title: Plasma acid-base regulation above and below ventilatory threshold in late gestation.
abstract: Stewart's physicochemical approach was used to study the effects of pregnancy on acid-base regulation in arterialized blood. Responses of 15 healthy pregnant women (PG; gestational age, 37.1 +/- 0.2 wk) were compared with those of 15 nonpregnant controls (CG) at rest and during cycling at 70 and 110% of the ventilatory threshold (T(vent)). Hydrogen ion concentration ([H(+)]) was lower in the PG vs. CG at rest and during exercise (P < 0.05 at rest and 70% T(vent)). Exercise-induced changes in [H(+)] were similar between groups. Lower resting [H(+)] values in the PG vs. CG resulted from lower values for arterialized PCO(2) (Pa(CO(2))) and total weak acid ([A](tot)), which were partly offset by a lower strong-ion difference ([SID]). Reductions in [A](tot) and [SID] at rest were primarily the result of reductions in albumin [Alb] and sodium [Na(+)], respectively. In the transition from rest to 70% T(vent), small increases in Pa(CO(2)) and [A](tot) contributed to moderate increases in [H(+)] in both groups, however [SID] increased in the PG and decreased in the CG (P < 0.05 between groups). In the transition from rest to 110% T(vent), decreases in [SID] made a significantly greater contribution to changes in [H(+)] in the CG vs. PG. Exercise-induced increases in [H(+)] are similar in the pregnant vs. nonpregnant state, but there is a reduced contribution of [SID] both above and below T(vent) during pregnancy.
authors.affiliation: School of Physical and Health Education and Department of Physiology, Queen's University, Kingston, Ontario, Canada K7L 3N6.
authors.forename: A P
authors.initials: AP
authors.lastname: Heenan
authors.forename: L A
authors.initials: LA
authors.lastname: Wolfe
mesh_terms: D000136:Acid-Base Equilibrium / Q000502:physiology*; D000328:Adult; D001642:Bicycling / Q000502:physiology; D001798:Blood Proteins / Q000032:analysis; D015992:Body Mass Index; D002245:Carbon Dioxide / Q000097:blood; D015444:Exercise / Q000502:physiology*; D005260:Female; D006339:Heart Rate; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008597:Menstrual Cycle; D010100:Oxygen / Q000097:blood; D011247:Pregnancy / Q000097:blood* / Q000502:physiology*; D011263:Pregnancy Trimester, Third; D011659:Pulmonary Gas Exchange; D012123:Pulmonary Ventilation / Q000502:physiology*; D012964:Sodium / Q000097:blood
chemical_list: D001798:Blood Proteins; D002245:Carbon Dioxide; D012964:Sodium; D010100:Oxygen