Autonomic cardiovascular control in pregnancy.

Pregnancy is associated with profound adaptive changes in the maternal hemodynamics. Although the autonomic nervous system plays a central role in the adaptation of the cardiovascular system to various needs, its role in the adaptation of the circulation to the demands of pregnancy is poorly understood. This paper reviews the literature of autonomic cardiovascular control in pregnancy as studied with the cardiovascular reflex tests. A Medline search and manual cross-referencing for prior publications were used. All papers found on the hemodynamic effects of the Valsalva maneuver, the orthostatic test, the deep breathing test, the isometric handgrip test and maternal heart rate variability in pregnancy were reviewed and all publications that studied short-term changes in maternal heart rate and blood pressure were included. The beginning of pregnancy is associated with sympathetic reactivity, whereas the latter half of pregnancy is characterized by increased hemodynamic stability during orthostatic stress. The heart rate response to the Valsalva maneuver is blunted in mid-pregnancy, possibly due to changes in the baroreflex and increased maternal blood volume. Heart rate variability is significantly reduced in the second trimester. Cardiovascular reflex tests can be used to study drug effects on maternal circulation non-invasively.