Pump flow rate compensation system

• US 4,468,219 A
• Filed: 12/20/1983
• Issued: 08/28/1984
• Est. Priority Date: 12/20/1983
• Status: Expired due to Term

• Current Assignee: Gambro, Inc. (DaVita Incorporated)
• Original Assignee: International Business Machines Corporation
• Inventors: Steinmetz, Michael J., Weber, Robert A., George, Dennis R.
• Primary Examiner(s): Coven, Edward M.
• Application Number:
  US06/563,718
• Time in Patent Office: 252 Days
• Field of Search: 604/50, 604/66, 604/67, 128/DIG. 12, 128/DIG. 13
• US Class Current: 604/66
• CPC Class Codes: A61M 1/3639 Blood pressure control, pressure transducers specially adapted therefor
• CPC Class Codes: F04B 2205/01 Pressure before the pump inlet
• CPC Class Codes: F04B 49/20 by changing the driving speed
• CPC Class Codes: Y10S 128/12 Pressure infusion

Abstract

This invention relates generally to systems for handling biological fluids such as blood and more particularly relates to apparatus for maintaining a constant flow rate of fluid by a peristaltic pump when the pressure at the input of such a pump goes negative or positive. More specifically, the invention uses a microprocessor which provides an output signal representative of the incremental change in pump speed required when the pump input experiences a negative or positive pressure regime.

The microprocessor output is based on a sensed input pump pressure, P_o, a pressure, P_i, which is the pressure at which extensions of the linearly decreasing portions of the pump characteristic curves intersect the pressure axis on a plot of Pressure vs Flow Rate for a given pump and a desired flow rate, Q_o. The resulting output is applied to a stepper motor via a programmable timer and driver amplifier. The motor mechanically linked to the pump drives the pump at a speed which maintains the flow rate constant.

Claims

1. A system for setting the speed of a peristaltic pump when the pump input pressure P_o varies from zero said pump having a pressure vs flow rate characteristic which includes a family of curves each of which, for pressures equal to and greater than zero, exhibits a constant or increasing flow rate with increasing pressure and, for pressures less than zero, exhibits a linearly decreasing flow rate with decreasing pressure over at least a portion of said pressures less than zero comprising:

means for sensing said pump input pressure P_o when it varies from zero and providing an analog output representative thereof,

means for converting said analog output into digital form,

microprocessor means connected to said means for converting for providing an incremental output P_i /(P_i -P_o) when P_o is negative or an incremental output P_i /(P_i +P_o) when P_o is positive in digital form which is representative of the amount by which the speed S_o of said pump is changed to provide another speed S which will maintain a constant flow rate Q_o when said pump input pressure P_o varies from zero said incremental output being determined from the equations

space="preserve" listing-type="equation">Q/Q.sub.o =P.sub.i /(P.sub.i ±

P.sub.o), Q=KS and Q.sub.o =KS.sub.o where

Q=equivalent flow rate at zero pressure required to provide constant flow rate Q_o when P_o varies from zero,

Q_o =constant desired flow rate provided in digitized form as an input to said microprocessor,

P_i =pressure at which extrapolated linear portions of the curves of the pump characteristic intersect the pressure axis,

P_o =pump input positive or negative pressure provided in digitized form as an input to said microprocessor,

S=speed at which pump must be driven to provide Q_o when P_o varies from zero,

S_o =speed at which pump is driven to provide Q_o when P_o is equal to zero,

K=pump constant provided in digitized form as an input to said microprocessor and,

means responsive to said incremental output connected to said microprocessor means for changing the speed S_o of said pump to said another speed S.

2. A system for setting the speed of a peristaltic pump according to claim 1 wherein said means for sensing pump input pressure and for providing an analog output is a noninvasive pressure sensor.

3. A system for setting the speed of a peristaltic pump according to claim 1 wherein said means for converting is an analog-to-digital converter.

4. A system for setting the speed of a peristaltic pump according to claim 1 wherein said means for changing the speed includes a programmable timer connected to said microprocessor which provides a variable frequency square wave output, and a stepper motor connected to said pump and said programmable timer responsive to said variable frequency output to set the speed of said pump to said another speed.

