Gas-disabled Liquid-pumping Apparatus

Abstract

Improved liquid-pumping apparatus uses a pumping chamber having a residual volume many times larger than the displacement volume and includes an outlet valve which is disposed within the lowermost region of the residual volume and which is biased against outflow of fluid therethrough for fluid pressures below a selected value.

Description

Certain known liquid-pumping devices have been specifically adapted for metered administration of liquids into the vein or artery of a patient. These pumping devices, however, are generally limited by the hazardous disadvantage that gas or air as well as liquid can be pumped into the patient's vein or artery as, for example, when the bottle or other supply of liquid is expended and the system fills with air. Frequent examination of the pumping device and liquid supply are consequently required to avoid pumping air into a patient's vascular system. This inherently hazardous procedure has thus been costly to use and has not provided entirely satisfactory operating results.

Accordingly, the pumping apparatus of the present invention for administering liquids by positive displacement into the vascular system of a patient provides inherent protection against administration of gas or air. The present pumping apparatus includes a pumping chamber having a residual volume which is many times larger than the displacement volume and having a biased outlet valve disposed in the lowermost region of the residual volume. The careful selection of interrelated values for displacement volume, residual volume and outlet valve bias pressure assures that the present pumping apparatus becomes selectively disabled from pumping liquid in the presence of a predetermined volume of gas or air enclosed within the pumping chamber.

DESCRIPTION OF THE DRAWING

FIG. 1 is a pictorial representation of the pumping apparatus of the present invention;

FIG. 2 is a graph showing the relationship between the displaced liquid, the volume of trapped air in units of displacement volume and the bias pressure provided by the outlet valve in the pumping apparatus of FIG. 1;

FIG. 3 is a graph showing the relationship between fluid pressure and the volume of trapped gas in units of displacement volume during operation of the pumping apparatus of FIG. 1;

FIG. 4 is a sectional view of electromagnetically actuated piston-type pumping apparatus according to the present invention; and

FIG. 5 is a sectional view of a peristaltic or roller-type pumping apparatus in accordance with the present invention;

FIG. 6 is a sectional view of mechanically actuated bellows-type pumping apparatus according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to FIG. 1, there is shown a simplified pictorial diagram of the pumping apparatus of the present invention. It is convenient to refer to the volume of the pumping chamber 9 in units of displacement volume of the piston 11. Accordingly, for the purpose of analysis herein the pumping chamber may be considered to comprise one, two or more units of displacement volume 13. The pumping chamber includes an outlet valve 15 which is biased against outflow therethrough for fluid pressures below a selected value and an inlet means 17 which admits fluid into the chamber 9 below the piston while the piston 11 is in its maximal position prior to a pumping stroke. A reserve chamber 19 above the piston 11 is coupled to the inlet means via port 21 and thus serves as a reservoir of liquid and as a trap for air or gas bubbles, as later described herein. The piston 11 and the inlet means 17 cooperate to permit equilibration of pressures between the pumping chamber 9 and the reserve chamber 19 between pumping strokes.

For the purposes of analysis, the performance of the system may be considered when the pumping chamber 9 has only one unit of displacement volume 13 (i.e., that outlet valve 15 is disposed at level 12). In this form, the downward movement of piston 11 by one unit of displacement volume to its minimal position at level 12 produces potentially indefinitely large fluid pressure within the chamber and leaves no residual volume within the chamber. This is ideally suited for efficient and accurate pumping of known volumes of fluid but unfortunately is capable or pumping both liquid and gas or air contained within the chamber volume 13.

A different situation pertains however, when the pumping chamber is enlarged to contain significant residual volume. Under these conditions, in the presence of a mixture of liquid and gas, the quantity of fluid pumped will depend upon the bias pressure provided by the outlet valve 15. Thus, as shown in the graph of FIG. 2, if no air is trapped within chamber 9 then one-displacement volume 23 of liquid is pumped per piston stroke, substantially independently of the fluid-pressure bias of the outlet valve. However, when gas is trapped within the chamber, the volume of liquid displaced from the chamber by each piston stroke is less than one displacement-volume; the actual volume being a function of both the volume of trapped gas and of the pressure bias provided by the outlet valve, as shown in the graph of FIG. 2.

FIG. 2 illustrates that the liquid pumping apparatus will be disabled when the trapped gas volumes are 2, 2.5, 4 and 6 times the stroke volumes, when the bias pressures provided by the outlet valve 15 are respectively 15, 10, 5 and 3 pounds per square inch (p.s.i.).

