Alterations in Lower Extremity Venous Hemodynamics Associated with Normal Pregnancy

Abstract

This study was performed to define physiologic changes in lower extremity venous hemodynamics during and after normal, healthy pregnancy. Lower extremity venous physiology was evaluated by using air plethysmography in 24 healthy primigravid females (48 extremities) with no known venous disease. All patients were studied during their first, second, and third trimester, and at 6 weeks, 3 months, and 6 months postpartum. Data were evaluated for changes over time and for differences between the right and left lower extremity by use of repeated measures analysis of variance. None of the patients developed overt signs of venous reflux during pregnancy although there was an increase in venous filling index in advanced stages of pregnancy. All values remained within normal range (1.0-1.7 mL/sec, p = 0.52). There was a statistically significant decrease in residual volume fraction that reached a nadir during the third trimester and returned to below-baseline values immediately postpartum (p = 0.02). An increase in venous outflow fraction was demonstrated as pregnancy progressed (p = 0.05). This trend peaked during the third trimester. Calf muscle pump function did not change appreciably during the study period (p = 0.61). There was no difference between right and left lower extremities with regard to venous filling index (p = 0.25), residual volume fraction (p = 0.33), venous outflow fraction (p = 0.17), or calf muscle pump function (p = 0.33). Some alterations in venous hemodynamics are associated with pregnancy. Venous outflow fraction overall is increased coincident with a decrease in residual volume fraction. The significant decrease in residual volume fraction and augmentation in venous filling index may be related to venous dilation and an increase in venous capacitance secondary to hormonally influenced smooth muscle relaxation.