WO1991009636A1 - Spring powered flow rate iv controller - Google Patents
Spring powered flow rate iv controller Download PDFInfo
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- WO1991009636A1 WO1991009636A1 PCT/US1990/007365 US9007365W WO9109636A1 WO 1991009636 A1 WO1991009636 A1 WO 1991009636A1 US 9007365 W US9007365 W US 9007365W WO 9109636 A1 WO9109636 A1 WO 9109636A1
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- flow rate
- tube
- fluid
- detector
- flow
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Classifications
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61M—DEVICES FOR INTRODUCING MEDIA INTO, OR ONTO, THE BODY; DEVICES FOR TRANSDUCING BODY MEDIA OR FOR TAKING MEDIA FROM THE BODY; DEVICES FOR PRODUCING OR ENDING SLEEP OR STUPOR
- A61M5/00—Devices for bringing media into the body in a subcutaneous, intra-vascular or intramuscular way; Accessories therefor, e.g. filling or cleaning devices, arm-rests
- A61M5/14—Infusion devices, e.g. infusing by gravity; Blood infusion; Accessories therefor
- A61M5/168—Means for controlling media flow to the body or for metering media to the body, e.g. drip meters, counters ; Monitoring media flow to the body
- A61M5/16804—Flow controllers
- A61M5/16813—Flow controllers by controlling the degree of opening of the flow line
Definitions
- the present invention relates to controlling fluid flow. More particularly, the present invention relates to controllably restricting flow of intravenous (IV) fluid through the use of spring power.
- a typical infusion device includes a fluid source or reservoir, a drip chamber and an IV tube set. Fluid drips from the reservoir through the drip chamber into the IV tube. The rate at which the fluid drips from the fluid reservoir is proportional to the flow rate of the fluid through the IV tube.
- flow rate controllers were developed which used electromechanical devices to apply a pinching force to the IV tube. By pinching the IV tube, the flow of IV fluid through the IV tube was restricted and the flow rate was controlled. The degree of flow restriction varied based on a feedback system.
- this type of IV controller requires a large amount of electrical energy to drive the electromechanical pinching device. This is especially true where the pinching device is used with a standard set of IV tubes because of the stiffness of the IV tubes. For this IV controller to be provided with an adequate amount of electrical energy, it must either be connected to an AC source or have a large battery. In either case, this type of IV device is not a practical device to be used with ambulatory patients.
- Krum e U.S. Patent No. 4,645,489 illustrates an attempt to provide a small IV control device with self-contained energy requirements.
- the device in Krumme uses a shaped memory alloy driven by electrical energy to provide the pinching force.
- the Krumme patent requires a special IV tube set to reduce the required pinching force.
- Another technique for controlling the flow of fluid in an IV tube involves a simple mechanical clamp.
- the flow rate through the IV tube is initially set by an attending medical person observing the drip rate in the drip chamber.
- the clamp is adjusted to maintain a set flow rate.
- the attending medical person returns to the IV set, monitors the flow rate and adjusts the mechanical clamp.
- the technique is inefficient because of the time required by the attending medical person to periodically monitor and adjust the mechanical clamp.
- this technique requires the attending medical person to make an accurate determination of the flow rate each time the mechanical clamp is adjusted. Therefore, errors are likely.
- Spring power has been used in the past to propel the IV fluid from the reservoir.
- the Brown U.S. Patent No. 4,741,736 teaches a programmable infusion pump which has a constant force spring to force the fluid from the reservoir.
- flow restriction is controlled by a mechanical screw clamp which is not automatically variable.
- Other spring power propulsion devices are taught by the Muller U.S. Patent No. 3,384,080; the Hargest U.S. Patent No. 3,647,117; the Hill U.S. Patent No. 3,670,926 and the Sealfon U.S. Patent No. 4,447,232. All of these devices teach the use of spring driven pumps to force the IV fluid from the reservoir.
- the present invention provides an IV flow rate controller with low power requirements. Therefore, the controller is compact and can be supplied with power by a small source.
- an apparatus controls flow rate of intervenous (IV) fluid through an IV tube.
- a restrictor adjacent the IV tube, restricts fluid flow of the IV fluid in the IV tube.
- a spring coupled to the restrictor variably controls the restrictor using spring power.
- the initial flow rate is set manually.
- the controller controls flow rate based on the initial flow rate set. This reduces power consumption.
- the flow rate controller only periodically monitors the flow rate during monitor periods using a flow rate sensor.
- the flow rate sensor is disabled at times other than during the monitor periods. This further reduces power consumption.
- FIG. 1 is a block diagram of the spring powered flow controller of the present invention.
- FIG. 2 shows a front view of the flow controller including a drop detector and a pole clamp.
- FIG. 2A shows a clamp partially broken away.
- FIG. 3 is a side view of the flow controller show in FIG. 2.
- FIG. 4 is a rear view of the flow controller shown in FIG. 3.
- FIG. 5A is a portion of a section view taken along section 5-5 of FIG. 2 showing part of the flow controller.
- FIG. 5B is a portion of a section view showing the rest of the controller shown in FIG. 5A.
- FIG. 6 is a sectional view taken along section line 6-6 of FIG. 2.
- FIG. 7 is a front view of the clamp shown in FIG. 6.
- FIG. 8 is an enlarged view of the back cover of the flow controller.
- FIG. 9 is an isometric view of a digitizing plate.
- FIG. 10 is an enlarged view of the digitizing plates in cooperation with the incrementing solenoid.
- FIG. 11 is an isometric view of the assembled digitizing plates.
- FIG. 12 is a schematic diagram of drop detector 14.
- FIG. 1 is a block diagram of intervenous (IV) fluid flow controller 10 and IV tube set 12.
- Flow controller 10 includes drop detector 14, control 16, display 18, first actuator 20, charging input 22, first spring motor 24, first gear train 26, second actuator 28, charging input 30, second spring motor 32, second gear train 34, clamp 36 and initial adjustment input 38.
- IV set 12 includes drip chamber 40, IV fluid 42 and IV tube 44.
- controller 10 In order to initialize controller 10 for operation, a physician or nurse or other medically trained person (the operator) must perform two steps. First, the operator must charge first spring motor 24 and second spring motor 32. (Controller 10 can be configured so that the spring motors are charged independently or so that they are both charged in one step.) The step of charging the spring motors is performed at charging inputs 22 and 30, respectively.
- first and second spring motors 24 and 32 When the first and second spring motors 24 and 32 are charged, they exert rotational pressure on first gear train 26 and second gear train 34, respectively.
- the interac ion between first and second gear trains 26 and 34 and first and second spring motors 24 and 32 will be explained in more detail later.
- the second step for initializing controller 10 for operation is an initial adjustment step.
- the medically trained operator must adjust the initial flow rate of IV fluid 42 through IV tube 44.
- the force of gravity propels IV fluid 42 from a reservoir (not shown) to drip chamber 40.
- the initial flow rate is adjusted at initial adjustment input 38.
- the degree to which clamp 36 restricts the flow rate of IV fluid 42 through IV tube 44 is varied.
- the flow rate of IV fluid 42 through IV tube 44 the operator varies the rate at which IV fluid 42 drips through drip chamber 40. This results because, as flow through IV tube 44 is restricted by clamp 36, the level of IV fluid 42 in drip chamber 40 increases.
- controller 10 begins a normal operation mode.
- drop detector 14 continues (either constantly or periodically) to detect a drop rate representing the rate at which IV fluid 42 is dripping in drip chamber 40.