Since for fail safe operation of the present pumping apparatus in medical applications it is desirable to assure that only liquid and not air trapped within chamber 9 can be pumped, it might be concluded that the bias pressure provided by the outlet valve should be set as high as possible to assure that even small bubbles of air entrapped within fluid chamber 9 inactivate the pumping mechanism. However, from the graph of FIG. 2, it is apparent that the higher the value selected for the bias pressure provided by the outlet valve, the greater the degradation of pump accuracy and efficiency, when volumes of air or gas inadequate to disable the pumping apparatus are trapped within pumping chamber 9. Under these conditions, a portion of the piston stroke volume is required to compress the trapped air or gas in order to build up fluid pressure to a valve which will overcome the bias of outlet valve 15 and thereafter, only the remaining portion of piston stroke volume displaces fluid from chamber 9 through outlet valve 15. Thus, the bias pressure provided by outlet valve 15 should be sufficiently high to disable the pumping apparatus when a selected volume of gas is present within pumping chamber 9 and should not be any higher than so required because system accuracy suffers.

There is a minimum value of bias pressure provided by outlet valve 15 which must be exceeded, and that value is determined by the height above the outlet valve at which the fluid reservoir may possible be disposed. Since the present apparatus may be used with a bottle or other reservoir of liquid which may be hung above the patient, the resultant fluid pressure at outlet valve 15 must be overcome to avoid a continuous outflow of liquid through the pumping chamber 9 and valve 15 between pumping strokes under the influence of such resultant fluid pressure. It is extremely unlikely that a reservoir bottle may be disposed more than 6 of 8 feet above outlet valve 15 (which corresponds to liquid pressure of approximately 3 to 4 pounds per square inch) and therefore about 3 to 4 pounds per square inch is an acceptable minimum value of the bias pressure provided by the outlet valve for use in parental fluid administration. In actual practice, a bias pressure of approximately 5 pounds per square inch for this application is a well selected value since it provides a reasonable safety factor in operation even if valve springs, or the like, which set the bias pressure tend to weaken or are initially below design specifications.

Referring, then, to the graph of FIG. 3, there is shown a family of curves of fluid pressure within the pumping chamber 9 as a function of the number of units of gas or air trapped within the chamber 9 expressed in units of piston displacement volumes. The fluid pressure within chamber 9 can never exceed the value of bias pressure provided by outlet valve 15. For the reasons discussed above, the value of bias pressure shown on the graph of FIG. 3 is 5 pounds per square inch (gauge pressure) above atmospheric pressure. Thus, from the graph of FIG. 3 it can be seen that if a volume of gas equal to the piston displacement volume is trapped within pumping chamber 9, about one-quarter of the displacement volume 22 will be occupied in compressing the gas to the outlet bias pressure and the volume pumped 26 will be about three-quarters of the piston displacement volume. If the volume of trapped gas is two times the piston displacement volume, the pumped volume 25 will be about one-half of the piston displacement volume. If the volume of trapped gas is three times the piston displacement volume, the pumped volume 29 will be about one-quarter of piston displacement volume. However, if the volume of trapped gas is four times the piston displacement, then no part of the volume is pumped. Under such conditions, the piston strike is used to increase the fluid pressure within the chamber 9 up to, but not exceeding, the value of bias pressure provided by outlet valve 15. The pumping apparatus of the present invention having an outlet valve bias pressure of 5 pounds per square inch gauge pressure and having a chamber volume 13, 24, 27, 28 of at least four times the unit displacement volume therefore becomes disabled to pump fluid when the volume of trapped gas or air within the chamber is about equal to the total volume of chamber 9 (i.e., four times the piston displacement volume). It should be apparent, however, from the graphs of FIGS. 2 and 3 that other values of outlet valve bias pressure and displacement units of residual volume may be used in pumping apparatus according to the present invention which becomes disabled to pump fluid in the presence of a selected volume of gas within the chamber. For fail safe operation, then, the present pumping apparatus may include a residual volume which is at least about one additional unit of displacement volume greater than is minimally required for a unit of displacement volume to produce fluid pressure (i.e., with gas present in chamber 9) approximately equal to the value of bias pressure provided by outlet valve 15. The outlet valve 15 should be located in the lowermost region of the residual volume (With the chamber 9 substantially vertically aligned) to assure that the outlet valve 15 is always disposed in the liquid phase of fluids within the chamber 9. If from practical considerations, a volume of gas approximately equal to four units of displacement volume requires too large a residual volume in chamber 9 in order to avoid having the present apparatus pump air, then the bias pressure provided by outlet valve 15 may be increased. From the graphs of FIGS. 2 and 3, it should be apparent that the volume of gas within chamber 9 which disables the present apparatus from pumping liquid decreases as the bias pressure provided by outlet valve 15 increases.

