U.S. patent application number 14/821206 was filed with the patent office on 2016-02-04 for method and system for assessing severity and stage of peripheral arterial disease and lower extremity wounds using angiosome mapping.
The applicant listed for this patent is VASAMED, INC.. Invention is credited to Daniel J. Bartnik, Rose A. Griffith, Paulita M. LaPlante.
Application Number | 20160029900 14/821206 |
Document ID | / |
Family ID | 55178756 |
Filed Date | 2016-02-04 |
United States Patent
Application |
20160029900 |
Kind Code |
A1 |
LaPlante; Paulita M. ; et
al. |
February 4, 2016 |
METHOD AND SYSTEM FOR ASSESSING SEVERITY AND STAGE OF PERIPHERAL
ARTERIAL DISEASE AND LOWER EXTREMITY WOUNDS USING ANGIOSOME
MAPPING
Abstract
The present invention provides a system for assessing the
severity and stage of PAD including at least one sensor that
measures skin perfusion pressure; a knowledge base that provides
data on lower extremity angiosomes; and a processing device in
operable communication with the sensor and the knowledge base, the
processing device that outputs a visual representation of at least
one of the lower extremity angiosomes that guides the sensor in the
mapping of a testing site relative to a target vessel where the
skin perfusion pressure measurement will be taken.
Inventors: |
LaPlante; Paulita M.; (Inver
Grove Heights, MN) ; Bartnik; Daniel J.; (Eden
Prairie, MN) ; Griffith; Rose A.; (Eden Prairie,
MN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
VASAMED, INC. |
Eden Prairie |
MN |
US |
|
|
Family ID: |
55178756 |
Appl. No.: |
14/821206 |
Filed: |
August 7, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13573989 |
Oct 18, 2012 |
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14821206 |
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12321813 |
Jan 26, 2009 |
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13573989 |
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12021938 |
Jan 29, 2008 |
8133177 |
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12321813 |
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11468203 |
Aug 29, 2006 |
7736311 |
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12021938 |
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61062476 |
Jan 25, 2008 |
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Current U.S.
Class: |
600/335 ;
600/364; 600/407; 600/481; 600/490; 600/504 |
Current CPC
Class: |
A61B 5/6828 20130101;
A61B 5/14551 20130101; A61F 5/566 20130101; A61B 5/4866 20130101;
A61B 5/022 20130101; A61B 5/6829 20130101; A61B 2560/063 20130101;
A61B 5/7278 20130101; A61B 5/7282 20130101; A61B 5/01 20130101;
A61B 5/02233 20130101; A61B 5/026 20130101; A61B 5/743 20130101;
A61B 5/0295 20130101; A61B 5/7246 20130101; A61B 5/02007
20130101 |
International
Class: |
A61B 5/026 20060101
A61B005/026; A61B 5/1455 20060101 A61B005/1455; A61B 5/0295
20060101 A61B005/0295; A61B 5/01 20060101 A61B005/01; A61B 5/00
20060101 A61B005/00; A61B 5/022 20060101 A61B005/022 |
Claims
1. An angiosome-based system for monitoring and assessing lower
extremity disease comprising: a compression device sized and shaped
for placement on a lower extremity limb of a patient, the
compression device including a pressure cuff configured to exert a
compressive force on said lower extremity limb, the compressive
force configured to substantially occlude blood flow in a skin
capillary bed adjacent said pressure cuff, said skin capillary bed
located in a lower extremity angiosome; at least one sensor
positioned adjacent said pressure cuff, said at least one sensor
for measuring peripheral vascular conditions of the patient in the
skin capillary bed and configured to generate a signal indicative
of the peripheral vascular condition; a processing device in
operable communication with said at least one sensor, said
processing device configured to (a) output a visual representation
of said lower extremity angiosome, said visual representation to
guide the placement of said sensor in the mapping of a testing site
relative to said skin capillary bed; (b) receive a peripheral
vascular measurement based on said angiosome mapping; and (c)
output data that is indicative of lower extremity disease based on
said angiosome mapping.
2. The system of claim 1 wherein said peripheral vascular
conditions include at least one of skin perfusion pressure, pulse
volume recordings, transcutaneous oxygen monitoring, ankle brachial
index, tissue CO2, temperature, spectral imaging, and hyperspectral
imaging.
3. The system of claim 1 wherein said at least one sensor comprises
a pulse oximetry sensor.
4. The system of claim 1 further comprising a knowledge base that
provides normative data on said at least one lower extremity
angiosome, said processing device in operable communication with
said knowledge base.
5. The system of claim 4 wherein said processing device is further
configured to cross reference said peripheral vascular measurement
with said knowledge base to generate a cross referenced data result
indicative of the severity and stage of the lower extremity
disease.
6. The system of claim 1 further comprising a knowledge base of
disease scoring and/or classification systems and a knowledge base
of peripheral arterial disease and lower extremity wounds, wherein
said processing device is further configured to cross reference
said peripheral vascular measurement with said knowledge base of
disease scoring and/or classification systems and said knowledge
base of peripheral arterial disease and lower extremity wounds to
generate a combined cross referenced data result indicative of the
severity and stage of lower extremity disease and further wherein
said processing device outputs data that is indicative of the
severity and stage of lower extremity disease based on said
combined cross referenced data result.
7. The system of claim 1 further comprising at least one metabolic
sensor for measuring at least one metabolic condition of the
patient, wherein said processing device is arranged to receive
inputs from said at least one metabolic sensor.
8. The system of claim 1 further comprising at least one skin
perfusion sensor for measuring skin perfusion.
9. The system of claim 1 further comprising: an inflatable cuff,
wherein said at least one sensor is a skin perfusion measurement
sensor in communication with the cuff; a pressure sensor in
communication with the cuff for reading pressure levels in the
cuff; a pressure instrument in fluid communication with the cuff
for inflation and deflation thereof, the pressure instrument
comprising: a source of pressurized air; and a conduit connected to
the source of pressurized air and the cuff, thereby placing the
source of pressurized air in fluid communication with the cuff,
wherein said processing device is operably coupled to said pressure
instrument and capable of controlling pressurized airflow to and
from the cuff, and further wherein said processing device is
arranged to receive inputs from said skin perfusion measurement
sensor and said pressure sensor; a computer program executable by
the processing device such that when executed, the computer program
causes the processing device to: initiate an automatic inflation
sequence resulting in a no flow condition; initiate an automatic
deflation sequence; automatically qualify a perfusion measurement
as a skin perfusion pressure value upon all conditions of a set of
predetermined conditions being met during the deflation sequence;
wherein said processing device receives said skin perfusion
pressure value based on said angiosome mapping, and cross
references said skin perfusion pressure value with said knowledge
base to generate a cross referenced data result indicative of said
severity and stage of lower extremity disease.