- the drop rate is provided to control 16. Because the drop rate in drip chamber 40 is proportional to the flow rate of IV fluid 42 through IV tube 44, control 16 can determine the flow rate of IV fluid 42 through IV tube 44 based on the drop rate provided by drop detector 14.
- Control 16 updates display 18 with the current flow rate and then determines whether the flow rate through IV tube 44 should be increased or decreased based on the flow rate detected by drop detector 14 and the initial flow rate set by the operator.
- control 16 determines that the flow rate through IV tube 44 should be decreased, control 16 energizes first actuator 20.
- First actuator 20 releases first gear train 26 so it rotates under the rotational pressure exerted by first spring motor 24.
- first gear train 26 rotates, it causes clamp 36 to apply a restriction force to IV tube 44 so that the flow of IV fluid 42 through IV tube 44 is restricted and the flow rate is decreased.
- control 16 determines that the flow rate through IV tube 44 should be increased based on the drip rate provided by drop detector 14 and the initial flow rate set by the operator, control 16 energizes second actuator 28. Second actuator 28, in turn, releases second gear train 34 allowing it to rotate under the rotational pressure applied by second spring motor 32. As second gear train 34 rotates, it applies a releasing force to clamp 36 which causes clamp 36 to exert less pressure on IV tube 44. This, in turn, increases the flow rate of IV fluid 42 through IV tube 44.
- FIG. 2 is a front view of controller 10 showing drop detector 14 connected to drip chamber 40. Also, outer housing 46 of controller 10 is shown connected to pole 48 by pole clamp 50. FIG. 2 also shows clamp 36 which is partially broken away and shown in FIG. 2A. Clamp 36 comprises spring bias member 52 and movable pinching member 54. Spring bias member 52 is shown cut away in FIG. 2A so that movable pinching member 54 is visible. IV tube 44 is positioned between spring bias member 52 and movable pinching member 54. When control 16 determines that flow through IV tube 44 should be decreased, movable pinching member 54 is moved away from housing 46, toward spring bias member 52. This effectively pinches IV tube 44 between movable pinching member 54 and spring bias member 52. The operation of clamp 36 will be explained in greater detail later in the specification.
- FIG. 3 shows a side view of controller 10.
- Charging input knobs 22 and 30, which are used for charging first and second spring motors 24 and 32, respectively, are shown protruding from housing 46.
- drop detector 14 is shown in cross section.
- Drop detector 14 is an optical drop detector which has an optical emitter 56 and an optical detector 58.
- Clamp 60, ring 62, ring 64 and shaft member 66 are disposed about emitter 56.
- ring 70, clamp 72, ring 74 and shaft member 76 are disposed about optical detector 58.
- Springs 78 and 80 urge optical emitter 56 and optical detector 58 to an outer circumference in housing 68.
- Springs 78 and 80 also provide a frictional fit between drip chamber 40 and drop detector 14.
- Optical emitter 56 emits radiation which is detected by optical detector 58. As a drop of IV fluid 42 moves through drip chamber 40, a disturbance in the optical emission is detected by optical detector 58. Each time optical detector 58 detects disruption of the radiation emitted by optical emitter 56, it provides a signal along conductor 82 to control 16, which is mounted inside housing 46.
- FIG. 4 shows a rear view of housing 46 attached to pole 48 by pole clamp 50. Charging input knobs 22 and 30 are also shown. Windows 31 and 31' are provided in housing 46. As first spring motor 24 and second spring motor 32 are charged, the operator verifies the state of the charge on each spring motor by looking through windows 31 and 31'.
- FIGS. 5A and 5B are each portions of a sectional view taken across section 5-5 in FIG. 2. By placing FIG. 5A to the right of FIG. 5B, the entire sectional view can be seen.
- First spring motor 24 is comprised of spring power output spool 88, spring storage spool 90, washer 92, shaft 94 and shaft lock spring 96.
- First actuator 20 is comprised of solenoid 98, shaft lock rings 100 and 102, return spring 114, block 116 and incrementing plate 118.
- First gear train 26 is comprised of digitizing plates 120 and 122, hub 124, shaft lock ring 126, gears 128, 130, 132, 134, shaft 136, hub 138, shaft lock ring 140, locking pin 142, gear 144, shaft lock ring 146, shaft 148 and worm 150.
- Second actuator 28, second spring motor 32, and second gear train 34 are substantially mirror images of first actuator 20, first spring motor 24 and first gear train 26. Hence, the parts comprising the second spring motor 32, second actuator 28 and second gear train 34 are numbered the same as the corresponding parts in the first actuator 20, first spring motor 24 and first gear train 26 except that a prime designation is added. (For example, the solenoid of first actuator 20 is solenoid 98 while the solenoid of second actuator 28 is solenoid 98') .
- Clamp 36 is comprised of spring bias member 52, pinching member 54, worm wheel 155 and bracket 154.
- FIG. 6 is a cross-sectional view taken along line 6-6 of FIG 2.
- FIG. 6 shows spring bias member 52, tube 44, pinching member 54, initial adjustment knob 38, shaft 39, worm wheel 155, bracket 154, centering block 190, probe holding block 192, lock block 194, guard 196 and adjustment block 198.
- the operator adjusts initial adjustment knob 38 so that it moves inward toward block 198.
- lock block 194 can be slid (through the cooperation of slot 204 with shaft 39 shown in FIG. 7) out of engagement with spring bias member 52.
- IV tube 44 is then inserted between spring bias member 52 and pinching member 54. As IV tube 44 is slid between spring bias member 52 and pinching member 54, it contacts detent 206 which centers IV tube 44 on pinching member 54.
- control 16 Part of the system check conducted by control 16 is to determine whether the first and second spring motors, 24 and 32 are fully charged. In checking the charge on the spring motors, control 16 uses signals from probes similar to probe 193. The position of these probes, 208 and 210, respectively, with respect to spring power output spools 88 and 88' of the first and second spring motors is shown in FIG. 8. When the spring motors are fully charged, springs 166 and 166' are coiled around spring power output spools 88 and 88' and contact probes 208 and 210, respectively. This contact is sensed by control 16 and interpreted as indicating that spring motors 24 and 32 are fully charged.
- FIG. 8 shows a rear view of flow controller 10. Windows 31 and 31* are provided in housing 46. By observing the position of springs 166 and 166' , the operator can determine the state of charge on the spring motors. For instance, if springs 166 and 166' are located at position D (the discharged position) in windows 31 and 31', respectively, then the springs are more coiled on spring storage spools 90 and 90' than on output spools 88 and 88' . That indicates that spring motors 24 and 32 are not fully charged.
- springs 166 and 166' are located at position C (the charged position) in windows 31 and 31', respectively, then the springs are more coiled on output spools 88 and 88' than on storage spools 90 and 90' and are charged.
- Control 16 determines the flow rate based on the output from drop detector 14 and displays it at display 18. When the desired rate is indicated at display 18, the operator stops adjusting knob 38 and depresses switch 15 (shown in FIGS. 1 and 5) . This indicates to control 16 that the initial flow rate has been set. b.
- control 16 enters a normal operation mode and maintains the flow rate through IV tube 44 at the present rate (i.e., the initial flow rate shown at display 18 when switch 15 is depressed) by manipulating worm wheel 155 to increase and decrease flow through IV tube 44.
- control 16 causes worm wheel 155 to dither around its initial position to maintain the initial flow rate set.
- This normal operation mode is now described with reference to FIG. 5.
- spring 166 is coiled onto output spool 88, a recoiling force urges shaft 148 to rotate.
