireless communication circuitry,
accelerometer sensors and/or circuitry and many sensors and
electronics components and structures as described above. Adherent
device 410 comprises at least four electrodes. In many embodiments,
the at least four electrodes comprises four electrodes, for example
a first electrode 412A, a second electrode 412B, a third electrode
412C and a fourth electrode 412D. Work in relation to embodiments
of the present invention suggests that embodiments in which the at
least four electrodes comprises four electrodes can decrease a
footprint, or size, of the device on the patient and may provide
improved patient comfort. In many embodiments, first electrode 412A
and fourth electrode 412D comprise outer electrodes, and second
electrode 412B and third electrode 412C comprise inner electrodes,
for example in embodiments where the electrodes are arranged in an
elongate pattern.
[0119] Adherent device 410 comprises impedance circuitry 420 that
can be used to measure hydration and respiration of the patient,
and ECG circuitry 430 that is used to measure an electrocardiogram
signal of the patient. Impedance circuitry 420 comprises force
circuitry connected to the outer electrodes to drive a current
between the electrodes. Impedance circuitry 420 comprises sense
circuitry to measure a voltage between the inner electrodes
resulting from the current passed between the outer force
electrodes, such that the impedance of the tissue can be
determined. Impedance circuitry 420 may comprise known 4-pole, or
quadrature, low power circuitry. ECG circuitry 430 can be connected
to the outer electrodes, or force electrodes, to measure an ECG
signal. Work in relation to embodiments of the present invention
suggests that this use of the outer electrodes can increase the ECG
signal as compared to the inner electrodes, in some embodiments,
that may be due to the increased distance between the outer
electrodes. ECG circuitry 430 may comprise known ECG circuitry and
components, for example low power instrumentation and/or
operational amplifiers.
[0120] In many embodiments, electronic switch 432A and electronic
switch 432D are connected in series between impedance circuitry 420
and electrode 412A and 412D, respectively. In many embodiments,
electronic switch 432A and electronic switch 432D open such that
the outer electrodes can be isolated from the impedance circuitry
when the ECG circuitry measures ECG signals. When electronic switch
432A and electronic switch 432D are closed, impedance circuitry 420
can force electrical current through the outer electrodes to
measure impedance. In many embodiments, electronic switch 432A and
electronic switch 432D can be located in the same packaging, and
may comprise CMOS, precision, analog switches with low power
consumption, low leakage currents, and fast switching speeds.
[0121] A processor 440 can be connected to electronic switch 423A,
electronic switch 432D, impedance circuitry 420 and ECG circuitry
430 to control measurement of the ECG and impedance signals.
Processor 430 comprises a tangible medium, for example read only
memory (ROM), electrically erasable programmable read only memory
(EEPROM) and/or random access memory (RAM). In many embodiments,
processor 440 controls the measurements such that the measurements
from impedance circuitry 420 and ECG circuitry 430 are time
division multiplexed in response to control signals from processor
440.
[0122] FIG. 4B shows a method 450 of measuring the impedance signal
and the electrocardiogram signal with processor 440. A step 452
closes the switches. A step 454 drives the force electrodes. A step
456 measures the impedance signal with the inner electrodes. A step
458 determines the impedance, hydration and/or respiration from the
impedance signal. A step 460 opens the switches. A step 462
measures the ECG signal with the outer electrodes. A step 464
stores the data from the impedance signals and ECG signals. A step
466 processes the data. A step 468 transmits the data, for example
wirelessly to the remove center. A step 470 repeats the above
steps.
[0123] It should be appreciated that the specific steps illustrated
in FIG. 4B provide a particular method of measuring signals,
according to an embodiment of the present invention. Other
sequences of steps may also be performed according to alternative
embodiments. For example, alternative embodiments of the present
invention may perform the steps outlined above in a different
order. Moreover, the individual steps illustrated in FIG. 4B may
include multiple sub-steps that may be performed in various
sequences as appropriate to the individual step. Furthermore,
additional steps may be added or removed depending on the
particular applications. One of ordinary skill in the art would
recognize many variations, modifications, and alternatives.