10. An angiosome-based perfusion monitoring system for peripheral
artery disease, the monitoring system comprising: a control device
including a source of pressurized fluid for introducing into a
compression device that is placed on a limb of a subject; and a
control circuit configured to (i) pressurize at least one bladder
of a compression device when the compression device is placed on a
limb of a subject to substantially occlude blood perfusion in skin
capillary beds adjacent to the at least one bladder, (ii)
depressurize the at least one bladder at a controlled rate after
pressurizing the bladder, (iii) receive a sensor signal from at
least one perfusion sensor on the compression device during
depressurization of the at least one bladder, wherein the sensor
signal is indicative of perfusion parameters of at least one skin
capillary bed adjacent said at least one perfusion sensor for
quantifying skin capillary bed perfusion, and (iv) map sensor
signals from said at least one perfusion sensor to at least one of
a first angiosome and at least one artery of the limb to determine
whether the received sensor signal is indicative of peripheral
artery disease.
11. The monitoring system of claim 10, wherein the control device
is configured to determine at least one of: adequate perfusion, no
flow, baseline flow, skin perfusion pressure value, and return of
microcirculation based on the received sensor signals.
12. The monitoring system of claim 10, wherein the control device
is configured to determine skin perfusion pressure value based on
the received sensor signals and compare the skin perfusion pressure
value to a threshold value to determine whether the received sensor
signals are indicative of peripheral artery disease.
13. The monitoring system of claim 10, wherein the control device
is configured to determine the baseline flow and the return of
microcirculation based on the received sensor signals and determine
a time elapsed between the baseline flow and the return of
microcirculation to determine whether the received sensor signals
are indicative of peripheral artery disease.
14. The monitoring system of claim 10, wherein the control device
comprises a user interface display, wherein the control circuit is
configured to generate a graphical rendering of the limb and
identify on the graphical rendering the location of the determined
peripheral artery disease.
15. A method of monitoring for peripheral artery disease, the
method comprising: pressurizing a bladder of a compression device
that is placed on a limb of a wearer so as to substantially occlude
blood perfusion to skin capillary beds adjacent the bladder of the
compression device; depressurizing the bladder at a controlled rate
after said pressurizing the bladder; detecting, during said
depressurizing the bladder and using at least one sensor, a
perfusion parameter of a skin capillary bed located in at least one
angiosome of the limb; generating a sensor signal indicative of the
perfusion parameter detected by said at least one sensor;
receiving, by a control circuit, said at least one sensor signal;
mapping, by the control circuit, said at least one sensor signal to
at least one of the first angiosome and a first artery associated
with the first angiosome; mapping, by the control circuit, the
second sensor signal at least one of said angiosome; and
determining, by the control circuit, whether the first and second
sensor signals are indicative of peripheral artery disease.
16. The method of claim 15, further comprising determining, by the
control circuit, at least one of: adequate perfusion, no flow,
baseline flow, skin perfusion pressure value, and return of
microcirculation based on the received sensor signals.
17. The method of claim 16, further comprising determining, by the
control circuit, skin perfusion pressure value based on the
received sensor signals and comparing the skin perfusion pressure
value to a threshold value to determine whether the received sensor
signals are indicative of peripheral artery disease.
18. The method of claim 16, further comprising determining, by the
control circuit, the baseline flow and the return of
microcirculation based on the received sensor signals, and
calculating, by the control circuit, a time elapsed between the
baseline flow and the return of microcirculation for use in
determining whether the received sensor signals are indicative of
peripheral artery disease.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. Ser. No.
13/573,989, filed on Oct. 18, 2012, now allowed; which is a
continuation-in-part of U.S. Ser. No. 12/321,813, abandoned; which
claims the benefit of priority to U.S. Prov. Ser. No. 61/062,476,
filed Jan. 25, 2008; and which is a continuation in part of U.S.
Ser. No. 12/021,938, filed Jan. 29, 2008, now U.S. Pat. No.
8,133,177; and which is a continuation-in-part of U.S. Ser. No.
11/468,203 filed Aug. 29, 2006, now U.S. Pat. No. 7,736,311. The
entireties of all of the foregoing applications are hereby
incorporated by reference.
COPYRIGHT
[0002] A portion of the disclosure of this patent document contains
material which is subject to copyright protection. The copyright
owner has no objection to the facsimile reproduction by anyone of
the patent document or the patent disclosure, as it appears in the
Patent and Trademark Office file or records, but otherwise reserves
all copyright rights whatsoever.
FIELD OF THE INVENTION
[0003] This invention relates generally to a method and system for
assessing the severity and stage of peripheral arterial disease and
lower extremity wounds using angiosome mapping.
BACKGROUND OF THE INVENTION
[0004] Atherosclerotic disease is widespread but commonly
associated only with coronary heart disease. However,
atherosclerosis of the peripheral vascular system, e.g. in the
lower extremities, also contributes to significant morbidity and
mortality in patients. Peripheral arterial disease (PAD), includes
all diseases caused by the obstruction of large arteries in the
arms and legs. PAD can result from atherosclerosis, inflammatory
processes leading to stenosis, an embolism or thrombus formation.
It causes either acute or chronic ischemia (lack of blood supply),
typically of the legs. Lower extremity occlusive PAD can be defined
on the basis of anatomical or functional considerations.
Anatomically it is defined as atherosclerotic arterial disease,
while functionally it is defined as arterial narrowing, causing a
mismatch between the oxygen supply and demand resulting in symptoms
of intermittent claudication (IC), exercise limitations, or tissue
loss. These two definitions help divide PAD into asymptomatic and
symptomatic disease states.
[0005] Worldwide, the prevalence of peripheral vascular disease in
people 55 years of age is 10%-25% and steadily increases with age.
Over 70%-80% of affected individuals are asymptomatic. In the
United States, peripheral arterial disease affects from 12% to 20%
of Americans age 65 and older. Despite its prevalence and
cardiovascular risk implications, only 25% of PAD patients undergo
treatment principally due to lack of diagnosis. However, diagnosis
is critical, as people with PAD have a four to five times higher
risk of heart attack and/or stroke. Thus, the prognosis for
patients with PAD is poor.
[0006] Several of the present inventors have collaborated on
developing a novel instrument that measures skin perfusion pressure
as more particularly described in U.S. Publication Nos.
2006/0287603 and 2008/0183059. Briefly, the novel instrument
measures skin perfusion pressure (SPP), which assists the physician
in assessing a patient's micro-circulatory health. The instrument
utilizes laser Doppler to evaluate reactive hyperemia, the
transient increase in organ or limb blood flow following a brief
period of occlusion, by measuring in millimeters of mercury the
pressure at which blood flow first returns to capillaries following
controlled occlusive release. This generates an SPP value. The
instrument also assesses macro-circulatory health by utilizing air
plethysmography to evaluate changes in arterial blood volume with
each cardiac cycle to generate a pulse volume recording (PVR);
these waveforms are rated according to severity ranging from
"likely severely abnormal" to "likely normal." Alone or together,
SPP and PVR may be used to assess the severity and stage of
peripheral arterial disease and the potential for wound healing.
However, because the diagnosis of peripheral arterial disease is
critical the present inventors have developed improvements to the
system using angiosome mapping that existing scoring systems, such
as Fontaine Stages, Rutherford Category, S(AD) Foot Ulcer
Classification, Wagner Scale for wound classification and the like,
are unable to objectify.
