REGULATION OF BREATHING AND PERCEPTION OF DYSPNEA IN HEALTHY PREGNANT-WOMEN

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. Patien ts and interventions: At weeks 12, 24, and 36 of gestation and 4 month s after delivery, 11 healthy pregnant women with dyspnea and 12 asympt omatic pregnant women were studied. Progesterone plasma levels, lung v olumes, diffusion capacity, maximal respiratory pressures, rest oxygen uptake, breathing pattern, and mouth occlusion pressure (P0.1) were m easured. Progressive isocapnic hypoxic stimulation and progressive hyp eroxic hypercapnic stimulation were performed. Results: Oxygen ventila tion equivalent during pregnancy was significantly higher for the dysp neic group than for nondyspneic pregnant women. Dyspneic patients exhi bited greater minute ventilation, tidal volume, and P0.1 than the nond yspneic group. The mean values of ventilatory and P0.1 slopes to hypox ia and CO2 during pregnancy were significantly greater in the patients with dyspnea than in asymptomatic subjects. These changes were not du e to differences in progesterone plasma levels. A significant relation among the Borg score, inspiratory drive, and chemosensitivity was fou nd. Conclusions: In some pregnant women, a higher sensitivity to CO2 a nd hypoxia may induce excessive ventilation to metabolic demand, which would contribute to dyspnea.