Referring now to FIG. 4, there is shown a sectional view of a disposable, cartridge-type pump assembly according to the present invention. In this embodiment, the outer housing 61 includes a reservoir or bubble chamber 63, the chamber 65 containing the pump-actuator and return spring, the piston chamber 67 defining the displacement volume, the residual-volume chamber 69 and the chamber 71 containing the outlet valve assembly. These chambers are all disposed along the direction of liquid flow through the pumping apparatus substantially in the order named.

The piston 73 is a conventional flexible-skirted cupped piston which moves a very short distance (typically a few thousandths of an inch) down the length of the piston chamber 67 in response to electromagnetic force applied to the piston actuator. This actuator includes a plate 75 of magnetic material which is attached to (and, ideally, encapsulated in) a plastic or other nonmagnetic piston driver 77. This piston driver, which is coupled to the piston 73, is captivated within the outer housing 61 and is held against stops 79 at the upper end of is travel by spring 81. The plate 75 and the piston driver 77 with the piston 73 attached thereto are all urged downwardly by the electromagnet 83 which is disposed about the housing 61 below plate 75 when the electromagnet is energized at a selected repetition rate of electrical pulses from source 85.

Fluid flows into the top of bubble chamber 63 from the drip chamber 35 and thence substantially axially through apertures 86 in the piston driver 77 to the top of piston 73. Longitudinal ports cut into the cylinder wall of the outer housing 61 about the piston 73 in its uppermost most position permit fluid to flow around the piston prior to a pumping stroke and into the pumping chamber 67, 69. As soon as the piston 73 moves downward from its uppermost position, these ports are closed off so that the volume of displaced fluid can only flow out of the pumping chamber during a pumping stroke through the outlet valve assembly 72. The lower chamber 71 of the outer housing may include suitable means for "bleeding" trapped gas out of the pump chamber initially upon placing the pumping apparatus in service. For example, the lowermost portion 78 of the housing may be axially or longitudinally slidable and may be spring-biased upwardly against the stop 74. Thus, manually urging the housing portion 78 downward against the return force provided by spring 76 relieves the force of the outlet valve spring 72 and permits air to "bleed" through the outlet valve. Return spring 76 positions the housing portion 78 against stop 74 when released, to assure reestablishment of the proper bias pressure provided by outlet valve 72.

Such design factors as displacement volume, residual volume 69 and outflow bias pressure may be determined in the manner previously discussed in connection with FIG. 1 and the graphs of FIGS. 2 and 3. In addition, the volume of chamber 63 may be chosen to be larger than the total volume of the pumping chamber to permit any gas trapped therein to escape back through ports 87 for harmless collection in chamber 63. Also, this chamber establishes an ample reservoir of liquid below drip chamber 35 to provide a reasonably long period of continuous normal operation after the supply of liquid in reservoir 33 is depleted.

Referring now to FIG. 5 there is shown one embodiment of the present pumping apparatus which uses peristaltic action to pump only liquid. This embodiment of the present apparatus includes a length of flexible tubing 31 which provides a fluid conduit from the reservoir 33 and conventional drip chamber 35 to the hollow needle or catheter 37 positioned within a vein or artery of a patient's body. The pump includes an anvil 39 positioned on one side of the tubing 31 and having a stator portion 41 and a valve body portion 43. A rotatable roller carrier or rotor 45 includes a plurality of arms 47, each supporting a roller 49 at the end thereof for engaging and squeezing the tubing 31 closed against the stator 41. The angular separation of the arms 47 of rotor 45 is greater than the angle subtended by the arcuate surface of the stator 41. This assures that the chamber portion of the tubing 31 which extends from the outlet valve 48 to the upper edge 50 of the stator 41 is vented to fluid pressure from reservoir 33 before each pumping cycle. Thus, it should be noted that rotation of rotor 45 by suitable means (e.g., a variable-speed spring-driven or battery-operated motor) causes a roller 47 to squeeze the tubing 31 and thereby displace the quantity of fluid contained within only the length of tubing 31 which is disposed adjacent the arcuate surface of the stator 41. The remaining length of tubing 31 disposed between the lower edge 52 of stator 41 and the outlet valve 48 serves as the residual volume of the pumping chamber formed by the entire length of tubing 31 from the upper edge 50 to the outlet valve 48. This residual volume (or, more conveniently, this residual length where tubing 31 has a known internal diameter) may thus be selected by the same design considerations previously discussed in connection with FIG. 1 and the graphs of FIGS. 2 and 3. The value of outlet bias pressure is determined by the spring 54 which overcomes the resiliency of the tubing 31 and squeezes it closed against the valve body 43. Also, to permit convenient visual observation of the pumping rate, it is desirable to select the displacement volume per pumping stroke to approximately equal the volume of one drop of the liquid to be pumped (approximately 1/10 to 1/50 c.c.) so that the drip rate as observed in drip chamber 35 may provide a quick indication of the volume of liquid being pumped per unit time.

