Methods and apparatus for measuring the volume of fluid in the peritoneal cavity

• US 7,354,417 B1
• Filed: 09/29/2000
• Issued: 04/08/2008
• Est. Priority Date: 10/05/1999
• Status: Expired due to Term

• Current Assignee: Daniel Schneditz, Fansan Zhu, Nathan W. Levin
• Original Assignee: Daniel Schneditz, Fansan Zhu, Nathan W. Levin
• Inventors: Schneditz, Daniel, Levin, Nathan W., Zhu, Fansan
• Primary Examiner(s): Sirmons; Kevin C.
• Assistant Examiner(s): WITCZAK, CATHERINE
• Application Number:
  US10/089,831
• Time in Patent Office: 2,748 Days
• Field of Search: 604 27- 31, 600/382, 600/384, 600/547
• US Class Current: 604/29
• CPC Class Codes: A61B 5/0531 Measuring skin impedance
• CPC Class Codes: A61B 5/107 Measuring physical dimensions, e.g. size of the entire body or parts thereof
• CPC Class Codes: A61B 5/4869 Determining body composition
• CPC Class Codes: A61B 5/6823 Trunk, e.g., chest, back, abdomen, hip
• CPC Class Codes: A61B 5/6831 Straps, bands or harnesses
• CPC Class Codes: A61M 1/28 Peritoneal dialysis ; Other peritoneal treatment, e.g. oxygenation
• CPC Class Codes: A61M 1/284 Continuous flow peritoneal dialysis [CFPD]

Abstract

Methods and apparatus for determining peritoneal cavity fluid volume include four groups of two electrodes applied to a subject'"'"'s skin. Measuring electrodes (MLL, MRL) are applied to the subject'"'"'s loins, measuring electrodes (MLB, MRB) are applied to the subject'"'"'s buttocks, and upper and lower current-providing electrodes (IRU, ILU, IRL, ILL) are applied to the subject'"'"'s left and right sides distal from the measuring electrodes (MLL, MRL, MLB, MRB). The resistance between left measuring electrodes (MLL, MLB) is measured and the resistance between right measuring electrodes (MRL, MRB) is measured while current is applied between the upper and lower current-providing electrodes. By averaging resistance values, in combination with a calibration procedure, measurements of peritoneal cavity fluid volume are obtained. The measurement techniques can be used in continuous flow peritoneal dialysis to control or adjust dialysis parameters based on peritoneal cavity fluid.

Claims

1. A method for determining the volume of fluid in the peritoneal cavity of a subject comprising:

(a) placing measuring electrodes M_LL and M_RL on the loins of the subject, M_LL being placed on the left loin and M_RL being placed on the right loin, M_LL and M_RL defining a loin plane;

(b) placing measuring electrodes M_LB and M_RB on the buttocks of the subject, M_LB being placed on the left buttock and M_RB being placed on the right buttock, M_LB and M_RB defining a buttock plane;

(c) placing upper current-providing electrodes I_LU and I_RU on the subject, I_LU being outboard of measuring electrode M_LL and I_RU being outboard of measuring electrode M_RL;

(d) placing lower current-providing electrodes I_RL and I_LL on the subject, I_RL being outboard of measuring electrode M_RB and I_LL being outboard of measuring electrode M_LB;

(e) connecting upper current-providing electrode I_LU to upper current-providing electrode I_RU;

(f) connecting lower current-providing electrode I_LL to lower current-providing electrode I_RL;

(g) applying current I between the connected upper current-providing electrodes and the connected lower current-providing electrodes;

(h) measuring the voltage Φ

_L between M_LL and M_LB while current I is applied;

(i) measuring the voltage Φ

_R between M_RL and M_RB while current I is applied; and

(j) determining the volume V of fluid in the peritoneal cavity based on the equation;

V=(K_P/σ

)·

(L_P²/R)

where;

(1) K_P is a subject-specific calibration constant;

(2) σ

is the conductivity of the fluid in the peritoneal cavity;

(3) L_P is the distance between the loin plane and the buttock plane; and

(4) R is the average of R_L and R_R, where

R_L=Φ

_L/I, and

R_R=Φ

_R/I.

