VENOUS AND ARTERIAL BEHAVIOR DURING NORMAL-PREGNANCY

To assess the contribution of the arterial and venous systems in the h emodynamic changes of normal pregnancy, we studied blood flow, vascula r resistance, venous tone, and the viscoelastic properties (''creep'') of the upper and lower limbs (using plethysmography), aortic distensi bility (using pulse wave velocity measurements), and cardiac dimension s (using echocardiography) in nine healthy women. Studies were longitu dinally performed at the first (10-13 wk) and third (33-38 wk) trimest ers of pregnancy in comparison with the period between the third and s ixth month after delivery. From the first trimester, heart rate signif icantly increased while systemic blood pressure and limb vascular resi stances did not change significantly and aortic distensibility increas ed (P < 0.05). Lower limb viscoelastic properties decreased at the thi rd trimester (P < 0.05) and venous tone increased from the first trime ster (P < 0.01), whereas little changes were observed at the site of u pper limbs. The decrease in calf venous tone was significantly correla ted with the increase in left ventricular diastolic diameter at the fi rst (P < 0.001) and the third trimester (P < 0.05). The study provides evidence that during normal pregnancy, changes in the arterial and ve nous sides of the circulation occur independently of pressure alterati ons. The increase in venous tone, contributing to preload augmentation , and the decrease in aortic stiffness, reducing afterload, both optim ize cardiac function until delivery.