Renal response to short term hypocapnia in man

Abstract

This study examines the renal response to moderate hyperventilation in healthy man. 8 men hyperventilated for 26 hr (PaCO2 30 to 32 mm Hg) in normoxia (barometric pressure, P(B) 740 mm Hg) and hypobaric hypoxia (P(B) 530 mm Hg). Anaerobic samples of arterial blood and urine were studied at 2 hr intervals. Plasma [HCO3-] fell with time during sustained hypocapnia and after 26 hr was reduced 2.5 mEq/liter, with plasma pH compensated 60%. Statistically, significant changes in renal H+ handling were observed within the initial 2 hr of hyperventilation and were evident over the first 12 hr. Over 26 hr, mean total HCO3- excretion in hypocapnia was 10.2 mEq above control and mean total acid excretion (UV(TA) + UV(NH4+)) was 17.5 mEq below control. An increased urinary excretion of cations, especially sodium, accompanied the decrease in acid excretion. Plasma lactic acid accumulation was negligible. The authors conclude that renal mechanisms contribute significantly and relatively quickly to plasma pH compensation during the early phase of adaptation to hypocapnia in man.