[0124] FIG. 5A shows a method 500 for monitoring a patient and
responding to a signal event. A step 501 activates a processor
system. A step 503 calculates a risk of sudden cardiac death. A
step 506 reports to a remote center and/or physician. A step 509
combines at least two of the electrocardiogram signal, respiration
signal, and/or activity signals. A step 512 detects an adverse
cardiac event. An adverse cardiac event may comprise an atrial
fibrillation in response to the electrocardiogram signal and/or an
acute myocardial infarction in response to an ST segment elevation
of the electrocardiogram signal. A step 515 triggers an alarm. A
step 518 continuously monitors and stores in tangible media at
least two of the electrocardiogram signal, the respiration signal,
or the activity signal. In some embodiments, a step may also
comprise monitoring a high risk patent post myocardial infarction
with the at least two of the electrocardiogram signal, the
respiration signal or the activity signal, and/or a bradycardia of
the patient at risk for sudden death. The electrocardiogram signal
may comprise at least one of a Brugada Syndrome with an ST
elevation and a short QT interval or long-QT interval. A step 521
loop records the aforementioned data. A step 524 determines a
tiered response. In many embodiments, the tiered response may
comprise tiers, or levels, appropriate to the detected status of
the patient. A step 527 comprises a first tier response which
alerts an emergency responder. A step 530 comprises a second tier
response which alerts a physician. A step 533 comprises a third
tier response which alerts a patient, family, or caregiver. A step
537 comprises a fourth tier response which alerts a remote center.
A tiered response may also comprise of wirelessly transmitting the
at least two of the electro cardiogram signal, the respiration
signal, or the activity signal with a single wireless hop from a
wireless communication circuitry to an intermediate device.
[0125] The signals can be combined in many ways. In some
embodiments, the signals can be used simultaneously to determine
the impending cardiac decompensation.
[0126] In some embodiments, the signals can be combined by using
the at least two of the electrocardiogram signal, the respiration
signal or the activity signal to look up a value in a previously
existing array.
TABLE-US-00001 TABLE 1 Lookup Table for ECG and Respiration
Signals. Heart Rate/Respiration A-B bpm C-D bpm E-F bpm U-V per min
N N Y W-X per min N Y Y Y-Z per min Y Y Y
[0127] Table 1 shows combination of the electrocardiogram signal
with the respiration signal to look up a value in a pre-existing
array. For example, at a heart rate in the range from A to B bpm
and a respiration rate in the range from U to V per minute triggers
a response of N. In some embodiments, the values in the table may
comprise a tier or level of the response, for example four tiers.
In specific embodiments, the values of the look up table can be
determined in response to empirical data measured for a patient
population of at least about 100 patients, for example measurements
on about 1000 to 10,000 patients. The look up table shown in Table
1 illustrates the use of a look up table according to one
embodiment, and one will recognize that many variables can be
combined with a look up table.
[0128] In some embodiments, the table may comprise a three or more
dimensional look up table, and the look up table may comprises a
tier, or level, of the response, for example an alarm.
[0129] In some embodiments, the signals may be combined with at
least one of adding, subtracting, multiplying, scaling or dividing
the at least two of the electrocardiogram signal, the respiration
signal or the activity signal. In specific embodiments, the
measurement signals can be combined with positive and or negative
coefficients determined in response to empirical data measured for
a patient population of at least about 100 patients, for example
data on about 1000 to 10,000 patients.
[0130] In some embodiments, a weighted combination may combine at
least two measurement signals to generate an output value according
to a formula of the general form
OUTPUT=aX+by
[0131] where a and b comprise positive or negative coefficients
determined from empirical data and X, and Z comprise measured
signals for the patient, for example at least two of the
electrocardiogram signal, the respiration signal or the activity
signal. While two coefficients and two variables are shown, the
data may be combined with multiplication and/or division. One or
more of the variables may be the inverse of a measured
variable.
[0132] In some embodiments, the ECG signal comprises a heart rate
signal that can be divided by the activity signal. Work in relation
to embodiments of the present invention suggests that an increase
in heart rate with a decrease in activity can indicate an impending
decompensation. The signals can be combined to generate an output
value with an equation of the general form
OUTPUT=aX/Y+bZ
[0133] where X comprise a heart rate signal, Y comprises an
activity signal and Z comprises a respiration signal, with each of
the coefficients determined in response to empirical data as
described above.
[0134] In some embodiments, the data may be combined with a tiered
combination. While many tiered combinations can be used a tiered
combination with three measurement signals can be expressed as
OUTPUT=(.DELTA.X)+(.DELTA.Y)+(.DELTA.Z)
[0135] where (.DELTA.X), (.DELTA.Y), (.DELTA.Z) may comprise change
in heart rate signal from baseline, change in respiration signal
from baseline and change in activity signal from baseline, and each
may have a value of zero or one, based on the values of the
signals. For example if the heart rate increase by 10%, (.DELTA.X)
can be assigned a value of 1. If respiration increases by 5%,
(.DELTA.Y) can be assigned a value of 1. If activity decreases
below 10% of a baseline value (.DELTA.Z) can be assigned a value of
1. When the output signal is three, a flag may be set to trigger an
alarm.
