ACID-BASE REGULATION AFTER MAXIMAL EXERCISE TESTING IN LATE-GESTATION

This study employed Stewart's physicochemical approach to quantify the effects of pregnancy and strenuous exercise on the independent determ inants of plasma H+ concentration ([H+]). Subjects were nine physicall y active pregnant women [mean gestational age = 33 +/- 1 (SE) wk] and 14 age-matched nonpregnant controls. Venous blood samples and respirat ory data were obtained at rest and during 15 min of recovery from a ma ximal cycle ergometer test that involved 20 W/min increases in work ra te to exhaustion. Mean values for [H+], PCO2, and total protein increa sed, whereas those for bicarbonate concentration ([HCO3-]) and the str ong ion difference ([SID]) decreased in the transition from rest to ma ximal exercise within both groups. At rest and throughout postexercise recovery, the pregnant group exhibited significantly lower mean value s for PCO2, [HCO3-], and total protein, whereas [SID] was significantl y lower at rest and early recovery from exercise. [H+] was also lower at all sampling times in the pregnant group, but this effect was signi ficant only at rest. Our results support the hypothesis that reduced P -CO2 and weak acid concentration are important mechanisms to regulate plasma [H+] and to maintain a less acidic plasma environment at rest a nd after exercise in late gestation compared with the nonpregnant stat e. These effects are established in the resting state and appear to be maintained after maximal exertion.