D.B. Scott

A STUDY OF CARDIAC OUTPUT AT REST THROUGHOUT PREGNANCY

IN order to describe the overall pattern of change in cardiac output during pregnancy it is necessary to establish four facts-the time of onset of rise in cardiac output, the time at which it reaches its maximum value, the magnitude of this rise, and its behaviour after it attains this peak value. Many studies have been undertaken to investigate central haemodynamics during pregnancy and there is no unanimity on any of these four points. It is unlikely that these discrepancies are due entirely to real variations between individuals and they are more probably determined by the variability of experimental conditions. The controversy about haemodynamics in pregnancy is thus to a large extent a problem of methodology. Four criteria should be carefully considered in assessing any study of cardiac output during pregnancy. (1) The method used for measuring cardiac output should be accurate. All of the work done prior to 1939 was based on the use of foreign gases, usually nitrous oxide or acetylene. These studies have been fully summarized (Burwell et al., 1938). The limitations of these techniques have been described (Wade and Bishop, 1962), and they have been shown to give results which correlate very poorly with cardiac catheterization studies using the direct Fick principle. Pulse pressure analysis has been used (Brehm and Kindling, 1955) on the basis that stroke volume is proportional to pulse pressure. This method involves many assumptions and variables and its accuracy is poor. It may be of limited

HAEMODYNAMIC CHANGES ASSOCIATED WITH LABOUR

DURING parturition considerable changes in the maternal circulation take place. In the main, these are associated with uterine contractions during the first two stages of labour, and with the re-adjustments that occur following delivery of the baby and the placenta. Only in recent years have techniques been available that will demonstrate such rapid changes accurately. Six patients in labour have been investigated in an attempt to examine both qualitatively and quantitatively the effects of labour on the central haemodynamics of the mother.