Pressure variations in small veins in the hindleg of the dog.

DURING measurements of pressure in the small veins of a dog's hindleg, it was observed that fluctuations in pressure, associated with respiration, varied considerably from animal to animal. In some instances, venous pressure fell during the inspiratory phase; in other instances, venous pressure rose. In addition, spontaneous pressure changes, seemingly independent of respiratory movements, were occasionally seen. It seemed possible that some factor, or factors, other than thoracic pressure changes during respiration might be involved in varying small vein pressure. It has been stated that respiratory waves seen in small veins were probably transmitted through the arterial side and that they followed in time the respiratory waves seen in large systemic arteries. In a more recent paper, Irisawa and Rushmer recorded venous and lymphatic pressures in the dog's leg and noted that oscillatory changes in these pressures were associated with respiration and that an increase in pressure in these vessels coincided with expiration. To clarify the origin of pressure variations, as seen in the small cutaneous veins in the hindleg of the dog, simultaneous recordings were made of small vein pressure, direction of intra-abdominal pressure changes, small and large artery pressure, and respiratory movements. Methods Mongrel dogs were anesthetized with sodium pentobarbital (33 nig./Kg.), injected intravenously and were placed in a supine position. Polyethylene tubing, with an outside diameter