EFFECT OF ALTERED INTRATHORACIC PRESSURE ON RENAL HEMODYNAMICS, ELECTROLYTE EXCRETION AND WATER CLEARANCE*

Abstract

Continuous positive pressure breathing has been associated with a decrease in rate of urine flow and continuous negative pressure breathing with an increase in urine excretion. This study, done on healthy adults, was designed to evaluate the role of hemodynamic and humoral factors in the production of changes in rate of urine flow in response to pressure breathing. During water diuresis, continuous positive pressure breathing was associated with an antidiuresis, decreased free water clearance, decreased renal plasma flow and glomerular filtration rate, and increased osmolar urine to plasma ratio. During alcohol-water diuresis and mannitol osmotic diuresis, positive pressure breathing did not produce an antidiuresis. Negative pressure breathing produced a marked diuresis, increase in free water clearance, insignificant change in renal plasma flow and glomerular filtration rate, and a decrease in osmolar urine to plasma ratio. This response was blocked by administration of vasopressin and did not occur during intravenous infusion of hypertonic saline. It is believed that alteration in antidiuretic hormone activity is the primary mechanism by which continuous pressure breathing changes the rate of urine flow. It is speculated that this response is initiated by volume receptor areas in the vascular system within the thorax.