GB2365928A

GB2365928A - Pneumatic control system

Info

Publication number: GB2365928A
Application number: GB0021158A
Authority: GB
Inventors: Fergal Mctiernan; Frank Mckeown; Michael Maguire
Original assignee: CASEY TECHNOLOGY Ltd
Current assignee: CASEY TECHNOLOGY Ltd
Priority date: 2000-08-21
Filing date: 2000-08-30
Publication date: 2002-02-27
Anticipated expiration: 2020-08-30
Also published as: GB2365928B; GB0021158D0; IE20000659A1

Abstract

A pneumatic system for delivery of a controlled air supply to an inflatable cuff for applying pressure to a patient's limb comprises an inlet air filter 5, a rotary vane pump 6, a normally open solenoid valve 7, an air reservoir 8 and a pressure transducer 9 for sensing a manifold pressure and providing a control signal. Control means 10 controls the operation of the rotary vane pump 6 and the solenoid valve 7 in response to the pressure detected by the pressure transducer 9.

Description

<Desc/Clms Page number 1> "A pneumatic control system" Introduction The invention relates to a pneumatic system for delivery of an air supply to an inflatable cuff or sleeve for applying pressure to a patient's limb, or limbs. The blood flow in a patient's limbs, especially the legs, decreases significantly if the patient is unable to move around. The slowing of the blood flow is particularly apparent if a patient is confined to bed for an extended period and can result in the formation of thrombi which may be life threatening. To address this serious problem various devices have been developed which generally comprise a cuff or sleeve which is wrapped around a patients limb, especially the legs. The cuff is inflatable and air is delivered to and from the cuff to apply pressure to the patient's limbs and thereby improve the blood flow. Such cuff or sleeve devices have proven to be effective in use, however, the air delivery systems that are generally used are not user friendly and, in some cases, are not particularly effective in controlling the flow of air.

There is therefore a need for an improved pneumatic system which will overcome at least some of these difficulties.

Statements of Invention According to the invention there is provided a pneumatic system for delivery of a controlled air supply to an inflatable cuff for applying pressure to a patients limb, the pneumatic system comprising:-

a rotary vane pump having a pump air inlet and a pump air outlet; a solenoid valve having a valve inlet connected to the pump air outlet and a valve outlet; an air reservoir having a reservoir inlet connected to the valve outlet and a reservoir outlet for connection to an inflatable cuff; a pressure transducer for sensing the pressure downstream of the air reservoir and providing a control signal; and control means for controlling the operation of the rotary pump and the solenoid valve in response to the pressure detected by the pressure transducer.

In one embodiment of the invention the system includes an inlet filter having a filter air inlet and a filter air outlet connected to the air inlet of the pump. Preferably the filter air inlet also provides an outlet for exhaust of air from the system.

In a particularly preferred embodiment of the invention the solenoid valve is a normally open valve.

In a preferred embodiment of the invention the ratio of a pressure output of the pump to a target pressure for inflation of the cuff is from 2:1 to 4:1, ideally about 3:1.

In one embodiment of the invention a the control means includes a user interface, the interface having output means and input means for user inputs to the control means.

In a particularly preferred embodiment of the invention the input means is live for a set-up period after a power supply to the control means is activated. Ideally, the set-up period is less than 60 seconds and may, for example, be about 20 seconds.

In one embodiment of the invention the control means includes means for closing the valve in response to a pre-set target pressure detected by the pressure transducer. Preferably the control means includes means for stopping the pump in response to a pre-set target pressure detected by the pressure transducer. Ideally, the control means includes means for opening the valve a pre-set time after the target pressure has been reached.

The pneumatic system preferably includes a portable housing for the system. The housing preferably has an outlet port bulkhead. Usually, the outlet port bulkhead includes at least two outlets, one associated with each of two inflatable cuffs.

The housing also includes a power supply port for connection to a power supply. In a particularly preferred embodiment the housing includes a handle. Preferably the housing includes means for mounting the housing on an intravenous line support device. Ideally the housing has a handle and the means for mounting the housing on an intravenous line support device comprises a groove in an underside of the handle.

In one embodiment of the invention the housing includes hook means for mounting the housing on a bed frame or the like.

Ideally the hook means is movable from a recessed position against the housing to a support position extending from the housing. Preferably the housing has groove means to accommodate the hook means in the recessed position.

The system may also include at least one inflatable cuff for applying pressure to a patient's limb.

