Hemodynamic,Fluid,and Electrolyte Changes during Sodium Depletion in Conscious Dogs

Abstract

Summary

Hemodynamic, fluid and electrolyte changes were studied during sodium depletion and repletion in six conscious dogs. Blood pressure (BP), plasma renin activity (PRA), heart rate (HR), cardiac output (CO), stroke volume (SV), and plasma volume (PV) were determined on 3 separate days in sodium replete conscious animals, similarly during sodium depletion, and again after sodium repletion. During sodium depletion, HR increased from 73 to 91 beats/min (P < 0.01). CO fell from 2.32 liters/min to 1.87 liters/min (P < 0.01). SV decreased from 32.6 ml to 21.7 ml (P < 0.01). Peripheral resistance (PR) increased from 41.5 to 49.2 mm Hg (liters/min)⁻¹ (P < 0.01). BP was unchanged. PRA increased from 0.83 to 7.51 ng angiotensin I/ml/hr (P < 0.01). During the 8 days of sodium depletion, water intake was elevated on 6 days, urine volume was elevated on 5 days, and water balance was positive on 3 days. With sodium and volume repletion, all functions returned to control levels. The results demonstrate that sodium depletion produced significant decreases in CO and PV with BP maintained by increased PR and HR. An important incidental finding was the failure of whole body autoregulation to occur during the sodium and volume repletion and volume expansion of the recovery period.