- gear 134 which is rigidly attached to shaft 148, is also urged to rotate.
- Gear 134 cooperates with gear 132 which is rigidly attached to shaft 136. This, in turn, urges gear 130, which is rigidly attached to hub 138 on shaft 136 and which cooperates with gear 128, to rotate. As gear 128 is urged to rotate, digitizing plates 120 and 122, which are rigidly attached via hub 124, to gear 128, are also urged to rotate. Therefore, when spring 166 urges spool 88 to rotate (i.e. when first spring motor 24 is charged) digitizing plates 120 and 122 are urged to rotate with respect to incrementing plate 118. During the normal operation mode, when control
- control 16 determines that flow of IV fluid 42 through IV tube 44 should decrease, control 16 energizes solenoid 98.
- solenoid 98 When solenoid 98 is energized, shaft 115 and incrementing plate 118 are moved in the direction indicated by arrow 168. As the incrementing plate 118 moves downward, digitizing plates 120 and 122 increment or rotate one half step. Then, when solenoid 98 is de- energized, spring 114 returns shaft 115 and incrementing plate 118 to their original position. This causes digitizing plates 120 and 122 to rotate or increment another half step.
- FIG. 9 is an isometric view of digitizing plate 120.
- FIG. 11 shows the orientation of digitizing plate 120 with respect to digitizing plate 122.
- FIG. 11 also shows that digitizing plates 120 and 122 have a plurality of gear teeth about their periphery including teeth 172, 174 and 176 of digitizing plate 122 and teeth 178 and 180 of digitizing plate 120.
- FIG. 10 is an enlarged view of shaft 115 of solenoid 98, spring 114, incrementing plate 118 and digitizing plates 120 and 122.
- FIG. 10 shows that incrementing plate 118 includes fork portions 168 and 170. Incrementing plate 118 is shown in FIG. 10 in the position it occupies when solenoid 98 is energized.
- incrementing plate 118 moves to the position shown in FIG. 10. As incrementing plate 118 moves, fork portion 170 slides off of face A of tooth 172 and digitizing plates 120 and 122 rotate in the direction indicated by arrow 182 because of the rotational force applied by spring 166. Eventually, face A of tooth 178 comes to rest against fork portion 168 of incrementing plate 118.
- the distance between fork portions 168 and 170 of incrementing plate 118 is shorter than the combined thickness of digitizing plates 120 and 122, but is greater than the thickness of either digitizing plate 120 or 122 separately. Therefore, it is impossible for incrementing plate 118 to reach a position where digitizing plates 120 and 122 would be free to rotate. This provides a failsafe incrementation of digitizing plates 120 and 122.
- gear 128 (which is rigidly attached to shaft 94) also rotates.
- gear 130 (which is rigidly attached to hub 138 on shaft 136 and which cooperates with gear 128) also rotates.
- gear 132 (which is rigidly attached to shaft 136) rotates as well.
- gear 134 (which is rigidly attached to shaft 148 and which cooperates with gear 132) also rotates. This, in turn, causes rotation of worm 150.
- worm wheel 155 (which cooperates with worm 150) also rotates. This moves the center of worm wheel 155, as well as bracket 154, in a linear direction indicated by arrow 157. Since pinching member 54 is attached to worm wheel 155, through bracket
- pinching member 54 is forced outward with respect to housing 46. This causes pinching member 54 to be pressed against IV tube 44. This motion pinches IV tube
- FIG. 5 shows that digitizing plates 120 and
- the gear reduction assembly reduces a single increment of digitizing plates 120 and 122 down to a linear distance of movement desired for pinching member 54.
- control 16 determines that the flow rate of IV fluid 42 through IV tube 44 should be increased, control 16 energizes solenoid 98 • .
- Energization of solenoid 98' initiates the same type of rotation just described. However, the rotation initiated by energization of solenoid 98' causes shaft 148' and corresponding worm 150' to rotate in a direction which causes the center of worm wheel 155, and consequently pinching member 54, to move in a linear direction away from spring clamp member 52. This releases the restrictive pinching force on IV tube 44 and allows the flow rate of IV fluid 42 through IV tube 44 to increase.
- control 16 Each time control 16 causes the flow rate to be adjusted, by energizing either solenoid 98 or 98*, it stores the adjustment in memory. When the IV infusion has been completed and tube 44 is removed, control 16 determines the linear displacement of worm wheel 155 from its starting, nominal position based on the adjustments stored in memory. Then, control 16 causes worm wheel 155 to return to its nominal position by energizing either solenoid 98 or 98' a desired number of times.
- FIG. 12 is a schematic diagram of drop detector 14 coupled to control 16.
- Drop detector 14 includes transistors Tl, T2, T3, T4 and T5; resistors Rl, R2, R3, R4, R5, R6, R7 and R8; diode Dl; amplifier 200 and comparitors 202 and 204.
- Diode Dl is a light emitting diode and comprises emitter 56 shown in FIG. 3.
- Transistor T2 is a photosensitive transistor and comprises detector 58 in FIG. 3.
- Photosensitive transistor T2 is most sensitive while operating in its active region. Therefore, maximum efficiency can be achieved by operating transistor T2 in the active region.
- the saturation level of T2 is a function of ambient light. Therefore, drop detector 14 is designed so that control 16 is capable of performing adjustments to achieve maximum sensitivity under a range of ambient light conditions.
- Control 16 monitors the DC voltage on collector terminal 206 of transistor T2 through the use of comparitors 202 and 204. If the voltage at terminal 206 falls below a low-reference saturation voltage (V L ) or rises above a high-reference saturation voltage (V H ) , control 16 manipulates transistors T3, T4 and T5 accordingly.
- V L low-reference saturation voltage
- V H high-reference saturation voltage
- comparitor 204 emits a signal to control 16 indicating that the voltage on terminal 206 is out of limits.
- control 16 turns on any or all of transistors T3, T4 and T5. This increases the load on transistor T2 thus pulling it into the active region.
- comparitor 202 If, on the other hand, the voltage at terminal 206 rises above V H , comparitor 202 emits a signal indicating that the voltage on terminal 206 is out of limits. In response, control 16 turns off any or all of transistors T3, T4 and T5 thereby decreasing the load on transistor T2 and keeping it in the active region.
- control 16 operates drop detector 14 to achieve maximum efficiency in another way. Since the flow rate of the IV fluid through IV tube 44 does not typically change quickly, control 16 can maintain a reasonably accurate flow rate while only monitoring the flow rate periodically. This means that drop detector 14 need not be continuously enabled during the operation of flow controller 10. Therefore, to reduce power consumption, control 16 turns off drop detector 14 during all times when it is not monitoring the flow rate of IV fluid 42.
- the flow rate can be maintained by making relatively infrequent mechanical adjustments to pinching member 54.
- power consumption can be reduced by reducing the number of mechanical repositions of worm wheel 155.
- control 16 only monitors the flow rate of IV fluid 42 for a short monitor period once each minute.
- the flow rate monitored during the first monitor period is stored.
- control 16 calculates a cumulative average flow rate.
- control 16 causes adjustments to be made in the position of pinching member 54 based on the cumulative average. This results in control 16 only causing adjustments to be made to the position of pinching member 54 once each five minutes.
- control 16 turns off transistors Tl, T3, T4 and T5 during all periods except when it is monitoring the flow rate of IV fluid 42. This, along with the infrequent mechanical adjustments of pinching member 54, as well as the technique of maintaining operation of photosensitive transistor T2 in the active region, provides maximum power efficiency in drop detector 14 as well as flow rate controller 10.
