Peritoneal dialysis systems and methods employing pneumatic pressure and temperature-corrected liquid volume measurements

• US 5,474,683 A
• Filed: 03/03/1993
• Issued: 12/12/1995
• Est. Priority Date: 03/03/1993
• Status: Expired due to Term

• Current Assignee: Deka Products Limited Partnership
• Original Assignee: Deka Products Limited Partnership
• Inventors: Kamen, Dean, Vincent, Douglas E., Bryant, Robert J.
• Primary Examiner(s): Kim, John
• Application Number:
  US08/026,458
• Time in Patent Office: 1,014 Days
• Field of Search: 210/646, 210/741, 210/742, 210/90, 210/103, 210/134, 210/252, 417/383, 417/384, 417/385, 417/395, 604/28, 604/29, 604/31, 604/30, 604/65, 604/67, 73/149, 73/290 B, 364/509, 364/510, 364/564
• US Class Current: 210/646
• CPC Class Codes: A61M 1/1524 the interface providing means for actuating on functional elements of the cassette, e.g. plungers
• CPC Class Codes: A61M 1/154 with sensing means or components thereof
• CPC Class Codes: A61M 1/155 with treatment-fluid pumping means or components thereof
• CPC Class Codes: A61M 1/1561 at least one cassette surface or portion thereof being flexible, e.g. the cassette having a rigid base portion with preformed channels and being covered with a foil
• CPC Class Codes: A61M 1/1565 Details of valves
• CPC Class Codes: A61M 1/159 specially adapted for peritoneal dialysis
• CPC Class Codes: A61M 1/28 Peritoneal dialysis ; Other peritoneal treatment, e.g. oxygenation
• CPC Class Codes: A61M 1/281 Instillation other than by gravity
• CPC Class Codes: A61M 1/288 Priming priming in extracorporeal blood circuits A61M1/3643
• CPC Class Codes: A61M 2205/12 with interchangeable cassettes forming partially or totally the fluid circuit
• CPC Class Codes: A61M 5/16809 by repeated filling and emptying of an intermediate volume pressure infusion using positive displacement pumps A61M5/142
• CPC Class Codes: A61M 5/16854 by monitoring line pressure
• CPC Class Codes: G01F 1/34 by measuring pressure or differential pressure
• CPC Class Codes: G01F 15/046 involving digital counting

Abstract

Peritoneal dialysis systems and methods move liquid using a pump chamber that is operated in response to pneumatic pressure variations applied by a pump actuator. The systems and methods periodically measure air pressures in the actuator and an associated reference air chamber and derive from these a measurement of liquid volume moved through the pump chamber. The systems and methods minimize derivation errors by compensating for temperature differences among the pump chamber; the pump actuator; and the reference chamber.

Claims

1. A method for performing peritoneal dialysis comprising the steps of

establishing flow communication with a patient'"'"'s peritoneal cavity through a pumping mechanism that comprises a pump chamber and a diaphragm, and

emulating a selected gravity flow condition by applying pneumatic pressure to the diaphragm through an actuator to operate the pump chamber to draw dialysis liquid into the pump chamber and to expel dialysis liquid from the pump chamber to either move dialysis liquid from the peritoneal cavity or move dialysis liquid into the peritoneal cavity, and

deriving a measurement of liquid volume pumped through the pump chamber by deriving an initial air volume measurement V_i, after operating the actuator to draw liquid into the pumping chamber;

deriving a final air volume measurement V_f after operating the actuator to expel liquid from the pumping chamber; and

deriving the liquid volume delivered (V_d) by the pumping chamber as follows;

space="preserve" listing-type="equation">V.sub.d =V.sub.f -V.sub.i, and

wherein V_i and V_f are derived by controlling communication between a reference chamber having a known air volume V_s and the actuator by;

