Closing volume during normal pregnancy.

Serial lung function studies were performed in ten healthy, primiparous women aged 21--28. Measurements were made at two-monthly intervals during pregnancy and included functional residual capacity (FRC), total lung capacity (TLC), vital capacity (VC), specific conductance (SGaw) and closing volume (CV) on each occasion. Closing volume expressed as formular: (see text), showed a progressive rise during pregnancy in all subjects with a linear relationship to time (P less than 0.001, P greater than 0.01, respectively). No consistent changes in lung volume could be shown during pregnancy over the study period. It is suggested that the increase in closing volume during pregnancy might result in abnormalities of distribution of ventilation sufficient to explain the maternal blood gas disturbances of pregnancy.