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THAT the venous pressure in the lower limbs is raised in late pregnancy has been shown by many workers. Two main theories have been advanced to explain this; first, simple mechanical obstruction to the venous return by the gravid uterus (McLennan, 1943) and, second, increased blood flow resulting from the placenta in situ (Burwell, 193 8).Most of these studies were carried out using the femoral venous pressure. This indicates changes in pressure occurring below the uterus, but does not throw light upon the exact site of venous obstruction (if any). Moreover, the great majority of investigations used water manometry. This method, though simple, cannot show rapid pressure changes that may occur and also requires the use of large bore needles. Modern techniques using pressure transducers are extremely sensitive to rapid changes in pressure, require only very fine catheters and allow continuous recording over long periods. The catheters can be inserted percutaneously into the femoral vein and advanced into the inferior vena cava, thus indicating the pressure at various levels up to the right atrium.In carrying out our investigations we were immediately impressed by the fact that the pressure within the lower vena cava in advanced pregnancy was raised in the supine position to a level comparable with that obtained by complete vena caval occlusion in non-pregnant women (Scott, 1963). Moreover, the pressure was raised to some extent throughout the length of the inferior vena cava, only becoming normal above the diaphragm. These results indicated that the venous return from the abdomen and lower limbs was of a very different pattern from that of the non-pregnant state.

Five hundred and sixty-six Irish wolfhound puppies aged six to 15 weeks were tested for congenital portosystemic shunts by the dynamic bile acid method. Plasma ammonia concentration was also measured in 165 of the puppies both fasting and postprandially. Nineteen puppies (3.4 per cent), nine males and 10 females, had portosystemic shunts. Smaller litters appeared to be more likely to contain affected puppies. The postprandial bile acid concentration was a reliable predictor of the presence of a shunt, with the highest concentration in a normal puppy being 38 mumol/litre and the lowest in an affected puppy being 43 mumol/litre. In contrast, fasting bile acid concentrations were normal in the majority of the affected puppies. There was considerable overlap in fasting plasma ammonia concentrations between normal and affected puppies (26 puppies, 15.8 per cent of those tested). Postprandial ammonia concentration appeared to give better separation between the two groups, apart from two individuals which produced bizarre results. It was concluded that the postprandial or dynamic bile acid test is an appropriate test for the mass screening of Irish wolfhound puppies for portosystemic shunts, and guidelines are proposed for the interpretation and follow-up of the test.

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