Respiratory function in pregnant obese women.

Lung volumes and other ventilatory variables were measured in 10 women with a mean age of 28 years, a mean height of 163 cm., and weights which were 50 to 140 per cent above the normal. Measurements were made during the last trimester of pregnancy and after the second month postpartum. Mean values of lung volumes in liters during these two time periods were: vital capacity (VC), 3.7 and 3.92; expiratory reserve volume (ERV), 0.79 and 0.94; functional residual capacity (FRC), 2.06 and 2.14; and forced expiratory volume at one second (FEV1) 3.2 and 3.3. Mean blood gas values were as follows: pH, 7.44 during both times; PaCO2, 29.7 and 35 torr; standard bicarbonate, 22 and 28.8 mEq; base excess, -4.2 and 0.03 PaO2 breathing air, 85 and 86 and breathing 100 per cent oxygen, 527 and 515 torr; AaDO2, 162 and 167 torr. We conclude that, with the exception of FRC, pregnant obese women who are 50 to 140 per cent overweight develop respiratory changes similar to those seen in normal-weight gravidas. These findings suggest that obesity of this magnitude does not exaggerate changes in ventilation induced by pregnancy as generally believed. Why in this obese population the decrease in FRC during pregnancy did not occur to the same degree as that seen in normal-weight gravidas cannot be defined from our study. Evidence is presented for a ventilation/perfusion imbalance in obese subjects which is not corrected during pregnancy.