Central circulatory responses in normotensive and hypertensive pregnancy.

Haemodynamic responses in normotensive pregnancy in the antenatal phase show that cardiac output is elevated by the end of the first trimester, and remains elevated throughout pregnancy, although it may fall very slightly at the end of the third trimester of pregnancy. Heart rate remains virtually static throughout pregnancy, although it may fall very slightly at the end of the third trimester of pregnancy. Arterial blood pressure remains virtually unaltered. During labour in patients with traditional anaesthesia, cardiac output is elevated by 40% overall at the end of the labour, and this rise may be as much as 60% in the immediate post-partum period. Patients with epidural analgesia show no overall rise in cardiac output throughout labour. Following Caesarean section there may be massive rises in cardiac output. In patients who become hypertensive as a result of pregnancy, there are marked individual patterns. These different groups show patients with elevated levels of cardiac output, patients with a pure elevation of systemic vascular resistance, and a third group in which there is elevation of both resistance and output. It seems certain that different syndromes are occurring, the theoretical explanations for which are discussed.