CA1282737C - Flow control system using boyle's law - Google Patents

Abstract

ABSTRACT

A system is provided for controlling fluid flow, particularly from a reservoir to a patient. A dispensing device isolates a region of a first fluid in a line from the effects of pressure in the line outside of the region.
Increments of the first fluid are repetitively dispensed into and out of the region, as a result of which pressure changes occur in the first fluid in the region. These pressure changes are measured. A measurement fluid in a housing is so related to the region that a change in the measurement fluid pressure causes a change in the first fluid pressure in the region. Predetermined volume incre-ments of measurement fluid are repetitively displaced by a displacement device. A control device which is in communication with the pressure measurement device, the displacement device and the dispensing device causes the dispensing device to dispense first fluid in increments that are calibrated by the displacement device and monitor-ed by the pressure measurement device.

Description

~28'~737 DESCR I PTION

Field of Invention The present invention relates to 8ystems for controiling fluid flow, particularly ~rom a reservoir to a patient, although other embodiment~ are discussed below.

Ba~ .g~.Q.~lnd A~, Numerous devices exist in the prior art for controlling fluid flow for use in intravenous administeation arrangement~ and si~ilar applications. Many of these desiqns, includinq the design disclo~ed in United States Patent No. 4~515,58B, utilize elaborate systems for pressure regulation. The in~entor l~ unaware, however, of any syctem which utilizes an e~ternal ~olume displacement ? arrangement for c~l ibrating a dispellslng arrangement that is monitored by a pressure sensit~ve device.

pis~losure of InYentiQn A preferred embodiment o the invention utilizes a dispensing arrangement in a fluid line that isolates a region of fluid in the line from pressure effects in the line outside the region. The dispen~ng arrangement also has a provision for repetitively dispensing fluid into and out of the region. A pressure transducer monitors pressure changes in the region. The system al~o includes a provi~ion for houæing a measurement fluid (such as air) in relation to the region in such a manner that a change in the r.~easurement fluid pressure causes a change in the 3~

~82737 pressure of the original fluid in the region. There is also a displacement arrangement for repetitively displacing predetermined volume increments of the measurement fluid, so that these volume increments cause changes in the original fluid pressure in the region which are measured by the pressure transducer. Finally, a control arrangement causes the dispensing arrangement to dispense the original fluid in increments that are calibrated by the displacement arrangement and monitored by the pressure transducer. In a further embodiment, the control arrangement is operated so that the predetermined volume increments of measurement fluid are matched by the increments of original fluid dispensed by the dispensing arrangement.
Various aspects of this invention are as follows:
An intravenous line valving system, comprising:
a drip chamber, spike means for connecting the drip chamber to a fluid source, the spike means disposed at one end of the drip chamber, the spike means including a tip, an exterior, an intravenous fluid path from the tip of the spike means into the drip chamber, an interior surface, that surrounds the intravenous fluid path, and an aperture through the exterior of the spike means permitting communication with the intravenous fluid path;
a flexible tube mounted onto the interior surface of the spike means proximate to the aperture, the flexible tube disposed so as to prevent intravenous fluid from flowing out of the aperture; and squeezing means, removably attached about the spike means proximate to the aperture, operable through the aperture, for squeezing the flexible tube against the interior surface of the spike means so as to regulate the flow of intravenous fluid through the 5 intravenous fluid path.
An intravenous line valving system comprising:

lX8273~
2a a drip chamber, spike means for connecting the drip chamber to a fluid source, the spike means disposed at one end of the drip chamber, the spike means including a tip, an exterior, an intravenous fluid path S from the tip of the spike means into the drip chamber, an interior surface, that surrounds the intravenous fluid path, and an aperture through the exterior of the spike means permitting communication with the intravenous fluid path;
a flexible tube mounted onto the interior surface of the spike means proximate to the aperture, the flexible tube disposed so as to prevent intravenous fluid from flowing out of the aperture; and squeezing means for squeezing the flexible tube against the interior surface of the spike means so as to regulate the flow of intravenous fluid through the intravenous fluid path, the squeezing means including a screw and a screw holder that may be removably attached to the spike means, whereby the flexible tube may be compressed by the screw.
An improved intravenous line system of the type having a drip chamber, and spike means for connecting the drip chamber to a fluid source, the spike means disposed at one end of the drip chamber and including a tip, an exterior, an intravenous fluid path from the tip of the spike means into the drip chamber, and an interior surface that surrounds the intravenous fluid path, wherein the improvement comprises:
an aperture through the exterior of the spike means permitting communication with the intravenous fluid path;
a flexible tube mounted onto the interior surface of the spike means proximate to the aperture, the flexible tube disposed so as to prevent intravenous fluid from flowing out of the aperture; and ~8~37 2b attachment means inclllded in the spike means, for removably attaching to the spike means, proximate to the apertur~, a squeszing means for regulating the flow of intravenous fluid through the intravenous path by squeezing the flexible tube against the interior surface .

