U.S. patent application number 16/592217 was filed with the patent office on 2020-06-11 for system for management and prevention of venous pooling.
This patent application is currently assigned to NATIONAL UNIVERSITY OF IRELAND, GALWAY. The applicant listed for this patent is NATIONAL UNIVERSITY OF IRELAND, GALWAY UNIVERSITY OF LIMERICK. Invention is credited to Paul BREEN, Barry BRODERICK, Gavin CORLEY, Pierce A. GRACE, Derek O'KEEFFE, Gearoid O'LAIGHIN.
Application Number | 20200178813 16/592217 |
Document ID | / |
Family ID | 47297344 |
Filed Date | 2020-06-11 |
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United States Patent
Application |
20200178813 |
Kind Code |
A1 |
CORLEY; Gavin ; et
al. |
June 11, 2020 |
SYSTEM FOR MANAGEMENT AND PREVENTION OF VENOUS POOLING
Abstract
A monitoring system (1) comprises sensors (102) adapted to be
worn by a user, and, a processor (101, 302) linked with the sensor.
The processor receives sensor data and processes this data to
determine user posture data including data indicative of vertical
distance between level of the user's heart and ankle (.DELTA.h, Vd
1, Vd2, Vd3). Based on the posture data together with a value for
degree of user chronic venous insufficiency and/or blood density,
generate an estimate of user static venous pressure while the user
is static, without calf muscle pump activity. The processor (101,
302) also processes the sensor data to determine if there is calf
muscle pump activity, and generates an estimate of user active
venous pressure according to the static venous pressure estimate,
rate of calf muscle activity, and a value for degree of user
chronic venous insufficiency. The processor (101, 302) may generate
the venous pressure estimate in real time, and may control an NMES
device accordingly.
Inventors: |
CORLEY; Gavin; (Ennis,
IE) ; O'LAIGHIN; Gearoid; (Ennis, IE) ; BREEN;
Paul; (Emly, IE) ; BRODERICK; Barry; (O'Briens
Bridge, IE) ; GRACE; Pierce A.; (Patrickswell,
IE) ; O'KEEFFE; Derek; (Limerick, IE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NATIONAL UNIVERSITY OF IRELAND, GALWAY
UNIVERSITY OF LIMERICK |
Galway
Limerick |
|
IE
IE |
|
|
Assignee: |
NATIONAL UNIVERSITY OF IRELAND,
GALWAY
Galway
IE
UNIVERSITY OF LIMERICK
Limerick
IE
|
Family ID: |
47297344 |
Appl. No.: |
16/592217 |
Filed: |
October 3, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14357181 |
May 8, 2014 |
10470667 |
|
|
PCT/IE2012/000047 |
Nov 9, 2012 |
|
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16592217 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61B 5/1072 20130101;
A61B 5/1116 20130101; A61B 5/1071 20130101; A61B 5/0205 20130101;
A61B 5/746 20130101; A61N 1/36003 20130101; A61B 5/6823 20130101;
A61B 5/4836 20130101; A61N 1/36135 20130101; A61B 5/6829 20130101;
A61B 5/0295 20130101; A61B 5/6828 20130101; A61B 5/02007 20130101;
A61B 5/1118 20130101; A61B 5/021 20130101 |
International
Class: |
A61B 5/0205 20060101
A61B005/0205; A61B 5/00 20060101 A61B005/00; A61B 5/11 20060101
A61B005/11; A61B 5/0295 20060101 A61B005/0295; A61N 1/36 20060101
A61N001/36; A61B 5/107 20060101 A61B005/107; A61B 5/02 20060101
A61B005/02; A61B 5/021 20060101 A61B005/021 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 11, 2011 |
IE |
2011/0494 |
Claims
1-39. (canceled)
40. A monitoring system comprising: at least one sensor adapted to
be worn by a user; and a processor linked with the sensor, wherein
the processor is adapted to: receive sensor data and process said
sensor data to determine user posture data including data
indicative of vertical distance between a level of the user's heart
and ankle; based on said posture data together with blood density,
generate in real time an estimate of user static venous pressure
while the user is static, without calf muscle pump activity;
process said sensor data to determine a change in user posture; and
start or reset a timer on determining a change in user posture.
41. The monitoring system as claimed in claim 40, wherein the
processor is adapted to: compare a value of the timer to a
pre-defined time threshold for maintaining a single user posture;
and provide audio, visual or tactile feedback to the user if the
timer value exceeds the pre-defined time threshold.
42. The monitoring system as claimed in claim 40, wherein the
processor is adapted to: calculate a pressure-time integral value
by multiplying an average user static venous pressure for a user
posture by a value of the timer; compare the pressure-time integral
value to a pre-defined pressure-time integral threshold; and
provide audio, visual or tactile feedback to the user if the
pressure-time integral value exceeds the predefined pressure-time
integral threshold.
43. The monitoring system as claimed in claim 40, wherein the
processor is adapted to time stamp sensor data.
44. The monitoring system as claimed in claim 40, wherein the
processor is located on an external device for post-processing
sensor data.
45. The monitoring system as claimed in claim 40, wherein the
processor is adapted to communicate the venous pressure data to one
or more external devices.
46. A monitoring system comprising: at least one sensor adapted to
be worn by a user; and a processor linked with the sensor, wherein
the processor is adapted to: receive sensor data and process said
sensor data to determine user posture data including data
indicative of vertical distance between a level of the user's heart
and ankle; based on said user posture data together with blood
density, generate in real time an estimate of user static venous
pressure while the user is static, without calf muscle pump
activity.
47. The monitoring system as claimed in claim 46, wherein the
processor is adapted to process said sensor data to determine if
there is calf muscle pump activity.
48. The monitoring system as claimed in claim 47, wherein the
processor is adapted to generate an estimate of user active venous
pressure according to said user static venous pressure and a value
for degree of user chronic venous insufficiency, if the processor
determines that there is calf muscle pump activity.
49. The monitoring system as claimed in claim 48, wherein the
processor is adapted to generate the estimate of user active venous
pressure based additionally on a rate of calf muscle pump
activity.
50. The monitoring system of claim 49, wherein the processor is
adapted to estimate a rate of calf muscle pump activity from rapid
changes in acceleration caused by impact forces during impact of
the user's heel during calf muscle pump activity.
51. The monitoring system as claimed in claim 46, wherein the at
least one sensor is selected from accelerometers, ultrasound range
detectors, piezoelectric sensors, gyroscopes, flex sensors,
magnetometers, foot switches and smart textiles incorporated
electrical sensing elements.
52. The monitoring system as claimed in claim 46, wherein the at
least one sensor is adapted to be worn on one or more of a hip,
thigh, lower leg, ankle, sole of a foot and trunk of the user.
53. The monitoring system as claimed in claim 46, wherein the at
least one sensor comprises one or more selected from a hip-worn
sensor to detect step counts and postural transitions, a thigh-worn
sensor to detect walking, lying, sitting and/or standing events,
and a sensor arranged to be worn on the lower leg to measure step
counts, distinguish between standing, sitting, and lying and to
measure lower leg elevation.
54. The monitoring system as claimed in claim 46, wherein: the at
least one sensor comprises two tri-axial accelerometers; and the
processor is adapted to analyse static and dynamic accelerometer
signals to determine said user posture and to determine user
activity data including data indicative of calf muscle pump
activity.
55. The monitoring system as claimed in claim 54, wherein one of
the accelerometers is adapted to be placed distal to a knee joint
of the user, and the other of the accelerometers is adapted to be
placed proximal to the knee joint of the user.
56. The monitoring system as claimed in claim 46, wherein the at
least one sensor and the processor are incorporated into a
garment.
57. The monitoring system as claimed in claim 46, comprising at
least two sensors adapted to detect walking, lying, sitting, and/or
standing posture events, and wherein the posture data includes: a.
a first joint angle made by a thigh of the user with a first
reference axis; b. a second joint angle made by a lower leg of the
user with a second reference axis; c. any angle between the first
and second reference axes; wherein the processor is adapted to
calculate the vertical distance (.DELTA.h) between the level of the
heart and the ankle of the user using the length of the thigh (L1),
the length of the shank of the leg (L2), the distance from the hip
to the level of the heart (Vd1), and the first and second joint
angles using determined postural data.
