Renal response to short-term hypocapnia in man

Abstract

This study examines the renal response to moderate hyperventilation in healthy man. Eight men hyperventilated for 26 hr (PaCO2 approximately 30 to 32 mm Hg) in normoxia (barometric pressure, PB approximately 740 mm Hg) and hypobaric hypoxia (PB approximately530 mm Hg). Anaerobic samples of arterial blood and urine were studied at two-hour intervals. Plasma [HCO3-] fell with time during sustained hypocapnia and after 26 hr was reduced 2.5 mEq/liter, with plasma pH compensated approximately 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 (UVTA + UVNH4+) 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. We conclude that renal mechanisms contribute significantly and relatively quickly to plasma pH compensation during the early phase of adaptation to hypocapnia in man.

Normal pregnancy: A model of sustained respiratory alkalosis

“…under controlled conditions was 26 hours [12]. Blood lactic acid level in the normal pregnant However, such significance bands were generated women was 1.316 ± 0.66 mmol/L.…”

Osmoregulation during Pregnancy in the Rat

“…However, the decrement in Posm at high altitudes rarely exceeds 2-3 mosmol (30), and the decrease observed during pregnancy is much greater. Furthermore, although chronic hypoxemic or normoxemic hyperventilation of volunteers results in reduction of their Pco2 and PHCO3 to values similar to those measured in gravidas, PNa (thus presumably Posm) remains unaltered (31).…”

Acid-Base Homeostasis

“…These changes within the kidney take several days for completion and in general, do not return systemic pH completely back to normal. With chronic hypocapnia and the resultant increase in systemic pH, decreases in reabsorption of HCO 3 2 in the proximal tubule and distal tubule H 1 secretion result in a fall in plasma HCO 3 2 ; these changes can begin within a very few hours (81). With chronic hypercapnia, increased proximal and distal H 1 secretion results in increased HCO 3 2 reabsorption and increased production of new HCO 3 2 , resulting in a higher level of plasma HCO 3 2 ; most of the cell and molecular mechanisms parallel the response to metabolic acid loads, where these have been studied (82).…”