Brief Description of the Drawings The foregoing objects and features of the invention are better understood with reference to the following description taken with the accompanying drawings in which:
Fig. 1 is a simplified schematic of a first embodiment of the invention;
Figs. 2-4 illustrate operation of the embodiment of Fig. 1, Figs. 5 and 6 show different perspective views of a second embodiment of the invention;
Fig. 7 shows a detailed drawing of a drip chamber for use in the embodiment of Figs. 5 and 6; and 20Fig. ~ shows a schematic diagram of the system illustrated in Figs. 5 and 6.

Detailed Description of Specific Embodiments Fig. 1 :illustrates a fluid control system in accordance with the present invention for controlling fluid from a reservoir 11 into a patient 12. The fluid line 14 passes through a measurement housing 13 that is substantially airtight. The measurement housing 13 is provided with an upper valve 132 and a lower valve 131 for controlling flow 73~7 into and vut of flexible enclosure 141 located within the measurement housing. The portion of the interior 16 of the housing not occup1ed by the flexible eficlosure 141 i~
filled with air. The interior 16 of the hou~ing 13 is in communication wlth a volume standard that comprises a cylinder 161 in vhich travels a p~ston 162. The air preEsure within the housing 13 is monitored by pressure trandsucer 15. It can be ~een that the pressure in the interior 16 of the housing is a function of the volume occupied by flexible enclosure 141 and the effective volume of the interior ~16) as modified by d~placement of t~e piston 162 within the cylinder 161.
Study of Fig. 1 will reveal that displ~cement of the piston by ~ome amount, for example 1 cc~ from position Y~
to position Vl removes 1 cc from the total effective volume of the interior 16 of the ~eaRurement housing l3.
As a result of Boyle's Law, there is an increase in air pressure in the lnterior 16 that i mon~tored by the pressure transducer 15~ (Because the enclosure 141 i flexible, there is a concomitant ~n~rea~e in fluid pres-~ure within the enclo~ure 141.) Let u~ as~ume that there is sufficient fluid in the enclosure 141 that it occ~pies the position shown in da6hes as item 142. If the lower valve 131 is opened, fluid will drain from the enclosure shown as item 142 through the line 14 into the patient 12. Since valve 132 i~ clssed, the walls of the flexible enclosure 142 will occupy a decreasing volu~e as the fluid leaves the enclosure, and at some point the decre~se in volume occupied by the enclosure 142 will equal l cc. At this point, the pressure within the interlor 16 of the measurement hou~ing 13 has returned to the original pressure, ~ince the total volume of ~he interior 16 that is available for occupancy by sir has returned to the original volume. Thus the pressure transducer 15 can be used to 35 determine when the ori~inal pressure has returned and can be u~ed to e~t~blish the point in ~ime when valve 131 should be closed in order for exactly 1 cc of fluid to have been dispen~ed into the pa~ient. In this fashion, the .

