Reduction of free water clearance with cephalic venous hypertension

A laboratory model was developed in the dog to quantitate the effects of cerebral venous hypertension on inappropriate antidiuretic hormone (ADH) secretion. When cerebral venous pressure was abruptly increased during continuous water loading, there was a sharp rise in urine osmolality within 30 minutes. Urine osmolality continued to increase during, and ten minutes after, the period of hypertension. On lowering cerebral venous pressure, the osmolality returned to baseline within 60 minutes. The effects could be extended for at least three hours and presumably longer. A 50% response threshold for this ADH effect occurred at a cerebral venous pressure between 18 and 19 cm of water. The effect correlated with plasma ADH levels. The study paralled documented clinical observations. The results are discussed in light of the recognition and management of surgical states where increased cerebral venous pressure might produce a severe antidiuretic effect.