2. The method of claim 1 wherein K_P3 is determined by:

(i) performing steps (g), (h), and (i) before the introduction of a predetermined volume V_C of dialysis fluid into the subject'"'"'s peritoneal cavity to obtain Φ

_LB and Φ

_RB, said dialysis fluid having a conductivity σ

_C;

(ii) performing steps (g), (h), and (i) after the introduction of a predetermined volume V_C of dialysis fluid into the subject'"'"'s peritoneal cavity to obtain Φ

_LA and Φ

_RA; and

(iii) determining K_P from the equation;

K_P=(σ

_C)·

(V_C/L_P²)·

(R_BR_A)/(R_B−

R_A)

where

R_B=(Φ

_LB+Φ

_RB)/(2I), and

R_A=(Φ

_LA+Φ

_RA)/(2I).

3. The method of claim 2 where V_C is at least one liter.

4. The method of claim 1 wherein K_P is determined by:

(i) introducing dialysis fluid into the subject'"'"'s peritoneal cavity;

(ii) performing steps (g), (h), and (i) to obtain Φ

_LB and Φ

_RB;

(iii) removing fluid from the subject'"'"'s peritoneal cavity;

(iv) performing steps (g), (h), and (i) to obtain Φ

_LA and Φ

_RA; and

(v) determining K_P from the equation;

K_P=(σ

_C)·

(V_C/L_P²)·

(R_BR_A)/(R_A−

R_B)

where

R_B=(Φ

_LB+Φ

_RB)/(2I),

R_A=(Φ

_LA+Φ

_RA)/(2I), and

V_C and σ

_C are, respectively, the volume and conductivity of the fluid removed in step (iii).

5. The method of claim 4 where V_C is at least one liter.

6. The method of claim 1 wherein the current I is alternating current having a frequency in the range from about 5 kilohertz to about 500 kilohertz.

7. The method of claim 6 wherein the current I has a frequency of about 5 kilohertz.

8. The method of claim 1 wherein the upper current-providing electrodes are placed on the subject'"'"'s hands and the lower current-providing electrodes are placed on the subject'"'"'s feet.

9. The method of claim 1 wherein the upper current-providing electrodes are placed on the subject'"'"'s trunk and the tower current-providing electrodes are placed on the subject'"'"'s thighs.

10. The method of claim 1 wherein the upper current-providing electrodes and the measuring electrodes M_LL and M_RL are carried by a common support which is placed on the subject'"'"'s trunk.

11. The method of claim 1 wherein the lower current-providing electrode I_LL and the measuring electrode M_LB are carried by a first common support which is placed at least in part on the subject'"'"'s left leg and the lower current-providing electrode I_RL and the measuring electrode M_RB are carried by a second common support which is placed at least in part on the subjects right leg.

12. A method of controlling a peritoneal dialysis procedure comprising:

(A) continuously flowing dialysis fluid through a subject'"'"'s peritoneal cavity;

(B) while step (A) is being performed, determining the volume of fluid in the peritoneal cavity by a bioimpedance measurement directed at the peritoneal cavity; and

(C) controlling step (A) based on the volume of fluid in the peritoneal cavity determined in step (B).

13. The method of claim 12 wherein step (B) is performed by:

(a) placing measuring electrodes M_LL and M_RL on the loins of the subject, M_LL being placed on the left loin and M_RL being placed on the right loin, M_LL and M_RL defining a loin plane;

(b) placing measuring electrodes M_LB and M_RB on the buttocks of the subject, M_LB being placed on the left buttock and M_RB being placed on the right buttock, M_LB and M_RB defining a buttock plane;

(c) placing upper current-providing electrodes I_LU and I_RU on the subject, I_LU being outboard of measuring electrode M_LL and I_RU being outboard of measuring electrode M_RL;

(d) placing lower current-providing electrodes I_RL and I_LL on the subject, I_RL being outboard of measuring electrode M_RB and I_LL being outboard of measuring electrode M_LB;

