BLOOD FLOW ASSESSMENT OF VENOUS INSUFFICIENCY

• US 20090287102A1
• Filed: 02/13/2009
• Published: 11/19/2009
• Est. Priority Date: 02/15/2008
• Status: Active Grant

• Current Assignee: ImpediMed Limited
• Original Assignee: ImpediMed Limited
• Inventors: Ward, Leigh Cordwin
• Granted Patent: US 9,392,947 B2
• Time in Patent Office: Days
• US Class Current: 600/506
• CPC Class Codes: A61B 5/0265 using electromagnetic means, e.g. electromagnetic flowmeter
• CPC Class Codes: A61B 5/0295 using plethysmography, i.e. measuring the variations in the volume of a body part as modified by the circulation of blood therethrough, e.g. impedance plethysmography
• CPC Class Codes: A61B 5/053 Measuring electrical impedance or conductance of a portion of the body
• CPC Class Codes: A61B 5/4519 Muscles A61B5/389, A61B5/224 take precedence

Abstract

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.

Claims

1. ) A method for use in analysing impedance measurements performed on a subject, the method including, in a processing system:

a) determining a change in impedance, as a subject undergoes calf extension or exercise; and

,

b) determining an indicator using the change impedance, the indicator being indicative of an ejection volume to allow assessment of CMP function.

2. ) A method according to claim 1, wherein the method includes, in a processing system:

a) determining a first impedance value prior to calf extension;

b) determining a second impedance value following or during calf extension; and

,

c) 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 an ejection volume using the formula:

$\mathrm{EV}=\frac{-{\mathrm{\rho <br><br>}}_b<br><br>L^2<br><br>\mathrm{\Delta <br><br>}<br><br><br><br>R}{R_{\mathrm{MV}}^2}$

where;

ρ

_b is the resistivity of blood;

L is the length of the segment;

Δ

R is the change in impedance;

R_MV is the maximum volume impedance value.

4. ) A method according to claim 1, wherein the method includes, in a processing system:

a) determining a third impedance value with the subject in a supine position;

b) determining a fourth impedance value with the subject in a standing position;

c) determining a second impedance change using the third and fourth impedance values;

d) 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.

5. ) A method according to claim 4, wherein:

a) the third impedance value is a minimum volume impedance value R_mv; and

,

b) the fourth impedance value is a maximum volume impedance value R_MV.

6. ) A method according to claim 4, wherein the method includes, in a processing system, determining a functional venous volume using the formula:

$\mathrm{VV}=\frac{{\mathrm{\rho <br><br>}}_b<br><br><br><br>L^2<br><br>\left(R_{\mathrm{mv}}-R_{\mathrm{MV}}\right)}{R_{\mathrm{mv}}<br><br>R_{\mathrm{MV}}}$

where;

R_mv is the third impedance value;

R_MV is the fourth impedance value;

ρ

_b is the resistivity of blood; and

,

L is the length of the segment.

7. ) A method according to claim 1, wherein the method includes, in a processing system, determining at least one of:

a) an ejection volume;

b) a venous volume; and

,

c) an ejection fraction.

8. ) A method according to claim 1, wherein the method includes, in a processing system:

a) comparing an indicator to a reference; and

,

b) providing an indication of the results of the comparison to allow assessment of CMP function.

9. ) A method according to claim 8, wherein the reference includes at least one of:

a) an indicator determined for another calf segment of the subject;

b) a indicator determined from a sample population; and

,

c) a previous indicator determined for the subject.

10. ) A method according to claim 1, wherein the impedance is measured at a measurement frequency of less than 10 kHz.

11. ) A method according to claim 1, wherein the method includes, in the processing system:

a) determining a plurality of impedance values; and

,

b) determining at least one impedance parameter value from the plurality of impedance values.

12. ) A method according to claim 11, wherein the impedance parameter values include at least one of:

R₀ 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.

13. ) A method according to claim 12, wherein the method includes, in the processing system, determining the parameter values using the equation:

$Z=R_{\mathrm{\infty <br><br>}}+\frac{R_0-R_{\mathrm{\infty <br><br>}}}{1+{\left(\mathrm{j\omega <br><br>\tau <br><br>}\right)}^{\left(1-\mathrm{\alpha <br><br>}\right)}}$

where;

Z is the measured impedance at angular frequency ω

,

τ

is a time constant, and

α

has a value between 0 and 1.

14. ) A method according to claim 1, wherein the method includes, in the computer system, causing the impedance measurements to be performed.

15. ) A method according to claim 14, wherein the method includes, in the computer system:

a) causing one or more electrical signals to be applied to the subject using a first set of electrodes;

b) measuring electrical signals across a second set of electrodes applied to the subject in response to the applied one or more signals; and

,

c) determining from the applied signals and the measured signals at least one measured impedance value.

16. ) Apparatus for use in analysing impedance measurements performed on a subject, the apparatus including a processing system for:

a) determining a change in impedance, as a subject undergoes calf extension; and

,

b) determining an indicator using the change impedance, the indicator being indicative of an ejection volume to allow assessment of CMP function.

17. ) Apparatus according to claim 16, wherein the apparatus includes a processing system for:

a) causing one or more electrical signals to be applied to the subject using a first set of electrodes;

b) measuring electrical signals across a second set of electrodes applied to the subject in response to the applied one or more signals; and

,

c) determining from the applied signals and the measured signals at least one measured impedance value.

18. ) Apparatus according to claim 17, wherein the apparatus includes:

a) a signal generator for generating electrical signals; and

,

b) a sensor for sensing electrical signals.

19. ) A method for use in assessing CMP function, the method including, in a processing system:

a) determining a change in impedance, as a subject undergoes calf extension or exercise; and

,

b) determining an indicator using the change impedance, the indicator being indicative of an ejection volume to allow assessment of CMP function.