Chest
Volume 110, Issue 2, August 1996, Pages 446-453
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Clinical Investigations: Sexual Pulmonary
Regulation of Breathing and Perception of Dyspnea in Healthy Pregnant Women

https://doi.org/10.1378/chest.110.2.446Get rights and content

Study objective

To examine if the perception of dyspnea during normal pregnancy may be related to an inappropriate ventilatory response to the increased metabolic rate, due to a higher chemosensitivity.

Patients and interventions

At weeks 12, 24, and 36 of gestation and 4 months after delivery, 11 healthy pregnant women with dyspnea and 12 asymptomatic pregnant women were studied. Progesterone plasma levels, lung volumes, diffusion capacity, maximal respiratory pressures, rest oxygen uptake, breathing pattern, and mouth occlusion pressure (P0.1) were measured. Progressive isocapnic hypoxic stimulation and progressive hyperoxic hypercapnic stimulation were performed.

Results

Oxygen ventilation equivalent during pregnancy was significantly higher for the dyspneic group than for nondyspneic pregnant women. Dyspneic patients exhibited greater minute ventilation, tidal volume, and P0.1 than the nondyspneic group. The mean values of ventilatory and P0.1 slopes to hypoxia and CO2 during pregnancy were significantly greater in the patients with dyspnea than in asymptomatic subjects. These changes were not due to differences in progesterone plasma levels. A significant relation among the Borg score, inspiratory drive, and chemosensitivity was found.

Conclusions

In some pregnant women, a higher sensitivity to CO2 and hypoxia may induce excessive ventilation to metabolic demand, which would contribute to dyspnea.

Section snippets

Subjects

Thirty-five healthy pregnant women without history of cardiovascular or respiratory diseases were recruited for the protocol. All women had uncomplicated singleton pregnancies. Each woman was studied serially at weeks 12, 24, and 36 of gestation and again 4 months postpartum for a measurement in the nonpregnant state. Twelve of the subjects failed to complete all trials (for reasons unrelated to the study), and their data were not included in the analysis. Twenty-three women completed the

RESULTS

Eleven of the 23 subjects had dyspnea at rest and comprise the dyspneic group. Dyspnea started within the first trimester and it disappeared after delivery. In four subjects, the dyspnea remained at a constant level, although this condition partially improved as the pregnancy progressed in seven women. Nevertheless, none of the dyspneic women with Borg scores greater than 0 at 12 weeks subsequently became nondyspneic at 24 and 36 weeks. The mean intensity ratings (Borg score) fell between 1 and

DISCUSSION

Our results suggest that the P0.1 and the responses to the hypercapnia and hypoxia are higher in pregnant women with physiologic dyspnea than in those who are asymptomatic, and that these alterations are related to the intensity of dyspnea.

Several methodologic issues should be considered. Pregnancy dyspnea was classified as physiologic only in accordance with clinical aspects. The typical clinical manifestations (dyspnea that does not affect normal activity and that appears to remain stable

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