(e) connecting upper current-providing electrode I_LU to upper current-providing electrode I_RU;

(f) connecting lower current-providing electrode I_LL to lower current-providing electrode I_RL;

(g) applying current I between the connected upper current-providing electrodes and the connected lower current-providing electrodes;

(h) measuring the voltage Φ

_L between M_LL and M_LB while current I is applied;

(i) measuring the voltage Φ

_R between M_RL and M_RB while current I is applied; and

(j) determining the volume V of fluid in the peritoneal cavity based on the equation;

V=(K_P/σ

)·

(L_P²/R)

where;

(1) K_P is a subject specific calibration constant;

(2) σ

is the conductivity of the fluid in the peritoneal cavity;

(3) L_P is the distance between the loin plane and the buttock plane; and

(4) R is the average of R_L and R_R, where

R_L=Φ

_L/I, and

R_R=Φ

_R/I.

14. The method of claim 12 where the rate of flow of dialysis fluid into, out of, or both into and out of the peritoneal cavity is controlled in step (C).

15. The method of claim 12 where the composition of the dialysis fluid is controlled in step (C).

16. The method of claim 12 including the additional step of determining the conductivity of dialysis fluid removed from the subject while step (A) is being performed.

17. The method of claim 12 wherein in step (A), the continuous flowing of dialysis fluid through the subject'"'"'s peritoneal cavity is performed for a period of at least three hours and step (B) is performed at least at regular intervals throughout said period.

18. The method of claim 17 wherein step (B) is performed substantially continuously throughout said period.

19. The method of claim 12 wherein in step (A), the continuous flowing of dialysis fluid through the subject'"'"'s peritoneal cavity is performed for a period of at least six hours and step (B) is performed at least at regular intervals throughout said period.

20. The method of claim 19 wherein step (B) is performed substantially continuously throughout said period.

21. The method of claim 12 wherein in step (B), the bioimpedance measurement employs measuring electrodes located in the subject'"'"'s loin and buttock regions.

22. Apparatus for determining the volume of fluid in the peritoneal cavity of a subject comprising:

(a) measuring electrodes M_LL and M_RL for placement on the loins of the subject, M_LL to be placed on the left loin and M_RL to be placed on the right loin such that, when so placed, M_LL and M_RL define a loin plane;

(b) measuring electrodes M_LB and M_RB for placement on the buttocks of the subject, M_LB to be placed on the left buttock and M_RB to be placed on the right buttock such that, when so placed, M_LB and M_RB define a buttock plane;

(c) upper current-providing electrodes I_LU and I_RU for placement on the subject;

(d) lower current-providing electrodes I_RL and I_LL for placement on the subject;

(e) means for connecting upper current-providing electrode I_LU to upper current-providing electrode I_RU;

(f) means for connecting lower current-providing electrode I_LL to lower current-providing electrode I_RL;

(g) means for applying a current I between the connected upper current-providing electrodes and the connected lower current-providing electrodes;

(h) means for measuring the voltage Φ

_L between M_LL and M_LB while current I is applied;

(i) means for measuring the voltage Φ

_R between M_RL and M_RB while current I is applied; and

(j) means for determining the volume V of fluid in the peritoneal cavity based on the equation;

V=(K_P/σ

)·

(L_P²/R)

where;

(1) K_P is a subject-specific calibration constant;

(2) σ

is the conductivity of the fluid in the peritoneal cavity;

(3) L_P is the distance between the loin plane and the buttock plane; and

(4) R is the average of R_L and R_R, where

R_L=Φ

_L/I, and

R_R=Φ

_R/I.

