The effect of pregnancy upon pulmonary function in normal women

Abstract

The literature on pulmonary function during pregnancy is reviewed.Pulmonary function studies were performed on 8 healthy women between the thirty-eighth and fortieth weeks of pregnancy and 7 to 14 weeks post partum. 1.1. The mean vital capacity was significantly lower (294 c.c.) (P > .02 < .05) during late pregnancy than when the patients were not pregnant.2.2. The reduction in vital capacity was due to a decrease in expiratory reserve. Inspiratory capacity did not change.3.3. Maximal air flow rates, timed vital capacity, and maximal breathing capacity did not change significantly during pregnancy.4.4. “Alveolar” pressure-air flow curves revealed a significantly higher air flow during pregnancy (P < .01), indicating a lowered pulmonary resistance to air flow in the pregnant state.It is suggested that the higher air flow during pregnancy may be due to relaxation of the smooth muscle of the tracheobronchial tree. This would permit an increase in the lumen of the airways and hence less resistance to the flow of air. This greater ease of air flow would tend to offset any increased effort of breathing brought about by the physical handicaps of late pregnancy, and be particularly useful when increased exertion is required. It is suggested that during pregnancy there may be a general pattern of smooth-muscle relaxation which affects the tracheobronchial musculature in addition to producing is also suggested that relaxin or the adrenal cortical hormones may be a major the well-known changes in the urinary, biliary, and gastrointestinal tracts. It factor in these alterations.