The maternal cardiovascular system at rest and in response to functional haemodynamic testing during healthy pregnancy

Abstract

Healthy pregnancy results in significant maternal cardiac adaptation to match the increased circulatory demands of the developing fetoplacental unit. Specifically, cardiac output, heart rate (HR), stroke volume (SV) and end-diastolic volume (EDV) increase, whereas mean arterial pressure and systemic vascular resistance decrease. Despite a large body of research, there is a lack of consensus over the magnitude and timing of these adaptations in pregnancy. Additionally, previous studies have reported reduced systolic function in the late stages of pregnancy, indicating that gestation may negatively influence left ventricular pumping capacity. Testing the ability of the maternal heart to respond to additional physiological challenge may elucidate how cardiac function is affected by healthy pregnancy. This thesis investigated cardiovascular adaptation and functional responses before, during and after healthy pregnancy. Firstly, a series of meta-analyses were completed to characterise global cardiac function across healthy gestation. These analyses showed that resting cardiac output is elevated during pregnancy, peaking late in the third trimester but reducing towards term. Secondly, a comprehensive assessment of cardiac structure and function was completed in healthy nonpregnant, pregnant and postpartum females at rest. The significantly greater cardiac output in pregnant females was result of significantly higher HR and SV. The greater SV was result of significantly higher EDV and systolic functional parameters (longitudinal and circumferential left ventricular strain), the latter of which may be linked to greater sympathetic activity. Finally, the functional cardiovascular responses of the aforementioned groups to sustained isometric handhold and submaximal aerobic exercise were tested. During both challenges, systolic function of pregnant females remained significantly greater. In conclusion, healthy pregnancy alters the function of the maternal heart through lower afterload, greater preload and enhanced systolic function. Additionally, healthy pregnant females in the late second trimester have adequate functional responses to increased demand and altered haemodynamic load.