- Flow controller 10 of the present invention uses spring power to restrict flow of IV fluid 42 through IV tube 44.
- Flow controller 10 also uses a feedback system to vary restriction of the flow to maintain a desired flow rate. Since spring power is used in restricting flow of IV fluid 42, the present flow control requires very little electrical power consumption. Therefore, the entire system can be powered by a battery 185. Hence, the present flow controller is small and portable and can be easily transported by patients. Similarly, by using gravity as the propulsion force to move IV liquid 42 from its reservoir, and by providing a manual initialization mechanism which allows an operator to manually adjust the initial flow rate through IV tube 44, the present flow controller further reduces power requirements. This enhances the ability of the present controller to be self-energy sufficient.
- the energy consumption of the present controller is further reduced by manipulation of the drop detector.
- the drop detector By only enabling the drop detector periodically, by only mechanically manipulating worm wheel 155 periodically, and by operating the drop detector in the active region, power consumption during the normal operation mode of the present controller is reduced.
- the present invention teaches that two independent springs 166 and 166' can be used as spring motors. Therefore, no complex mechanism is required to switch directions of the spring force when the flow of IV fluid 42 through IV tube 44 is being increased and decreased.
- the present invention is self- compensating. Even though pinching member 54 is moving with respect to IV tube 44, and even though the flow rate of IV fluid 42 through IV tube 44 is being increased and decreased, IV tube 44 does not move. Hence, this is a more trouble free and less complex controller than a repositioning controller.
- Digitizing plates 120 and 122 interact with incrementing plate 118 of solenoid 98 so that digitizing plates 120 and 122 are never free to rotate in an unchecked manner. This is also true for digitizing plates 120' and 122'.
Abstract
An apparatus controls flow rate of intravenous (IV) fluid (42) through an IV tube (44). A restricter (52), (54) is adjacent the IV tube (44) for restricting fluid flow of the IV fluid (42) in the IV tube (44). The restrictor (52), (54) is manually adjusted to set on initial flow rate.
Description
SPRING POWERED FLOW RATE IV CONTROLLER BACKGROUND OF THE INVENTION The present invention relates to controlling fluid flow. More particularly, the present invention relates to controllably restricting flow of intravenous (IV) fluid through the use of spring power.
Infusion devices are used to deliver (IV) fluids to patients. A typical infusion device includes a fluid source or reservoir, a drip chamber and an IV tube set. Fluid drips from the reservoir through the drip chamber into the IV tube. The rate at which the fluid drips from the fluid reservoir is proportional to the flow rate of the fluid through the IV tube.
Physicians often require IV fluid to be delivered to patients at a certain rate. Therefore, it is necessary to control the flow rate of the IV fluid through the IV tube.
In the past, flow rate controllers were developed which used electromechanical devices to apply a pinching force to the IV tube. By pinching the IV tube, the flow of IV fluid through the IV tube was restricted and the flow rate was controlled. The degree of flow restriction varied based on a feedback system. However, this type of IV controller requires a large amount of electrical energy to drive the electromechanical pinching device. This is especially true where the pinching device is used with a standard set of IV tubes because of the stiffness of the IV tubes. For this IV controller to be provided with an adequate amount of electrical energy, it must either be connected to an AC source or have a large battery. In either case, this type of IV device is not a practical device to be used with ambulatory patients.
For these reasons, there have been several attempts to provide the medical community with an IV control device that is small and that contains its own power source. One example is the Danby U.S. Patent No. 4,533,350 which utilizes a battery for control power. In order to keep the power requirements of the controller low, a special IV tube set having a special control valve is used. The special IV tube set is designed to decrease the amount of pinching force required to restrict flow in the IV tube in order to achieve a corresponding decrease in the power requirements of the controller.
Similarly, the Krum e U.S. Patent No. 4,645,489 illustrates an attempt to provide a small IV control device with self-contained energy requirements. The device in Krumme uses a shaped memory alloy driven by electrical energy to provide the pinching force. However, as with Danby, the Krumme patent requires a special IV tube set to reduce the required pinching force.
Because of the special IV tube sets required in both the Danby and Krumme patents, the cost of the IV device is higher than it would be if a standard IV tube set were used. Additionally, this extra cost is recurring each time the device is used since a new IV tube set is required for each infusion.
Another technique for controlling the flow of fluid in an IV tube involves a simple mechanical clamp. The flow rate through the IV tube is initially set by an attending medical person observing the drip rate in the drip chamber. The clamp is adjusted to maintain a set flow rate. Periodically, the attending medical person returns to the IV set, monitors the flow rate and
adjusts the mechanical clamp. There is no automatic feedback system for variably controlling the clamp to adjust the flow rate to compensate for deviations caused by varying environmental conditions such as hydrostatic pressure or venous pressure. Hence, the technique is inefficient because of the time required by the attending medical person to periodically monitor and adjust the mechanical clamp. In addition, this technique requires the attending medical person to make an accurate determination of the flow rate each time the mechanical clamp is adjusted. Therefore, errors are likely.
Spring power has been used in the past to propel the IV fluid from the reservoir. For example, the Brown U.S. Patent No. 4,741,736 teaches a programmable infusion pump which has a constant force spring to force the fluid from the reservoir. However, flow restriction is controlled by a mechanical screw clamp which is not automatically variable. Other spring power propulsion devices are taught by the Muller U.S. Patent No. 3,384,080; the Hargest U.S. Patent No. 3,647,117; the Hill U.S. Patent No. 3,670,926 and the Sealfon U.S. Patent No. 4,447,232. All of these devices teach the use of spring driven pumps to force the IV fluid from the reservoir.
SUMMARY OF THE INVENTION The present invention, provides an IV flow rate controller with low power requirements. Therefore, the controller is compact and can be supplied with power by a small source.
In one embodiment, an apparatus controls flow rate of intervenous (IV) fluid through an IV tube. A restrictor, adjacent the IV tube, restricts fluid flow
of the IV fluid in the IV tube. A spring, coupled to the restrictor variably controls the restrictor using spring power.
In another embodiment, the initial flow rate is set manually. The controller controls flow rate based on the initial flow rate set. This reduces power consumption.
Also, in one embodiment, the flow rate controller only periodically monitors the flow rate during monitor periods using a flow rate sensor. The flow rate sensor is disabled at times other than during the monitor periods. This further reduces power consumption.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of the spring powered flow controller of the present invention.
FIG. 2 shows a front view of the flow controller including a drop detector and a pole clamp.
FIG. 2A shows a clamp partially broken away. FIG. 3 is a side view of the flow controller show in FIG. 2.
FIG. 4 is a rear view of the flow controller shown in FIG. 3.
FIG. 5A is a portion of a section view taken along section 5-5 of FIG. 2 showing part of the flow controller.
FIG. 5B is a portion of a section view showing the rest of the controller shown in FIG. 5A.
FIG. 6 is a sectional view taken along section line 6-6 of FIG. 2.
FIG. 7 is a front view of the clamp shown in FIG. 6.
FIG. 8 is an enlarged view of the back cover of the flow controller.
FIG. 9 is an isometric view of a digitizing plate. FIG. 10 is an enlarged view of the digitizing plates in cooperation with the incrementing solenoid.
FIG. 11 is an isometric view of the assembled digitizing plates.
FIG. 12 is a schematic diagram of drop detector 14.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
1. Overview FIG. 1 is a block diagram of intervenous (IV) fluid flow controller 10 and IV tube set 12. Flow controller 10 includes drop detector 14, control 16, display 18, first actuator 20, charging input 22, first spring motor 24, first gear train 26, second actuator 28, charging input 30, second spring motor 32, second gear train 34, clamp 36 and initial adjustment input 38. IV set 12 includes drip chamber 40, IV fluid 42 and IV tube 44.
