Closing volume and pregnancy.

Measurements of closing volume have been made in 20 women between the 36th and 40th weeks of pregnancy. The patients were studied in the erect and supine positions and the point of airway closure was related to functional residual capacity. The results show that airway closure occurred during tidal ventilation in 10 patients in the erect position and in six patients in the supine position. These results may explain the variation found in maternal arterial oxygen tension during pregnancy.