58. The monitoring system as claimed in claim 46, wherein the at
least one sensor is adapted to measure acceleration and/or tilt of
a limb segment in one or more axes.
59. The monitoring system as claimed in claim 46, wherein: the at
least one sensor is adapted to continuously record data; and the
processor is adapted to process sensor data to provide a continuous
estimate of user venous pressure.
60. A monitoring system comprising: at least one sensor adapted to
be worn by a user; and a processor adapted to: continuously
calculate a vertical distance between a heart and an ankle of a
user based on sensor data; based on the calculated vertical
distance, continuously estimate one of a user static venous
pressure and a user active venous pressure using a first pressure
algorithm and a second pressure algorithm respectively.
Description
INTRODUCTION
Field of the Invention
[0001] The invention relates to artificial stimulation of flow from
the leg and foot and specifically to its application for the
prevention and treatment of chronic venous insufficiency
("CVI").
Prior Art Discussion
[0002] In the healthy lower leg, blood flow in the veins must
typically work against gravity to return to the heart. This
unidirectional flow is facilitated by the presence of two
mechanisms: venous valves and the calf muscle pump. Venous valves
are located throughout the veins and maintain unidirectional flow
towards the heart. During contraction, the calf muscles eject blood
through the veins and back towards the heart. Both correctly
functioning valves and healthy calf muscle pump function are
essential for maintaining healthy venous flow and avoiding venous
pooling.
[0003] Pooling of venous blood in the lower leg is a major
contributory factor in the development of chronic venous
insufficiency (CVI) which can result from breakdown of the venous
valves and/or poor calf muscle pump function. It leads to blood
pooling in the veins resulting in increased venous pressure. These
pressures are highest during standing and lowest when lying due to
the effect of gravity. This increased pressure results in: pain,
swelling, oedema, skin changes, varicose veins, deep vein
thrombosis and venous leg ulcers. Venous leg ulcers are the most
severe and costly manifestation of CVI and are an enormous problem
for both patients and healthcare providers.
[0004] Circumstances that predispose a person to prolonged venous
pooling and the resultant conditions of CVI are: [0005]
Occupational--work posture that requires long periods of sitting or
standing (shopkeepers, barmen, hairdressers, pilots, computer
programmer). [0006] Patients--during surgery, during recovery,
patients with leg casts. [0007] Older persons--inactivity, chronic
disease and chronic vascular disorders. [0008] Muscle
paralysis--wheelchair bound patients, stroke patients, multiple
sclerosis.
[0009] Currently, a common treatment for varicose veins and venous
leg ulcers is graduated compression therapy. Compression stockings
are the most common form of compression therapy and are typically
prescribed for the prevention of varicose veins and deep vein
thrombosis ("DVT") and for the prevention of the recurrence of
venous ulcers. Graduated compression stockings have been shown to
reduce the incidence of DVT and are believed to alleviate some of
the symptoms of varicose veins. However, compression hosiery is
limited by poor compliance and has not been demonstrated to slow
the progression of varicose veins.
[0010] Graduated compression bandaging is typically used for the
most severe symptoms of CVI such as oedema and venous leg
ulceration. Graduated compression bandaging consists of several
layers of tightly wrapped bandages which exert an inward force on
the leg, helping to close venous valves and to counteract the
harmful venous pressures in the leg. Despite being the current gold
standard treatment for venous leg ulcer care, this treatment
modality doesn't allow the clinician to fully address the
underlying cause of venous leg ulcers--blood pooling.
[0011] Individuals who are predisposed to prolonged venous pooling
and CVI currently have very limited options to prevent the
progression of symptoms of CVI. Furthermore, clinicians treating
this condition are not able to closely monitor the status of venous
pooling in these patients and the treatment regimen is based on
changes in the severity of the symptoms of this pooling--swelling
and ulceration. Consequently it is desirable to monitor and report
the status of venous pooling in these patients and apply an
intervention for reducing this pooling where possible so that the
worsening of symptoms of CVI such as varicose veins and venous leg
ulcers may be prevented.
NMES Blood Flow Stimulation:
[0012] If prolonged venous pooling is detected it would be
desirable to intervene to reduce the pooling. The lower leg muscles
act as a natural muscle pump which helps to eject venous blood from
the lower leg. Voluntary activity such as walking naturally
activates and conditions this muscle pump. However, CVI patients
are typically unable to maintain healthy muscle pump function, due
to a sedentary lifestyle and exercise is often painful. Therefore
an alternative means for activating this muscle pump or
rehabilitating it is desirable in these patients.
[0013] Neuromuscular electrical stimulation (NMES) is the
application of electrical stimuli to a muscle or nerve resulting in
a stimulated muscle contraction. Application of NMES to the lower
leg muscles has been shown to result in artificial activation of
the calf muscle and has been shown to promote venous outflow from
the leg and promote muscle strengthening. NMES can be applied via
surface electrodes placed over a nerve or muscle on the user's leg
(surface NMES) or using implanted micro-stimulators within the
patient's leg (implanted NMES).
[0014] Surface NMES devices exist today for the treatment of a
range of conditions. Several investigators have assessed the use of
NMES of the leg muscles for the promotion of venous blood flow
through the leg veins and arteries. WO2009/150652, U.S. Pat. No.
5,707,400, WO2007/135667, WO1999/55413, WO2000/006076 describe both
NMES or combined NMES and pneumatic systems for the promotion of
venous blood flow using stimulation of human limb muscles.
Implanted NMES:
[0015] Implanted NMES can be delivered through the use of an
implanted micro-stimulator which delivers a stimulus to surrounding
tissue. If the micro-stimulator is placed adjacent to a nerve it
can stimulate an action potential in that nerve, resulting in
muscular contraction. Alternatively direct stimulation of the nerve
may be achieved through the use of a stimulating cuff electrode
which is placed around the target nerve. Stimulus is generated in
an implanted device, and is delivered to the cuff electrodes via
implanted wires. An advantage of this approach is that the stimulus
generation circuitry does not need to be placed adjacent to the
nerve. In both cases, radio-frequency (RF) signals can be used to
communicate with the implanted devices, facilitating transmission
of data to and from the devices and also allowing for charging of
the implanted devices.
[0016] Currently, implanted NMES devices require a large cuff to be
placed around the limb of interest to facilitate RF transmission to
the implanted devices via inductive coupling. These cuffs are bulky
and difficult to apply and consequently they may not be suitable
for long term use such as CVI prevention.
Compliance Monitors
[0017] In the management of CVI patient compliance to a treatment
program which encourages lower limb compression and reduction of
venous pooling and increased muscle pump activity is significant
for effectively implementing the therapy. Furthermore goal setting
and feedback for the patients may help to motivate and improve
patient compliance to the therapy as well as inform their carer's
decision-making process in relation to their treatment. Several
disclosures relate to the monitoring of patient compliance to a
prescribed treatment or exercise protocol. U.S. Pat. No. 5,800,458
describes an external system to monitor usage of existing
electrotherapy devices by monitoring applied current. WO2002/018019
describes a method for monitoring usage of exercise devices for
good practice and home-based rehabilitation, while WO2001/087150
describes a generic compliance monitoring system consisting of the
sensing of electrical signals using a microprocessor, a docking
station type recharging and transmission device and a database for
Web-based access to patient data. WO2008/003920 A1 describes a
method and apparatus, including a compliance monitor, for
monitoring external physical parameters having an influence on the
onset or progression of a medical condition.
[0018] Breen, Paul P et al: "A programmable and portable NMES
device for drop foot correction and blood flow assist applications"
Medical Engineering & Physics, Butterworth-Heinemann, GB, vol.
31, no. 3, 1 Apr. 2009 (2009-04-01), pages 400-408, describes an
NMES which accepts a variety of sensor inputs, including
accelerometer signals. A processor uses accelerometer signals to
identify periods of inactivity and modulates stimulation based on
this.