In order to initialize controller 10 for operation, a physician or nurse or other medically trained person (the operator) must perform two steps. First, the operator must charge first spring motor 24 and second spring motor 32. (Controller 10 can be configured so that the spring motors are charged independently or so that they are both charged in one step.) The step of charging the spring motors is performed at charging inputs 22 and 30, respectively.
When the first and second spring motors 24 and 32 are charged, they exert rotational pressure on first gear train 26 and second gear train 34, respectively. The
interac ion between first and second gear trains 26 and 34 and first and second spring motors 24 and 32 will be explained in more detail later.
The second step for initializing controller 10 for operation is an initial adjustment step. The medically trained operator must adjust the initial flow rate of IV fluid 42 through IV tube 44. The force of gravity propels IV fluid 42 from a reservoir (not shown) to drip chamber 40. The initial flow rate is adjusted at initial adjustment input 38. By varying the amount of pressure that clamp 36 exerts on IV tube 44, the degree to which clamp 36 restricts the flow rate of IV fluid 42 through IV tube 44 is varied. By varying the flow rate of IV fluid 42 through IV tube 44, the operator varies the rate at which IV fluid 42 drips through drip chamber 40. This results because, as flow through IV tube 44 is restricted by clamp 36, the level of IV fluid 42 in drip chamber 40 increases. This causes an increase in air pressure inside drip chamber 40 which, in turn, creates a pressure differential between drip chamber 40 and the fluid reservoir (not shown) . This pressure differential slows the rate at which IV fluid 42 drips from the reservoir to drip chamber 40. Drop detector 14 detects the drop rate of IV fluid 42 in drip chamber 40 and provides the drop rate to control 16. Based on that drop rate, control 16 calculates the flow rate of IV fluid 42 through IV tube 44. Control 16, in turn, displays the flow rate at display 18. Therefore, the operator watches display 18 and, using initial adjustment input 38, adjusts the flow rate through IV tube 44 to a desired flow rate. Once the desired flow rate is achieved, the operator sets
control 16, using operator set input 15, to maintain that flow rate.
Once the spring motors are charged and the initial adjustment step has been performed, controller 10 begins a normal operation mode. During operation, drop detector 14 continues (either constantly or periodically) to detect a drop rate representing the rate at which IV fluid 42 is dripping in drip chamber 40. The drop rate is provided to control 16. Because the drop rate in drip chamber 40 is proportional to the flow rate of IV fluid 42 through IV tube 44, control 16 can determine the flow rate of IV fluid 42 through IV tube 44 based on the drop rate provided by drop detector 14. Control 16 updates display 18 with the current flow rate and then determines whether the flow rate through IV tube 44 should be increased or decreased based on the flow rate detected by drop detector 14 and the initial flow rate set by the operator.
If control 16 determines that the flow rate through IV tube 44 should be decreased, control 16 energizes first actuator 20. First actuator 20 releases first gear train 26 so it rotates under the rotational pressure exerted by first spring motor 24. As first gear train 26 rotates, it causes clamp 36 to apply a restriction force to IV tube 44 so that the flow of IV fluid 42 through IV tube 44 is restricted and the flow rate is decreased.
If control 16 determines that the flow rate through IV tube 44 should be increased based on the drip rate provided by drop detector 14 and the initial flow rate set by the operator, control 16 energizes second actuator 28. Second actuator 28, in turn, releases second gear train 34 allowing it to rotate under the
rotational pressure applied by second spring motor 32. As second gear train 34 rotates, it applies a releasing force to clamp 36 which causes clamp 36 to exert less pressure on IV tube 44. This, in turn, increases the flow rate of IV fluid 42 through IV tube 44.
FIG. 2 is a front view of controller 10 showing drop detector 14 connected to drip chamber 40. Also, outer housing 46 of controller 10 is shown connected to pole 48 by pole clamp 50. FIG. 2 also shows clamp 36 which is partially broken away and shown in FIG. 2A. Clamp 36 comprises spring bias member 52 and movable pinching member 54. Spring bias member 52 is shown cut away in FIG. 2A so that movable pinching member 54 is visible. IV tube 44 is positioned between spring bias member 52 and movable pinching member 54. When control 16 determines that flow through IV tube 44 should be decreased, movable pinching member 54 is moved away from housing 46, toward spring bias member 52. This effectively pinches IV tube 44 between movable pinching member 54 and spring bias member 52. The operation of clamp 36 will be explained in greater detail later in the specification.
2. The Hardware FIG. 3 shows a side view of controller 10. Charging input knobs 22 and 30, which are used for charging first and second spring motors 24 and 32, respectively, are shown protruding from housing 46. Also, drop detector 14 is shown in cross section. Drop detector 14 is an optical drop detector which has an optical emitter 56 and an optical detector 58. Clamp 60, ring 62, ring 64 and shaft member 66 are disposed about emitter 56. Similarly, ring 70, clamp 72, ring 74 and shaft member 76 are disposed about optical detector
58. Springs 78 and 80 urge optical emitter 56 and optical detector 58 to an outer circumference in housing 68. Springs 78 and 80 also provide a frictional fit between drip chamber 40 and drop detector 14. Optical emitter 56 emits radiation which is detected by optical detector 58. As a drop of IV fluid 42 moves through drip chamber 40, a disturbance in the optical emission is detected by optical detector 58. Each time optical detector 58 detects disruption of the radiation emitted by optical emitter 56, it provides a signal along conductor 82 to control 16, which is mounted inside housing 46.
FIG. 4 shows a rear view of housing 46 attached to pole 48 by pole clamp 50. Charging input knobs 22 and 30 are also shown. Windows 31 and 31' are provided in housing 46. As first spring motor 24 and second spring motor 32 are charged, the operator verifies the state of the charge on each spring motor by looking through windows 31 and 31'. FIGS. 5A and 5B are each portions of a sectional view taken across section 5-5 in FIG. 2. By placing FIG. 5A to the right of FIG. 5B, the entire sectional view can be seen. First spring motor 24 is comprised of spring power output spool 88, spring storage spool 90, washer 92, shaft 94 and shaft lock spring 96.
First actuator 20 is comprised of solenoid 98, shaft lock rings 100 and 102, return spring 114, block 116 and incrementing plate 118. First gear train 26 is comprised of digitizing plates 120 and 122, hub 124, shaft lock ring 126, gears 128, 130, 132, 134, shaft 136, hub 138, shaft lock ring
140, locking pin 142, gear 144, shaft lock ring 146, shaft 148 and worm 150.
Second actuator 28, second spring motor 32, and second gear train 34 are substantially mirror images of first actuator 20, first spring motor 24 and first gear train 26. Hence, the parts comprising the second spring motor 32, second actuator 28 and second gear train 34 are numbered the same as the corresponding parts in the first actuator 20, first spring motor 24 and first gear train 26 except that a prime designation is added. (For example, the solenoid of first actuator 20 is solenoid 98 while the solenoid of second actuator 28 is solenoid 98') .
Clamp 36 is comprised of spring bias member 52, pinching member 54, worm wheel 155 and bracket 154.
