Blood flow assessment of venous insufficiency
View Patent ↗Impedance analysis can be used to measure calf muscle pump (CMP) function in a patient. This may be done by applying electrical signals via a first set of electrodes, and measuring the impedance via a second set of electrodes. The change in impedance as the patient undergoes calf extension or exercise may be measured, and the change in impedance may then be used to assess CMP function. The change in impedance may be used to determine an indicator indicative of the volume of blood ejected by the CMP.
1. A method for use in analysing impedance measurements performed on a subject for use in diagnosing the presence, absence, or degree of venous insufficiency in the subject, the method including, in a processing system:
determining a change in impedance, caused by calf extension of the subject or by exercise by the subject;
determining an indicator using the change in impedance, the indicator being indicative of an ejection volume to allow assessment of calf muscle pump (CMP) function, wherein the method further includes, in the processing system, determining the ejection volume using the formula:
EV
=
-
ρ
b
L
2
Δ
R
R
MV
2
where:
ρ b is the resistivity of blood;
L is a length of a segment of a calf of the subject;
ΔR is the change in impedance; and
R MV is a maximum volume impedance value; and
displaying the indicator via the processing system to a user to thereby allow assessment of CMP function, wherein, at least one of the indicator or CMP function is used in the diagnosis of the presence, absence or degree of venous insufficiency.
2. A method according to claim 1 , wherein the method includes, in a processing system:
determining a first impedance value prior to calf extension;
determining a second impedance value following or during calf extension; and,
determining the impedance change using the first and second impedance values.
3. A method according to claim 1 , wherein the method includes, in a processing system:
determining a third impedance value with the subject in a supine position;
determining a fourth impedance value with the subject in a standing position;
determining a second impedance change using the third and fourth impedance values; and
determining a second indicator using the second impedance change, the second indicator being indicative of a venous volume for use in assessment of CMP function.
4. A method according to claim 3 , wherein:
the third impedance value is a minimum volume impedance value R mv ; and,
the fourth impedance value is a maximum volume impedance value R MV .
5. A method according to claim 4 , wherein the method includes, in a processing system, determining a functional venous volume using the formula:
VV
=
ρ
b
L
2
(
R
mv
-
R
MV
)
R
mv
R
MV
where:
R mv is the third impedance value which is a minimum volume impedance value;
R MV is the fourth impedance value which is a maximum volume impedance value;
ρ b is the resistivity of blood; and,
L is the length of the segment of a calf of the subject.
6. A method according to claim 1 , wherein the method includes, in a processing system, determining at least one of:
a venous volume; and
an ejection fraction.
7. A method according to claim 1 , wherein the method includes, in a processing system:
comparing an indicator to a reference; and,
providing an indication of the results of the comparison to allow assessment of CMP function.
8. A method according to claim 7 , wherein the reference includes at least one of:
an indicator determined for another calf segment of the subject;
a indicator determined from a sample population; and,
a previous indicator determined for the subject.
9. A method according to claim 1 , wherein the impedance is determined at a frequency of less than 10 kHz.
10. A method according to claim 1 , wherein the method includes, in the processing system:
determining a plurality of impedance values; and,
determining at least one impedance parameter value from the plurality of impedance values.
11. A method according to claim 10 , wherein at least one of the at least one impedance parameter value includes any one of:
R 0 which is the resistance at zero frequency;
R ∞ which is the resistance at infinite frequency; and,
Z c which is the resistance at a characteristic frequency.
12. A method according to claim 1 , wherein determining a change in impedance includes, in the processing system, causing the change in impedance to be measured by:
causing one or more electrical signals to be applied to the subject using a first set of electrodes;
measuring electrical signals across a second set of electrodes applied to the subject in response to the applied one or more signals; and,
determining from the applied signals and the measured signals at least one measured impedance value.
13. Apparatus for use in analysing impedance measurements performed on a subject for use in diagnosing the presence, absence, or degree of venous insufficiency in the subject, the apparatus including a processing system configured to:
determine a change in impedance, caused by calf extension of a subject or by exercise by a subject;
determine an indicator using the change in impedance, the indicator being indicative of an ejection volume to allow assessment of calf muscle pump (CMP) function, wherein the processing system is further configured to determine the ejection volume using the formula:
EV
=
-
ρ
b
L
2
Δ
R
R
MV
2
where:
ρ b is the resistivity of blood;
L is a length of a segment of a calf of the subject;
ΔR is the change in impedance; and
R MV is a maximum volume impedance value; and
display the indicator via the processing system to a user to thereby allow assessment of CMP function, wherein, the indicator is used in the diagnosis of the presence, absence or degree of venous insufficiency.
14. Apparatus according to claim 13 , wherein the processing system is further configured to:
cause one or more electrical signals to be applied to the subject using a first set of electrodes;
measure electrical signals across a second set of electrodes applied to the subject in response to the applied one or more signals; and,
determine from the applied signals and the measured signals at least one measured impedance value.
15. Apparatus according to claim 14 , wherein the apparatus includes:
a signal generator for generating electrical signals; and,
a sensor for sensing electrical signals.
16. A method for use in analysing impedance measurements performed on a subject for use in diagnosing the presence, absence, or degree of venous insufficiency in the subject, the method including:
applying, using a signal generator, one or more electrical signals to the subject using a first set of electrodes;
measuring, using a sensor, electrical signals across a second set of electrodes applied to the subject in response to the applied one or more signals, and in a processing system:
determining a change in impedance, caused by calf extension of a subject or by exercise by a subject, the change in impedance determined from the applied signals and the measured signals; and,
determining an indicator using the change in impedance, the indicator being indicative of an ejection volume to allow assessment of calf muscle pump (CMP) function, wherein the method further includes, in the processing system, determining the ejection volume using the formula:
EV
=
-
ρ
b
L
2
Δ
R
R
MV
2
where:
ρ b is the resistivity of blood;
L is a length of a segment of a calf of the subject;
ΔR is the change in impedance; and,
R MV is a maximum volume impedance value; and
displaying the indicator via the processing system to a user to thereby allow assessment of CMP function, wherein, at least one of the indicator or CMP function is used in the diagnosis of the presence, absence or degree of venous insufficiency.