[0019] GB2439750 (Wound Solutions' Ltd.) describes a system which
monitors a limb wound, and includes motion and inclination
sensors.
[0020] US2009/0234262 (Reid, J R et al) describes a health
monitoring system with sensors for parameters such as skin
temperature, muscle activity, and body motion. An aspect is sensing
of edema by means of electrical impedance measurements.
[0021] WO2011/075769 (Impedimed Ltd.) describes use of impedance
plethysmography to monitor body fluid changes over time.
[0022] JP06285046 (Res. Dev. Corp. of Japan) describes use of
kinematic sensors such as inclination angle sensors for monitoring
patient activity.
[0023] The invention is directed towards providing improved
management and prevention of venous pooling.
SUMMARY OF THE INVENTION
[0024] According to the invention there is provided a monitoring
system comprising: [0025] at least one sensor adapted to be worn by
a user, and, [0026] a processor linked with the sensor, [0027]
wherein the processor is adapted to: [0028] receive sensor data and
process said sensor data to determine user posture data including
data indicative of vertical distance between level of the user's
heart and ankle, and [0029] based on said posture data together
with a value for degree of user chronic venous insufficiency and/or
blood density, generate an estimate of user static venous pressure
while the user is static, without calf muscle pump activity.
[0030] In one embodiment, the processor is adapted to process said
sensor data to determine if there is calf muscle pump activity, and
to generate an estimate of user active venous pressure according to
said static venous pressure estimate, rate of calf muscle activity,
and a value for degree of user chronic venous insufficiency.
[0031] In one embodiment, the processor is adapted to estimate the
rate of calf muscle activity from rapid changes in acceleration
caused by impact forces during impact of the user's heel during
calf muscle activity.
[0032] In one embodiment, the processor is adapted to generate said
venous pressure estimate in real time.
[0033] In one embodiment, the processor is adapted to log the
sensor data in real time and to subsequently generate the
estimate.
[0034] In another embodiment, at least one sensor is adapted to
detect walking, lying, sitting, and/or standing posture events, and
wherein the posture data includes: [0035] (a) the angle (.theta.2)
made by the thigh with a reference axis A, [0036] (b) the angle
(.theta.1) made by the shank of the leg with a reference axis B.
[0037] (c) any angle between the reference axes A and B wherein the
vertical distance (.DELTA.h) between the level of the heart and the
ankle is calculated using the length of the thigh (L1), the length
of the shank of the leg (L2), the distance from the hip to the
level of the heart (Vd1), and the joint angles at the hip
(.theta.2) and the knee (.theta.1) using determined postural
data.
[0038] In one embodiment, the processor is adapted to determine a
refill time for a patient using indirect measurement of their
venous haemodynamics using air-plethysmography, or direct venous
pressure measurements, or estimated measurements based on degree of
chronic venous insufficiency, and said refill time is configured
into the processor or is automatically selected by the processor
from a list of standard values.
[0039] In one embodiment, the processor is adapted to process
interval time data to determine if an interval being analyzed is
less than a refill time, and/or if a postural change occurred
during that interval, and/or estimate the average pressure during
that interval using estimates of static venous pressures, the
duration of the interval, and the venous refill rate.
[0040] In one embodiment, the processor is adapted to identify
lower leg activity primary phases including an emptying phase, and
a plateau phase in which the veins do not empty any further and
active venous pressure is maintained at a depressed level. In one
embodiment, the processor is adapted to determine a value for mean
slope of the active venous pressure change in the emptying phase by
the rate of muscle activation and ankle range of motion, and to
determine minimal pressure in the plateau phase by the degree of
chronic venous insufficiency, calf circumference, ankle range of
motion and head change .DELTA.h.
[0041] In one embodiment, the processor is adapted to communicate
the venous pressure data to one or more external devices.
[0042] In one embodiment, the system comprises a neuromuscular
electrical stimulation (NMES) device, and the processor is adapted
to activate said NMES device according to the estimated venous
pressure.
[0043] In one embodiment, the system comprises at least one RF
transmission coil adapted to be mounted on a fixed or mobile object
such as a wall or furniture in order to perform ambient activation
of the NMES device. In one embodiment, the RF transmission coil is
adapted to be mounted in a chair.
[0044] In one embodiment, the processor is adapted to control the
NMES device in order to minimize venous pooling.
[0045] Preferably, the processor is adapted to determine or select
NMES device parameters according to at least one of: a venous
pressure estimate, a venous pressure-time integral, physical
activity levels, leg elevation levels, NMES device usage
statistics. In one embodiment, the processor is adapted to generate
or select NMES device stimulation parameters including at least one
of: stimulation amplitude; pulse width: frequency; stimulation
envelope ramp-up, ramp-down, on and off times; number of channels
and stimulation schedule. In one embodiment, the NMES device is
arranged to stimulate both the posterior and anterior muscle groups
of the lower leg. In a further embodiment, at least some NMES
devices are arranged to apply stimulation to the peroneal nerve. In
one embodiment, the NMES device includes an output stage having a
3-way H-bridge circuit.
[0046] In one embodiment, the sensor is wirelessly linked with the
processor.
[0047] In one embodiment, at least one sensor is adapted to measure
the acceleration and tilt of a limb segment in one or more
axes.
[0048] In another embodiment, the processor is adapted to provide
feedback to the user when a predefined time threshold has been
reached, the feedback comprising at least one of auditory, visual,
or tactile alerts. Preferably, the time threshold is determined by
at least one of the following inputs: venous refill time, posture,
and activity levels.
[0049] In one embodiment, at least one sensor is adapted to provide
sensor data indicating step counts and postural transitions, and
the processor is adapted to process said data to estimate rate of
calf muscle activity in an algorithm for estimating active venous
pressure.
[0050] In one embodiment, the system includes a docking station for
recharging an NMES device and/or a sensor.
[0051] In one embodiment, the processor is at least partly
incorporated into a housing of the sensor.
[0052] In one embodiment, the processor is adapted to transmit and
receive time-stamped activity, and/or compliance, and/or usage data
with an external device.
[0053] In one embodiment, at least one sensor is a pressure
transducer adapted to detect status of a dressing, and wherein the
processor is adapted to use an input from the pressure transducer
as a conditional input for an algorithm.
[0054] In one embodiment, the processor is adapted to determine a
time threshold for a posture as a function of a patient's height.
In one embodiment, the processor is adapted to analyze patient
adherence to a prescribed activity level, including lower leg
elevation and/or NMES device usage. In one embodiment, the sensor
comprises one or more selected from accelerometers, ultrasound
range detectors, piezoelectric sensors, gyroscopes, flex sensors,
magnetometers, foot switches, smart textiles incorporating
electrical sensing elements. In a further embodiment, the sensor
comprises one or more selected from a hip-worn sensor to detect
step counts and postural transitions, a thigh-worn sensor to detect
walking, lying, sitting and/or standing events, and a sensor
arranged to be worn on the lower leg to measure step counts,
distinguish between standing, sitting, and lying and to measure
lower leg elevation.
[0055] In one embodiment, the processor is adapted to operate
according to the finite state machine paradigm. In one embodiment,
the processor is adapted to define a user static state and a user
active state. Preferably, the processor is adapted to define a
state for a transition phase of pressure increasing and a state for
a transition phase of pressure decreasing. In one embodiment, the
processor is adapted to define a state for checking for user
activity.
[0056] Preferably, the processor is adapted to execute a state
machine algorithm in which: [0057] if the state machine is in the
static state and an activity interrupt indicating a stepping motion
is detected the processor moves the static state to an activity
check state, [0058] if the state machine is in the static state and
no activity interrupt or no-change in vertical height (Hv) is
detected, the static state remains and the processor updates the
time associated with the current posture, [0059] if the state
machine is in the static state and there is no activity interrupt
but a decrease in vertical height (Hv) is detected, the processor
moves from the static state moves to a pressure-decreasing state,
and [0060] if the state machine is in the static state and there is
no activity interrupt but an increase in vertical height (Hv) is
detected, the processor moves from the STATIC state to a
pressure-increasing state.