2. Operation a. Initialization To initialize flow controller 10 for operation, the operator charges first spring motor 24 by rotating charging input knob 22. This uncoils spring 166 from storage spool 90 and coils it onto spring power output spool 88. Spring power output spool 88 freely rotates on shaft 148 operating as a ratchet during the charging operation so it is only capable of rotating in one direction. Second spring motor 32 is similarly charged using charging input knob 22 to transfer spring 166 ' from storage spool 90* to spring power output spool 88'. Charging spring motors 24 and 32 causes them to store mechanical energy. The next step in initializing flow controller
10 for operation is to set the initial flow rate. FIG. 6 is a cross-sectional view taken along line 6-6 of FIG 2. FIG. 6 shows spring bias member 52, tube 44,
pinching member 54, initial adjustment knob 38, shaft 39, worm wheel 155, bracket 154, centering block 190, probe holding block 192, lock block 194, guard 196 and adjustment block 198. In order to set the initial flow rate, after the spring motors are charged, the operator adjusts initial adjustment knob 38 so that it moves inward toward block 198. When tab 200 has moved toward block 198 far enough so that it is no longer within notch 202 in lock block 194, lock block 194 can be slid (through the cooperation of slot 204 with shaft 39 shown in FIG. 7) out of engagement with spring bias member 52. IV tube 44 is then inserted between spring bias member 52 and pinching member 54. As IV tube 44 is slid between spring bias member 52 and pinching member 54, it contacts detent 206 which centers IV tube 44 on pinching member 54.
When IV tube 44 is initially placed between spring bias member 52 and pinching member 54, lock block 194 is not engaged with spring bias member 52.
Therefore, the flow of IV fluid 42 through IV tube 44 is closed off by the spring force of spring bias member 52 pinching IV tube 44 closed against pinching member 54. Also, guard 196 and notch 202 interact to prevent lock block 194 from being moved out of engagement with spring bias member 52 unless initial adjustment knob 38 is manually adjusted inward. Therefore, IV tube 44 will always be pinched closed, or in a non-flow position while it is being inserted and removed. Once IV tube 44 is in place, the operator slides lock block 194 back into engagement with spring bias member 52. As lock block 194 is slid back into engagement with spring bias member 52, it contacts probe
193. Contact between probe 193 and lock block 194 is sensed by control 16 and is interpreted as an initialization signal. In other words, control 16 senses the contact and interprets it as meaning that an IV infusion is being set up. Control 16 then conducts a system check to determine proper operation of system functions. If the system check reveals difficulties, an alarm condition is indicated.
Part of the system check conducted by control 16 is to determine whether the first and second spring motors, 24 and 32 are fully charged. In checking the charge on the spring motors, control 16 uses signals from probes similar to probe 193. The position of these probes, 208 and 210, respectively, with respect to spring power output spools 88 and 88' of the first and second spring motors is shown in FIG. 8. When the spring motors are fully charged, springs 166 and 166' are coiled around spring power output spools 88 and 88' and contact probes 208 and 210, respectively. This contact is sensed by control 16 and interpreted as indicating that spring motors 24 and 32 are fully charged. Hence, at the start of each IV infusion, the first and second spring motors must be fully charged so control 16 does not indicate a warning condition. The state of charge on spring motors 24 and 32 can also be checked visually. FIG. 8 shows a rear view of flow controller 10. Windows 31 and 31* are provided in housing 46. By observing the position of springs 166 and 166' , the operator can determine the state of charge on the spring motors. For instance, if springs 166 and 166' are located at position D (the discharged position) in windows 31 and 31', respectively, then the springs are more coiled on spring storage spools 90 and 90' than
on output spools 88 and 88' . That indicates that spring motors 24 and 32 are not fully charged. On the other hand, if springs 166 and 166' are located at position C (the charged position) in windows 31 and 31', respectively, then the springs are more coiled on output spools 88 and 88' than on storage spools 90 and 90' and are charged.
Once all the initial system conditions are satisfied, the operator adjusts knob 38 outward with respect to block 198 while observing display 18. This allows IV fluid 42 to begin dripping through drip chamber 40 and flowing through IV tube 44. Control 16 determines the flow rate based on the output from drop detector 14 and displays it at display 18. When the desired rate is indicated at display 18, the operator stops adjusting knob 38 and depresses switch 15 (shown in FIGS. 1 and 5) . This indicates to control 16 that the initial flow rate has been set. b. Normal Operation Mode When switch 15 has been depressed, control 16 enters a normal operation mode and maintains the flow rate through IV tube 44 at the present rate (i.e., the initial flow rate shown at display 18 when switch 15 is depressed) by manipulating worm wheel 155 to increase and decrease flow through IV tube 44. In other words, control 16 causes worm wheel 155 to dither around its initial position to maintain the initial flow rate set. This normal operation mode is now described with reference to FIG. 5. When spring 166 is coiled onto output spool 88, a recoiling force urges shaft 148 to rotate. As shaft 148 is urged to rotate, gear 134, which is rigidly attached to shaft 148, is also urged to rotate. Gear 134 cooperates with gear 132 which is
rigidly attached to shaft 136. This, in turn, urges gear 130, which is rigidly attached to hub 138 on shaft 136 and which cooperates with gear 128, to rotate. As gear 128 is urged to rotate, digitizing plates 120 and 122, which are rigidly attached via hub 124, to gear 128, are also urged to rotate. Therefore, when spring 166 urges spool 88 to rotate (i.e. when first spring motor 24 is charged) digitizing plates 120 and 122 are urged to rotate with respect to incrementing plate 118. During the normal operation mode, when control
16 determines that flow of IV fluid 42 through IV tube 44 should decrease, control 16 energizes solenoid 98. When solenoid 98 is energized, shaft 115 and incrementing plate 118 are moved in the direction indicated by arrow 168. As the incrementing plate 118 moves downward, digitizing plates 120 and 122 increment or rotate one half step. Then, when solenoid 98 is de- energized, spring 114 returns shaft 115 and incrementing plate 118 to their original position. This causes digitizing plates 120 and 122 to rotate or increment another half step.
Incrementation of digitizing plates 120 and 122 is better illustrated in FIGS. 9, 10 and 11. FIG. 9 is an isometric view of digitizing plate 120. FIG. 11 shows the orientation of digitizing plate 120 with respect to digitizing plate 122. FIG. 11 also shows that digitizing plates 120 and 122 have a plurality of gear teeth about their periphery including teeth 172, 174 and 176 of digitizing plate 122 and teeth 178 and 180 of digitizing plate 120. FIG. 10 is an enlarged view of shaft 115 of solenoid 98, spring 114, incrementing plate 118 and digitizing plates 120 and 122. FIG. 10 shows that incrementing plate 118 includes
fork portions 168 and 170. Incrementing plate 118 is shown in FIG. 10 in the position it occupies when solenoid 98 is energized.
Before solenoid 98 is energized, fork portion 170 of incrementing plate 118 rests against face A of tooth 172 of digitizing plate 122 shown in FIG. 11. Face A of tooth 172 is urged against fork portion 170 of incrementing plate 118 because of the rotational pressure applied by spring 166 to digitizing plates 120 and 122 when first spring motor 24 is charged.
When solenoid 98 is energized, incrementing plate 118 moves to the position shown in FIG. 10. As incrementing plate 118 moves, fork portion 170 slides off of face A of tooth 172 and digitizing plates 120 and 122 rotate in the direction indicated by arrow 182 because of the rotational force applied by spring 166. Eventually, face A of tooth 178 comes to rest against fork portion 168 of incrementing plate 118.