~olume standard that includes cylinder 161 and piston 162 serves as a template for determining the increment of fluid that may be dispensed through the flexible enclosure 141.
The 5y~tem may be re~tored to an initlal position by retractlng piston 162 to position VO, ~nd opening valve 132 until ~uf icient fl~id flows into enclosure 141 that again the pre6sure indicated by tr~nsducer lS has returned to the original level.
This cycle 15 lllus~rated in the gr~phs of Pigs. 2 through 4. In Fig. 2, atmospheric pre5~ure is indicated by Po. When the volume shrinks from Vo to Vl the pressure immediately rises to a new pres6ure Pl~ After a desired interval, valve 131 is opened, and the pressure within the interior 16 of the measurement hou~ing 13 i5 permitted to return to pressure Po, at which point valve 131 is closed. Thus there has been di~pensed from flexible enclosure 141 a volume increment of fluid equal to (VO - Vl). After an additional desired interval, the piston 162 ig returned to position VO, at which point the pressure drops to amount P2 in the interior 16. After another desired lnterval, the upper valve 132 is opened and the pressure i8 ~onitored until it returns to point Po, whereupon valve 132 is closed and the s3me volume increment (Vo - Vl) has been diEpensed into flexible enclosure 141. After ~nother desired interval, the cycle can begin again with displacement of the piston to position Vl and so forth.
Fig. 3 illuEtrates that the same proce~s shown in Fig.
2 may be conducted at an elevated pre~Bure~ 50 that the system acts in effect as a pump rather than merely a flow control device. In this embodiment atmospheric pressure indicated by Po i5 below the elevated operating pressure PE. The pi~ton 162 ~s used to displace volume from initial positlon Vo to position V2, whereupon the pre~sure in the interior 16 of the measurement housing 13 exceeds pressure PE by an amount ~P. When valve 131 is opened, the pressure is permitted to fall to PE, and when after 131 is closed, the piston is not moved back to ~ ~Z73~7 position V0, but rather only to positlon Vl, so that pressure fall by an amount ~P from PE, but does not reach Po. In this fashion pressure is maintained within a predetermined li~it ~ P of the desired elevated pressure PE-In connection with Figs. 2 and 3 lt ~ay be remarked that in fact the relation between pre~ure and volume is also a function of temperature, and that compression of the air by piston 162 would also cause ~ ~omentary increase in temperature of the air within the ~easurement housing 13 and that the elevated temperature could lead to errors. In this regard, lt ~ within the domain of the present invention to monltor the temperature change and compensate the pressure system for temperature effects. ~owever, I
have conducted experiments and perfor~ed calculations that indicate that r~l~tively high accuracy ~meMSUre~ent of volume within a percent or so) can be achieved without temperature co~pensation. It should al80 be noted that points Pl ~nd P2 ~re somewhat arbitrary, and that, therefore, a~ long as the pressure transducer has e!rors in accuracy that are reproducible, the 6y6tem will avoid errors introduced by the pressure tran~ducer in any form, and the accuracy of the system will tend to be limited by the reproducibillty of the volume di placements caused by piston 162.
Fig. 4 illustrates another mode of operation of the system. In this mode, the piston 162 is repeatedly displaced to the left in small increment~ l~V. Each time the resulting pres~ure increase from Po is thereafter cancelled out by opening valve 131 until the pressure returns to Po, whereupon valve 131 i~ closed. In this fashion, an amount of fluid V is dispensed each time through the fluid line. At some point after the piston has fully traversed lts stroke to the left, valve 131 is closed for the last time, the piston is moved to the right, returning the ~ystem to volume Vo, at which point the upper valve 132 ls opened, the 1exible enclo~ure 141 is refilled, and upper valve 132 is closed when pressure again ~'~8~73~7 ret~rns to Po. Numerous other configurations are y~ibl~, the polnt being only that the pl~ton 162 an-J
cylinder 161 permit calibration of the dispensing system, the pressure of which can be monitored by a pressure transducer 15. Although the illustration has been made using alr as the measurenlen~ fluid ln the intecior 16 of the measurement housing 13, other fluids, including other gases and other liquids, may alco be fea6ibly utilized. It should also be noted that the pressure transducer produces more in~ormation than simply departures from equalibrium pressure Po or PE. In particular, the slope of the curve in these figures may also be monitored, thereby providing an extremely accurate sytem for determining on an instantaneous basis the flow rate. In fact, flow rate can he monitored 80 that a sudden decrease from a statistically determined average f~ow rate (i.e., slope of the pressure versus time curve) for 3 giYen patient can be used for causing the ~ystem to enter an alarm sta~e indicating, for exam21e, that the needle is no longer in the vein. That is, a sudden decrease in ~he rate of change of pressure with time during the flo~ pc~tion of the cycle may be used as an indication of inf iltration. The horizontal portions of the curve~ in Fig. 2 and 3 may al~o be used to monitor the system for air leaks and related phenomena; that is, the elevated or depressed pressures will not remain constant in the presence of such leaks.
The arrangement described above also permits detec~ing the presence of air ~n the fluid line. Under such circumstances, the pressure ehange when the volume is changed by piston 162 will be smaller than in the case when fluid is properly flowing. For example, with respect to Fig. 2, in the presence of air within the flexible enclosure 141, the usual threshhold Pl will not be reached when the vol~me changes to ~1- The failure to achieve the normal presFIre differential can be viewed as an alar~n state. ~owever, since the valve arrangement 131 and ]32 is quite flexil:d-. he~ore entering the alarm state, valve 131 may be retain~d in its closed position and the 7~37 piston 162 could be displaced maxim~lly to the left to cause a great increase in pressure in the interior 16 of the measurement houfiing 13 with valve 132 open, so as to cause enclo~ure 141 to shrink to minimum volume;
thereafter, piston 162 can be moved back to the right and flexible enclosure 141 be permitted to expand again and the test repeated to see if the normal r~se in pressure has occurred. If it has not occurred a second time, then the alarm state would be entered. Otherwi~e, the appr~ach just described is a rea~onable method of purging the enclosure 141 from minor air bubbles. All of thi6 bas been done without risk of h~rm to the patient, 6ince valve 131 has remained clo~ed.