Brief Description of the Drawings The invention will be more clearly understood from the following description thereof given by way of example only with reference to the accompanying drawings, in which:- Fig. 1 is a block diagram of a pneumatic system according to the invention; Fig. 2 is a graph of a pressure characteristic-time generated by the pneumatic system of Fig. 1; Fig. 3 is a plan view of a back part of an open housing for the pneumatic system of Fig. 1; Fig. 4 is a perspective view of the back part of the open housing of Fig. 3 with some components removed; Fig. 5 is a plan view of the rear of the back part of the housing; Fig. 6 is a perspective view of a front part of the open housing; Fig. 7 is a plan view of the front part of the open housing; and

Fig. 8 is a perspective view of a bulkhead forming part of the housing. Detailed Description Referring to the drawings there is illustrated a pneumatic system for delivery of a controlled air supply to inflatable cuffs, 1, 2 for applying pressure to a patients limb to improve the blood circulation.

The system is used in providing intermittent pneumatic compression, especially of a patients legs, to prevent venous stasis and postoperative deep venous thrombosis. Such a therapy regime is described for example by Nicolaides, Fernandes a Fernandes and Pollock in Surgery 87(1) pages 69 to 76, January 1980.

The pneumatic system comprises an inlet filter 5, a rotary vane pump 6, a solenoid valve 7, an air reservoir 8, a pressure transducer 9 and control means 10 for controlling the operation of the pump 6 and the solenoid valve 7 in response to the pressure detected by the pressure transducer 9.

The inlet filter 5 has a filter air inlet 10 and a filter air outlet 11 connected to a pump air inlet 12 of the rotary vane pump 6. A pump air outlet 13 is connected to a valve air inlet 14 of the solenoid valve 7 and a valve air outlet 15 is connected to an inlet 16 of the reservoir 8. An outlet 17 from the reservoir 8 is connected to a connector 18 and then to spigots 19 of a manifold or bulkhead 20 (Fig. 8). Sockets 21 in the bulkhead 20 are connected by air lines to the cuffs 1, 2. The bulkhead 20 also has a power supply socket 25 for connection to a mains power supply which drives the control means 10.

The rotary vane pump 6 has a pressure output of about 180 mm Hg and the target inflation pressure is usually 60mm Hg. Thus the ratio of the pressure output of the pump 6 to the target pressure is about 3:1. The rotary vane pump 6 is relatively small in size and is symmetrical and provides a relatively smooth output flow which passes through the normally open solenoid valve 7. The air flow from the valve 7 is damped by delivering the air into the reservoir 8 before being sampled by the pressure transducer 9. In this way, an accurate and repeatable pressure is read by the transducer 9 which therefore provides an accurate and repeatable signal to the control means 10. The control means 10 is an onboard microprocessor which controls the operation of the rotary vane pump 6 and the solenoid valve 7 to produce a smooth pressure characteristic over a pre-set time cycle as illustrated in Fig. 2. The upper target sleeve pressure is usually 60 mm Hg.

The control means 10 includes a user interface having an output means 30 such as an LED display and an input means 31 such as input keys for user inputs. The input means 31 is live only for a set up period of less than 60 seconds, usually about 20 seconds after a power supply to the control means 10 is activated. Thus, there is a short time period in which an operator can reset operating parameters such as target sleeve pressure. The reset is then disabled to prevent unauthorised adjustment in use. The control means 10 includes means for closing the solenoid valve 7 in response to a pre-set target pressure, means for stopping the pump 6 in response to the pre-set pressure and means for opening the valve 7 a pre-set time after the target pressure has been reached.

In use, in a rest mode the solenoid valve 7 is open and the rotary vane pump 6 is static. Under control of the microprocessor the rotary vane pump 6 is started and, with the valve 7 still open, the pressure transducer 9 reads the manifold pressure. After a pre-set target pressure has been reached, as detected by the transducer 9. The pump 6 is then stopped and the valve 7 is closed and held

closed for a period of time such that the total time that the target pressure is maintained is twelve seconds. The valve 7 is then opened, and, with the pump 6 stopped, air is exhausted back through the system to exit via the filter inlet 10. In this way the system and especially the filter r5 is cleared by the reverse flow of air. After a pre-set rest period of 48 seconds the cycle is repeated.

The control means 10 provides an audio and/or visual alarm output in the event of error conditions arising such as the rate of pressure rise being higher than expected, a high pressure or a low pressure being detected by the transducer 9 at an incorrect point in the cycle.

