MEASURING VENOUS CAPACITANCE AND BLOOD-FLOW IN PREGNANCY

Forearm or calf venous plethysmography has been used in pregnant women to examine the effects of pregnancy on the vascular system and more r ecently to measure blood flow changes in response to intra-arterial in fusion of vasoactive substances. To examine the assumption that venous capacitance and blood flow measurements are the same in the forearm a nd calf, venous plethysmography was conducted simultaneously on the fo rearm and calf in normal (NP) and hypertensive pregnant women (HTP) in their third trimester and in normal nonpregnant women (N). AU studies were made on the right forearm and calf with subjects in the left lat eral recumbent position. There was no significant difference between v enous capacitance in the forearm (median: 124 x 10(-3)mL/100mL/mmHg fo r both NP and HTP) and leg (134 [NP] and 106 [HTP] x 10(-3)mL/100mL/mm Hg) for both pregnant groups but venous capacitance in the nonpregnant group was greater in the leg than arm (174 versus 112 x 10(-3)mL/100m L/mmHg, p <0.001). Blood now was similar in the leg and forearm (media n: 4.9 versus 3.9mL/100mL/min respectively) in nonpregnant women. Fore arm blood flow was also similar to calf flow in NP women (6.2 versus 4 .3mL/100mL/min respectively) but greater than calf blood flow in HTP ( 9.7 versus 5.3mL/100mL/min, p <0.01). Using left lateral recumbency, f orearm and calf vein capacitances are similar in pregnant women, in co ntrast to nonpregnant women. Blood flow is higher in the forearm than the calf only in hypertensive pregnant women. These observations shoul d be borne in mind when interpreting studies of regional blood flow in pregnancy.