Although the system has been described as appropriate for controlllng flow from a reservoir lnto a patient, this system may al~o be used for monitorlng fluid flow out from a patient, for example in the measurement of urine volume.
In such an embodiment, item 11 would constitute the catheter or other connection to the patient and item 12 of Fig. 1 would oonst~tute a reservoir. Valve 131 would be closed while valve 132 could be opened. Periodically, valve 132 would be closed and then a measurement cycle such as illustrated in Fig. 2 would be performed ~o dispense a determined amount of fluid from the enclosure 141.
It ~hould be noted that ~ig. 1 also provides a simple arrangement for measuring the blood pressure of the patient. In thi~ srrangement, the upper valve 132 is closed, and lower valve 131 is opened and the system is permitted to reach equilibrium. In thi6 fashion, the pressure in line 14 is indicative of the patient's blood pressure, which m~y be monitored by pressure transducer 15.
Although the invention has been deficribed thus far with a separate measurement housing 13, such a housing may be combined with a drip chamber, as illustrated in Fi~. 5.
In Fig. 5 one may ee a drip chamber 51 including a spike end 55, a fluid llne end 511 that ls held in a case 56.
The drip chamber ~ provided with a fitting 54 for attachment both to a pressure transducer such as indicated 3~7 -B-by item 15 in Fig. 1 and to a volume 6tandard including a piston 162 and cyllnder 161 such as illustrated in Fig. 1.
The volume standard can cause changes ln the air pressure withln the drlp chamber 51 in the same fashion discussed above in connection with Fig. 1, except that the pressure changes are directly transmitted to the fluid, rather than through the intermediary of the flexible enclosure 141.
The case 56 is provided with a valve in the lower region 52 of the drip chamber and ano~her valve in the upper region 53 of the drip chamber. The valve ln region 52 can be a normal crimp type valve operative on the fluid line. The upper valve 52 may be any suitable valve, although one is described in further detail in connection with Figs. 6 and 7.
Fig. 6 presents another view of the system of Fig. 5.
The drip chamber 51 in the spike end 55 is provided with a hole 61. ~he hole 61 is in the external rigid plastic portion of the drip chamber and would reach directly into the fluid line, except that the interior of the spike portion 55 is fltted with a piece of ~llicon rubber tubing, the outside walls of which engage tightly within the inside walls of the spike. Thus, hole 61 provides direct access to the outer wall of the silicon tubing but ~s outside the fluid flow path from the tip of spike 55 into the drip chamber 51. The upper valve acctuator housing 611, nowever, conta~n~ an actuator pin which is capable of moving lnto and out of the hole 61 in such fashion as to squeeze the silicon tubing when the pin is in the closed position. In this fashion flow through the spike 55 is halted when the pin is in the closed position. When the pin is in the open position, flow is permitted through spike 55. In thi~ embodiment the sillcon tubing, the hole 61, and the pin in upper valve actuator housing 611 provide an upper valve.
As illustrated in Fig. 7, the upper valve access hole 61 may be provided with a manual adjustment in lieu of the automatic system described in connection with the previous figures. ~n the manual adjustment embodiment, adjustment 3L~8~7;37 g ring ~2 may be inserted over the spike end 75 until the thumb screw 73 cnn be ~urned to cause the inside portion of the screw to enter hole 61 and compress the ~ilicon tube inside the spike 75. The degree of compres~ion of the tube will regulate the flow through the spike 75. When the manual adjustment ring assembly 73 i~ removed from the spike, it may be used in the system of Figs. 5 and 6.
The system of Figs. 5 and 6 is illustrated schematically ln Fig. 8, where there is ~hown the drip chamber 82 having 6pike end 87, upper v~lve 821, and lower valve 822, which valves are operated by control circuitry 81. A piston arrangement 85 compre6se~ air in line 851, which is connected at fitting 823 ints the drip chamber 82. Pressure in the interior of the drip chamber 82 is monitored by transducer 83, which i8 al80 connected to control circuitry al. Motor 84 drives piston 85 in any of a variety method~ well known in the art. The motor 84, which is also connected to control circuitry 81, may, for example, be a ctepper motor which drive6 the piston by a conventional rack and pinion arrangement. In this fashion the control circuitry 81 will always know the relative position of the pi6ton 85. Altern4tlve ~ensing arrangements may utilize a simpler motor with Hall effect devices, for example, to monitor positlon of the rack. The cycles of operation of this system are identical to those as discussed above in connection with Fig. 1.
It should be noted that the embodiments of Fig. 1 and Pig. 8 can be used to determine the volume of fluid in the flexible enclo~ure 141 and the drip chamber 82 by a related but somewhat different technique. In particular one may cause a slight perturbation in volume by the piston 162 or 85. If the resulting increase in pressure is measured by the pres~ure tran~ducer 15 or 83, Boyle~s Law may be used directly in order to determine the volume of ~luid in the drip chamber or the flexible enclosure. This approach could be used to determine the volume of fluid in any flexible enclosure in the case of Fig. 1 or ~n any rigid enclosure in the case of Fig. 8.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An intravenous line valving system, comprising:
a drip chamber, spike means for connecting the drip chamber to a fluid source, the spike means disposed at one end of the drip chamber, the spike means including a tip, an exterior, an intravenous fluid path from the tip of the spike means into the drip chamber, an interior surface, that surrounds the intravenous fluid path, and an aperture through the exterior of the spike means permitting communication with the intravenous fluid path;
a flexible tube mounted onto the interior surface of the spike means proximate to the aperture, the flexible tube disposed so as to prevent intravenous fluid from flowing out of the aperture; and squeezing means, removably attached about the spike means proximate to the aperture, operable through the aperture, for squeezing the flexible tube against the interior surface of the spike means so as to regulate the flow of intravenous fluid through the intravenous fluid path.

