Pneumatically coupled direct drive fluid control system and process
A fluid control system for delivery of a liquid includes a pneumatic drive that incorporates a linear actuator to effect known volume changes in a gas reservoir. The gas reservoir is in fluid communication with a gas-side reservoir that is separated from a fluid-side reservoir by a flexible membrane. Movement of the linear actuator effects positive or negative volume differences on the gas in the gas-side reservoir, resulting in a decrease or increase in pressure of the gas that is transmitted to the fluid-side reservoir to draw fluid, primarily liquid, in from a source or deliver liquid out to a sink. In another aspect, a mechanism is provided for the detection and elimination of air bubbles in the fluid path.
1. A fluid control system for delivery of a fluid, comprising:
a fluid flow path comprising an inlet valve configured for fluid communication with a fluid source and an outlet valve configured for fluid communication with a fluid sink;
a chamber comprising a fluid-side chamber and a gas-side chamber, the fluid-side chamber and the gas-side chamber separated by a flexible membrane, the membrane configured so that there is substantially no pressure differential between the fluid-side chamber and the gas-side chamber across the membrane;
the fluid-side chamber disposed on the fluid flow path downstream of the inlet valve and upstream of the outlet valve such that pressure changes in the fluid-side chamber are communicated to the inlet valve and the outlet valve;
a pneumatically coupled drive in communication with the gas-side chamber configured to provide known incremental positive or negative volume changes that cause positive or negative pressure changes of gas in the gas-side chamber, and wherein said pressure changes in the gas-side chamber are communicated to the fluid-side chamber via the flexible membrane;
a pressure sensor disposed to sense pressure of gas in the gas-side chamber; and
a controller in communication with the pressure sensor to receive sensed pressure data and in operative communication with the pneumatically coupled drive, the controller configured to operate the pneumatically coupled drive to effect the delivery of the fluid using a plurality of the incremental volume changes performed as a series of discrete steps, the controller further configured to control the incremental volume changes responsive to a predetermined fluid delivery schedule.
2. The system of claim 1 , wherein the pneumatically coupled drive comprises:
a gas reservoir in fluid communication with the gas-side chamber, and
a linear actuator coupled to a reciprocating element to produce bi-directional linear motion, the reciprocating element disposed to interface with gas in the gas reservoir to provide known incremental volume changes within the gas reservoir.
3. The system of claim 2 , wherein the reciprocating element includes a bellows end coupled at one end to the linear actuator, an interior of the bellows comprising at least part of the gas reservoir.
4. The system of claim 2 , wherein the reciprocating element includes a piston reciprocable within a cylinder, the cylinder comprising at least part of the gas reservoir.
5. The system of claim 2 , wherein the linear actuator includes a motor operable to move bi-directionally in discrete increments, the motor coupled to the reciprocating element to actuate reciprocating motion of the reciprocating element in discrete increments of known length.
6. The system of claim 1 , wherein the inlet valve and the outlet valve each comprise a passive one-way check valve having a predetermined cracking pressure.
7. The system of claim 6 , wherein the predetermined cracking pressure is at least 0.5 PSId.
8. The system of claim 6 , wherein the fluid has a maximum head height limited by one or more physical limits of an associated administration set and further wherein the predetermined cracking pressure is sufficiently high to prevent the fluid at a pressure equal to or less than the maximum head height from flowing freely through the check valve.
9. The system of claim 1 , further comprising a vent valve in fluid communication with the gas-side chamber and in communication with the controller, the controller operative to open the vent valve to ambient to provide discharge of positive and negative pressures to ambient.
10. The system of claim 1 , wherein the pneumatically coupled drive is fluidly coupled to the gas-side chamber by a conduit comprising flexible tubing having a length, wherein the fluid flow path can be separated from the pneumatically coupled drive by a distance determined by the length of the flexible tubing.
11. The system of claim 1 , wherein at least a portion of the fluid flow path of the fluid flow control system, including the inlet valve and the outlet valve, and the chamber are configured as a cassette housed separately from the pneumatically coupled drive.
12. The system of claim 1 , wherein the controller is operable to decrease a volume of gas in communication with the gas-side chamber, whereby pressure in the fluid-side chamber also decreases until a cracking pressure of the inlet valve is reached, whereupon the inlet valve opens and fluid from the fluid source enters the fluid-side chamber.
13. The system of claim 1 , wherein the controller is operable to increase a volume of gas in communication with the gas-side chamber, whereby pressure in the fluid-side chamber also increases until a cracking pressure of the outlet valve is reached, whereupon the outlet valve opens and fluid in the fluid-side chamber exits to the fluid sink.
14. The system of claim 1 , wherein the controller is operable to control delivery of liquid to the fluid sink by determining a volume of liquid to be delivered as the difference between a target volume of liquid to be delivered and a volume of liquid already delivered and operating the pneumatically coupled drive in increments calculated to deliver the volume of liquid to be delivered.
15. The system of claim 14 , wherein the controller is operable to calculate the volume of liquid to be delivered at successive time intervals and update the volume of liquid already delivered after each calculation of the volume of liquid already delivered.
16. The system of claim 1 , wherein the controller is operable to:
receive sensed pressure data before and after a controlled movement of the pneumatically coupled drive,
compare the pressure data change resulting from a known change in gas volume resulting from said controlled movement, and
calculate a volume of gas based on the pressure data change and the known change in gas volume based on an ideal gas law relationship between the sensed pressure data and the known gas volume.
17. The system of claim 16 , wherein the controller is operable to repeat the calculation of a volume of gas based on the pressure data and the known change in gas volume over multiple times during delivery of a liquid to the fluid sink such that accumulated rate errors are eliminated from accuracy errors.
18. The system of claim 1 , wherein the controller is operable to determine a pressure trend indicative of a hydrostatic pressure or an impedance or a resistance in the fluid flow path from the fluid source.
19. The system of claim 18 , wherein the hydrostatic pressure or the impedance or the resistance in the fluid source is indicative of at least one of an occlusion in a line on the fluid flow path, an amount of liquid remaining in the fluid source, a viscous liquid at the fluid source, and a syringe.
20. The system of claim 1 , wherein the controller is operable to determine a pressure trend indicative of a hydrostatic pressure or an impedance or a resistance in the fluid flow path to the fluid sink.
21. The system of claim 20 , wherein the hydrostatic pressure of the impedance or the resistance in the fluid flow path to the fluid sink is indicative of at least one of an occlusion in a line on the fluid flow path and a disconnected connection to the fluid sink.
22. The system of claim 1 , wherein the controller is operable to determine a pressure trend indicative of air in the fluid flow path.
23. An infusion pumping system comprising:
the fluid flow control system of claim 1 ; and
a host controller in communication with the controller of the fluid flow control system, the host controller operable to receive instructions for determining a course of an infusion, the instructions including one of a rate of infusion or a volume of liquid to be delivered over a determined time interval, the instructions further including a start time.
24. The infusion pumping system of claim 23 , further comprising a user interface and a power supply.
25. The infusion pumping system of claim 23 , further comprising a chassis, and wherein at least a portion of the fluid flow path of the fluid flow control system, including the inlet valve and the outlet valve, and the chamber are supportable on the chassis.