[0007] Angiosomes are three dimensional blocks of tissue supplied
by a single "source" artery. Dr. Ian Taylor, expanding on the work
of previous anatomists, conducted a landmark anatomic study that
detailed the angiosome principal and identified over 40 angiosomes
of the body. Dr. Christopher Attinger further investigated
angiosomes of the foot and ankle for their impact on limb salvage,
specifically in relation to incision planning, blood flow
preservation, tissue reconstruction, and revascularization
procedures to afford optimal healing of wounds in ischemic limbs.
Knowledge of the angiosome principal is frequently utilized by
plastic surgeons wherein detailed and specific understanding of
vascular sources to skin tissue is critical to successful outcome
for the patient. However, knowledge of the angiosome principal is
not well understood within other medical disciplines.
[0008] One such area is the management of PAD, critical limb
ischemia (CLI) and diabetic (DM) foot where there are six distinct
angiosomes. The six angiosomes of the foot and ankle originate from
the three main arteries to the foot and ankle. The posterior tibial
artery supplies the medial ankle and the plantar foot, the anterior
tibial artery supplies the dorsum of the foot, and the peroneal
artery supplies the anterolateral ankle and the lateral rear foot.
The large angiosomes of the foot can be further broken into
angiosomes of the major branches of the above arteries. The three
main branches of the posterior tibial artery each supply distinct
portions of the plantar foot: the calcaneal branch (heel), the
medial plantar artery (instep), and the lateral plantar artery
(lateral midfoot and forefoot). The two branches of the peroneal
artery supply the anterolateral portion of the ankle and rear foot,
the anterior perforating branch (lateral anterior upper ankle) and
the calcaneal branch (plantar heel). The anterior tibial artery
supplies the anterior ankle and then becomes the dorsalis pedis
artery that supplies the dorsum of the foot.
[0009] Angiosomes are inherently three-dimensional. Currently,
however, angiosome concepts are communicated by presenting a
combination of two-dimensional flat images and/or flat
illustrations of anatomical vasculature. Further, existing
representations for angiosomes are not integrated into systems for
assessing PAD, CLI or DM conditions. Moreover current use of
angiosome concepts, if any, is limited to the subjective
interpretation of combined sets of data by the physician.
[0010] There is a need to provide health care professionals with a
method and system to visually represent lower extremity angiosomes
to guide the placement of a skin perfusion sensor and map a testing
site relative to a target vessel in the angiosome. A skin perfusion
measurement, which is based on the aforementioned angiosome
mapping, will enable an accurate assessment of severity and stage
of peripheral arterial disease and lower extremity wound healing
potential. There is a further need to provide expanded utility with
regard to angiosome mapping in identifying a medical condition to
objectify changes to skin, pallor, temperature, etc. An additional
need is to incorporate angiosome mapping with functional markers
and other clinical indices to provide a PAD, CLI and/or wound
healing evaluation system. The inclusion of angiosomes brings new
perspective to the anatomical and functional considerations that
inform education, diagnosis, therapeutic management and
communication applications.
BRIEF SUMMARY OF THE INVENTION
[0011] The foregoing invention overcomes the problems and
disadvantages of current methods that subjectively assess the
severity and stage of peripheral arterial disease and lower
extremity wounds.
[0012] The present invention combines mechanical measurements such
as flow, which includes blood flow, fluid flow, arterial flow,
capillary or arterial distal flow, micro and macro flow, and
angiosome mapping as the foundation of a PAD, CLI and/or wound
healing evaluation and/or classification system to more effectively
assess and communicate the severity and stage of disease states.
Optional inputs include established disease scoring and/or
classification systems as hereinafter described.
[0013] The present invention incorporates angiosome mapping with
functional markers and other clinical indices to provide a PAD, CLI
and/or wound healing evaluation system. The inclusion of angiosome
mapping brings new perspective to the anatomical and functional
considerations that inform education, diagnosis, therapeutic
management and communication applications.
[0014] The invention includes a method and system for assessing the
severity and stage of PAD and/or wound healing. The invention
includes at least one sensor adapted to measure peripheral vascular
conditions of a patient; a lower extremity angiosome knowledge base
that provides data on lower extremity angiosomes; and a processing
device in operable communication with the sensor and the lower
extremity angiosome knowledge base. The processing device outputs a
visual representation of at least one of the lower extremity
angiosomes included in the knowledge base, the visual
representation to guide the placement of the sensor in the mapping
of a testing site relative to a target vessel for the skin
perfusion pressure measurement. The processing device receives the
vascular measurements based on the angiosome mapping and produces
data that is indicative of the severity and stage of lower
extremity disease. The sensors may include one or more sensors for
measuring skin perfusion pressure, tissue CO2, temperature as other
sensors known to those of skill in the art. Lower extremity disease
includes but is not limited to peripheral arterial disease and
wound healing potential.
[0015] The invention also includes a method of providing a sensor
for measuring peripheral vascular conditions, a knowledge base that
provides data on lower extremity angiosome and a processing device
in operable communication with the knowledge base. The processing
device displays an angiosome map based upon the expected normal
underlying arterial architecture. Vascular inputs from sensors,
images, or other means are used to assess and interrogate the skin
to "inform" the angiosome map by overlaying sensor-acquired
information, (referred to herein as sensor fusion). This sensor
fusion can then be used to localize disease to an angiosome, assist
intervention planning and assess outcomes following intervention.
The processing device outputs data that is indicative of the
severity and stage of peripheral arterial disease and wound healing
potential to produce a new understanding of the angiosome as it has
been altered by disease.
[0016] The system in accordance with the present invention
optionally includes a knowledge base of disease scoring and/or
classification systems and a knowledge base for providing
information on peripheral arterial disease.
[0017] The system in accordance with the present invention
optionally includes a display device for displaying the output.
[0018] The present invention automates and, therefore, objectifies
the method and system of assessing and communicating the severity
and stage of peripheral arterial disease and lower extremity wounds
using angiosome mapping.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] The patent or application file contains at least one drawing
executed in color. Copies of this patent or patent application
publication with color drawings will be provided by the Office upon
request and payment of the necessary fee.
[0020] FIG. 1 is a schematic representation of an embodiment of the
measurement device in use with a patient in accordance with the
present invention in which the pressure cuff and applicable sensors
are placed peri-wound.
[0021] FIG. 2 depicts a flow chart that represents the typical flow
of the test procedure.
[0022] FIG. 3 is a flow chart schematically depicting inputs into
the angiosome map, sensor fusion and output data.
[0023] FIG. 4 is an illustrative three-dimensional angiosome map
prior to the inputting of data in accordance with the present
invention depicting the posterior tibial, anterior tibial,
calcaneal branch and lateral plantar angiosomes.
[0024] FIG. 5 is a further illustration of an angiosome map prior
to the inputting of data in accordance with the present invention
depicting the lateral plantar, medial plantar and calcaneal branch
angiosomes.
[0025] FIG. 6 is a further illustration of an angiosome map prior
to the inputting of data in accordance with the present invention
depicting the anterior tibial, medial plantar and calcaneal branch
angiosomes.
[0026] FIG. 7 is a flowchart representing the operation of a
perfusion pressure monitor with respect to inflation of the system
for assessing severity and stage of peripheral arterial disease and
wound healing potential in accordance with the invention.