[0061] In another aspect, the invention provides a computer
readable medium comprising software code adapted to be executed by
a digital processor to perform the steps of a processor of a system
as defined above in any embodiment, including the steps of: [0062]
receiving sensor data and processing said sensor data to determine
user posture data including data indicative of vertical distance
between level of the user's heart and ankle (.DELTA.h, Vd1, Vd2,
Vd3), and [0063] based on said posture data together with a value
for degree of user chronic venous insufficiency and/or blood
density, generating an estimate of user static venous pressure
while the user is static, without calf muscle pump activity.
DETAILED DESCRIPTION OF THE INVENTION
Brief Description of the Drawings
[0064] The invention will be more clearly understood from the
following description of some embodiments thereof, given by way of
example only with reference to the accompanying drawings in
which:--
[0065] FIG. 1 is a general overview of the main components of a
system of the invention in use;
[0066] FIG. 2 shows possible locations for wearing sensors on the
trunk and legs;
[0067] FIG. 3 is a functional block diagram of a sensor unit of the
system;
[0068] FIG. 4 shows sensors incorporated into a garment;
[0069] FIG. 5 shows one possible configuration for the enclosure of
the sensor unit;
[0070] FIG. 6 is a diagram showing how static venous pressure is
calculated using postural data joint angles determined from
sensors;
[0071] FIG. 7 shows two postures illustrating a postural transition
from sitting to standing and the corresponding venous pressure
waveform;
[0072] FIG. 8 is a flow diagram for the system controller to
generate an alert based on a determination of venous pooling;
[0073] FIG. 9 shows a static and active venous pressure as a
pressure waveform during walking, a transition phase, and a steady
state phase;
[0074] FIG. 10 is a flow diagram for operation of the system
controller to analyzing and recording venous pressure profiles
during static, transition, and activity phases;
[0075] FIG. 11 shows a neuromuscular electrical stimulation (NMES)
device of a system of another embodiment;
[0076] FIG. 12 is a functional block diagram of the stimulator unit
of FIG. 11;
[0077] FIG. 13 shows an electrode design and placement which would
facilitate stimulation of the anterior and posterior muscle groups
of the lower leg;
[0078] FIG. 14 shows ambient activation of an implanted
stimulator;
[0079] FIG. 15 is a set of diagrams showing a sample application of
the system for venous leg ulcer healing;
[0080] FIG. 16 shows a sample application of the system for CVI
prevention; and
[0081] FIG. 17 is a state diagram for operation of the controller
of a system of the invention.
DESCRIPTION OF THE EMBODIMENTS
[0082] FIG. 1 is a schematic view of a system 1 of the invention of
one embodiment, in use. The system 1 comprises a battery-powered
NMES device 101, and a wearable battery-powered sensor unit 102 for
detecting data in order to determine venous pressure changes. A
docking station 103 recharges the NMES and sensor devices, through
a power outlet 106 when they are not being used by the patient. The
docking station also facilitates transmission of time-stamped
activity and compliance/usage data to a remote server 104 and to a
PC 105 where it is stored for later access by patients and/or their
carers or clinicians and can be viewed as softcopy or hardcopy
reports.
[0083] A processor in the sensor unit 102 records and displays
sensing and NMES data, and this data can be used to assess patient
adherence to a prescribed program for alleviating venous pooling.
The processor implements algorithms which analyze sensor data to
estimate venous pressure both when the patient is static and
active. It alerts the user according to estimated venous pressure
arising from posture status such as when prolonged periods of
immobility or inactivity are detected. Also, the system may be
integrated with existing compression therapies for ease of use in
CVI patients. In this specification the term "static" means that
the patient is not contracting the calf muscles which act as a
pump. The term "active" or "activity" means that such contraction
is occurring, such as when walking or not moving but nevertheless
performing exercises to contract the calf muscles for venous
pumping.
[0084] The system assists with the important aspects for
alleviating venous pooling for the prevention and treatment of CVI,
namely promotion of various postures and activities (such as
walking, or exercises/interventions which activate the lower leg
muscles) which help to reduce venous pressures, and the limiting of
activities or postures which predispose and individual to
sustained, elevated venous pressures.
[0085] The system of one embodiment on a continuous basis monitors
posture and postural changes, monitors activity, and calculates
venous pressure for both static and active phases. Also, it
stimulates calf muscle contractions to promote venous blood flow
and to compensate for reduced voluntary activity. It provides
instantaneous patient feedback to warn of elevated venous pressure
levels, and assesses patient adherence to prescribed patient
activity levels, including for example lower leg elevation.
[0086] Under static conditions, the hydrostatic venous pressure, at
a given point in a person's venous system, is directly related to
the vertical distance between that point and the person's heart,
the degree of chronic venous insufficiency, and blood density.
Consequently the venous pressure can be calculated in various
postures, under static conditions if the height of the individual
and their trunk and leg lengths and orientations are known.
[0087] During activity (dynamic conditions such as walking or
performing ankle exercises) venous pressure is determined partially
by posture but also by degree of chronic venous insufficiency
and/or several other parameters such as rate of muscle activity,
body weight, height, calf circumference, and ankle range of motion.
Consequently, venous pressure can be estimated under active as well
as static conditions.
[0088] Monitoring of patient activity levels, i.e. time spent
exercising, rate of exercise, step counts etc, is also important
for helping clinicians to understand a patient's general health
status. Tracking of this information by patients themselves may
also aid patient compliance to treatment programs, and may
facilitate goal-setting to encourage increased levels of
activity.
[0089] A variety of sensor types (accelerometers, ultrasound range
detectors, piezoelectric sensors, gyroscopes, flex sensors,
magnetometers, foot switches, smart textiles incorporating
electrical sensing elements) and positions (hip, thigh, lower leg,
ankle, sole of the foot) can be used alone or in combination with
each other to determine activity, posture and lower leg elevation.
Different sensing configurations may be used to suit a variety of
circumstances.
[0090] FIG. 2 shows a number of possible sensor positions that can
be used to measure posture, activity and lower leg elevation using
accelerometers and gyroscopes. By measuring the acceleration and
tilt of a limb segment in one or more axes, posture and activity
levels can be determined. FIG. 2 shows (A) a sensor 102 worn on the
hip to detect step counts and postural transitions; (B) the sensor
102 worn on the thigh to detect walking, lying/sitting and standing
events; and (C and D) the sensor 102 worn in two different
positions on the lower leg, which arrangement can be used to
measure step counts, to distinguish between standing/sitting and
lying and to measure lower leg elevation.
[0091] FIG. 3 shows a block diagram for the system 1 circuitry. The
system 1 comprises a communications block 301 to facilitate two-way
wired or wireless communication to external devices; a
microprocessor 302 for control of the system; alert circuitry 303
to provide the wearer with visual, tactile or audio feedback
indicating a pre-determined postural or activity threshold has been
exceeded; a variety of sensors for detection of postural data and
activity levels 304, a power supply circuit 305 to facilitate
powering and recharging of the device, a real-time clock circuit
306 to facilitate time stamping of activity and posture data, and a
memory block 307 to facilitate storage and buffering of data.
[0092] In a preferred embodiment the sensing block 304 comprises
two tri-axial accelerometers for sensing of postural and activity
levels by analysing the static and dynamic accelerometer signals in
each measured axis (FIG. 4). Two accelerometer sensors (404, 402)
are used to provide better identification of posture by comparing
the orientation of the upper and lower leg. To achieve this one
accelerometer 402 is placed distal to the knee joint, on the tibial
ridge of the lower leg. The other one, 404, is placed proximal to
the knee joint along the anterior midline of the upper leg. The
accelerometers are incorporated into a garment 405 along with a
control unit 401, for ease of donning and doffing and are connected
via conductive wires routed under or through the garment 403. The
garment may also incorporate status light emitting diodes 406 which
are indicative of a high level of venous pooling (red), a moderate
degree of venous pooling (orange) or a low level of venous pooling
(green).
