ANTITHROMBOTIC DEVICE

Abstract: A prophylaxis for venous thrombosis in the leg of a bedridden person, which comprises attachment of a device having two pivoting body portions (3 and 4) to the patient's foot (11) and lower leg (10), respectively, there being power driving means (14) interconnecting the body portions for pivoting thereof to effect forced dorsiflexion and passive release of the patient's ankle to promote venus blood flow through intracompartmental pressure in the patient's leg.

Description: "ANTITHROMBOTIC DEVICE" This invention relates to the prophylaxis of venous thrombosis * " by mechanical means. BACKGROUND ART The prevention of venous thrombosis in bedridden persons is a significant problem. For example, in hospitals it has been found that some surgical procedures, including orthopaedic surgery on the lower limbs, are associated with an exceptionally high risk of postoperative venous thromboembolism, i.e. venous thrombosis or pulmonary embolism, or sometimes both. Several preventive measures are presently used including drugs or physical methods. In respect of the latter a relatively new external pneumatic-compression device has been used which comprises segments in the form of cuffs for encircling the calves and thighs of a patient. In one form the calf segment contains four circumferential chambers and the thigh segment two. By the application of pneumatic pressure the chambers of the two segments inflate sequentially commencing at the ankle thus promoting blood flow through the deep venous system. These cuffs have been tested with continuous use in post-operative patients and have reduced the incidence of deep-vein thrombosis. This method has been found to have both a physical and a pharmacological effect without risk of bleeding and virtually free of side-effects. However, whereas pneumatic pressure is often supplied to operating theatres and intensive care wards, very seldom is it made available within general wards of a hospital, and, of course, is not available in the home. It is the main object of this invention to provide a mechanical antithro botic device which is effective and operative from a readily available power source. DISCLOSURE OF INVENTION In accordance with this invention there is provided an antithrombotic device for attachment to a leg of a patient to induce repetitive compression of the calf muscle to aid deep-vein circulation, said device comprising a first body member, means for attaching said body member to the patient's lower leg, a second body member pivotally connected with the first body member for engagement with the patient's foot, a driving connection between said first and second body members for effecting pivoting movement therebetween on the axis of the patient's ankle, and power means carried by said first body member for actuating said driving connection. The effectiveness of the invention flows from the realisation that deep posterior i-vtracompartmeαtal-pressures within the calf muscle between full passive dorsiflexion and full passive plantar flexion of the ankle occur on an average within the ratio of about 9:1, and that such changing pressures with repeated ankle movement effect adequate deep-vein circulation for thrombotic prophylaxis. Therefore, also according to the invention there is provided a method for preventing the Incidence of venous thrombosis in the leg of a person at risk, comprising attaching to the foot and lower leg of the person a device having two articulated body members with pivotal driving means therebetween, and forcibly effecting reciprocating movement of the patient's foot between plantar flexion and dors.fle ion of the patient's ankle to. achieve fluctuating intracompartmental pressure in the patient's leg thereby promoting blood flow therein. By way of preferred embodiment the invention will be described in more detail with reference to the accompanying drawings, in which: BRIEF DESCRIPTION OF DRAWINGS Fig. 1 shows in perspective a device of the invention attached to the leg of a user; and Fig. 2 is a cross-sectional view on the line II—II of Fig.l; Fig.3 i a vlew ^ of the internal drivrng "means of the .device; and, Fig. 4 is a block diagrammatic representation of the electronic control means. BEST MODE OF CARRYING OUT THE INVENTION With reference to Fig. 1 and 2 of the drawings, the device of _the invention, .consists of an tipper body portion 3 connected to a lower body portion 4 by confronting pairs of flanges 5 and 6 integral with respective ones of the body portions 3 and 4, with each pair being interconnected at their distal ends 7 and 8 by a pivot pin 9. Both portions 3 and 4 are channelled shells of thermoplastic material, contoured to enclose at least -part"of the user's calf TO and foot 11 (Fig. 1). Preferably, resiliant padding (not shown) is provided in the upper body portion 3. The confronting brackets 5 extend laterally from the bottom 17 of the upper body portion 3, while the confronting brackets " 6" re -u stan ing rom the lower body portion ' 4. The position and the length of the brackets 5 and 6 is such that each pivot pin 9 corresponds to approximately the centre of the user's ankle. Attachment strap 12 secures the upper body portion 3 firmly to the user's calf 10 while straps 13 secure the lower body portion 4 to the foot 11.. The straps 12 and 13 may include fastening means of the Velcro type. It will be appreciated, therefore, that movement of the foot 11 is permitted between the passive dorsiflexion and plantar flexion positions by pivoting of the lower body portion 4 about the pivot pins 9. Consequentially, the foot 11 can be moved by an outside agency between these positions, and this is attained by the provision of a driving connection 14 ( Fig. 2) fixed to the heel 15 of the lower body portion 4 and activated by driving means 16 carried within the housing of the upper body portion 3. The driving means (as shown in Fig. 3) 16 may include an electric motor 17 connected through a rotatable driving shaft 18 to the driving connection 14. The driving shaft 18 is rotatably journalled in a bearing 19 at its distal end 20 and is provided with a threaded intermediate portion 21. An internally threaded follower 22 is threadibly engaged upon the threaded portion 21 of the shaft 18 and is held against rotation thereon by the driving connection 14 so as to move axial ly along the shaft 18 with rotation thereof. The direction of axial movement of the follower 22 will depend upon the direction of rotation of the shaft 18. The driving connection 14 preferably consists of a metal plate 24 displaceable along a narrow slot 25 in the upper body portion 3, provided with a yoke 23 at one end which encloses the follower 22, and a securing bracket 26 at its other end for attachment to the heel portion 15 of the lower body portion 4 of the device. The follower 22 is connected to the yoke 23 by pins 27 displaceable along slots 28 in the yoke 23 to permit a degree of linear movement of the driving connection 14 with respect to the follower 22 which is necessary due to the pivoting action of the two body portions 3 and 4. The electric motor 17 is reversible under the control of electronic means, to be described, and the limits of pivoting movement of the body portion 4 with respect of body portion 3 may be determined by a set of micro switches 29 responding to movement of a cam 30 carried by the yoke 23. The driving shaft 18 is in two parts interconnected by a shock absorbing pad 31 to minimize shocks to the motor 17 imposed by muscular reaction of the patient. Electronic control means is provided upon a PCB 32 positioned within the upper body portion 3 of the device. Thus, when the motor 17 is energised reciprocation of the -driving connection 14 is eff-ected for repeated forced dorsiflexion of the user's foot 11. The device may be utilised in all areas of a hospital, and even for home care, as readily available electrical mains power will be used for actuation of the device. As a result deep-vein circulation can be maintained within the patient's legs to avoid development of venous thrombi. In at least some instances separate ones of the present devices will be attached to both legs of the patient. It is envisaged that mutual timing of their operations will be required for alternate, simultaneous or other related operation. Preferably, also the operation of each device will incorporate a pause at a rest position and controlled timing, speed and degree of pivoting action between the body portions 3 and 4. " Electronic means for control of the electric motor 17 is shown by block diagram in Fig. 4. The circuit is based upon a dedicated microprocessor device which is used to allow flexibility of operation to suit most patients. The circuit consists of a motor drive circuit 33 and positional feedback sensor 34 coupled to a microprocessor 35. The sensor 34 allows detection of the current position of the patient's foot Tl relative to a centre or 'rest' position. This enables positioning of the device prior to attachment to thepatient and also synchronization wth a mani ulator (not 'shown) coupled to the other foot where applicable. The programming switches 36 allow variating in stroke length and speed for both directions of movement from the rest position. This would normally be preset to a standard level but allows alteration to suit individual patient needs and comfort. In most post operative applications, both feet of the patient would need to have a device attached. In order to avoid discomfort to the patient, synchronization is used between the two devices. The devices may be operated in identical motion, i.e. both feet moving in the same direction at the same speed, or the motion for each foot may be set to Opposing phase such hat'one- OQt will be travelling up while the other is travelling in a downward direction. This control is derived from the synchronisation interface 38. The device requires an external power supply 37 to allow for proper isolation and statutory approvals. The cycle of.foot movement preferabl occupies a time span of one minute, i.e. 30 seconds up and 30 seconds down, with a pause in a neutral, or rest, position of 1 minute. Detection is provided to determine stalling and other malfunctions of the motor 17. Control by the patient of the movement is also provided which will give a short term rest on demand where the patient is experiencing discomfort. This control can be limited or inhibited by the nursing staff where it is deemed necessary. A control switch 39 may be provided on the end of the upper body portion 3 but preferably is extended by cable for ready accessibility by the patient. The control circuit utilizes low power CMOS components wherever possible for minimum power and resistance to external interference. Whereas a preferred embodiment has been described in the foregoing passages it should be understood that other forms, modifications and refinements are feasible within the scope of this invention.

