Assessment of left ventricular adaptation to extrauterine circulation.

Left ventricular systolic time intervals (STI) were recorded by non-invasive technique from the axillary artery in fifteen normal newborns from 10-15 min to 70-74 hours after birth. The observed changes in the different STI could almost entirely be related to changes in the isovolumic contraction time (ICT). At the early postnatal recording ICT was only 21.0 msec suggesting an enhanced left ventricular performance compared to prenatal observations. During the following hours ICT increased to 31.6 msec which in some infants may imply a reduced left ventricular performance. This is suggested to coincide with ductal closure.