[0093] A more detailed illustration of the control unit 401 and
distal sensor 402 is shown in FIG. 5. There are status light
emitting diodes (LEDs) 501, to provide visual feedback to the user.
The control unit 401 may also comprise a tactile actuator, such as
a vibration motor which provides mild sensory stimulation as a more
discreet form of feedback. Belt hooks 504 facilitate mounting of
the unit 401 on an elastic belt/strap which can then be attached to
the lower leg. The presence of a belt (passing over the front of
the device) may facilitate the inclusion of a compliance monitoring
switch 505, which is pressed when the belt is firmly attached to
the sensor and wrapped around the leg, indicating periods when the
device is in use. The sensor may also comprise wired (502, 503) or
wireless connections to external devices such as the NMES device
101 and docking station 103, additional sensor elements 404 or
status LEDs 406. Finally the control unit 401 also incorporates an
alphanumeric display 507 for displaying measured parameters and
estimates of venous pressure time integral.
[0094] The system achieves monitoring of venous pressure during
static and active conditions by analyzing the accelerometer signals
which identify a postural change to a static posture or an activity
which can be achieved using thresholds. When a new postural change
is detected the sensor estimates the venous pressure profile for
the posture or activity since the last postural change. The venous
pressure profile estimation for a given interval will depend on
whether a static posture was maintained or an activity was carried
out in that interval.
[0095] In general terms the system processor processes sensor data
to determine user posture data including data indicative of
vertical distance between level of the user's heart and ankle, and
based on this data generates an estimate of user static venous
pressure while the user is static, without calf muscle pump
activity. Preferably, it also determines from the sensors if there
is calf muscle pump activity, and generates an estimate of user
venous pressure according to the above static venous pressure
estimate along with the rate of calf muscle activity and a value
for degree of user chronic venous insufficiency. The value for
degree of user chronic venous insufficiency is preferably a CEAP
value, as this is a well-known standard scale. The rate of calf
muscle activity is preferably determined by changes in acceleration
detected by the accelerometer located on the lower leg. These rapid
changes in acceleration are caused by impact forces created during
impact of the user's heel during calf muscle activity.
[0096] In some applications the wearable sensor unit could act as a
data logging unit, saving the raw sensed data to internal memory
for post-processing at a later stage. In this post-processing step
the raw data is uploaded to another device with a fast processor in
order to apply all of the venous pressure estimation algorithms.
This allows a smaller, less complex processor to be used in the
wearable sensor and may also offer power saving benefits as the
processor isn't required to carry out complex mathematical
operations. However this approach would limit the types of alerts
that could be provided to the wearer in real-time. It will be
appreciated that the term "processor" is not limited to a single
device, but could be multiple devices, possible at different
locations. The links may be wired or wireless, remote or local.
Static Venous Pressure Estimation
[0097] During static conditions venous pressures stabilizes, as
shown by the plot of FIG. 9. Venous pressure during the static
phase can be estimated by measuring the orientation of the trunk,
thigh and shank body segments (FIGS. 6 and 7). If the distance
between the heart and hip (Vd1), thigh length (L1), and the
distance between the knee and ankle (L1) are known, then the
overall vertical distance from the heart to the ankle can be
calculated using tilt angles from the accelerometers. Assuming a
vertical trunk orientation (during sitting or standing) the tilt of
the thigh and shank can be measured by examining the gravity
component in relation to each of the accelerometer axes placed on
both the shank and thigh and using an inverse trigonometric
function to determine the total vertical distance between the ankle
and the heart .DELTA.h, by adding Vd1, Vd2 & Vd3. Venous
pressure can then be calculated by using the equation for
hydrostatic pressure:
Hydrostatic pressure=.rho.g.DELTA.h.
[0098] Where .rho. corresponds to the density of blood (.about.1052
kg/m.sup.2), g corresponds to the acceleration due to gravity, and
.DELTA.h corresponds to the vertical distance between the ankle and
the heart. In individuals with standard blood density the value of
.rho.g is 0.77 mmHg/cm, i.e. venous pressure increases by 0.77 mmHg
for every 1 cm increase in .DELTA.h.
[0099] The sensor can facilitate manual input of the length of the
trunk, thigh and shank (distance from the ankle to the knee joint)
for calibration of the system so that an accurate estimate of
venous pressure may be determined.
[0100] A sample algorithm for detecting and logging venous
pressures is outlined in FIG. 8. When the algorithm begins (1001,
1002) a timer is started and the initial posture/activity is
tracked (1003) from a previous postural transition. When a
subsequent postural change is detected, this marks the end of the
initial posture. The timer is then stopped (1006) and the pressure
profile for the period of the previous posture/activity is
calculated (1007). The delay between loops is programmed
(1009).
[0101] The calculation of the pressure profile for a static posture
depends largely on .DELTA.h. For more accuracy in the estimation
the refill rate of the veins, which is largely determined by the
degree of chronic venous insufficiency (CVI) of the user should be
included in the algorithm. This may be inputted as a configuration
setting of the system. The dynamic (active) pressure measurements
depend more heavily on the degree of CVI and rate of calf muscle
pump activity.
[0102] Following a postural change consisting of a change from one
static posture to another, the venous pressure waveform (FIG. 7),
measured at the level of the ankle is biphasic, comprising: a
transition phase lasting for the length where venous pressure
increases or decreases linearly due to a change in .DELTA.h and a
steady state phase where the venous pressure is fixed. The length
of the transition phase (refill time) is determined by the function
of the venous valves and the degree of chronic venous insufficiency
and the arterial inflow and will vary for each individual. The
refill time can be inputted as a specific input, measured for this
patient, or it can be selected from a pre-set value by the
processor based on the patient's degree of chronic venous
insufficiency. Refill time can be determined for an individual and
programmed into the sensor using indirect measurement of their
venous haemodynamics using air-plethysmography, or direct venous
pressure measurements. Alternatively refill times may be estimated
based on degree of chronic venous insufficiency (i.e. CEAP class or
equivalent), which can be programmed by a clinician or the user
into the sensor.
[0103] If the interval being analyzed is less than the refill time,
then a postural change occurred during the transition phase. The
pressure at the time of the current posture can be determined from
the starting pressure value and the interval time multiplied by the
refill rate (change in pressure during the transition phase divided
by the refill time). The average of the previous and current
pressures will give the average pressure during the transition
phase. This average value and the interval value are then stored to
memory.
[0104] If the interval time is greater than or equal to the refill
time than the average pressures during the transition and during
the steady state period need to be saved separately. The average
pressure during the transition can be determined by averaging the
pre-transition pressure and post-transition pressure which are
determined directly from the .rho.g.DELTA.h value of the start and
end static postures. This average pressure is then stored with the
refill time. The steady state pressure is also stored along with
its duration.
[0105] By storing the average pressures for a given phase along
with their respective durations, a pressure time integral can be
estimated which can give the users or clinicians a continuous
projection of pressure changes during static postures and postural
transitions (achieved by multiplying the average pressure by its
associated time). This pressure-time integral is reported to the
users and clinicians and thresholds may be set to trigger alerts in
the form of visual, tactile or audible feedback if the pressure
time integral exceeds a predefined value.
Active Venous Pressure Estimation
[0106] During movement, venous pressures are modulated by the
activity of the lower leg muscles, which have a pumping effect on
the veins of the lower leg, which helps to alleviate venous
pooling. Consequently during voluntary or electrically stimulated
contractions of the lower leg muscles, venous pressures are
intermittently depressed immediately following muscular
contractions and rise again in the post contraction period when
venous refilling occurs. As a result, venous pressure during
activity (venous pressure during voluntary or involuntary exercise)
is determined in part by .DELTA.h, rate of muscle activation, calf
circumference, degree of chronic venous insufficiency and ankle
joint range of motion. The most important parameter is the degree
of chronic venous insufficiency, and indeed this is sufficient
together with the postural data to perform a satisfactory
estimation of venous pressure during activity.