(i) applying a temperature correction factor (F_t) to the known volume of the reference chamber V_s to derive a temperature-corrected reference air volume V_st, as follows;

space="preserve" listing-type="equation">V.sub.st =F.sub.t * V.sub.s

(ii) when liquid is either drawn into or expelled from the pump chamber, closing communication between reference chamber and the actuator to initialize the reference chamber to a measured initial air pressure (P_s1) while applying a measured pressure to the actuator (P_d);

(iii) opening communication between the reference chamber and the actuator to allow pressure equilibration at a measured new air pressure in the actuator (P_d2) and a measured new air pressure in the reference chamber (P_s2), and (iv) deriving the air volume measurement V_i or V_f as follows;

##EQU11##

2. A method according to claim 1

wherein the step of applying a temperature correction factor (F_t) includes the steps of

sensing temperature in the reference chamber, and

sensing temperature in the pump chamber so that ##EQU12## where:

C_t is the temperature sensed in the pumping chamber (expressed in degrees Rankine or Kelvin), and

R_t is the temperature sensed in the reference chamber (expressed in the same units as C_t).

3. A peritoneal dialysis system comprising

a liquid distribution cassette including

a cassette body,

a pumping mechanism comprising a pump chamber in the cassette body and a diaphragm associated with the pump chamber, and

tubing establishing flow communication between the pump chamber and a patient'"'"'s peritoneal cavity,

an operating station for the cassette including an interior in which a temperature condition exists, the operating station also including

a holder for receiving the cassette body within the operating station interior for exposure to the temperature condition,

a pressure actuator mounted within the operating station interior for exposure to the temperature condition and, when the cassette body is received within the holder, contacting the diaphragm to apply pneumatic pressure to the diaphragm to draw liquid into the pump chamber and to expel liquid from the pump chamber, and

a reference chamber having a known volume V_s mounted within the operating station interior for exposure to the temperature condition, the reference chamber being in communication with the pressure actuator, and

a liquid volume measurement system including

first means for deriving an initial air volume measurement V_i after conveying pneumatic pressure to draw liquid into the pump chamber by

(i) closing communication between reference chamber and the pressure actuator to initialize the reference chamber to a measured initial air pressure (IP_s1) while conveying a measured pressure to the pressure actuator (IP_d1);

(ii) then opening communication between the reference chamber and the pressure actuator to allow pressure equilibration at a measured new air pressure in the pressure actuator (IP_d2) and a measured new air pressure in the reference chamber (IP_s2), and

(iii) then deriving the air volume measurement V_i as follows;

##EQU13## second means for deriving a final air volume measurement V_f after conveying pneumatic pressure to expel liquid from the pump chamber by

(i) closing communication between reference chamber and the pressure actuator to initialize the reference chamber to a measured air pressure (FP_s1) while conveying a measured pressure to the pressure actuator (FP_d1);

(ii) then opening communication between the reference chamber and the pressure actuator to allow pressure equilibration at a measured new air pressure in the pressure actuator (FP_d2) and a measured new air pressure in the reference chamber (FP_S2), and

(iii) then deriving the air volume measurement V_f as follows;

##EQU14## and third means for deriving a measurement of liquid volume delivered (V_d) by the pumping chamber as follows;

space="preserve" listing-type="equation">V.sub.d =V.sub.f -V.sub.i.

4. A system according to claim 3

wherein the liquid volume measurement system further includes means for applying a temperature correction factor (F_t) to the known volume of the reference chamber V_s to derive a temperature-corrected reference volume V_st, as follows:

space="preserve" listing-type="equation">V.sub.st =F.sub.t *V.sub.s

wherein the first means derives the liquid volume measurement V_i as follows;

##EQU15## and wherein the second means derives the liquid volume measurement V_f as follows;

##EQU16##

5. A system according to claim 4

wherein the means for applying a temperature correction factor (F_t) includes first sensing means for sensing temperature in the reference chamber and second sensing means for sensing temperature in the pump chamber so that ##EQU17## where:

C_t is the temperature sensed by the second sensing means in the pumping chamber (expressed in degrees Rankine or Kelvin), and

R_t is the temperature sensed by the first sensing means in the reference chamber (expressed in the same units as C_t).