Then, when solenoid 98 is de-energized, spring 114 urges shaft 115 of solenoid 98 upward and incrementing plate 118 also moves. As incrementing plate 118 moves, fork portion 168 slides out of contact with face A of tooth 178 and digitizing plates 120 and 122 again rotate in the direction indicated by arrow 182. Eventually, face A of tooth 174 is urged against fork portion 170 of incrementing plate 118. In this way, digitizing plates 120 and 122 are incremented one half step each time solenoid 98 is energized. Similarly, they are incremented another one half step each time solenoid 98 is de-energized.
In this preferred embodiment, the distance between fork portions 168 and 170 of incrementing plate 118 is shorter than the combined thickness of digitizing
plates 120 and 122, but is greater than the thickness of either digitizing plate 120 or 122 separately. Therefore, it is impossible for incrementing plate 118 to reach a position where digitizing plates 120 and 122 would be free to rotate. This provides a failsafe incrementation of digitizing plates 120 and 122.
The description is now continued again with reference to FIG. 5. As digitizing plates 120 and 122 rotate under the force of spring 166, gear 128 (which is rigidly attached to shaft 94) also rotates. As gear 128 rotates, gear 130 (which is rigidly attached to hub 138 on shaft 136 and which cooperates with gear 128) also rotates. As gear 130 rotates, gear 132 (which is rigidly attached to shaft 136) rotates as well. Similarly, as gear 132 rotates, gear 134 (which is rigidly attached to shaft 148 and which cooperates with gear 132) also rotates. This, in turn, causes rotation of worm 150.
As worm 150 rotates, worm wheel 155 (which cooperates with worm 150) also rotates. This moves the center of worm wheel 155, as well as bracket 154, in a linear direction indicated by arrow 157. Since pinching member 54 is attached to worm wheel 155, through bracket
154, pinching member 54 is forced outward with respect to housing 46. This causes pinching member 54 to be pressed against IV tube 44. This motion pinches IV tube
44 between pinching member 54 and spring clamp member
52. This pinching action restricts the flow of IV fluid
42 through IV tube 44. FIG. 5 shows that digitizing plates 120 and
122 along with gears 128, 130, 132, 134 and worm 150 operate with worm wheel 155 as a gear reduction assembly. The gear reduction assembly reduces a single
increment of digitizing plates 120 and 122 down to a linear distance of movement desired for pinching member 54.
If control 16 determines that the flow rate of IV fluid 42 through IV tube 44 should be increased, control 16 energizes solenoid 98• . Energization of solenoid 98' initiates the same type of rotation just described. However, the rotation initiated by energization of solenoid 98' causes shaft 148' and corresponding worm 150' to rotate in a direction which causes the center of worm wheel 155, and consequently pinching member 54, to move in a linear direction away from spring clamp member 52. This releases the restrictive pinching force on IV tube 44 and allows the flow rate of IV fluid 42 through IV tube 44 to increase.
Each time control 16 causes the flow rate to be adjusted, by energizing either solenoid 98 or 98*, it stores the adjustment in memory. When the IV infusion has been completed and tube 44 is removed, control 16 determines the linear displacement of worm wheel 155 from its starting, nominal position based on the adjustments stored in memory. Then, control 16 causes worm wheel 155 to return to its nominal position by energizing either solenoid 98 or 98' a desired number of times.
It should be noted that even though the flow rate through IV tube 44 undergoes numerous adjustments comprising increases and decreases, IV tube 44 never shifts position with respect to housing member 46, spring bias member 52 and pinching member 54. In other words, the flow rate controller shown in FIG. 5 is self- compensating. It should also be noted that by using two independent springs in the first and second spring
motors 24 and 32, respectively, the spring force is not required to be reversed in either motor. This feature substantially reduces the complexity of flow controller 10. C. Drop Detection
FIG. 12 is a schematic diagram of drop detector 14 coupled to control 16. Drop detector 14 includes transistors Tl, T2, T3, T4 and T5; resistors Rl, R2, R3, R4, R5, R6, R7 and R8; diode Dl; amplifier 200 and comparitors 202 and 204. Diode Dl is a light emitting diode and comprises emitter 56 shown in FIG. 3. Transistor T2 is a photosensitive transistor and comprises detector 58 in FIG. 3.
As a drop of IV fluid passes between light emitting diode Dl and photosensitive transistor T2, the voltage on collector terminal 206 of transistor T2 changes. Then, as the drop passes beyond light emitting diode Dl and photosensitive transistor T2, the voltage on terminal 206 returns to its previous level. This, in effect, causes a pulse signal at terminal 206. This pulse signal is amplified by amplifier 200 and provided to control 16. The pulse signal to control 16 represents one drop passing between light emitting diode Dl and photosensitive transistor T2. By monitoring the amplified pulse signal over a period of time, control 16 is able to calculate the flow rate of IV fluid 42 using an average volume per drop. This flow rate is then supplied to display 18 where it is displayed in one of any number of formats including volume of liquid per unit of time.
Photosensitive transistor T2 is most sensitive while operating in its active region. Therefore, maximum efficiency can be achieved by operating
transistor T2 in the active region. The saturation level of T2 is a function of ambient light. Therefore, drop detector 14 is designed so that control 16 is capable of performing adjustments to achieve maximum sensitivity under a range of ambient light conditions. Control 16 monitors the DC voltage on collector terminal 206 of transistor T2 through the use of comparitors 202 and 204. If the voltage at terminal 206 falls below a low-reference saturation voltage (VL) or rises above a high-reference saturation voltage (VH) , control 16 manipulates transistors T3, T4 and T5 accordingly. For example, where the voltage at terminal 206 falls below VL, comparitor 204 emits a signal to control 16 indicating that the voltage on terminal 206 is out of limits. In response, control 16 turns on any or all of transistors T3, T4 and T5. This increases the load on transistor T2 thus pulling it into the active region.
If, on the other hand, the voltage at terminal 206 rises above VH, comparitor 202 emits a signal indicating that the voltage on terminal 206 is out of limits. In response, control 16 turns off any or all of transistors T3, T4 and T5 thereby decreasing the load on transistor T2 and keeping it in the active region. In one preferred embodiment, drop detector 14 is designed for a three volt rail system (V=3 volts) . VL is set at 0.25 volts and VH is set at 0.75 volts. Since photosensitive transistor T2 is most sensitive in its active region, maximum power efficiency is achieved by operating transistor T2 between these voltage limits.
In addition, control 16 operates drop detector 14 to achieve maximum efficiency in another way. Since the flow rate of the IV fluid through IV tube 44 does
not typically change quickly, control 16 can maintain a reasonably accurate flow rate while only monitoring the flow rate periodically. This means that drop detector 14 need not be continuously enabled during the operation of flow controller 10. Therefore, to reduce power consumption, control 16 turns off drop detector 14 during all times when it is not monitoring the flow rate of IV fluid 42.
Also, the flow rate can be maintained by making relatively infrequent mechanical adjustments to pinching member 54. Hence, power consumption can be reduced by reducing the number of mechanical repositions of worm wheel 155.
For example, in one preferred embodiment, control 16 only monitors the flow rate of IV fluid 42 for a short monitor period once each minute. The flow rate monitored during the first monitor period is stored. After each subsequent monitor period, control 16 calculates a cumulative average flow rate. After five monitor periods, control 16 causes adjustments to be made in the position of pinching member 54 based on the cumulative average. This results in control 16 only causing adjustments to be made to the position of pinching member 54 once each five minutes. It should be noted that, if control 16 detects a great variance in flow rates from one monitor period to the next, it adjusts pinching member 54 without waiting the entire five minutes. Therefore, control 16 turns off transistors Tl, T3, T4 and T5 during all periods except when it is monitoring the flow rate of IV fluid 42. This, along with the infrequent mechanical adjustments of pinching member 54, as well as the technique of maintaining operation of photosensitive transistor T2 in
the active region, provides maximum power efficiency in drop detector 14 as well as flow rate controller 10.