23. The apparatus of claim 22 further comprising means for determining K_P, said means comprising:

(i) means for determining the voltage Φ

_LB between M_LL and M_LB and the voltage Φ

_RB between M_RL and M_RB while current I is applied, said determination being made before the introduction of a predetermined volume V_C of dialysis fluid into the subject'"'"'s peritoneal cavity, said dialysis fluid having a conductivity ac;

(ii) means for determining the voltage Φ

_LA between M_LL and M_LB and the voltage Φ

_RA between M_RL and M_RB while current I is applied, said determination being made after the introduction of a predetermined volume V_C of dialysis fluid into the subject'"'"'s peritoneal cavity; and

(iii) means for determining K_P from the equation;

K_P=(σ

_C)·

(V_C/L_P²)·

(R_BR_A)/(R_B−

R_A)

where

R_B=(Φ

_LB+Φ

_RB)/(2I), and

R_A=(Φ

_LA+Φ

_RA)/(2I).

24. The apparatus of claim 22 further comprising means for determining K_P, said means comprising:

(i) means for introducing dialysis fluid into the subject'"'"'s peritoneal cavity;

(ii) means for determining the voltage Φ

_LB between M_LL and M_LB and the voltage Φ

_RB between M_RL and M_RB while current I is applied, said determination being made before removal of fluid from the subject'"'"'s peritoneal cavity;

(iii) means for removing fluid from the subject'"'"'s peritoneal cavity;

(iv) means for measuring the volume V_C of fluid removed from the subject'"'"'s peritoneal cavity;

(v) means for determining the voltage Φ

_LA between M_LL and M_LB and the voltage Φ

_RA between M_RL and M_RB while current I is applied, said determination being made after the removal of the volume V_C of fluid from the subject'"'"'s peritoneal cavity; and

(vi) means for determining K_P from the equation;

K_P=(σ

_C)·

(V_C/L_P²)·

(R_BR_A)/(R_A−

R_B)

where

R_B=(Φ

_LB+Φ

_RB)/(2I),

R_A=(Φ

_LA+Φ

_RA)/(2I), and

σ

_C is the conductivity of the fluid removed from the subject'"'"'s peritoneal cavity.

25. The apparatus of claim 22 wherein the current I is alternating current having a frequency in the range from about 5 kilohertz to about 500 kilohertz.

26. The apparatus of claim 25 wherein the current I has a frequency of about 5 kilohertz.

27. The apparatus of claim 22 further comprising a support for carrying the upper current-providing electrodes and the measuring electrodes M_LL and M_RL.

28. The apparatus of claim 22 further comprising a first support for carrying the lower current-providing electrode I_LL and the measuring electrode M_LB and a second support for carrying the lower current-providing electrode I_RL and the measuring electrode M_RB.

29. Apparatus for performing a peritoneal dialysis procedure comprising:

(A) first means for continuously flowing dialysis fluid through a subject'"'"'s peritoneal cavity, said flowing of dialysis fluid being capable of causing the accumulation of ultrafiltrate from the subject in the peritoneal cavity;

(B) second means for determining the volume of fluid in the peritoneal cavity while dialysis fluid is flowed through the subject'"'"'s peritoneal cavity, said second means comprising means for performing a bioimpedance measurement directed at the peritoneal cavity; and

(C) third means for controlling the first means based on the volume of fluid in the peritoneal cavity determined by the second means.

30. The apparatus of claim 29 wherein the means for performing a bioimpedance measurement directed at the peritoneal cavity comprises:

(a) measuring electrodes M_LL and M_RL for placement on the loins of the subject, M_LL to be placed on the left loin and M_RL to be placed on the right loin such that, when so placed, M_LL and M_RL define a loin plane;

(b) measuring electrodes M_LB and M_RB for placement on the buttocks of the subject, M_LB to be placed on the left buttock and M_RB to be placed on the right buttock such that, when so placed, M_LB and M_RB define a buttock plane;

(c) upper current-providing electrodes I_LU and I_RU for placement on the subject;

(d) lower current-providing electrodes I_RL and I_LL for placement on the subject;

(e) means for connecting upper current-providing electrode I_LU to upper current-providing electrode I_RU;

(f) means for connecting lower current-providing electrode I_LL to lower current-providing electrode I_RL;

(g) means for applying a current I between the connected upper current-providing electrodes and the connected lower current-providing electrodes;

(h) means for measuring the voltage Φ

_L between M_LL and M_LB while current I is applied;

(i) means for measuring the voltage Φ

_R between M_RL and M_RB while current I is applied; and

(j) means for determining the volume V of fluid in the peritoneal cavity based on the equation;

V=(K_P/σ

)·

(L_P²/R)

where;

(1) K_P is a subject-specific calibration constant;

(2) σ

is the conductivity of the fluid in the peritoneal cavity;

(3) L_P is the distance between the loin plane and the buttock plane; and

(4) R is the average of R_L and R_R, where

R_L=Φ

_L/I, and

R_R=Φ

_R/I.

