Medical treatment system and methods using a plurality of fluid lines
Improvements in fluid volume measurement systems are disclosed for a pneumatically actuated diaphragm pump in general, and a peritoneal dialysis cycler using a pump cassette in particular. Pump fluid volume measurements are based on pressure measurements in a pump control chamber and a reference chamber in a two-chamber model, with different sections of the apparatus being modeled using a combination of adiabatic, isothermal and polytropic processes. Real time or instantaneous fluid flow measurements in a pump chamber of a diaphragm pump are also disclosed, in this case using a one-chamber ideal gas model and using a high speed processor to obtain and process pump control chamber pressures during fluid flow into or out of the pump chamber. Improved heater control circuitry is also disclosed, to provide added or redundant safety measures, or to reduce current leakage from a heater element during pulse width modulation control of the heater. Improvements are also disclosed in the application of negative pressure during a drain phase in peritoneal dialysis therapy, and to control the amount of intraperitoneal fluid accumulation during a therapy. Improvements in efficiency are also disclosed in the movement of fluid into and out of a two-pump cassette and heater bag of a peritoneal dialysis cycler, and in the synchronization of the operation of two or more pumps in a peritoneal dialysis cycler or other fluid handling devices using a multi-pump arrangement.
1. A system for measuring an amount of liquid in a pumping chamber of a pneumatically actuated diaphragm pump comprising:
a fluid inlet and fluid outlet valve connected to the pumping chamber;
a diaphragm separating a pneumatically actuated control chamber from the pumping chamber, the control chamber fluidly connected to a reference chamber of known volume via a conduit that includes a reference chamber valve;
the control chamber fluidly connected via one or more actuation valves to a source of positive or negative pneumatic pressure;
a controller configured to control the fluid inlet and outlet valves, the reference chamber valve, and the one or more actuation valves, and to receive pressure data from a first pressure sensor connected to the actuation chamber and a second pressure sensor connected to the reference chamber;
wherein the controller is configured to isolate the pumping chamber by closing the fluid inlet and outlet valves, charge the control chamber with a first pneumatic pressure; vent the reference chamber or fix a pneumatic pressure in the reference chamber that is different from the control chamber pneumatic pressure; the controller further configured to measure a first control chamber pressure and a first reference chamber pressure, connect the control chamber to the reference chamber by opening the reference chamber valve and equalizing pressures between the control chamber and the reference chamber, measure a third equalized pneumatic pressure in the control and reference chambers, and
compute a control chamber volume based on an ideal gas model that assumes the presence of three closed mass systems of a gas comprising:
a first mass system that occupies the control chamber at the end of pressure equalization;
a second mass system that occupies the reference chamber before pressure equalization; and
a third mass system that occupies the conduit, a part of the control chamber and a part of the reference chamber after equalization of pressure begins between the control and reference chambers.
2. The system of claim 1 , wherein the model assumes an expansion of the first mass system after pressure equalization begins, the expansion being modeled as a polytropic process.
3. The system of claim 1 , wherein the model assumes a compression of the second mass system after pressure equalization begins, the compression being modeled as an adiabatic process.
4. The system of claim 1 , wherein the third mass system is modeled to be subdivided into component volumes, a first component volume occupying part of the control chamber and being modeled polytropically, a second component volume occupying part of the reference chamber and being modeled adiabatically, and a third component volume occupying the conduit and being modeled isothermally.
5. A system for measuring an amount of liquid in a pumping chamber of a pneumatically actuated diaphragm pump comprising:
a fluid inlet and fluid outlet valve connected to the pumping chamber;
a diaphragm separating a pneumatically actuated control chamber from the pumping chamber, the control chamber fluidly connected to a reference chamber of known volume via a conduit that includes a reference chamber valve;
the control chamber fluidly connected via one or more actuation valves to a source of positive or negative pneumatic pressure;
a controller configured to control the fluid inlet and outlet valves, the reference chamber valve, and the one or more actuation valves, and to receive pressure data from a first pressure sensor connected to the actuation chamber and a second pressure sensor connected to the reference chamber;
wherein the controller is configured to isolate the pumping chamber by closing the fluid inlet and outlet valves, charge the control chamber with a first pneumatic pressure; vent the reference chamber or fix a pneumatic pressure in the reference chamber that is different from the control chamber pneumatic pressure; the controller further configured to measure a first control chamber pressure and a first reference chamber pressure, connect the control chamber to the reference chamber by opening the reference chamber valve and equalizing pressures between the control chamber and the reference chamber, measure a third equalized pneumatic pressure in the control and reference chambers, and
compute the control chamber volume based on an ideal gas model that assumes the presence of three closed mass systems of a gas comprising:
a first mass system that occupies the control chamber before pressure equalization;
a second mass system that occupies the reference chamber at the end of pressure equalization; and
a third mass system that occupies the conduit, a part of the control chamber and a part of the reference chamber after equalization of pressure begins between the control and reference chambers.
6. The system of claim 5 , wherein the model assumes a compression of the first mass system after pressure equalization begins, the compression being modeled as a polytropic process.
7. The system of claim 5 , wherein the model assumes an expansion of the second mass system after pressure equalization begins, the expansion being modeled as an adiabatic process.
8. The system of claim 5 , wherein the third mass system is modeled to be subdivided into component volumes, a first component volume occupying part of the control chamber being modeled polytropically, a second component volume occupying part of the reference chamber being modeled adiabatically, and a third component volume occupying the conduit being modeled isothermally.