In summary, the major physiologic changes that occur in pregnancy are the increased minute ventilation, which is caused by increased respiratory center sensitivity and drive; a compensated respiratory alkalosis; and a low expiratory reserve volume. The vital capacity and measures of forced expiration are well preserved. Patients with many lung diseases tolerate pregnancy well, with the exception of those with pulmonary hypertension or chronic respiratory insufficiency from parenchymal or neuromuscular disease.