31. The apparatus of claim 29 wherein the third means controls the ultrafiltration rate of the first means.

32. The apparatus of claim 29 wherein the third means controls the rate at which the first means flows dialysis fluid through the subject'"'"'s peritoneal cavity.

33. The apparatus of claim 29 wherein the third means controls the composition of the dialysis fluid which the first means flows through the subject'"'"'s peritoneal cavity.

34. The apparatus of claim 29 wherein the third means includes means for determining the conductivity of the dialysis fluid removed from the subject by the first means.

35. An article of manufacture comprising a computer usable medium having computer readable code means embodied therein for:

(a) determining the volume V of fluid in the peritoneal cavity of a subject based on the equation;

V=(K_P/σ

)·

(L_P²/R)

where;

(1) K_P is a subject-specific calibration constant

(2) σ

is the conductivity of the fluid in the peritoneal cavity;

(3) L_P is the distance between a loin plane and a buttock plane of the subject, the loin plane being established by the locations of measuring electrodes M_LL and M_RL placed on the subject'"'"'s left and right loins, respectively, and the buttock plane being established by measuring electrodes M_LB and M_RB placed on the subject'"'"'s left and right buttocks, respectively; and

(4) R is the average of R_L and R_R, where

(i) R_L=Φ

_L/I,

(ii) R_R=Φ

_R/I, and

(iii) I is an applied current between connected upper current-providing electrodes I_LU I_RU and connected lower current-providing electrodes I_RL and I_LL placed on the subject with I_LU and I_RU being outboard of measuring electrode M_LL, I_RU being outboard of measuring electrode M_RL, I_RL being outboard of measuring electrode M_RB and I_LL being outboard of measuring electrode M_LB, and

(iv) Φ

_L and Φ

_R are measured voltages between M_LL and M_LB and between M_RL and M_RB, respectively, while current I is applied; and

(b) displaying the value of the calculated volume V to the subject and/or to a care provider and/or controlling the flow of dialysis fluid through the suibject'"'"'s peritoneal cavity using the calculated volume V.

36. An article of manufacture comprising a computer usable medium having computer readable code means embodied therein for:

(a) determining a subject-specific for use in determining the volume of fluid in the subject'"'"'s peritoneal cavity calibration constant K_P from the equation;

K_P=(σ

_C)·

(V_C/L_P²)·

(R_BR_A)/(R_B−

R_A)

where

(i) R_B=(Φ

_LB+Φ

_RB)/(2I);

(ii) R_A=(Φ

_LA+Φ

_RA)/(2I);

(iii) V_C and σ

_C are, respectively, the volume and conductivity of a predetermined volume of dialysis fluid;

(iv) L_P is the distance between a loin plane and a buttock plane of the subject, the loin plane being established by the locations of measuring electrodes M_LL and M_RL placed on the subject'"'"'s left and right loins, respectively, and the buttock plane being established by measuring electrodes M_LB and M_RB placed on the subject'"'"'s left and right buttocks, respectively;

(v) I is an applied current between connected upper current-providing electrodes I_LU and I_RU connected lower current-providing electrodes I_RL and I_LL placed on the subject with I_LU being outboard of measuring electrode M_LL, I_RU being outboard of measuring electrode M_RL, I_RL being outboard of measuring electrode M_RB and I_LL being outboard of measuring electrode M_LB,

(vi) Φ

_LA and Φ

_RA are measured voltages between M_LL and M_LB and between M_RL and M_RB, respectively, obtained before introduction of the predetermined volume of dialysis fluid into the subject'"'"'s peritoneal cavity and while current I is applied; and

