The role of intraabdominal pressure in venous blood drainage from the prostate into the vertebral vein system.

We investigated venous blood drainage from the prostate into the vertebral vein system by cineangiography in five mongrel dogs and measured intraabdominal pressure and venous blood pressure in the dog or human to study the role of intraabdominal pressure in the drainage. The averages of intraabdominal pressure and caudal vena caval pressure in the dog were 32.2 +/- 3.0 and 12.8 +/- 1.3 mmHg, respectively, in the supine position, and 39.2 +/- 3.0 and 23.8 +/- 4.0 mmHg, respectively, in the head-up tilt position, when the radiopaque medium injected into the dorsal penile vein appeared in the vertebral vein system. Intraabdominal pressure in the head-up tilt position was significantly higher than that in the supine position when the venous drainage into the vertebral veins happened. In eight continuous ambulatory peritoneal dialysis patients, intraabdominal pressure showed 8.1 +/- 2.4 mmHg in the supine position, 24.6 +/- 4.3 mmHg in the sitting position, and 30.4 +/- 4.9 mmHg in the standing position at rest. During voluntary contraction of the abdominal muscles, the pressure was increased up to 50.6 +/- 21.6 mmHg in the supine position, 69.3 +/- 19.8 mmHg in the sitting position, and 73.8 +/- 19.8 mmHg in the standing position. These pressure values in the human were significantly higher than those observed at the time when the radiopaque medium appeared in the vertebral veins in both supine and head-up tilt positions in the canine. These results suggest that the increase of intraabdominal pressure causes inflow of prostatic venous blood into the vertebral veins via the inferior vena cava, common iliac vein, or internal iliac vein.