[0107] FIG. 9 illustrates the changes well, and the
positively-sloped ramp between active and static phases. The flow
diagram of FIG. 10 shows how such phases are monitored and used to
generate pressure profiles. The venous pressure profile during
lower leg activity can be divided into two primary phases: an
emptying phase (A) and a plateau phase (B) where the veins don't
empty any further and venous pressure is maintained at a depressed
level. The mean slope of the pressure change in the emptying phase
is determined by the rate of muscle activation (i.e. stepping
rate/walking speed), .DELTA.h and ankle range of motion. The
minimal pressure in the plateau phase is determined by the degree
of chronic venous insufficiency, calf circumference, ankle range of
motion and .DELTA.h. If the slope of the emptying phase and the
minimal pressure of the plateau phase are known, the mean pressure
and duration of each phase can be saved to memory and will provide
a good estimate of pressure time integral during that activity.
[0108] The slope of the emptying phase and the minimal pressure in
the plateau phase for an individual can be obtained from direct
venous pressure measurements or air plethysmography assessments and
programming it directly into the stimulator. Alternatively the
slope may be estimated by measuring the rate and strength of muscle
activation or stepping and comparing by analyzing the dynamic
accelerometer signals, calculating .DELTA.h, (which can also be
determined from the accelerometer waveforms) and calculating a
slope based on existing standardized values from direct venous
pressure measurements. Ankle range of motion can also be programmed
into the sensor to adjust the calculated slope. A poor ankle range
of motion (e.g. a ankle range of motion <40.degree.) would scale
the slope by at least a factor of 2, making emptying twice as slow.
A normal ankle range of motion would have no scaling effect on the
slope of the venous emptying phases.
[0109] Similarly, the minimal pressure in the plateau phase can be
determined by the degree of chronic venous insufficiency, the calf
circumference, the ankle range of motion (programmed into the
stimulator) and .DELTA.h which is determined from the static
accelerometer signals. These parameters can be used to look up
standardized values for the minimal pressure levels, permanently
stored in the memory of the stimulator unit.
Venous Pooling Alert Algorithm
[0110] The system preferably has sufficient memory to accommodate
logging of the raw sensor data. Post processing can be carried out
on the data to determine the parameters of interest (time stamped
activity data, posture data, leg elevation and daily venous
pressure estimates) for report generation. Ideally, the sensor
would incorporate one or more algorithms to facilitate real-time
detection and estimation of venous pressures based on sensed
postural and activity data.
[0111] As referred to above FIG. 8 illustrates an example program
flow for such an algorithm. When an upright posture is detected
(1001) a timer is started 1002. The timer counts to a predefined
time value, which represents the allowed time for the user to
maintain a static upright posture. As the timer counts, the posture
(1003) and activity (1004) of the user is periodically checked, if
the user changes from an upright posture or commences activity
(1005) the timer is reset (1006). If the user exceeds the allowed
duration for static upright posture (1007), the sensor devices
alert the user (1008) to the risk of venous pooling via audio,
visual or tactile feedback. Once the user has been alerted the
alarm system is halted using a programmable delay (1009), before
posture and activity checking begins again. If a posture change or
activity is detected, the timer is reset and the process halts
until an upright posture is detected again. If a posture change or
activity is not detected, the sensor system will alert the user
again once a programmable delay has expired. The alerted system may
be programmed to avoid the device becoming an irritation to the
user, either through the use of a very long alert hold-off delay or
through the use of a user-controlled interrupt, which might halt
the algorithm for a predefined period.
NMES Devices
[0112] The invention in some embodiments uses the venous pressure
estimation outputs to achieve improved artificial blood flow
through neuromuscular electrical stimulation (NMES) of the foot and
leg of the affected side for the prevention, treatment and
management of various manifestations of CVI. NMES improves venous
return from the legs of CVI patients, when used in conjunction with
compression bandaging, leading to an improvement in the healing
rates of venous leg ulcers.
[0113] NMES can be delivered in two ways, through the use of
surface electrodes ("surface NMES") or through implanted techniques
called "implanted NMES". We would envisage NMES to be delivered
predominantly through the use of surface NMES as it is less
invasive. However in circumstances where surface NMES is
impractical, i.e. for the long-term prevention of venous leg
ulcers, implanted NMES may offer a more convenient solution.
[0114] There may be ambient activation of devices such as implanted
micro-stimulators, such as the BION system (G. Loeb, F. Richmond,
J. Singh, R. Peck, W. Tan, Q. Zou, and N. Sachs, "RF-powered
BIONs.TM. for stimulation and sensing," in Engineering in Medicine
and Biology Society, 2004. IEMRS'04. 26th Annual International
Conference of the IEEE, 2004, pp. 4182-4185). This approach makes
implanted NMES devices more suitable for long term applications
involves embedding the control and RF circuitry into a household
object for convenient activation of NMES using the implanted
device.
Surface NMES
[0115] An NMES device is shown in FIG. 11. It is for connection to
the lower extremity of the patient via wires which connect to one
or more stimulus output port 1109 on the device and surface
electrodes placed on the intended stimulation site. It has a simple
user interface 1101 to display status messages and alerts and has
controls to allow the user to control and test the amount of
stimulation they would like to select (1102-1107). The NMES device
is portable and discreet enough to be worn on the hip or in a
pocket. In addition to providing an electrical connection to the
electrodes, a wired connection can also be used to provide a data
and power connection to a sensor unit and/or docking station via
additional sockets 1110 on the stimulator. Furthermore, the device
should be able to accommodate a range of external additional sensor
inputs 1108 for the development of more sophisticated stimulation
algorithms. In a preferred embodiment, this sensor input may
comprise levels of venous pooling, leg elevation or activity
levels.
[0116] The NMES device is programmable so that typical stimulation
parameters such as: stimulation amplitude, pulse width, frequency,
stimulation envelope: ramp-up, ramp-down, on and off times, number
of channels and the stimulation schedule may be programmed. This
can be done directly by the clinician or may be selected
automatically on the basis of a range of sensor inputs such as
levels of venous pooling, leg elevation and activity levels. For
example, if an individual is found to have excessive levels of
venous pooling in a given day, an increased duration of stimulation
or additional stimulation sessions are recommended to counteract
the excessive pooling observed. Additionally, stimulation
parameters such as duty cycle, stimulation frequency or intensity
may be adjusted to provide a more intensive stimulation session
which provides greater hemodynamic benefit. Thus, the system is
capable of an adaptive response to the degree of venous pooling in
such a way that it ensures maximum venous return and user comfort.
The stimulator unit should also be capable of acting as a portable
programming interface to the sensor unit.
[0117] A general block diagram of the NMES device of FIG. 11 is
shown in FIG. 12. The device comprises: a microprocessor block 1201
for overall control; stimulus generation circuitry on one or
several channels 1202; flash memory 1203 for storing programs,
sensor and usage data; a real-time clock 1204 to facilitate patient
compliance monitoring and algorithm detection; a communication
block 1205 to facilitate two-way wired or wireless communication to
external devices; a sensor interface 1206 to accommodate a range of
external and internal sensors: and power supply circuitry 1207 for
regulation of the power supply to the device and to facilitate
recharging.
[0118] In one embodiment any of the following elements may be
implemented on a mobile phone running an NMES application: overall
control of the system 1201, memory storage 1203, real time clock
1204, the communication block 1205, the sensor interface 1206 and
the power supply circuitry 1207. The stimulus generation circuitry
1202 is implemented on an external device attached to the mobile
phone via a wired or wireless connection.
[0119] In a preferred embodiment NMES is applied via surface
electrodes to the tibial and peroneal nerves on the back of the
knee. FIG. 13 illustrates an electrode design that allows for
selective stimulation of the tibial nerve or the common peroneal
nerve, which branches from the tibial nerve. Selectively
stimulating the tibial nerve activates the muscles of the posterior
compartment of the leg such as the soleus and gastrocnemius
muscles. Selectively stimulating the common peroneal nerve
selectively stimulates the muscles of the anterior and lateral
compartments of the leg such as the tibialis anterior muscle. The
electrode consists of two electrically conductive portions
separated by a non-conductive portion, and must be placed
substantially medial to the tendon of the biceps femoris. A
reference electrode is required to complete the circuit and is
placed substantially central to the bulk of the tibialis anterior.
