WO1988005290A1

WO1988005290A1 - Control of blood flow to the liver

Info

Publication number: WO1988005290A1
Application number: PCT/AU1988/000008
Authority: WO
Inventors: Rodney James Lane; Peter Spencer
Original assignee: Vaso Products Australia Pty. Limited
Priority date: 1987-01-16
Filing date: 1988-01-15
Publication date: 1988-07-28

Abstract

A blood flow control system for controlling the flow of blood from the portal vein (13) to the liver (not shown), said blood flow control system comprising a shunt (17) between the portal venous drainage system (13) and the systemic venous system (10), flow control means (21) engaged with shunt (17) and means for actuating (22) the flow control means (21) so as to regulate the flow of blood through the shunt to the systemic venous system (10).

Description

CONTROL OF BLOOD FLOW TO THE LIVER

FIELD OF THE INVENTION

This invention relates to the control of blood flow to the liver. The vessels connected to the liver include the hepatic artery, the portal vein and the hepatic veins. Normal liver tissue derives its blood supply principally from the portal vein but also to a certain extent from the hepatic artery. The hepatic veins convey the blood from the liver. There are three such veins which converge towards the posterior surface of the liver and open into the inferior vena cava. BACKGROUND ART

In some liver disorders, such as those brought about by alcohol, the blood pressure within the liver and the portal vein is excessive. To some extent, this problem can be overcome by inserting a portacaval shunt between the inferior vena cava and the portal vein to lower portal hypertension. However, a difficulty with the insertion of a portacaval shunt is that the diameter of the fistula between the veins (which constitutes the shunt) largely determines the amount of portal vein decompression and the amount of blood diverted from the liver.

If the diameter of the fistula is too large, blood can tend to flow away from the liver (retrograde flow), down the fistula from the portal vein and cause a large increase in toxins in the blood stream resulting in porta systemic (or post-operative) encephalopathy. Also, a decreased flow renders the hepatic cells ischaemic.

One approach to limiting the amount of blood flowing down the fistula to the inferior vena cava is to choose carefully the limit of the diameter of the fistula - see CLINICAL IMPLICATIONS OF PORTAL HEMODYNAMICS AFTER SMALL- DIAMETER PORTACAVAL H GRAFT BY JAMES SARFEH et al SURGERY VOL. 96 No. 2 at page 223. DISCLOSURE OF INVENTION

It is an object of the present invention to provide an improved means of controlling blood flow to the liver which can be used post-operatively to give better control of the amount of blood being diverted from the liver and thereby eliminate occurrence of porta systemic encephalopathy.

According to the invention, there is provided a blood flow control system for controlling the flow of blood from the portal vein to the liver, said system comprising a shunt between the portal venous drainage system and the systemic venous system, flow control means engaged with the shunt and means for actuating the flow control means so as to regulate the flow of blood through the shunt to the systemic venous system.

The term "portal venous drainage system" as used in this specification embraces the portal vein, the splenic vein, the mesenteric vein and any branches or tributaries of the aforementioned veins. Thus, the blood flow control system of the invention could include a portacaval shunt, a mesocaval shunt, a mesorenal shunt or splenorenal shunt. The shunt may be in the form of a graft (fistula) or side-to-side anastomosis. The blood flow rate along the shunt can be infinitely controlled from a maximum when the flow control means does not restrict the diameter of the shunt to zero when the flow control means occludes the shunt.

Preferably, the flow control means consists of a cuff placed around the shunt and the actuating means which is operated transcutaneously inflates the cuff to change the internal cross-sectional area of the shunt to regulate the flow between the portal venous drainage system and the systemic venous system. In one form of the invention, the actuation means is a manually compressible reservoir balloon located beneath the skin but easily operated by externally applied pressure. A release valve which prevents fluid back-flow into the reservoir balloon is located adjacent to the reservoir balloon and is also operated and opened by externally applied pressure.

The reservoir balloon is connected to the cuff around the shunt by a thin tube so that compression of the reservoir balloon causes inflation of the cuff around the shunt thereby occluding or partly occluding the shunt. Activation of the release valve allows immediate reflux of the fluid into the reservoir balloon beneath the skin and deflation of the cuff inserted around the shunt. The fluid is forced back into the reservoir balloon by the blood pressure acting on the cuff through the shunt and due to the suction caused by the elastic recoil force of the compressible reservoir balloon.

The reservoir balloon and its valve may be operated transcutaneously by any convenient means apart from the externally applied manual pressure described above. BRIEF DESCRIPTION OF THE DRAWINGS In order that the invention may be more readily understood and put into practical effect, reference will now be made to the accompanying drawings, in which:-

Fig. 1 is a schematic diagram of the portal venous drainage system and the systemic venous system incorporating four different shunts in accordance with the principles of the invention, Fig. 2 is a schematic view of a blood flow control system according to one embodiment of the invention, Fig. 3 is a perspective view of an implantable device for controlling the flow of blood through one of the shunts shown in Fig. 1, and, Fig. 4 is a cross-sectional view of the implantable device shown in Fig. 3. Referring initially to Fig. 1, the tissue of the liver

11 derives its blood supply principally from the portal vein 13. Blood flow from the liver 11 is through the hepatic veins which converge towards the posterior surface of the liver 11 and open into the inferior vena cava 10. The portal venous drainage system embraces the portal vein 13, the splenic vein 14 and the superior mesenteric vein 15 together with any branches or tributaries of the aforementioned veins. The systemic venous system embraces the inferior vena cava 10 and the renal vein 16 leading to the kidney 12.