(vii) Φ

_LA and Φ

_RA are measured voltages between M_LL and M_LB and between M_RL and M_RB, respectively, obtained after introduction of the predetermined volume of dialysis fluid into the subject'"'"'s peritoneal cavity and while current I is applied; and

(b) displaying the value of the calculated subject-specific calibration constant K_P to the subject and/or to a care provider and/or controlling the flow of dialysis fluid through the subject'"'"'s peritoneal cavity using the calculated subject-specific calibration constant K_P.

37. An article of manufacture comprising a computer usable medium having computer readable code means embodied therein for:

(a) determining a subject-specific for use in determining the volume of fluid in the subject'"'"'s peritoneal cavity calibration constant K_P from the equation;

K_P=(σ

_C)·

(V_C/L_P²)·

(R_BR_A)/(R_B−

R_A)

where

(i) R_B=(Φ

_LB+Φ

_RB)/(2I);

(ii) R_A=(Φ

_LA+Φ

_RA)/(2I);

(iii) L_P is the distance between a loin plane and a buttock plane of the subject, the loin plane being established by the locations of measuring electrodes M_LL and M_RL placed on the subject'"'"'s left and right loins, respectively, and the buttock plane being established by measuring electrodes M_LB and M_RB placed on the subject'"'"'s left and right buttocks, respectively;

(iv) I is an applied current between connected upper current-providing electrodes I_LU and I_RU and connected lower current-providing electrodes I_RL and I_LL placed on the subject with I_LU being outboard of measuring electrode M_LL, I_RU being outboard of measuring electrode M_RL, I_RL being outboard of measuring electrode M_RB and I_LL being outboard of measuring electrode M_LB,

(v) Φ

_LB and Φ

_RB are measured voltages between M_LL and M_LB and between M_RL and M_RB, respectively, obtained after introduction of dialysis fluid into the subject'"'"'s peritoneal cavity and while current I is applied;

(vi) Φ

_LA and Φ

_RA are measured voltages between M_LL and M_LB and between M_RL and M_RB, respectively, obtained after removal of fluid from the subject'"'"'s peritoneal cavity and while current I is applied; and

(vii) V_C and σ

_C are, respectively, the volume and conductivity of the fluid removed from the subject'"'"'s peritoneal cavity; and

(b) displaying the value of the calculated subject-specific calibration constant K_P to the subject and/or to a care provider and/or controlling the flow of dialysis fluid through the subject'"'"'s peritoneal cavity using the calculated subject-specific calibration constant K_P.

38. Apparatus comprising a computer which has been programmed to:

(a) determine the volume V of fluid in the peritoneal cavity of a subject based on the equation;

V=(K_P/σ

)·

(L_P²/R)

where;

(1) K_P is a subject-specific calibration constant,

(2) σ

is the conductivity of the fluid in the peritoneal cavity;

(3) L_P is the distance between a loin plane and a buttock plane of the subject, the loin plane being established by the locations of measuring electrodes M_LL, and M_RL, placed on the subject'"'"'s left and right loins, respectively, and the buttock plane being established by measuring electrodes M_LB and M_RB placed on the subject'"'"'s left and right buttocks, respectively; and

(4) R is the average of R_L and R_R, where

(i) R_L=Φ

_L/I,

(ii) R_R=Φ

_R/I, and

(iii) I is an applied current between connected upper current-providing electrodes I_LU and I_RU and connected lower current-providing electrodes I_RL and I_LL placed on the subject with I_LU being outboard of measuring electrode M_LL, I_RU being outboard of measuring electrode M_RL, I_RL being outboard of measuring electrode M_RB and I_LL being outboard of measuring electrode M_LB, and

(iv) Φ

_L and Φ

_R are measured voltages between M_LL and M_LB and between M_RL and M_RB, respectively, while current I is applied; and

(b) display the value of the calculated volume V to the subject and/or to a care provider and/or control the flow of dialysis fluid through the subject'"'"'s peritoneal cavity using the calculated volume V.