[0027] FIG. 8 is a flowchart representing the operation of the
perfusion pressure monitor with respect to deflation of the system
for assessing severity and stage of peripheral arterial disease and
wound healing potential in accordance with the invention.
[0028] FIG. 9A is a schematic diagram illustrating the pressure
line output display of the skin perfusion pressure monitor of the
system for assessing severity and stage of peripheral arterial
disease and wound healing potential in accordance with the present
invention.
[0029] FIG. 9B is a schematic diagram illustrating the pressure
line output display of the skin perfusion pressure monitoring of
the system for assessing severity and stage of peripheral arterial
disease and wound healing potential in accordance with the present
invention with a spike indicating motion artifact.
[0030] FIG. 9C is a schematic diagram illustrating the pressure
line output display of the skin perfusion pressure monitoring of
the system for assessing severity and stage of peripheral arterial
disease and wound healing potential in accordance with the present
invention with a spike indicating motion artifact, bars, and a true
reading of surface perfusion pressure.
DETAILED DESCRIPTION OF THE INVENTION
[0031] The present invention is based on the inventors' discovery
that the measurement of mechanical factors alone, such as arterial
and distal arterial blood flow, does not necessarily objectively
assess the severity and stage of peripheral arterial disease and
lower extremity wounds. The present invention is also based on the
inventors' discovery that there are simple, objective parameters
that can be measured within discrete angiosomes and that the paired
use of parameter measurement and reporting within discrete
angiosomes replaces subjective diagnostic methods.
[0032] Thus, the present invention is directed to the measurement
of mechanical factors such as arterial and distal arterial blood
flow, optionally combined with established disease scoring and/or
classification systems, the foregoing integrated into and
correlated with angiosome mapping as the foundation of a PAD, CLI
and/or wound healing evaluation system to effectively assess the
severity and stage of peripheral arterial disease and lower
extremity wounds.
[0033] Optionally, the novel invention can utilize the foregoing in
combination with metabolic factors such as the measurement of
pCO2.
[0034] The methods and devices of the invention measure blood flow
in tissue at a relevant local site such as proximal to the wound or
peri-wound. Relevance is defined according to the location of the
wound within an angiosome. In situations where the ulcer or wound
is severe, peri-wound measurements are thus utilized effectively.
In general, these measurements are made by placing a blood-flow
sensor such as a laser-Doppler sensor or an ultrasound Doppler
sensor in an angiosome. If a wound is present, the measurement is
made reasonably close to, but not directly in, the wound site and
the sensor measures blood flow at the selected site. If a wound is
not present, several measurements may be made in various
angiosomes. Alternatively, continuous monitoring measurements can
be utilized. PVRs are made at several levels as prescribed by
standard arterial testing protocols. Optionally, all testing is
performed bilaterally for completeness.
[0035] SPP measurements are taken to determine whether local blood
flow, i.e. capillary perfusion, of a local or regional body site
having an ulcer or wound is sufficient to support wound healing.
The accurate measurement of this parameter, therefore, is critical
to physicians who treat patients suffering from open surface wounds
resulting from complications from diabetes, PAD, pressure ulcers,
trauma, venous insufficiency, and the like. SPP is also measured
when no wound exists as part of the assessment of the effects PAD
and CLI have on local or regional tissue perfusion.
[0036] Referring to FIG. 1, a schematic diagram depicting a
representative, but not limiting, perfusion pressure monitoring
system 10 is illustrated. The skin perfusion pressure monitoring
system 10 broadly includes optical probe or sensor 12, pressure
cuff 14, and skin perfusion pressure instrument 22 with display
monitor 30. The optical probe 12 is positioned underneath pressure
cuff 14 proximate the skin of the patient's limb 18. Alternatively,
optical probe 12 may be positioned distal to cuff 14 or inside cuff
bladder 14. In an alternative embodiment, cuff 14 may include a
transparent window to observe optical probe 12. The skin perfusion
pressure instrument inflates the pressure cuff 14 through tube 26.
The size of pressure cuff 14 may be varied depending on whether the
limb involved is the arm, toe, leg, ankle, etc. but must be capable
of sustaining a sufficiently high pressure (above systolic) to
temporarily stop tissue blood flow at the site of the optical probe
12 in the observation volume of tissue 20. The observation volume
of tissue 20 may be at the same location as the applied pressure,
at a location near the applied pressure, or distal from the applied
pressure, e.g. where flow is measured on the toe and pressure is
applied at the ankle. The skin perfusion instrument 22 is coupled
to the optical probe 12 via a fiber optic cable 24, and the
pressure cuff 14.
[0037] The optical probe 12 monitors microcirculatory flow within
the observation volume of tissue 20. Microcirculation detected
within the observation volume of tissue 20 is expressed as a
percent and displayed on the Y-axis of the perfusion pressure
display instrument. The percent value is shown as both a numeric
value, typically from 0% to 10% and graphically is shown as a bar
graph on the Y-axis of the instrument display 30. The skin
perfusion pressure instrument 22 also measures the pressure within
the cuff 14 and displays the applied cuff pressure in millimeters
of mercury on the X-axis of the display in descending uniform
increments.
[0038] Optical probe 12 depicted in FIG. 1 includes at least a
laser transmitter fiber 32 and at least one receiver photodiode 34.
In an alternative embodiment, the laser or photodiode, or both, may
be placed in probe 12 without a need for fiber optic elements. In
operation, coherent light supplied from a solid state, or other
laser device within the perfusion pressure display instrument 22 is
conducted to the transmitter fiber 32 that is in contact with the
patient's skin through the pressure cuff 14 bladder. Photons
emitted from the transmit fiber 32 are scattered by the patient's
tissues. A small portion (less than 5%) of the emitted photons is
collected by the receiver fiber 34. The spacing between the fibers
and the optical apertures of the fibers establish the volume of
tissue that is monitored. Typically a single transmitter fiber is
used with a pair of receiver fibers. The nominal fiber core
diameter is on the order of 50 to 100 microns and is used to
establish an observation volume of approximately one to two cubic
millimeters.
[0039] Notwithstanding, those skilled in the art will recognize
that there are many ways to determine the point at which
microcirculatory flow returns to a given observation volume. For
example, visual observation such as the change in color of the
observation site; ultra-sound; optical plethysmography,
measurements of increases in temperature; sound, e.g. a microphone
for pulsatile flow in the macrocirculation; metabolic indicators
such as pCO2 or lactate; and bioimpedance or pulse oximetry or
both, each with a pulsatile measurement and a blood volume
measurement.
[0040] The optical probe includes at least a laser transmitter
fiber and at least one receiver photodiode. In an alternative
embodiment, the laser or photodiode, or both, may be placed in the
optical probe without a need for fiber optic elements. In
operation, coherent light supplied from a solid state, or other
laser device within the perfusion pressure display instrument is
conducted to the transmitter fiber that is in contact with the
patient's wound through the pressure cuff bladder. Photons emitted
from the transmit fiber are scattered by the patient's tissues. A
small portion (less than 5%) of the emitted photons is collected by
the receiver fiber. The spacing between the fibers and the optical
apertures of the fibers establish the volume of tissue that is
monitored. Typically a single transmitter fiber is used with a pair
of receiver fibers. The nominal fiber core diameter is on the order
of 50 to 100 microns and, when combined with distance to receiving
fiber, is used to establish an observation volume of approximately
one to two cubic millimeters.