[0136] In some embodiments, the data may be combined with a logic
gated combination. While many logic gated combinations can be used,
a logic gated combination with three measurement signals can be
expressed as
OUTPUT=(.DELTA.X)AND(.DELTA.Y)AND(.DELTA.Z)
[0137] where (.DELTA.X), (.DELTA.Y), (.DELTA.Z) may comprise change
in heart rate signal from baseline, change in respiration signal
from baseline and change in activity signal from baseline, and each
may have a value of zero or one, based on the values of the
signals. For example if the heart rate increase by 10%, (.DELTA.X)
can be assigned a value of 1. If respiration increases by 5%,
(.DELTA.Y) can be assigned a value of 1. If activity decreases
below 10% of a baseline value (.DELTA.Z) can be assigned a value of
1. When each of (.DELTA.X), (.DELTA.Y), (.DELTA.Z) is one, the
output signal is one, and a flag may be set to trigger an alarm. If
any one of (.DELTA.X), (.DELTA.Y) or (.DELTA.Z) is zero, the output
signal is zero and a flag may be set so as not to trigger an alarm.
While a specific example with AND gates has been shown the data can
be combined in many ways with known gates for example NAND, NOR,
OR, NOT, XOR, XNOR gates. In some embodiments, the gated logic may
be embodied in a truth table.
[0138] The processor system, as described above, performs the
methods 500, including many of the steps described above. It should
be appreciated that the specific steps illustrated in FIG. 5A
provide a particular method of monitoring a patient and responding
to a signal event, according to an embodiment of the present
invention. Other sequences of steps may also be performed according
to alternative embodiments. For example, alternative embodiments of
the present invention may perform the steps outlined above in a
different order. Moreover, the individual steps illustrated in FIG.
5A may include multiple sub-steps that may be performed in various
sequences as appropriate to the individual step. Furthermore,
additional steps may be added or removed depending on the
particular applications. One of ordinary skill in the art would
recognize many variations, modifications, and alternatives.
[0139] FIG. 5B shows a method of using bioimpedance measurements to
determine changes in the body fluid of a patient for heart failure
monitoring. In step 550, an adhesive patch with at least four
electrodes is placed on the skin of the patient, as described above
with respect to other embodiments of the invention. In step 552,
the electrodes are coupled to the skin to form an interface. A
single frequency is used to measure the tissue resistance via the
impedance circuitry in step 554. A low frequency is preferably
chosen as the single measurement frequency. There are two
capacitances that must be considered when taking these
measurements: the capacitance of the skin-electrode interface and
the intracellular capacitance. Choosing a low frequency for the
measurement frequency isolates the skin-electrode interface
measurement, because at low frequencies the effect of the
intracellular capacitance is negligible. The low frequency is
preferably less than 200 kHz and more preferably less than 100 kHz.
In a particularly preferred embodiment, the frequency is about 10
kHz. The tissue resistance measurements are transmitted to a
processor in step 556.
[0140] In step 558, the processor determines whether the tissue
resistance measurements exhibit a "low frequency droop." A
threshold decline in the measured resistance may be selected in
order to identify a low frequency droop. For example, a decline of
over 10% from the nominal value of the measurements, or over 15 or
20%, may indicate an irregular or anomalous skin-electrode
coupling. Wetting of the skin, such as while showering or from
sweating during physical exercise, can cause a low frequency droop.
To verify that an abnormal reading is caused by a wetting of the
skin, a second measurement can be taken at an additional low
frequency, as in step 568. The additional frequency is preferably
lower than the frequency of the regular measurements. In a
particularly preferred embodiment, the additional frequency is
about 2 kHz. If the low frequency droop is determined to be caused
by wetting of the skin, measurements can be temporarily suspended,
or affected data points can be disregarded, if necessary. In step
570, the quality of the skin-electrode interface is determined, and
in step 572, the adhesive patch and electrodes are replaced when
necessary.
[0141] When the tissue resistance measurements do not show a low
frequency droop, the processor efficiently calculates a change in
the patient body fluid in step 560. As described above, the change
in body fluid is related to the amount of extracellular edema,
which is determined in step 562. In step 564, the amount of edema
is used to calculate the patient's risk of an adverse cardiac
event. An alert is transmitted in step 566 when the patient's risk
exceeds a preset level.
[0142] FIG. 5C shows a method of using bioimpedance measurements to
determine changes in the body fluid of a patient for heart failure
monitoring, where the bioimpedance measurements include tissue
resistance and tissue reactance. In step 650, an adhesive patch
with at least four electrodes is placed on the skin of the patient,
as described above with respect to other embodiments of the
invention. The electrodes are coupled to the skin to form an
interface in step 652. In step 654, tissue resistance and tissue
reactance are measured at successive time intervals via the
impedance circuitry. The measurements are then transmitted to a
processor in step 656. From the tissue resistance measurements, in
step 658, the processor calculates a change in the patient body
fluid. In steps 660 and 662, respectively, the amount of
extracellular edema is determined and the patient's risk of an
adverse cardiac event is calculated. When the risk is above a
preset level, an alert signal is transmitted in step 664.