The advantage of such a configuration is that by alternating
between stimulating the anterior and posterior/lateral muscle
compartments, muscle fatigue will essentially be halved, allowing
for extended periods of NMES therapy. This electrode configuration
facilitates stimulation of the posterior muscles which would
otherwise not be possible in leg ulcer patients, due to ulcerated
skin restricting the electrode placement.
[0120] Control circuitry in the stimulator unit is provided to
effectively use this electrode arrangement. The control circuitry
is located on the output stage of the stimulus-generating circuitry
of the stimulator device. The high voltage stimulus waveform
required to generate a tetanic muscle contraction is generated by
the stimulator output circuitry. The control circuitry selects
which of the two conductive portions of the electrode will be
connected to the stimulus output for the current stimulation cycle.
One skilled in the art will recognise that a three-way H-bridge
configuration is an effective way of implementing this control
circuit.
Implanted NMES Techniques Using Ambient Activation:
[0121] FIG. 14 shows a preferred embodiment of the system for
ambient activation of implanted NMES devices. RF transmission coils
and control circuitry 1401 are embedded into an armchair 1402. When
a user who has been implanted with an NMES device 1403 comes within
a predefined range of the armchair, the control circuitry commences
communication with the implanted device. NMES may commence
immediately or following confirmation from the user.
Logging Data
[0122] In one embodiment, usage data from the NMES device and
sensors is downloaded by plugging them into a docking station. The
station could facilitate recharging of the system's batteries at
night when the system is not in use as well as facilitate
downloading/transmission of usage and sensor data to a PC, a remote
server or to a desktop stimulator device which may have a colour
display. This data could either be printed directly from the PC via
a proprietary software interface or soft and hardcopy reports could
be generated remotely and sent to the user, their nurse or other
relevant stakeholders.
[0123] A summary of usage data would include: [0124] The date and
time during the day when stimulation was applied. [0125] Intensity
of stimulus. [0126] Duration of stimulation sessions. [0127] Device
error messages. [0128] Duration and time of user activity, posture
and lower leg elevation levels. [0129] Pressure Time Integral
summaries & statistics. [0130] Additional summaries and
statistics on individual or combined usage/sensed data.
[0131] This information is stored on a secure database, which can
be accessed by the patient's physician. The offline data can be
analysed to assess the effectiveness of the system, user
compliance, and monitor patterns of patient activity. This
information could be analysed for research purposes, or could be
used by the clinician to assess the effect of the system on the
user's quality of life, i.e. if the system is effective, the user
may become more active, as indicated by increased periods of
standing and activity, and greater numbers of sit-to-stand
transitions etc. This reporting interface provides both reports and
alerts on the patient's condition and may be customised for a
number of management applications such as venous leg ulcer healing,
venous leg ulcer recurrence prevention and varicose vein
prevention.
[0132] A fall detection algorithm could also be incorporated into
the control unit, using kinematic sensor data as input. Detection
of a fall would trigger an alert (e.g. via GSM alert), to be sent
to the clinician and/or primary carer(s).
Application of the System to Venous Leg Ulcer Healing
[0133] One application of the system is for the treatment of active
venous leg ulcers. A preferred embodiment of the system for this
application is shown in FIG. 15. FIGS. 15A and C show an example
use of the system, while the user is going about his/her daily
activity. FIGS. 15B & D show the user carrying out his/her
home-based NMES therapy. Two possible sensor positions are shown.
In diagram A the patient is wearing compression bandaging 1502 as a
standard part of their treatment. As shown in diagrams A and B the
sensor device 102 may be worn on the lower leg. It may be fixed in
place by placing it beneath the top layer of compression bandaging
or with the aid of an elastic strap 1506. In this way users do not
need to consider placing the sensor each day. Diagrams C and D show
that the sensor device 102 may be worn on the waist with the aid of
an elastic strap. The sensor device would be placed at the start of
each day by the user, and taken off to be recharged at night. In
the case of both the leg-worn and waist-worn sensor configurations
recharging may be achieved through direct, wired connection to the
NMES device or through the use of a docking station 103 which
provides a connection to recharging circuitry.
[0134] Electrodes 1504 are worn to facilitate NMES stimulation of
the lower leg muscles in response to the sensing of venous
pressure, for the purpose of promoting venous blood flow. At least
one of the electrodes is fitted beneath the compression bandaging
on the lower leg. They are positioned to facilitate stimulation of
those muscles which promote venous blood flow from the lower leg
when contracted, preferably the soleus, tibialis posterior and
tibialis anterior muscles. This may be achieved through nerve
stimulation or through direct stimulation of the muscle belly.
[0135] FIG. 15, diagram B shows the system arrangement as the user
carries out a prescribed NMES stimulation session. The NMES device
101 is connected to the electrodes 1504 via lead wires 1505. The
user can set the NMES device to carry out muscle stimulation at an
intensity level of their choice. At night, when the system is not
in use, the devices can be placed in the docking station 103 of
FIG. 1.
Application of the System to CVI Prevention
[0136] A further application of the system is for the prevention of
symptoms of chronic venous insufficiency such as varicose veins and
venous leg ulcers. An alternative embodiment of the system for this
application is shown in FIG. 16. FIG. 16, diagram A shows the
system as it may be used during the daily activities of someone at
risk of varicose veins or venous ulcers (i.e. people in a
profession requiring prolonged periods of standing, or people with
a history of venous disease). During daily activities the sensor
device 102 alerts the user to prolonged periods of standing. The
sensor device may be worn on the hip for convenience, using a belt
clip or elastic strap.
[0137] With reference to diagram B of FIG. 16, the user may also
use the NMES device 101 at home to promote their venous blood flow.
The sensor and electrode positioning and/or routing of the NMES
lead wires 1505 may be facilitated by the use of a garment such as
a cuff which may incorporate activity and posture sensors and
facilitates donning and doffing and correct electrode placement. At
night, when the system is not in use, the devices can be placed in
the docking station 103 of FIG. 1.
Garments for Electrode and Sensor Placement and Routing
[0138] It is envisaged that sensor and electrode positioning and/or
routing of the NMES lead wires may be facilitated by the use of a
garment 405 (FIG. 4). Each of these garments would facilitate:
[0139] Electrode positioning, which may be achieved through the use
of traditional gel electrodes which can be easily placed and routed
through the garment or integrated electrodes which are woven into
the garment itself. [0140] Placement of traditional discrete
sensors which can monitor activity levels and lower leg elevation
or integration of flexible sensors which may be developed using
printed electronic technologies [0141] Low-profile routing of data
and power connections through the garments using conductive threads
or flat wire connections.
Pressure Estimation Using a State Machine
[0142] Referring to FIG. 17 a controller of one embodiment includes
a processor with a non-invasive venous pressure data logger
structured around a state-machine design. Those skilled in the art
will recognize that the state machine structure provides a program
flow structure for logging of venous pressure profiles based on a
series of sensed and programmed inputs and the current state.