Thus, the pneumatic control system provides a closed control system which allows a set point to be accurately set and maintained over a long operation time regardless of any changes in the mechanical characteristics of the components. This represents a considerable advantage over conventional systems for operating such inflatable cuffs or sleeves.

The pneumatic system is contained in a relatively small sized housing of dimensions 190mm x 135mm x 65 mm approx with a handle extension of about 40mm. The housing has a rear part 50 to which the various pneumatic components are mounted and a front part 51 containing the microprocessor, user interface and alarm outputs. The bulkhead 20 is retained between the rear part 50 and front part 51, on assembly.

The front housing part 51 has a handle extension 52 with a groove 53 in the underside thereof for hanging the housing on an intravenous line support device. The housing also includes means for mounting the housing on a bed frame or the like. The mounting means comprises a pair of arms 55 normally housed in recesses in the rear wall of the rear housing part 50. The arms 55 are mounted

by clips 56 for pivoting outwardly of the recesses and the arms 55 have hook extension 57 for mounting on a bed frame or the like when the arms 55 are pivoted outwardly.

The invention provides a highly efficient system for controlling the operation of pressure applying cuffs.

The invention is not limited to the embodiments hereinbefore described which may be varied in detail.

Claims

Claims 1. A pneumatic system for delivery of a controlled air supply to an inflatable cuff for applying pressure to a patients limb, the pneumatic system comprising:- a rotary vane pump having a pump air inlet and a pump air outlet; a solenoid valve having a valve inlet connected to the pump air outlet and a valve outlet; an air reservoir having a reservoir inlet connected to the valve outlet and a reservoir outlet for connection to an inflatable cuff; a pressure transducer for sensing the pressure downstream of the air reservoir and providing a control signal; and control means for controlling the operation of the rotary pump and the solenoid valve in response to the pressure detected by the pressure transducer.
2. A system as claimed in claim 1 including an inlet filter having a filter air inlet and a filter air outlet connected to the air inlet of the pump.
3. A system as claimed in claim 2 wherein the filter air inlet also provides an outlet for exhaust of air from the system.
4. A system as claimed in any preceding claim wherein the solenoid valve is a normally open valve.

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5. A system as claimed in any preceding claim wherein the ratio of a pressure output of the pump to a target pressure for inflation of the cuff is from 2:1 to 4:1.
6. A system as claimed in claim 5 wherein the ratio is approximately about 3:1.
7. A system as claimed in any preceding claim wherein the control means includes a user interface, the interface having output means and input means for user inputs to the control means.
8. A system as claimed in claim 7 wherein the input means is live for a setup period after a power supply to the control means is activated.
9. A system as claimed in claim 8 wherein the set-up period is less than 60 seconds.
10. A system as claimed in any preceding claim wherein the control means includes means for closing the valve in response to a pre-set target pressure detected by the pressure transducer.
11. A system as claimed in any preceding claim wherein the control means includes means for stopping the pump in response to a pre-set target pressure detected by the pressure transducer.
12. A system as claimed in claim 10 or 11 wherein the control means includes means for opening the valve a pre-set time after the target pressure has been reached.

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13. A system as claimed in any preceding claim including a housing for the system.
14. A system as claimed in claim 13 wherein the housing has an outlet port bulkhead.
15. A system as claimed in claim 14 wherein the outlet port bulkhead includes at least two outlets, one associated with each of two inflatable cuffs.
16. A system as claimed in any of claims 13 to 15 wherein the housing includes a power supply port for connection to a power supply.
17. A system as claimed in any of claims 13 to 16 wherein the housing includes a handle.
18. A system as claimed in any of claims 13 to 17 wherein the housing includes means for mounting the housing on an intravenous line support device.
19. A system as claimed in claim 18 wherein the housing has a handle and the means for mounting the housing on an intravenous line support device comprises a groove in an underside of the handle.
20. A system as claimed in any of claims 13 to 19 wherein the housing includes hook means for mounting the housing on a bed frame or the like.
21. A system as claimed in claim 20 wherein the hook means is movable from a recessed position against the housing to a support position extending from the housing.

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22. A system as claimed in claim 21 wherein the housing has groove means to accommodate the hook means in the recessed position.
23. A system as claimed in any preceding claim including at least one inflatable cuff for applying pressure to a patients limb.
24. A system substantially as hereinbefore described with reference to the accompanying drawings.