[0143] In step 666, the processor uses the tissue reactance
measurements to determine the quality of the skin-electrode
interface. A threshold value for the reactance may be selected such
that a reactance value in excess of the threshold indicates that
the quality of the skin-electrode interface is poor. For example,
the reactance threshold may be set at between approximately 8 and
15 ohms, such as 10 ohms. As described above, the quality of the
interface can be affected by wetting of the skin or by degradation
of the adhesive strength of the adhesive patch. If the processor
determines that the adhesive patch requires replacement in step
668, then it is replaced in step 670. If the adhesive patch does
not require replacement, then further measurements of the tissue
resistance and tissue reactance are taken.
[0144] FIG. 5D shows a method of using bioimpedance measurements to
determine changes in the body fluid of a patient for heart failure
monitoring. The method is related to the method shown in FIG. 5C,
but uses the tissue impedance measured between any two electrodes
to determine the quality of the skin-electrode coupling. Steps 750
through 764 correspond to steps 650 through 664 of FIG. 5C.
[0145] In step 766, an impedance measurement is taken between any
two of the electrodes coupled to the skin. The processor uses the
impedance measurements to determine the quality of the
skin-electrode coupling in step 768. A poor connection at the
skin-electrode interface, such as when the adhesive patch begins to
lose its adhesive strength, will cause the impedance measured
between any two electrodes to increase. A threshold for the
impedance increase may be selected, such that when the impedance
measured between two electrodes exceeds the threshold, a poor
skin-electrode coupling is indicated. For example, a threshold may
be selected between 4 and 6 k.OMEGA., such as 5 k.OMEGA.. If the
impedance measurements indicate that the coupling is poor, then the
patch and electrodes will be replaced, as in steps 770 and 772. If
the patch does not require replacement, then measurements will
continue to be taken.
[0146] The processor system, as described above, can perform many
of the above described methods, including many of the steps
described above. It should be appreciated that the specific steps
illustrated above provide a particular methods of monitoring a
patient, according to some embodiments of the present invention.
Other sequences of steps may also be performed according to
alternative embodiments. For example, alternative embodiments of
the present invention may perform the steps outlined above in a
different order. Moreover, the individual steps illustrated may
include multiple sub-steps that may be performed in various
sequences as appropriate to the individual step. Furthermore,
additional steps may be added or removed depending on the
particular applications. One of ordinary skill in the art would
recognize many variations, modifications, and alternatives.
Experimental
[0147] FIG. 6A shows a graph of measurements of tissue resistance
over a range of measurement frequencies, and FIG. 6B shows a
portion of the graph of FIG. 6A enlarged. The data were measured
with a patch as described above.
[0148] FIG. 6A is a graph of tissue resistance measurements taken
at multiple frequencies over the range of approximately 5 to 200
kHz, where each curve represents a set of measurements taken at a
different point in time. In FIG. 6B, a portion of the graph from
FIG. 6A was enlarged and only four of the sets of measurements are
displayed. These four sets of measurements were taken at different
points in time during a single day and include one set that
exhibits a low frequency droop. Comparing the measurements taken at
8:05:30 AM to the others, the graph shows that at lower
frequencies, for example less than 10 kHz, the resistance may drop
off severely, such as when the patch adhered to the patient is
initially exposed to water, and then steadily rise back to a
nominal value. The nominal value can be seen from the measurements
taken at 7:42:35 AM, 10:19:05 AM and 5:39:11 PM. Here, the initial
drop in measured resistance is approximately 15 ohms; however, how
much the resistance measurement drops is related to the overall
variability of the measurements, which is discussed below.
[0149] Electrode-to-skin coupling can affect the quality of the
measurements. For example, in addition to showering, the size of
the electrode can affect coupling. For example, a variation in
measured resistance taken over 10 days may occur with a range of
about of about 5 ohms for a patch having hydrogels 23 mm by 23 mm
in size, whereas the variation in measured resistance taken over 10
days may occur with a range of about 15 ohms for a patch having
hydrogels 18 mm.times.18 mm in size. Such a difference in
variability may be due to the larger gel area providing more robust
contact and coupling to the skin of the patient.
[0150] While the exemplary embodiments have been described in some
detail, by way of example and for clarity of understanding, those
of skill in the art will recognize that a variety of modifications,
adaptations, and changes may be employed. Hence, the scope of the
present invention should be limited solely by the appended
claims.
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