Cardiovascular and renal responses to acute cold exposure in water-loaded man

Changes in oxygen uptake, cardiac output, heart rate, stroke volume, central blood volume, arteriovenous oxygen difference, aortic, pulmonary arterial, and right atrial blood pressure, systemic vascular resistance, hematocrit, circulating plasma volume, urine flow, fractional sodium excretion, and free water clearance were studied in eight healthy volunteers in stable water diuresis, exposed to cold by means of air at +15 degrees C and at a speed of 0.5 m/sec. A decrease in circulating plasma volume and systemic vascular resistance was found during cold stress. Mean aortic blood pressure, sodium excretion, cardiac output, oxygen uptake, arteriovenous oxygen difference, and hematocrit increased. No changes in urine flow or in clearance of free water could be demonstrated. Heart rate, stroke volume, and central blood volume showed significant increases in cold. The results are interpreted to suggest that exposure to cold raises the arterial blood pressure by an increase in cardiac output, thereby increasing capillary hydrostatic pressure in certain vascular areas, including the renal vascular bed. This negatively affects capillary reabsorption processes in the kidney, causing a reduction in tubular sodium reabsorption, thus giving rise to a natriuresis. In other areas it seems to cause a shift of fluid towards the intersitial space.