title: Physiological mechanisms of hyperventilation during human pregnancy.
abstract: This study examined the role of pregnancy-induced changes in wakefulness (or non-chemoreflex) and central chemoreflex drives to breathe, acid-base balance and female sex hormones in the hyperventilation of human pregnancy. Thirty-five healthy women were studied in the third trimester (TM(3); 36.3+/-1.0 weeks gestation; mean+/-S.D.) and again 20.2+/-7.8 weeks post-partum (PP). An iso-oxic hyperoxic rebreathing procedure was used to evaluate wakefulness and central chemoreflex drives to breathe. At rest, arterialized venous blood was obtained for the estimation of arterial PCO(2) (PaCO(2)) and [H(+)]. Blood for the determination of plasma strong ion difference ([SID]), albumin ([Alb]), as well as serum progesterone ([P(4)]) and 17beta-estradiol ([E(2)]) concentrations was also obtained at rest. Wakefulness and central chemoreflex drives to breathe, [P(4)] and [E(2)], ventilation and V CO(2) increased, whereas PaCO(2) and the central chemoreflex ventilatory recruitment threshold for PCO(2) (VRTCO(2)) decreased from PP to TM(3) (all p<0.01). The reductions in PaCO(2) were not related to the increases in [P(4)] and [E(2)]. The alkalinizing effects of reductions in PaCO(2) and [Alb] were partly offset by the acidifying effects of a reduced [SID], such that arterial [H(+)] was still reduced in TM(3) vs. PP (all p<0.001). A mathematical model of ventilatory control demonstrated that pregnancy-induced changes in wakefulness and central chemoreflex drives to breathe, acid-base balance, V CO(2) and cerebral blood flow account for the reductions in PaCO(2), [H(+)] and VRTCO(2). This is the first study to demonstrate that the hyperventilation and attendant hypocapnia/alkalosis of human pregnancy results from a complex interaction of pregnancy-induced changes in wakefulness and central chemoreflex drives to breathe, acid-base balance, metabolic rate and cerebral blood flow.
authors.affiliation: School of Kinesiology and Health Studies, Queen's University, Kingston, Ontorio, Canada K7L 3N6. Odj@queensu.ca
authors.forename: Dennis
authors.initials: D
authors.lastname: Jensen
authors.forename: James
authors.initials: J
authors.lastname: Duffin
authors.forename: Yuk-Miu
authors.initials: YM
authors.lastname: Lam
authors.forename: Katherine A
authors.initials: KA
authors.lastname: Webb
authors.forename: Jeremy A
authors.initials: JA
authors.lastname: Simpson
authors.forename: Gregory A L
authors.initials: GA
authors.lastname: Davies
authors.forename: Larry A
authors.initials: LA
authors.lastname: Wolfe
authors.forename: Denis E
authors.initials: DE
authors.lastname: O'Donnell
mesh_terms: D000136:Acid-Base Equilibrium / Q000502:physiology*; D000328:Adult; D002245:Carbon Dioxide / Q000097:blood / Q000134:cerebrospinal fluid; D004958:Estradiol / Q000097:blood; D005260:Female; D006801:Humans; D006863:Hydrogen-Ion Concentration; D006985:Hyperventilation; D008962:Models, Theoretical; D011247:Pregnancy / Q000502:physiology*; D011374:Progesterone / Q000097:blood; D012123:Pulmonary Ventilation / Q000502:physiology*; D012709:Serum Albumin; D014851:Wakefulness
chemical_list: D012709:Serum Albumin; D002245:Carbon Dioxide; D011374:Progesterone; D004958:Estradiol