POSTNATAL CHANGES IN CARDIAC-OUTPUT AND HAEMORRHEOLOGY IN NORMAL NEONATES BORN AT FULL TERM

Circulatory adaptation was studied serially in 11 healthy term neonates on days 1, 3, and 5 by cross sectional and pulsed Doppler echocardiography. Changes in the determinants of blood viscosity (packed cell volume, plasma viscosity, red cell aggregation, and red cell deformability) were studied on day 1 and day 5. There was a 27% increase in the cardiac output as a result of increasing stroke volume, whereas heart rate did not change significantly. Mean blood pressure increased by nearly the same extent as cardiac output (21%), so that the overall resistance remained unchanged. Packed cell volume, red cell aggregation, and red cell deformability did not change significantly during the first five post-natal days. Plasma viscosity rose significantly (by 12%) so that whole blood viscosity increased during that period. As there was no change in overall systemic vascular resistance the vascular hindrance-calculated as the ratio of resistance: blood viscosity-decreased, thereby indicating vasodilation.