Respiratory physiology in pregnancy.

Pregnancy induces marked changes in the respiratory and cardiovascular systems that are essential for meeting the increased metabolic demands of the mother and fetus. Important respiratory system changes occur in the upper airway, chest wall, static lung volumes, and ventilation and gas exchange. Marked cardiovascular changes also occur during pregnancy including increased plasma volume, increased cardiac output, and reduced vascular resistance. Knowledge of these physiologic adaptations is necessary for the clinician to distinguish the common "physiologic dyspnea" from disease states that occur during pregnancy.