CONCLUSION Flow controller 10 of the present invention uses spring power to restrict flow of IV fluid 42 through IV tube 44. Flow controller 10 also uses a feedback system to vary restriction of the flow to maintain a desired flow rate. Since spring power is used in restricting flow of IV fluid 42, the present flow control requires very little electrical power consumption. Therefore, the entire system can be powered by a battery 185. Hence, the present flow controller is small and portable and can be easily transported by patients. Similarly, by using gravity as the propulsion force to move IV liquid 42 from its reservoir, and by providing a manual initialization mechanism which allows an operator to manually adjust the initial flow rate through IV tube 44, the present flow controller further reduces power requirements. This enhances the ability of the present controller to be self-energy sufficient.
The energy consumption of the present controller is further reduced by manipulation of the drop detector. By only enabling the drop detector periodically, by only mechanically manipulating worm wheel 155 periodically, and by operating the drop detector in the active region, power consumption during the normal operation mode of the present controller is reduced. Further, to reduce the complexity of the controller, the present invention teaches that two independent springs 166 and 166' can be used as spring motors. Therefore, no complex mechanism is required to
switch directions of the spring force when the flow of IV fluid 42 through IV tube 44 is being increased and decreased.
In addition, the present invention is self- compensating. Even though pinching member 54 is moving with respect to IV tube 44, and even though the flow rate of IV fluid 42 through IV tube 44 is being increased and decreased, IV tube 44 does not move. Hence, this is a more trouble free and less complex controller than a repositioning controller.
Also, the mechanical energy stored in the first and second spring motors, 24 and 32 respectively, is released in a failsafe manner. Digitizing plates 120 and 122 interact with incrementing plate 118 of solenoid 98 so that digitizing plates 120 and 122 are never free to rotate in an unchecked manner. This is also true for digitizing plates 120' and 122'.
Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.
Claims
1. An apparatus for controlling flow rate of intravenous (IV) fluid in an IV tube, comprising: restriction means for restricting the flow of the IV fluid through the IV tube; sensing means for sensing the flow rate of the IV fluid; mechanical adjustment means, mechanically coupled to the restriction means, provided for manual adjustment of an initial flow rate; and control means, coupled to the sensing means and the restriction means, for controlling the flow rate as a function of the flow rate sensed and the manually adjusted initial flow rate.
2. The apparatus of claim 1 wherein the restriction means comprises: a first pinching member; and a second pinching member where the IV tube is restricted by being pinched between the first pinching member and the second pinching member.
3. The apparatus of claim 2 wherein the mechanical adjustment means comprises: an adjustment knob, coupled to the first pinching member, for adjusting position of the first pinching member relative to the second pinching member.
4. The apparatus of claim 3 wherein the mechanical adjustment means further comprises: a mechanical adjustment sensor, coupled to the control means, for providing the control means with an adjustment signal when the initial flow rate is being mechanically adjusted.
5. The apparatus of claim 4 and further comprising: display means, coupled to the sensing means, for displaying the flow rate sensed.
6. The apparatus of claim 5 wherein the controller causes the display means to display the flow rate being adjusted in response to the mechanical adjustment signal received.
7. A method for controlling flow rate of intravenous (IV) fluid in an IV tube, comprising: manually adjusting a flow restrictor to achieve an initial flow rate in the IV tube; sensing the flow rate of the IV fluid in the IV tube; and controlling restriction of the IV tube as a function of the flow rate sensed and the manually adjusted initial flow rate.
8. A method for controlling an intravenous (IV) fluid infusion device having a flow rate detector, comprising: activating a flow sensor during a plurality of sensor time periods; monitoring the flow sensor during the plurality of sensor time periods to determine a flow rate during each time period; and de-activating the flow sensor at least a portion of the time other than during the sensor time periods.
9. The method of claim 8 and further comprising: adjusting the flow rate based on the flow rate determined and a desired flow rate.
10. The method of claim 9 wherein the step of adjusting is performed only after a plurality of sensor time periods.
11. The method of claim 8 and further comprising: storing a cumulative average flow rate based on the flow rates determined during each sensor time period.
12. The method of claim 11 and further comprising: adjusting the flow rate based on the cumulative average flow rate and a desired flow rate.
13. The method of claim 12 wherein the step of adjusting is performed only after a cumulative average flow rate has been determined for a plurality of sensor time periods.
14. A drop detector for use in an infusion device of the type having a drip chamber where intravenous (IV) fluid drips along a drip path, the drop detector comprising: a light emitter, disposed on a first side of the drip path, for emitting light; a light detector, disposed on a second side of the drip path, for detecting light and emitting a drop signal responsive to a drop of IV fluid passing between the light emitter and the light detector, the light detector having a sensitivity that varies as a function of light detected; and a control, coupled to the light detector, for receiving the drop signal and controlling the light detector to compensate for changes in light conditions.
15. The drop detector of claim 14 wherein the light detector further comprises: a photosensitive transistor operable in a saturated region and an active region, where the photosensitive transistor operates in the saturated region and the active region as a function of the light detected.
16. The drop detector of claim 15 wherein the light detector further comprises: a load circuit, coupled to the photosensitive transistor, for variably loading the photosensitive transistor.
17. The drop detector of claim 16 wherein the control further comprises: a threshold detector, coupled to the photosensitive transistor, for detecting when the photosensitive transistor reaches a saturation threshold; and a load control, coupled to the load circuit and the threshold detector, for controlling the load circuit to keep the photosensitive transistor operating in the active region.
18. A method for controlling an intravenous (IV) fluid infusion device having a flow rate detector, comprising: activating a flow sensor; monitoring the flow sensor to determine a flow rate; storing a cumulative average flow rate based on the flow rates determined during each of a plurality of sensor time periods; and adjusting the flow rate based on the cumulative average flow rate and a desired flow rate, the step of adjusting being performed only after a cumulative average flow rate has been determined for a plurality of sensor time periods.
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US45828689A | 1989-12-28 | 1989-12-28 | |
US458,286 | 1989-12-28 |
Publications (1)
Publication Number | Publication Date |
---|---|
WO1991009636A1 true WO1991009636A1 (en) | 1991-07-11 |
Family
ID=23820168
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
PCT/US1990/007365 WO1991009636A1 (en) | 1989-12-28 | 1990-12-12 | Spring powered flow rate iv controller |
Country Status (2)
Country | Link |
---|---|
AU (1) | AU7051891A (en) |
WO (1) | WO1991009636A1 (en) |
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US5728077A (en) * | 1992-10-15 | 1998-03-17 | Health Care Technology Australia Pty. Ltd. | Intravenous delivery system |
US8211054B2 (en) | 2006-05-01 | 2012-07-03 | Carefusion 303, Inc. | System and method for controlling administration of medical fluid |
US9095652B2 (en) | 2006-05-01 | 2015-08-04 | Carefusion 303, Inc. | System and method for controlling administration of medical fluid |
US10463785B2 (en) | 2006-05-01 | 2019-11-05 | Carefusion 303, Inc. | System and method for controlling administration of medical fluid |
US11577021B2 (en) | 2006-05-01 | 2023-02-14 | Carefusion 303, Inc. | System and method for controlling administration of medical fluid |
Also Published As
Publication number | Publication date |
---|---|
AU7051891A (en) | 1991-07-24 |
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