In this and other practical embodiments of the present invention, since the pumping apparatus is designed to become disabled from pumping liquid in the presence of gas within the pumping chamber, it becomes necessary to vent any gas that may become trapped in the chamber when the pump is initially placed in service. One convenient procedure that may be used is simply to disable the outlet valve 48 initially (as by relieving the spring force which squeezes the tubing 31 closed) in order to allow liquid to fill the entire conduit from reservoir 33 to the catheter 37. For this purpose, a relief knob 56 which is springloaded toward the anvil 39 may be temporarily withdrawn from its normal position against a stop 57 in order to relieve the spring force and thereby "bleed" the air out of the system. The relief knob 56 is spring-loaded against the stop 57 to assure reestablishment of the proper setting of the outlet valve 48 upon release of the relief knob 56 following completion of the "bleeding" procedure. In addition, for pumping apparatus of substantially axially symmetrical design such as shown in FIGS. 4 and 6, or the like, an additional fail safe feature may be conveniently provided in order to inhibit operation when the outlet bias valve is not properly seated after a "bleeding" procedure. Specifically, the portion of the outer housing surrounding the outlet valve may include an unaligned guide key or pin or generally be altered in exterior shape or dimensions when the outlet bias valve is improperly reseated so that the pumping apparatus cannot be positioned in operating position with respect to the pump-actuating means, as shown, for example, in the embodiment of FIG. 4 in which a reference base 66 is disposed in fixed, spaced relationship to the top of coil 83.

Referring now to FIG. 6, there is shown a sectional view of another embodiment of a disposable, cartridge-type pumping apparatus according to the present invention. In this embodiment, the outer housing 91 includes a pumping chamber 93 having flexible chamber walls 95. In this embodiment, friction and wear associated with moving piston parts are eliminated and the pumping stroke may be provided by compressing the chamber, say in an axial or longitudinal direction to alter its volume. Suitable means such as a variable-speed, spring-driven or battery-operated motor may be used to develop the axial compressive force required to produce a minute decrease (typically, a few thousandths of an inch) in the longitudinal dimension of the chamber 93.

The inlet means to the pumping chamber 93 includes a valve which closes at the start of a pumping cycle to assure that displaced liquid may only be expelled from the pumping chamber during a pumping cycle by passing through outlet valve 103. In this embodiment, the inlet valve includes two valve faces 96 and 98 with an aperture 101 through the upper valve face into the bubble or reservoir chamber 105. Thus, in the position of maximum extension of the chamber 93 prior to a pumping stroke, the two valve faces 96 and 98 are spaced apart to permit fluid to flow from the upper reservoir chamber 105 through aperture 101 and between the valve faces into the pumping chamber 93. However, since one of the valve faces 96 is mounted on the bellows-type walls of the outer housing 91 for movement with respect to the other valve face 98, the passage for fluid flow between these faces and through aperture 101 is closed off so that the volume of fluid displaced from chamber 93 during a pumping stroke can only flow out through outlet valve 103. The other design factors such as displacement volume, residual volume, and outflow bias pressure may be determined in the manner previously discussed in connection with FIG. 1 and the graphs of FIGS. 2 and 3.

Therefore, the pumping apparatus of the present invention becomes disabled to pump liquid in the presence of a selected volume of gas or air trapped within the pumping chamber. Pump apparatus of this type is thus ideally suited for positive-displacement liquid infusion applications in medicine where a high degree of safety and reliability is required to prevent injury or death from accidental injection of air into the veins or arteries of a patient.

Claims

I claim:

1. Liquid infusion apparatus for selectively pumping a system in which gas may be present, the apparatus comprising: a pumping chamber for enclosing a volume of fluid, and having an outlet valve which is biased against outflow of fluid therethrough for fluid pressures below a selected value, said outlet valve being disposed to remain in communication only with liquid in the chamber in the presence of gas therein; means communicating with said chamber for decreasing the volume thereof by a selected displacement volume during a liquid-displacement period which preserves a residual volume of the chamber that is greater than said selected displacement volume; and inlet means communicating with said chamber and adapted to receive a supply of liquid at an ambient pressure which is below said selected value, said inlet means permitting bidirectional fluid passage therethrough into said chamber between liquid-displacement periods for substantially equalizing fluid pressure within the chamber to ambient pressure prior to a liquid-displacement period and preventing outflow therethrough from said chamber during the liquid-displacement period.