The blood flow control system of the invention includes a shunt between the portal venous drainage system and the systemic venous system which permits portal vein decompression and diversion of blood flow from the liver. In Fig. 1, four such shunts are identified: the porta caval shunt 17, the splenorenal shunt 18, the mesorenal shunt 19 and the mesocaval shunt 20. Although shown as grafts or fistulas, the shunts could be formed by side-to-side anastomosis.

The schematic blood flow control system of the embodiment of the invention shown in Fig. 2 includes a porta caval shunt 17 between the portal vein 13 and the inferior vena cava 10. Flow of blood through the shunt 17 is controlled by an inflatable cuff 21 secured around the shunt 17. Inflation of the cuff 21 is effected by squeezing the deformable reservoir 22 to force fluid down the fluid line 23 to the cuff 21. As can be seen in Fig. 3, the cuff 21 consists of an inflatable balloon 24 mounted on a balloon connector 25- having a passageway in communication with the interior of the balloon 24 and the first fluid line 23a. A strap 26 is connected by one end to the balloon connector 25 above the balloon 24 and has an aperture 27 at its other end which is passed over the fluid line 23a and the balloon connector 25 to encircle the inflatable cuff around the shunt 17 (see Fig. 4). A coupling 36 connects fluid line 23a to fluid line 23b connected to the reservoir 22. The reservoir 22 has a valve body 28 which defines a valve chamber as shown in Fig. 4. The valve chamber has an inlet 29 and an outlet 30. Within the valve chamber there is a valve seat 31 having a passageway 32 in communication with the inlet 29. A support member 33 having perforations 34 supports a valve plunger 35 normally biased to close the passageway 32.

When the reservoir 22 is compressed, the pressure of the fluid lifts the plunger 35 away from the passageway 32 and fluid passes through the perforations 34 to inflate the cuff 24. As soon as pressure on the reservoir 22 is released, the plunger 35 closes the passageway 32.

When the cuff 24 is to be deflated, the valve body is squeezed in the direction of arrows A whereupon the valve seat 31 is distorted away from the plunger 35 to allow the fluid to return to the reservoir 22 under the influence of the blood pressure in the shunt 17 acting on the cuff 24 and the suction caused by the elastic recoil of the reservoir 22. The implantable device is made of a bio-compatible material such as Silicone.

Five patients have had devices implanted in combination with a porta-systemic shunt procedure. Table 1 gives an outline of the patients and their treatment.

All patients had one or more documented cases of esophageal variceal hemorrhage prior to operation. Four patients were admitted to hospital with an esophageal variceal bleed which was treated by injection sclerotherapy to stablise them prior to operation during the same hospital admission. One patient was an elective case who had been previously treated by esophageal transection to stop variceal bleeding. Four patients received portacaval shunts and one a mesocaval shunt. Patient 3 died post-operatively of causes unrelated to the device. All other patients underwent doppler ultrasound assessment several months post-operatively to determine the hemodynamic effect of the device on the portal blood flow. Prior to device activation, the open shunt caused retrograde portal flow from the liver to the systemic venous system. In all cases device activation resulted in partial shunt occlusion causing increased shunt flow resistance and prograde portal flow into the liver. Hence, the device significantly effected portal flow as designed. Patient 5 developed an encephalopathic coma after which the device was activated. The patient woke up within 24 hours of device activation suggesting that shunt occlusion aided in encephalopathy control. No other patient has developed clinically significant signs of encephalopathy. These results suggest that the invention will be able to be used to effect significantly the occurrence and degree of shunt induced encephalopathy. Various modifications may be made to the system without departing from the scope and ambit of the invention.

Claims

1. A blood flow control system for controlling the flow of blood from the portal vein to the liver, said blood flow control system comprising a shunt between the portal venous drainage system and the systemic venous system, flow control means engaged with the shunt and means for actuating the flow control means so as to regulate the flow of blood through the shunt to the systemic venous system.

2. A blood flow control system for controlling the flow of blood from the portal venous drainage system to the liver by diverting blood flow to the systemic venous system, said blood flow control system comprising a shunt between the portal venous drainage system and the systemic venous system and blood flow control means engaged with the shunt, said blood flow control means including an inflatable cuff around the shunt adapted to modify the internal cross-sectional area of the shunt and thereby to modify the flow of blood to the shunt, means for inflating the cuff and means for deflating the cuff, said blood flow control means being fully implanted within the body and said inflating means and deflating means being operable by pressure applied through but not piercing the skin.

3. A blood flow control system according to claim 1 or claim 2 wherein the shunt is a portacaval shunt, a mesocaval shunt, or a mesorenal shunt or a splenorenal shunt.

4. A blood flow control system according to any one of the preceding claims wherein the blood flow through the shunt is controlled by the flow control means from a maximum when the flow control means does not restrict the cross-sectional area of the shunt to zero when the flow control means occludes the shunt.

5. A blood flow control system according to any one of the preceding claims wherein the shunt is a graft or a side-to- side anastomosis.

6. A blood flow control system according to claim 1 wherein the flow control means is fully implanted and consists of an inflatable cuff placed around the shunt and the actuation means is a manually deformable reservoir located beneath the skin that is operated by a force applied through but not piercing the skin.

7. A blood flow control system according to claim 6 wherein the reservoir has a release valve which allows flow of fluid from the reservoir to the cuff when the reservoir is deformed, and prevents fluid back flow to the reservoir until it is operated and opened by a force applied through but not piercing the skin.