5. A system for setting the speed of a peristaltic pump when the pump input pressure P_o drops below zero said pump having a pressure vs flow rate characteristic which includes a family of curves each of which, for pressures equal to and greater than zero, exhibits a constant flow rate and, for pressures less than zero, exhibits a linearly decreasing flow rate with decreasing pressure over at least a portion of said pressures less than zero comprising:

means for sensing said pump input pressure P_o when it drops below zero and providing an analog output representative thereof,

means for converting said analog output into digital form,

microprocessor means connected to said means for converting for providing an incremental output P_i /(P_i -P_o) in digital form which is representative of the amount by which the speed S_o of said pump is changed to provide another speed S which will maintain a constant flow rate Q_o when said pump input pressure P_o is less than zero said incremental output being determined from the equations

space="preserve" listing-type="equation">Q/Q.sub.o =P.sub.i /(P.sub.i -P.sub.o), Q=KS and Q.sub.o =KS.sub.o where

Q=equivalent flow rate at zero pressure required to provide constant flow rate Q_o when P_o <

O,

Q_o =constant desired flow rate provided in digitized form as an input to said microprocessor,

P_i =pressure at which extrapolated linear portions of the curves of the pump characteristic intersect the pressure axis,

P_o =pump input negative pressure provided in digitized form as an input to said microprocessor,

S=speed at which pump must be driven to provide Q_o when P_o drops below zero,

S_o =speed at which pump is driven to provide Q_o when P_o is equal to or greater than zero,

K=pump constant provided in digitized form as an input to said microprocessor and,

means responsive to said incremental output connected to said microprocessor means for changing the speed S_o of said pump to said another speed S.

6. A system for setting the speed of a peristaltic pump according to claim 5 wherein said means for sensing pump input pressure and for providing an analog output is a noninvasive pressure sensor.

7. A system for setting the speed of a peristaltic pump according to claim 5 wherein said means for converting is an analog-to-digital converter.

8. A system for setting the speed of a peristaltic pump according to claim 5 wherein said means for changing the speed includes a programmable timer connected to said microprocessor which provides a variable frequency square wave output, and a stepper motor connected to said pump and said programmable timer responsive to said variable frequency output to set the speed of said pump to said another speed.

9. A system for setting the speed of a peristaltic pump when the pump input pressure P_o goes above zero said pump having a pressure vs flow rate characteristic which includes a family of curves each of which, for pressures greater than zero, exhibits a linearly increasing flow rate with increasing pressure and, for pressures less than zero, exhibits a linearly decreasing flow rate with decreasing pressure over at least a portion of said pressures less than zero comprising:

means for sensing said pump input pressure P_o when it goes above zero and providing an analog output representative thereof,

means for converting said analog output into digital form,

microprocessor means connected to said means for converting for providing an incremental output P_i /(P_i +P_o) in digital form which is representative of the amount by which the speed S_o of said pump is changed to provide another speed S which will maintain a constant flow rate Q_o when said pump input pressure P_o is greater than zero said incremental output being determined from the equations

space="preserve" listing-type="equation">Q/Q.sub.o =P.sub.i /(P.sub.i +P.sub.o), Q=KS and Q.sub.o =KS.sub.o where

Q=equivalent flow rate at zero pressure required to provide constant flow rate Q_o when P_o <

O,

Q_o =constant desired flow rate provided in digitized form as an input to said microprocessor,

P_i =pressure at which extrapolated linear portions of the curves of the pump characteristic intersect the pressure axis,

P_o =pump input positive pressure provided in digitized form as an input to said microprocessor,

S=speed at which pump must be driven to provide Q_o when P_o goes above zero,

S_o =speed at which pump is driven to provide Q_o when P_o is equal to zero,

K=pump constant provided in digitized form as an input to said microprocessor and,

means responsive to said incremental output connected to said microprocessor means for changing the speed S_o of said pump to said another speed S.