2. A system according to claim 1, wherein the squeezing means includes a pin that is advanced and retracted by a medical infusion controller.

3. A system according to claim 2, wherein the drip chamber nests inside of the medical infusion controller such that, when the drip chamber is fixed in the medical infusion controller, the pin is aligned over the aperture.

4. A system according to claim 1, wherein the squeezing means includes a screw.
5. An intravenous line valving system comprising:
a drip chamber, spike means for connecting the drip chamber to a fluid source, the spike means disposed at one end of the drip chamber, the spike means including a tip, an exterior, an intravenous fluid path from the tip of the spike means into the drip chamber, an interior surface, that surrounds the intravenous fluid path, and an aperture through the exterior of the spike means permitting communication with the intravenous fluid path;
a flexible tube mounted onto the interior surface of the spike means proximate to the aperture, the flexible tube disposed so as to prevent intravenous fluid from flowing out of the aperture; and squeezing means for squeezing the flexible tube against the interior surface of the spike means so as to regulate the flow of intravenous fluid through the intravenous fluid path, the squeezing means including a screw and a screw holder that may be removably attached to the spike means, whereby the flexible tube may be compressed by the screw.

6. A system according to claim 5, wherein the spike means includes a ridged outer circumferential surface and the screw holder includes a ring assembly with inner recesses that correspond to the ridged outer circumferential surface of the spike means, such that the screw holder seats snugly around the spike means with the screw aligned over the aperture.

7. An improved intravenous line system of the type having a drip chamber, and spike means for connecting the drip chamber to a fluid source, the spike means disposed at one end of the drip chamber and including a tip, an exterior, an intravenous fluid path from the tip of the spike means into the drip chamber, and an interior surface that surrounds the intravenous fluid path, wherein the improvement comprises:
an aperture through the exterior of the spike means permitting communication with the intravenous fluid path;
a flexible tube mounted onto the interior surface of the spike means proximate to the aperture, the flexible tube disposed so as to prevent intravenous fluid from flowing out of the aperture; and attachment means included in the spike means, for removable attaching to the spike means, proximate to the aperture, a squeezing means for regulating the flow of intravenous fluid through the intravenous path by squeezing the flexible tube against the interior surface.