[0041] Those skilled in the art will recognize that there are many
ways to determine the point at which microcirculatory flow returns
to a given observation volume. For example, visual observation such
as the change in color of the observation site; ultra-sound;
optical plethysmography, measurements of increases in temperature;
sound, e.g. a microphone for pulsatile flow in the
macrocirculation; metabolic indicators such as PCO2 or lactate; and
bioimpedance or pulse oximetry or both, each with a pulsatile
measurement and a blood volume measurement.
[0042] Some back-scattered photons are frequency shifted by moving
cells present in the microcirculation. The collected photons are
collected by the capillary vitality instrument via a cable where
they impinge on a photodiode. Thus, photons are impinging on the
photodiode as a result of scattering off moving and stationary
cells. The photodiode voltage contains both frequency and power
information. The Doppler shifted frequency is related to cell
velocity while the spectral power information is related to the
volume of moving cells at that given frequency. The DC signal
component results from the total number of photons received by the
receive fiber. The AC signal component results from the mixing of
frequency shifted photons with photons from stationary structures.
If the number of moving cells present within the observation volume
increases then the magnitude of the AC component will increase
while the DC offset will remain nearly constant. The AC component
increases because more returned photons undergo a Doppler shift.
The DC component remains nearly constant because the total number
of photons scattered by collisions with stationary cells within the
measurement volume is reduced only slightly by moving cells.
Therefore, the perfusion measurement is proportional to the ratio
of the AC signal to the DC signal, which is an indication of the
volume of moving cells in the observation volume of tissue. This
type of measurement is commonly computed with both analog and
digital signal processing. For example, it is common to convert the
AC signal to an RMS equivalent through analog processing. It is
these values that are presented to the A/D converter. The
microprocessor then may square these digitized values prior to
forming the ratio. The ratio value may be scaled by an empirically
derived scaling factor that depends on the gain distribution
throughout the signal processing paths.
[0043] SPP measurements as described above measure the
microcirculation of the patient in the area of interest. It is a
distal arterial test and an indicator of wound healing potential
and disease severity. Skin perfusion pressure measures, in
millimeters of mercury, the pressure at which blood flow first
returns to the capillaries following controlled occlusive
release.
[0044] The inventors of the present invention have also discovered
that the measurement of skin perfusion pressure can be further
refined by measuring air plethysmography. Air plethysmography (APG)
is a technique that allows the measurement of limb volume changes
with different maneuvers. APG utilizes a cuff that is placed around
the leg, a calibratable pressure transducer, and in the case of the
present invention an instrument that provides a visual display.
Parameters derived from performing various APG measurements with
positional changes include the venous filling index, which
quantifies venous reflux, the ejection fraction, which correlates
with calf muscle pump function, and the residual volume fraction,
which correlates with ambulatory calf venous pressure. Venous
occlusion techniques allow the measurement of arterial flow into
the limb and the venous outflow fraction, which can be used to
evaluate venous obstruction. Differentiation of pathology in the
deep venous system from that in the superficial venous system is
possible.
[0045] Alternatively, the inventive instrument may utilize optical
plethysmography with light absorbance technology to reproduce
waveforms produced by pulsating blood. Typically non-visible
infrared light is emitted into the skin. More or less light is
absorbed, depending on the blood volume in the skin. The
backscattered light corresponds with the variation in blood volume.
Blood volume changes are then determined by measuring the reflected
light and using the optical properties of tissue and blood. The
optical plethysmography measurement may be obtained by volume
displacement plethysmography or by electrical impedance
plethysmography as those skilled in the art can appreciate.
Typically the tissue under investigation is bathed with light of a
suitable wavelength and the resultant scattered light is measured
with a silicon photodiode. The received signal is assumed to be a
measure of volume changes due to localized blood flow.
[0046] Optical or air plethysmography measurements may be used in
conjunction with the skin perfusion pressure measurements disclosed
herein.
[0047] The foregoing measurements have been named pulse volume
recordings and measure the macrocirculation of the patient. Alone
or in combination SPP and PVR may provide an assessment of arterial
circulation in the area of interest for diagnostic
consideration.
[0048] Thus, laser-Doppler, ultrasound-Doppler, and other
blood-flow measurement instruments that measure skin perfusion
pressure used in conjunction with air or optical plethysmography
can be used to assess micro-circulatory and macro-circulatory
health.
[0049] Referring now to FIGS. 1 and 7, the cuff inflation sequence
the commences the recording of a skin perfusion measurement is
illustrated. The skin perfusion instrument 22 commences the cuff
inflation process and the laser in optical probe 12 is enabled. The
cuff 14 bladder is initially filled with a low pressure, such as 5
to 10 mmHg, to ensure that the sensing probe is in contact with the
patient's skin so that adequate perfusion can be detected and
measured. If adequate perfusion cannot be measured, cuff inflation
is aborted and the test does not proceed. If adequate perfusion can
be measured, the pressure cuff 14 is inflated to the target
pressure, near or at systolic and perfusion is measured. If "no
flow" is not achieved at this target pressure and the maximum
target pressure has not been reached, pressure is increased
incrementally (e.g. 40 mmHg increments) and the "no flow" criteria
is tested again. If the maximum target pressure has been reached,
and the "no flow" criterion still has not been met, cuff inflation
is aborted and the test discontinued.
[0050] FIG. 8 depicts the cuff deflation sequence. As noted above,
if the skin perfusion pressure instrument recognizes a "no flow"
signal, cuff pressure starts to automatically deflate at a
controlled rate. A controlled rate of deflation provides
reproducibility from measurement to measurement on the same patient
and between patients. If the pressure is not dropping at the
controlled rate, which may be caused by severe patient movement,
cuff deflation is aborted and the test discontinued. If the
pressure is dropping at the controlled rate, P.sub.0 is analyzed
for an SPP value. If all conditions for an SPP value are met, e.g.
those discussed below, an SPP value is reported. If the conditions
are not met, the test continues for a specified time period after
which perfusion measurements are displayed for the physician to
interpret but an SPP value is not reported for that test. The
physician can then use the displayed perfusion data along with any
other information that is available to her to determine whether
another test should be conducted or if based on her expertise, she
can determine an appropriate SPP value.
[0051] FIGS. 9A-C illustrate different stages of output data as
depicted on the display monitor. Referring to FIG. 9A data being
recorded during the testing procedure is displayed. Moving line 15
rises as pressure decreases. As can be seen, points representing
adequate perfusion 35, no flow 36, baseline flow 37, SPP value 38,
and the return of normal microcirculation 39 are depicted. FIG. 9B
illustrates the same pressure line that rises as pressure decreases
but now displays motion artifact 40. As illustrated, the skin
perfusion pressure monitoring system in accordance with the present
invention rejects motion artifact as not being a perfusion
measurement and the test continues as seen by continuing line 15.