39. Apparatus comprising a computer which has been programmed to:

(a) determine a subject-specific for use in determining the volume of fluid in the subject'"'"'s peritoneal cavity calibration constant K_P from the equation;

K_P=(σ

_C)·

(V_C/L_P²)·

(R_BR_A)/(R_B−

R_A)

where

(i) R_B=(Φ

_LB+Φ

_RB)/(2I);

(ii) R_A=(Φ

_LA+Φ

_RA)/(2I);

(iii) V_C and σ

_C are, respectively, the volume and conductivity of a predetermined volume of dialysis fluid;

(iv) L_P is the distance between a loin plane and a buttock plane of the subject, the loin plane being established by the locations of measuring electrodes M_LL and M_RL placed on the subject'"'"'s left and right loins, respectively, and the buttock plane being established by measuring electrodes M_LB and M_RB placed on the subject'"'"'s left and right buttocks, respectively;

(v) I is an applied current between connected upper current-providing electrodes I_LU a I_RU and connected lower current-providing electrodes I_RL and I_LL placed on the subject with I_LU being outboard of measuring electrode M_LL, I_RU being outboard of measuring electrode M_RL, I_RL being outboard of measuring electrode M_RB and I_LL being outboard of measuring electrode M_LB,

(vi) Φ

_LB and Φ

_RB are measured voltages between M_LL and M_LB and between M_RL and M_RB, respectively, obtained before introduction of the predetermined volume of dialysis fluid into the subject'"'"'s peritoneal cavity and while current I is applied; and

(vii) Φ

_LA and Φ

_RA are measured voltages between M_LL and M_LB and between M_RL and M_RB, respectively, obtained after introduction of the predetermined volume of dialysis fluid into the subject'"'"'s peritoneal cavity and while current I is applied; and

(b) display the value of the calculated subject-specific calibration constant K_P to the subject and/or to a care provider and/or control the flow of dialysis fluid through the subject'"'"'s peritoneal cavity using the calculated subject-specific calibration constant K_P.

40. Apparatus comprising a computer which has been programmed to:

(a) determine a subject-specific for use in determining the volume of fluid in the subject'"'"'s peritoneal cavity calibration constant K_P from the equation;

K_P=(σ

_C)·

(V_C/L_P²)·

(R_BR_A)/(R_B−

R_A)

where

(i) R_B=(Φ

_LB+Φ

_RB)/(2I);

(ii) R_A=(Φ

_LA+Φ

_RA)/(2I);

(iii) L_P is the distance between a loin plane and a buttock plane of the subject, the loin plane being established by the locations of measuring electrodes M_LL and M_RL placed on the subject'"'"'s left and right loins, respectively, and the buttock plane being established by measuring electrodes M_LB and M_RB placed on the subject'"'"'s left and right buttocks, respectively

(iv) I is an applied current between connected upper current-providing electrodes I_LU and I_RU and connected lower current-providing electrodes I_RL and I_LL placed on the subject with I_LU being outboard of measuring electrode M_LL, I_RU being outboard of measuring electrode M_RL, I_RL being outboard of measuring electrode M_RB and I_LL being outboard of measuring electrode M_LB,

(v) Φ

_LB and Φ

_RB are measured voltages between M_LL and M_LB and between M_RL and M_RB, respectively, obtained after introduction of dialysis fluid into the subject'"'"'s peritoneal cavity and while current I is applied;

(vi) Φ

_LA and Φ

_RA are measured voltages between M_LL and M_LB and between M_RL and M_RB, respectively, obtained after removal of fluid from the subject'"'"'s peritoneal cavity and while current I is applied; and

(vii) V_C and σ

_C are, respectively, the volume and conductivity of the fluid removed from the subject'"'"'s peritoneal cavity; and

(b) display the value of the calculated subject-specific calibration constant K_P to the subject and/or to a care provider and/or control the flow of dialysis fluid through the subject'"'"'s peritoneal cavity using the calculated subject-specific calibration constant K_P.