Claims: CLAIMS "ANTITHROMBOTIC DEVICE" !_. An Lntithπ_mbotic device for attachment to a leg of a patient to induce repetitive compression of the calf muscle to aid deep-vein circulation, said device comprising a first body member, means for attaching said body member to the patient's lower- leg, a second body member pivotally connected with the first body member for engagement with the patient's foot, a driving connection between said first and second body members for effecting pivoting movement therebetween on the axis of the patient's ankle, and power means carried by said first body member for actuating said driving connecting. 2. An antithrombotic device according to claim 1, wherein said second body member has a heel portion for partly enclosing the heel of the patient's foot, and said driving connection is connected to said heel portion. 3. An antithrombotic device according to claim 1 or 2, wherein said power means is a reversible electric motor actuating said driving connection via rotation of a driving shaft. 4. An antithromboti device according to claim 3, wherein said driving shaft has a threaded portion, and a threaded follower engaged with said portion carries said driving connection to impart linear movement thereto with rotation of sai driving shaft. 5. An antithrombotic device according to any one of the preceding claims, comprising also an electronic circuit controlling application of power to said power means and including means for selecting the pattern of said pivoting movement of said body members. 6. An antithrombotic device according to claim 5, wherein said electronic circuit also includes means fo*- effecting a predetermined synchronism of said pivoting movement with respect to the pivoting movement of another of said devices when said devices are attached to respective ones of the patient's legs. 7. A method for preventing the incidence of venous thrombosis in the leg of a person at risk, comprising attaching to -the foot and lower leg of the person a device having two articulated body members with pivotal driving means therebetween, and forcibly effecting reciprocating movement of the patient's foot between plantar flexion and dorsfflejcion of the patient's ankle to achieve fluctuating intracompartmental pressure in the patient's leg thereby promoting blood flow therein. 8. The method of claim 7, wherein said reciprocating movement is interrupted for a rest pause after each cycle of movement of the patient's foot including forced dorsiflexion and plantar flexion of the patient's ankle. 9. The method of claim 7 or 8, wherein said reciprocating movement is controlled in a predetermined synchronism with the reciprocating movement of the other foot of the patient to which has been attached another device having two articulated body members with pivotal driving means therebetween. 10. The method of claim 8, wherein said cycle of movement of the patient's foot occupies a time span of one minute and said pause is of one minute duration.

Inventors: HOLT BRIAN WELLESLEY, HOLT, BRIAN, WELLESLEY
Applicants: BRIJA PTY LTD, BRIJA PTY. LIMITED
Application year: 1987
Main classification: A61H1
IPC codes: A61H1