Referring to FIG. 9C, the skin perfusion pressure monitor in
accordance with the present invention analyzes numerous different
criteria for detecting and rejecting motion artifact in qualifying
P.sub.0 for a SPP value. If P.sub.0 has been qualified as an SPP
value, a bar graph is overlaid on line 15, as best seen in FIG. 9C,
and the SPP value 38 is recorded. As those skilled in the art can
appreciate, any graphical representation can be used to depict the
perfusion measurement data set. The skin perfusion pressure
monitoring system 10 considers unique criteria in qualifying
P.sub.0 as an SPP value and in assessing whether motion artifact is
present. Those skilled in the art can appreciate that many or few
criteria may be considered. In addition, other criteria can be used
other than those described below. For example, linear regression,
slope intercept, differentiation, weighted average, and other known
mathematical models may be used in addition to or in lieu of the
criteria listed below. Whether the number of criteria considered is
few or many, all criteria will be used to reject unwanted noise,
environmental influences, or motion in combination with the
qualification of a pressure at which microcirculatory flow returns
to the observation or measurement volume.
[0052] Initially as a first criterion, P.sub.0 must be within a
valid range for the system to qualify an SPP value. If P.sub.0 is
not within a valid range, for example from approximately 1 mmHg to
approximately 150 mmHg, the system will not indicate that a
particular P.sub.0 is an SPP value.
[0053] Another criterion is whether the perfusion increase is large
enough relative to the measurement. If the perfusion increase is
not large enough an SPP value will not be qualified. In
interpreting "step size" (i.e. perfusion increase large enough from
the prior measurement) the instrument uses a perfusion sensitive
tolerance that progressively adjusts sensitivity thresholds as
perfusion returns. This allows the system to qualify SPP values
over a wide dynamic range while being less sensitive to motion
transients. For example, if perfusion is very low then the
instrument allows for the detection and rejection of motion
artifact due to its perfusion sensitive tolerance. If the perfusion
measurement is greater than 0.20% (i.e. high perfusion measurement)
and the applied cuff pressure is less than 100 mmHg a perfusion
increase of from 10% to 50% and preferably 25% relative to the
prior measurement, is necessary. If the perfusion measurement is
greater than 0.20% (i.e. high perfusion measurement) and the
applied cuff pressure is greater than or equal to 100 mmHg a
perfusion increase of from 20% to about 80%, and preferably 40%,
relative to prior measurement is necessary. If the perfusion
measurement is between 0.15 to 0.20% (i.e. medium perfusion
measurement) and the applied cuff pressure is any valid pressure a
perfusion increase of from 25% to 100%, and preferably 50%,
relative to the prior perfusion measurement is necessary. If the
perfusion measurement is less than 0.15% (i.e. low perfusion
measurement) and the applied cuff pressure is any valid pressure a
perfusion increase of from 50% to 200%, and preferably 100%,
relative to the prior perfusion measurement is necessary.
[0054] Those skilled in the art will recognize that the foregoing
criterion does not need to be limited to high, medium and low
perfusion measurements or a few isolated points for applied cuff
pressure, i.e. above and below 100 mmHg. These may be expressed as
a continuous function of perfusion measurements or applied cuff
pressure, or both.
[0055] Another criterion is whether the perfusion measurement under
evaluation, i.e. P.sub.0, is large enough, i.e. whether flow is
above baseline. The perfusion should be preferably from between
0.05 to 0.2% and more preferably at least 0.10% at point P.sub.0 or
no skin perfusion pressure will be recorded.
[0056] Another criterion determines whether the "next steps," i.e.
those following point P.sub.0, are increasing or decreasing. Next
steps must not be decreasing as this is not characteristic of a
typical signature for returning microcirculatory flow to an
observation volume with decreasing pressure. This fourth criterion
focuses on the duration of increasing perfusion change. As
microcirculation flow returns it produces a perfusion signal that
increases and holds in a signature pattern. Motion artifact
produces a perfusion signal that has more oscillatory content,
thereby having greater tendencies to decrease.
[0057] When applied cuff pressure is low, i.e. preferably from
about 0 to 20 mmHg and more preferably less than 15 mmHg, the
number of next steps analyzed in determining whether next steps are
increasing or decreasing is one. When the applied cuff pressure is
in a medium range, for example from about 10 to 50 mmHg and more
preferably from about 15 to about 20 mmHG, the number of next steps
analyzed in determining whether next steps are increasing or
decreasing is two. When applied cuff pressure is high, for example
from about 40 to 120 mmHg and preferably greater than 50 mmHg but
less than 100 mmHg, the number of next steps analyzed in
determining whether next steps are increasing or decreasing is
three. When pressure is very high, preferably from 80 to 150 mmHg,
and most preferably greater than 100 mmHg, the number of next steps
analyzed in determining whether next steps are increasing or
decreasing is five. The higher the number of next steps being
analyzed, i.e. N, the more confidence that the system has qualified
an SPP value.
[0058] Another criterion for detecting and rejecting motion
artifact is the profile of perfusion change. Microcirculation
produces a perfusion signal that increases step-wise while motion
produces a perfusion signal that has more oscillatory content.
Changes that do not follow a perfusion return signature are
ignored. Referring again to Table II, the perfusion change profile
criterion for detecting and rejecting motion artifact is whether
the specified number of steps following P.sub.1 are at least at or
above the perfusion value for P.sub.1. These steps must not be
decreasing. In other words, P.sub.2 to P.sub.N must all be greater
than P.sub.1. This criterion is especially effective in rejecting
motion, as those signals are not long-lived.
[0059] If all criteria are met the skin perfusion pressure system
will qualify P.sub.0 as the SPP value 38.
[0060] The instrument in accordance with the present invention may
utilize an entirely software embodiment or an embodiment containing
both hardware and software elements. In one embodiment, the
invention is implemented in software, which includes but is not
limited to firmware, resident software, microcode, etc. The
invention can also take the form of a computer program product
accessible from a computer-usable or computer-readable medium
providing program code for use by or in connection with a computer
or any instruction execution system. For the purposes of this
description, a computer-usable or computer readable medium can be
any apparatus that can contain, store, communicate, propagate, or
transport the program for use by or in connection with the
instruction execution system, apparatus, or device.
[0061] The medium can be an electronic, magnetic, optical,
electromagnetic, infrared, or semiconductor system (or apparatus or
device) or a propagation medium. Examples of a computer-readable
medium include a semiconductor or solid state memory, magnetic
tape, a removable computer diskette, a random access memory (RAM),
a read-only memory (ROM), a rigid magnetic disk and an optical
disk. Current examples of optical disks include compact disk-read
only memory (CD-ROM), compact disk-read/write (CD-R/W) and DVD.
[0062] A data processing system suitable for storing and/or
executing program code will include at least one processor coupled
directly or indirectly to memory elements through a system bus. The
memory elements can include local memory employed during actual
execution of the program code, bulk storage, and cache memories
which provide temporary storage of at least some program code in
order to reduce the number of times code must be retrieved from
bulk storage during execution.