Description of the States:
[0143] Five states are illustrated in (FIG. 17): [0144] (a) A
STATIC state (1701)--which represents time spent in a fixed
posture, where the sensed vertical height doesn't change. This
state keeps track of the time spent in a given stable posture and,
upon exiting the state, logs the pressure data. This state
corresponds to the steady state phase of the venous pressure
waveforms of FIG. 7 and FIG. 9. [0145] (b) An ACTIVITY CHECK state
(1702)--this represents a transition state where some initial
stepping activity has been detected. This state checks to see if a
predefined number of steps `N` in a predefined time interval have
been taken and determines whether or not the individual wearing the
sensor is walking or merely taking a short number of steps. This
state corresponds to the transition from any state to the Leg
Activity stage of the waveform of FIG. 9. [0146] (c) An ACTIVITY
state (1703)--this state tracks the number of steps and time
between steps taken by the wearer. The states then determine the
reduction in venous pressure due to walking based on the degree of
CVI, number of steps taken and the estimated walking speed of the
individual, (based on normative values from Kugler 2001). The
program exits the ACTIVITY state when an INACTIVITY interrupt is
detected. One example of an inactivity interrupt trigger could be a
lack of a significant change in a sensed input over a specified
time frame, representing a lack of movement. This state corresponds
to the Leg Activity stage of the waveform of FIG. 9. [0147] (d) A
TRANSITION DOWN state (1704)--this state which tracks changes in
venous pressure based on a drop in vertical height or venous
pressure. This state corresponds to the phase after the postural
change 2 outlined in FIG. 7, where the venous pressure is
decreasing. [0148] (e) A REFILL state (1705)--this state creates a
venous pressure profile corresponding to an increase in venous
pressure due to an increase in vertical height or cessation of
activity. This state corresponds to the transition phase of the
waveforms of FIG. 7 and FIG. 9.
Description of the Signals:
[0149] The state machine is driven by the following inputs which
may be sensed, calculated or programmed: [0150] Hv--Vertical Height
between the ankle and the heart. [0151] Steps--number of steps
detected by one of the kinematic sensors or other means. [0152]
INACT--inactivity interrupt indicating a lack of activity within a
predefined time period. [0153] ACT--activity interrupt indicating a
stepping motion based on a sensed input. [0154] Pr--Current
Pressure as determined by the hydrostatic pressure equation and the
Sensed vertical Height, Hv [0155] EPr--estimated stable venous
pressure at the end of a refill period.
[0156] For the purposes of data logging of venous pressure
profiles, each state keeps track of the venous pressure profile
within that state, and saves the data to memory upon exiting the
state. This allows the venous pressure profile to be read and
illustrated using the data saved to memory.
Description of the State Transitions:
[0157] There are 19 possible transitions between the 5 states, and
these are described in terms of the source state from which they
exit:
STATIC State Output Transitions:
[0158] STATIC to ACTIVITY CHECK (1716): if the state machine is in
the STATIC state and an activity interrupt indicating a stepping
motion is detected the program logs the pressure profile for the
STATIC state moves to the ACTIVITY CHECK state.
[0159] STATIC to STATIC (1706): if the state machine is in the
STATIC state and no activity interrupt or no-change in vertical
height (Hv) is detected, the program remains in the STATIC state
and updates the time associated with the current posture.
[0160] STATIC to TRANSITION DOWN (1721): if the state machine is in
the STATIC state and no activity interrupt but a decrease in
vertical height (Hv) is detected, the program logs the pressure
profile for the STATIC state moves to the TRANSITION DOWN
(pressure-decreasing) state.
[0161] STATIC to REFILL (1722): if the state machine is in the
STATIC state and no activity interrupt but an increase in vertical
height (Hv) is detected, the program logs the pressure profile for
the STATIC state moves to the REFILL state.
ACTIVITY CHECK State Output Transitions:
[0162] ACTIVITY CHECK to STATIC (1707): if the state machine is in
the ACTIVITY CHECK state and the number of steps detected in the
ACTIVITY CHECK state is less than `N` steps, and the vertical
height, Hv, hasn't changed from the previous state then the program
logs the pressure profile for the ACTIVITY CHECK state and moves to
the STATIC state.
[0163] ACTIVITY CHECK to TRANSITION DOWN (1718): if the state
machine is in the ACTIVITY CHECK state and the number of steps
detected in the ACTIVITY CHECK state is less than `N` steps, and
the vertical height, Hv, is less than the vertical height from the
previous state then the program logs the pressure profile for the
ACTIVITY CHECK state and moves to the TRANSITION DOWN state.
[0164] ACTIVITY CHECK to REFILL (1724): if the state machine is in
the ACTIVITY CHECK state and the number of steps detected in the
ACTIVITY CHECK state is less than `N` steps, and the vertical
height, Hv, is greater than the vertical height from the previous
state then the program logs the pressure profile for the ACTIVITY
CHECK state and moves to the REFILL state.
[0165] ACTIVITY CHECK to ACTIVITY (1708): if the state machine is
in the ACTIVITY CHECK state and the number of steps detected in the
ACTIVITY CHECK state is greater than `N` steps, and the vertical
height then the program logs the pressure profile for the ACTIVITY
CHECK state and moves to the ACTIVITY state.
ACTIVITY State Output Transitions:
[0166] ACTIVITY to ACTIVITY (1709): If no inactivity interrupt
(INACT) is detected, the program stays in the ACTIVITY state.
[0167] ACTIVITY to TRANSITION DOWN (1710): if the state machine is
in the ACTIVITY state and an inactivity interrupt (INACT) is
detected and the vertical height (Hv) is decreasing the program
logs the pressure profile for the ACTIVITY state and moves to the
TRANSITION down state.
[0168] ACTIVITY to REFILL (1711): if the state machine is in the
ACTIVITY state and an inactivity interrupt (INACT) is detected and
the calculated venous pressure at the end of the ACTIVITY state
(Pr) is less than the Estimated venous pressure (EPr) corresponding
to the current vertical height under static conditions then the
program logs the pressure profile for the ACTIVITY state and moves
to the REFILL state.
TRANSITION DOWN State Output Transitions:
[0169] TRANSITION DOWN to TRANSITION DOWN (1712): If no activity
interrupt (ACT) is detected, and the vertical height (Hv) continues
to decrease the program stays in the TRANSITION DOWN state.
[0170] TRANSITION DOWN to REFILL (1720): if the state machine is in
the TRANSITIONDOWN state and no activity interrupt (ACT) is
detected and the vertical height (Hv) is increasing, the program
logs the pressure profile for the TRANSITION DOWN state and moves
to the REFILL state.
[0171] TRANSITION DOWN to STATIC (1717): if the state machine is in
the TRANSITION DOWN and no activity interrupt (ACT) is detected and
the vertical height (Hv) is not changing, the program logs the
pressure profile for the TRANSITION DOWN state and moves to the
STATIC state.
[0172] TRANSITION DOWN to ACTIVITY CHECK (1719): if the state
machine is in the TRANSITION DOWN and an activity interrupt (ACT)
is detected the program logs the pressure profile for the
TRANSITION DOWN state and moves to the ACTIVITY CHECK state.
[0173] REFILL State Output Transitions:
[0174] REFILL to TRANSITION DOWN (1713): If no activity interrupt
(ACT) is detected, and the vertical height (Hv) is decreasing the
program the program logs the pressure profile for the REFILL state
and moves to the TRANSITION DOWN state.
[0175] REFILL to REFILL (1714): if the state machine is in the
REFILL state and no activity interrupt (ACT) is detected and the
vertical height (Hv) is increasing or the current calculated
pressure (Pr) is not equal to the estimated pressure (EPr) for the
current vertical height (Hv), the program stays in the REFILL
state.
[0176] REFILL to STATIC (1723): if the state machine is in the
REFILL and no activity interrupt (ACT) is detected and the vertical
height (Hv) is not changing, the program logs the pressure profile
for the REFILL state and moves to the STATIC state.
[0177] REFILL to ACTIVITY CHECK (1715): if the state machine is in
the REFILL and an activity interrupt (ACT) is detected the program
logs the pressure profile for the REFILL state and moves to the
ACTIVITY CHECK state.
[0178] It will be appreciated that the system of the invention can
continuously calculate the vertical height between the heart and
the ankle in order to estimate a specific physiological parameter,
the ankle venous pressure, which is of clinical use in
understanding chronic venous insufficiency. The pressure algorithms
accommodate two different types of venous pressure estimates: those
observed during a static posture, and those observed during a
change in posture of during walking.
[0179] Venous pressure measurement has previously only been
possible using invasive pressure measurement techniques using a
large needle which is only reliable over a short treatment period.
The invention, however, allows continuous non-invasive estimation
of venous pressure.
[0180] The invention is not limited to the embodiments described
but may be varied in construction and detail.
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