2. Liquid infusion apparatus as in claim 1 wherein: the ratio of volume of said pumping chamber to volume of said displacement volume is greater than the ratio of the value of said fluid pressure bias provided by said outlet valve plus atmospheric pressure to the value of said fluid bias pressure.

3. Liquid infusion apparatus as in claim 2 wherein: the selected value of fluid pressure bias provided by said outlet valve is greater than 3 pounds per square inch gauge pressure.

4. Liquid infusion apparatus as in claim 2 wherein: said selected value of fluid pressure bias provided by said outlet valve is approximately 5 pounds per said inch gauge pressure; and manipulatable outlet said residual volume of the chamber is at least approximately four times greater than said selected displacement volume.

5. Liquid infusion apparatus as in claim 1 comprising: means coupled to said chamber in the lowermost region of the residual volume thereof adjacent to said outlet valve for releasing gas from said chamber to establish communication between liquid in said chamber and said outlet valve.

6. Liquid infusion apparatus as in claim 5 wherein: said means coupled to said chamber includes a manually manipulatable element which is manually movable from a normally operational position to a position which disables the outlet valve from establishing said selected value of fluid pressure bias; and resilient biasing means coupled to said element for urging said element into said normally operational position following release thereof from manually applied forces to provide fail safe reestablishment of said selected value of fluid pressure.

7. Liquid infusion apparatus as in claim 5 wherein: said means coupled to said chamber includes a manually manipulatable element which is manually movable from a normally operational position to a position which disables the outlet valve from establishing said selected value of fluid pressure bias, and further includes means cooperating with said element for preventing normal operational communication between the chamber and said means for decreasing the volume thereof in response to said element being improperly positioned to establish said selected value of fluid pressure bias.

8. Liquid infusion apparatus as in claim 1 wherein: said inlet means includes a reserve chamber having a port passing between said chamber and said reserve chamber and having a volume greater than said residual volume, said port blocking outflow of fluid therethrough from said chamber during said liquid-displacement period.

9. Liquid infusion apparatus as in claim 1 wherein: said means communicating with said chamber includes a piston which forms a fluid-confining boundary of said chamber and which is longitudinally movable within said chamber; and said inlet means includes a fluid channel within the wall of the chamber positioned with respect to said piston for passing fluid therethrough into said chamber while said piston is disposed at a position along the path of longitudinal movement prior to said liquid-displacement period and for blocking fluid flow out of said chamber in response to movement of said piston along said path during said liquid-dsiplacement period.

10. Liquid infusion apparatus as in claim 9 wherein: said means communicating with said chamber includes an element of magnetic material coupled to said piston and a source of magnetic flux disposed with respect to said element for repetitively altering the position thereof and of the piston coupled thereto.

11. Liquid infusion apparatus as in claim 1 wherein: said means communicating with said chamber includes extensible boundary walls which define said chamber; said inlet means includes an aperture through the upper wall into the chamber, valve means disposed about said aperture for permitting fluid flow therethrough into said chamber for a selected longitudinal extension of said sidewalls, and for preventing fluid flow therethrough during decrease of the volume of said chamber in response to movement of the extensible sidewalls; and actuating means coupled to said sidewalls for cyclically moving the extensible boundary walls between selected dimensions at a predetermined repetition rate.

12. Liquid infusion apparatus as in claim 1 wherein: said chamber includes a selected length of resilient flexible tubing having an internal fluid-confining passage therethrough of substantially uniform cross section along the length thereof; said means communicating with said chamber includes a rotatable actuator having at least one element which is disposed with respect to said tubing for squeezing the same to close the passage therethrough, and which is responsive to rotation of said rotatable actuator for altering the location of the squeeze of the tubing over a selected portion of the length of said tubing between a first limit near a fluid inlet end to said internal passage and a second limit remote from the first limit; and said outlet valve includes another actuator resiliently biased to squeeze said tubing to close the passage therethrough at a location along the tubing remote from the fluid inlet end thereof and spaced from said second limit by a distance greater than the distance along said selected portion of the tubing between the first and second limits, said other actuator squeezing said tubing thereby establishing said selected value of fluid pressure bias.

13. Liquid infusion apparatus as in claim 12 wherein: said rotatable actuator being disposed with respect to said tubing to provide during a portion of the rotational cycle thereof an unclosed internal passage through said tubing from the fluid-inlet end thereof to said other actuator, and thereafter to provide during another portion of the rotational cycle thereof a closure of the internal passage through the tubing at a location therealong with advances over said selected portion of length from said first limit to said second limit in response to rotation of said rotatable actuator.