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Physiological mechanisms of hyperventilation during human pregnancy
Dennis Jensen1, James Duffin, Yuk-Miu Lam
1School of Kinesiology and Health Studies, Queen's University, Kingston, Ontorio, Canada K7L 3N6. Odj@queensu.ca
Respiratory Physiology & Neurobiology
|February 22, 2008
Summary
Pregnancy causes hyperventilation by altering breathing drives and acid-base balance. These changes, not solely due to hormones, lead to lower PCO2 and H+ levels during gestation.
Area of Science:
- Physiology
- Respiratory Medicine
- Reproductive Endocrinology
Background:
- Human pregnancy is characterized by hyperventilation, leading to hypocapnia and alkalosis.
- The underlying physiological mechanisms driving these respiratory changes remain incompletely understood.
- Existing hypotheses involve alterations in chemoreflex sensitivity, wakefulness, and hormonal influences.
Purpose of the Study:
- To investigate the roles of wakefulness, central chemoreflex, acid-base balance, and sex hormones in pregnancy-induced hyperventilation.
- To quantify changes in respiratory parameters and blood gas status from late pregnancy to postpartum.
Main Methods:
- Studied 35 healthy women in the third trimester (TM(3)) and postpartum (PP).
- Utilized an iso-oxic hyperoxic rebreathing procedure to assess wakefulness and central chemoreflex drives.
- Measured arterial PCO2 (PaCO2), arterial H+ ([H+]), plasma strong ion difference ([SID]), albumin ([Alb]), progesterone ([P(4)]), and 17beta-estradiol ([E(2)]).
Main Results:
- Increased wakefulness, chemoreflex drives, ventilation, and CO2 production (V CO(2)) from PP to TM(3).
- Decreased PaCO2 and ventilatory recruitment threshold for PCO2 (VRTCO(2)) during TM(3) compared to PP.
- Hormonal changes did not directly correlate with PaCO2 reduction; acid-base balance showed complex shifts.
Conclusions:
- Pregnancy-induced hyperventilation results from a complex interplay of increased wakefulness and central chemoreflex sensitivity.
- Changes in acid-base balance, metabolic rate (V CO(2)), and cerebral blood flow contribute to reduced PaCO2 and [H+] in pregnancy.
- This study provides the first comprehensive model linking these factors to the physiological respiratory adaptations of pregnancy.
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