[0063] Input/output or I/O devices (including but not limited to
keyboards, displays, pointing devices, etc.) can be coupled to the
system either directly or through intervening I/O controllers.
Network adapters may also be coupled to the system to enable the
data processing system to become coupled to other data processing
systems or remote printers or storage devices through intervening
private or public networks. Modems, cable modem, wireless devices
and Ethernet cards are just a few of the currently available types
of network adapters.
[0064] Referring now to FIGS. 2 and 3, history and physical exam
(H&P) parameters are provided by an operator. Alternatively,
H&P parameters can be obtained from an electronic medical
record. Physical examinations for peripheral vascular conditions
commonly assess: indications of trauma, muscle wasting, muscle
asymmetry, temperature, edema (swelling), erythema (redness),
ulcers, shiny skin, capillary refill, and absence of hair.
[0065] An angiosome map is displayed by the system. A skin
perfusion measurement sensor is overlaid on the angiosome map and
the sensor is mapped to a relevant angiosome where testing is to be
done. Tests and other measured parameters for assessment of
peripheral vascular conditions for assessment by the system may
include: SPP, PVR, transcutaneous oxygen monitoring (TCOM), ankle
brachial index (ABI), tissue CO2, temperature, spectral imaging,
and hyperspectral imaging.
[0066] The instrument utilizes all available information and
measured parameters, which are referred to as inputs. Each input
supports assessment of a disease state or is correlative or
otherwise associated with a disease state. As an example, measures
of SPP correlate with PAD and the likelihood of wound healing.
Similarly, PVR waveforms are indicative of large vessel disease.
Inputs would also be associated with a single angiosome or multiple
angiosomes, as applicable. Inputs can also be associated with a
specific location within an angiosome or specific site on a
limb.
[0067] Inputs can be highly varied. Inputs can consist of disparate
measures, for example SPP and PVR. Inputs can consist of multiple
measures within a single angiosome, for example several SPP
measures within a single angiosome. Inputs can even consist of
measures or information obtained at different points in time.
[0068] Angiosome mapping considers, for each input, the angiosome
where the input was acquired, left or right limb, and may also
consider the site within the angiosome. Inputs can be combined by
utilizing any of several known sensor fusion methods. Examples of
sensor fusion methods include Kalman filter, Bayesian network, and
Dempster-Shafer theory. Inputs can be weighted based on confidence,
reliability, or how recent input was obtained. Other methods for
sensor fusion and weighting are known to those skilled in the
art.
[0069] The output can be provided in one or more of several
methods. Output can be provided in a visual presentation associated
with the angiosome model where a disease state metric can be
displayed in a color coded or otherwise shaded manner specific to
each angiosome. Output can be provided in a tabular manner. Output
can be provided to an electronic medical record or medical
information system.
[0070] Referring now to FIGS. 4, 5, and 6 the instrument in
accordance with the present invention combines anatomical
structures (skin, vascular, and skeletal) into computer-generated
three dimensional angiosome map that objectifies the stage and
severity of PAD and lower extremity wounds. FIGS. 4, 5 and 6 depict
exemplary angiosome regions prior to the inputting of data. The
instrument in accordance with the present invention provides a
computer-generated novel and unobvious three-dimensional anatomical
model. This three-dimensional model contains skeletal structure,
vascular structure, and skin tissue blocks defined by particular
vascular structure. In addition, a unique aspect of this invention
allows for two-dimensional print out of the computer generated
three-dimensional model that contains skeletal, vascular and
angiosome structures. The angiosome map allows the physician to
view all foot and leg angiosomes even if located beneath the skin
surface, as will hereinafter be described. Placement of the laser
Doppler and other sensors in an angiosome of key interest provides
the most accurate readings of blood flow and other parameters, as
well as reliable and reproducible results.
[0071] The present invention combines all components integral to
utilizing angiosomes to assess the severity and stage of PAD both
in terms of etiology, location and severity to support optimal
diagnosis of PAD and healing of wounds in ischemic limbs and the
like.
[0072] The instrument in accordance with the present invention
generates an angiosome map that distinguishes between vascular
systems, in other words arterial and venous structures and other
anatomical information such as the nervous system.
[0073] Other attributes of the angiosome map include various
methods of color-coding, highlighting, ghosting or other means to
facilitate discrimination between structures and allows for
customization and scaling for patient-specific attributes such as
size, weight, age and gender.
[0074] The angiosome map in accordance with the present invention
may represent various disease states. One frequently seen condition
that could be represented is arterial constriction/obstruction and
secondary arterial development such as the presence of collaterals
resultant of chronic obstructions and small vessel disease
process.
[0075] The angiosome map in accordance with the invention can
optionally be used as the foundation of a PAD, CLI and/or wound
healing scoring system for incorporation into established
classification systems such as the Trans Atlantic Scoring
Classification (TASC), Rutherford Categorization System, Fontaine,
University of Texas Diabetic Wound Classification System and the
Wagner Scale for wound categorization.
[0076] The angiosome map in accordance with the invention can be
designed to be customized to a patient's position during evaluation
as well as stressors that are employed during testing. Examples of
stressors include but are not limited to limb elevation, changes in
externally applied pressure and temperature.
[0077] The angiosome map can be integrated with input obtained from
a patient. The input may be either directly measured input or
software-communicated input. An example of direct measurement input
is one wherein perfusion within one or more of the six angiosomes
is measured for input. An example of software-communicated input is
one in which the new model can obtain three dimensional magnetic
resonance imaging scans of a patient's vascular structure, overlay
the patient information with model information, and present this
information back to the user in a manner that includes angiosomes.
Input can consist of history and physical exam parameters such as
age, height weight, temperature, edema, erythema; skin perfusion
pressure measurements; pulse volume recording; transcutaneous
oxygen monitoring; ankle brachial index; tissue CO2; and other such
parameters.
[0078] The angiosome map in accordance with the present invention
can also optionally be integrated with existing disease scoring
and/or classification systems and wound healing assessment scoring
systems. In one example, a medical device in which a user places a
sensor on the skin for measurement of parameters measurable on
and/or through the skin. These include but are not limited to
images (photographic, thermographic, hyperspectral), electrical
signals, blood and blood component flow and the related attributes
of blood and blood component flow such as temperature and
metabolites (oxygen, hemoglobin, carbon dioxide) can benefit if the
user can be presented, via the invention, with a depiction of
vascular sources supplying the skin tissue. In one embodiment, the
user could maneuver a model by means of a computer interface to
analyze the vascular structure supporting the area of skin being
measured and also to indicate the location where a sensor is
placed.
[0079] Treatment or surgical medical devices can be improved by
this invention. In one example, a medical device in which a user
treats a wound can benefit if the user can be presented with the
underlying vascular structure and its relationship with the area of
skin in which the wound resides.
[0080] While the underlying angiosome model is inherently a
computer-generated, three-dimensional model, a two-dimensional
format can be generated and utilized when discussing diagnoses with
patients and other physicians and health care workers. Two
dimensional presentations of three dimensional structures could
also be provided on a computer display. Because the underlying
model is three dimensional, the viewpoint could be controlled by a
user such as being rotated or even stressed in some way. Also, a
user could be allowed to control several aspects of the
presentation. For example, a user could control whether certain
underlying structures are displayed, to what extent certain
underlying structures are highlighted or enhanced, or the user
could enable color coding of certain features such as having
different angiosome presented in different colors.
