SERIAL ASSESSMENT OF THE CARDIOVASCULAR-SYSTEM IN NORMAL-PREGNANCY - ROLE OF ARTERIAL COMPLIANCE AND PULSATILE ARTERIAL LOAD

Background Temporal changes in systemic arterial compliance and wave p ropagation properties (pulsatile arterial load) and their role in vent ricular-systemic arterial coupling during gestation have not been expl ored. Noninvasive methods combined with recently developed mathematica l modeling techniques were used to characterize vascular and left vent ricular (LV) mechanical adaptations during normal gestation. Methods a nd Results Fourteen healthy women were studied at each trimester of pr egnancy and again postpartum. Experimental measurements included insta ntaneous aortic pressure (subclavian pulse tracings) and flow (aortic Doppler velocities) and echocardiographic imaging of the LV. A small i ncrease in LV muscle mass and end-diastolic chamber dimension occurred by late gestation, with no significant alterations in myocardial cont ractility. Cardiac output increased and the steady component of arteri al load (total vascular resistance) decreased during pregnancy. Severa l changes in pulsatile arterial load were noted: Global arterial compl iance increased (approximate to 30%) during the first trimester and re mained elevated thereafter. The magnitude of peripheral wave reflectio ns at the aorta was reduced. The mathematical model-based analysis rev ealed that peripheral wave reflections at the aorta were delayed and t hat both conduit and peripheral Vessels contributed to the increased a rterial compliance. Finally, coordinated changes in the pulsatile arte rial load and LV properties were responsible for maintaining the effic iency of LV-to-arterial system energy transfer. Conclusions The rapid time course of compliance changes and the involvement of both conduit and peripheral vessels are consistent with reduced Vascular tone as be ing the main underlying mechanism. The pulsatile arterial load alterat ions during normal pregnancy are adaptive in that they help to accommo date the increased intravascular volume while maintaining the efficien cy of ventricular-arterial coupling and diastolic perfusion pressure.