[0081] The angiosome map in accordance with the present invention
provides more accurate information to assess stage and severity of
PAD because multiple anatomical features can be represented in one
model versus having to reference two different models (illustration
and photos) for a complete picture. Examples of multiple anatomical
features that might be included in a three dimensional angiosome
model are skin, vascular structure, and skeletal structure. The
invention allows the user to customize a view selection e.g.
allowing a user to view an angiosome structure from the same
viewpoint in which they are examining a subject or patient. It
further permits an illustrative venue for the user to gain greater
understanding of the physiological development of disease processes
and the effect of these processes on a specific condition (e.g.,
arterial obstruction in limb leading to either an ischemic
condition and non-wound healing, or chronic arterial obstruction
that over time is mitigated by development of collateral flow).
[0082] Based upon the degree of PAD, ranging from asymptomatic to
ischemic ulceration, gangrene, and tissue loss, two major
classifications of PAD have been developed. The Fontaine
classification uses four stages. Fontaine I represents those who
are asymptomatic; IIa and IIb are mild and moderate-severe pain are
Fontaine Ms; and ulcerations and gangrene represent Fontaine IV. A
similar classification scheme has been developed by Rutherford. The
Rutherford classification has four grades, 0-III, and six
categories, with grade I having three categories. This
classification system is similar to Fontaine's, except claudicants
have four categories and tissue loss is subdivided into two
categories, minor and major.
[0083] The TransAtlantic Inter-Society Consensus (TASC), a
diagnostic and therapeutic guideline, combined the Fontaine
classification with the Rutherford classification as the criteria
in 2000, re-defining degree I of class I as asymptomatic. The
Rutherford Classification is the currently recommended standard
describing the clinical assessment of patients with PAD.
Accordingly, patients with CLI fall into categories 4-6, designated
by ischemic rest pain, and minor and major tissue loss,
respectively. Foot pain at rest--generally referred to as ischemic
rest pain--is considered a milder form, whereas any tissue loss
represents a more advanced state of CLI. Categories 0-3 are
assigned to asymptomatic patients and those with mild, moderate,
and severe Intermittent Claudication. The wound classification
systems rely on size, shape and depth of ulceration and include
infection and PAD in order to better predict outcome.
[0084] The angiosome scoring system in accordance with the present
invention replaces subjective assessments with objectively measured
data within established classification and scoring systems. The new
system obtains knowledge of angiosome site for input data and
includes measurements of SPP. One or several angiosomes may be
included, dependent on available inputs. Input parameters include
skin perfusion pressures because understanding of microcirculatory
health is vital to evaluating disease state. Input parameters may
include additional parameters such as microcirculatory measures,
macrocirculatory measures, metabolic measures, and patient history
and physical information.
[0085] The present invention also provides the novel method of
using the foregoing measurements in conjunction with angiosome
mapping to detect and quantify blood flow in angiosome regions that
feed tissue that is susceptible to low blood to assess severity and
stage of PAD and lower extremity wounds in a patient. These
measurements may be used in conjunction with each other and
additionally in conjunction with measurements of metabolic factors
including pH, pCO.sub.2, NADH and SaO.sub.2. Measurement of
metabolic factors may be taken in the wound when for example the
sensors are integrated into the pressure cuff, as illustrated in
FIG. 1. Alternatively, and in accordance with physician preference,
the metabolic measurement sensors 13 may be utilized peri-wound
while the blood flow and pressure sensors are placed in the wound
W. Furthermore, measurements using blood flow and pressure sensors
may also be taken peri-wound in conjunction with measurements taken
by the metabolic sensors 13 as described hereinafter.
[0086] Preferably, the blood flow sensor in accordance with the
present invention may be positioned in the wound or peri-wound,
preferably with the sensor lying immediately above or at the
surface of the wound. To minimize patient discomfort, a patch may
be placed over the wound with the blood flow sensor placed in or on
top of the patch. Alternatively the patch may be a sterile, single
use cover that is integrated into the system in accordance with the
present invention. If the patch is used in conjunction with the
measurement of metabolic parameters as hereinafter described, the
patch must be permeable in order to accurately measure tissue
gases. The blood flow sensor may also be placed adjacent the
surface of the wound that will otherwise minimize discomfort to the
patient.
[0087] The blood-flow sensor lies in the wound or adjacent the
surface peri-wound, in order that it effectively measures blood
flow in the tissue. Placement of a blood-flow sensor adjacent the
tissue's surface provides a very good quantification of local
and/or regional perfusion at all times.
[0088] The blood-flow sensor used in the methods and devices of the
invention may be any single or arrayed blood-flow sensor suitable
for detection of blood flow in the manner described herein, such as
laser-Doppler blood-flow sensors, ultrasound-Doppler blood-flow
sensors, imaging sensors and so forth. For example, the preferred
blood-flow sensor is a laser-Doppler blood-flow sensor.
[0089] The blood flow measurement taken with the blood-flow sensor
placed against the tissue's surface may be used in conjunction with
the SPP index and/or the optical plethysmography index. In order to
assess perfusion failure in a patient with this embodiment, one
first determines the expected range of measurements for subjects of
similar age and health status as the patient as normal measurements
of skin perfusion pressure and optical plethysmography may vary
with the age of the subject. For a healthy patient, these two
indices will be close to one. The blood flow in the wound of the
patient, or peri-wound, is determined. Next, the skin perfusion
pressure and/or the optical plethysmography measurement is taken.
Each of these values are compared with the expected value for a
normal subject. In addition, the rate-of-change of the patient's
blood flow is measured over time with these measurements. Rising
values of blood flow, and an SPP index and an air plethysmography
index close to one may tend to indicate recovery but the
measurement of PCO2 and factors in conjunction with these
measurements is critical to an accurate assessment of stage of PAD
and/or wound severity.
[0090] In addition, as there are many co-morbid factors, e.g.
diabetes, that may affect an accurate measurement of blood flow,
the use of blood flow measurements in conjunction with the SPP
index and the air plethysmography index allows the physician to
more accurately monitor capillary vitality and recovery. These
measurements may also be used in conjunction with each other and
additionally in conjunction with measurements of pH, PCO2, and Sa
O2 as hereinafter described.
[0091] Additional inputs into the instrument in accordance with the
present invention, as previously described, may be made. The new
system tabulates and/or visually presents disease stage as a
function of angiosome resultant from analysis of input parameters.
The existing classification and scoring systems will be updated
with this tabulated and/or visual quantified perfusion information
obtained from specified angiosomes.
[0092] While the invention has been described with reference to the
specific embodiments thereof, those skilled in the art will be able
to make various modifications to the described embodiments of the
invention without departing from the true spirit and scope of the
invention. The terms and descriptions used herein are set forth by
way of illustration only and are not meant as limitations. Those
skilled in the art will recognize that these and other variations
are possible within the spirit and scope of the invention.
* * * * *