Normal radiographic heart volume in the neonate. 1. Dependence of ductal closure.

The hypothesis that the normal distribution of relative heart volume in the neonatal period is a mixture of two different populations, with different means and variances, has been tested. The definition of the two populations was (i) normally patent ductus and (ii) closed ductus arteriosus. The assumed frequencies of the patency in different age-groups were taken from Gentile et coll. [5]. A material consisting of 100 neonates found to be normal has been analysed radiologically during the first 360 hours after birth. The results strongly supports the hypothesis and explains the large normal range of relative heart volume during the first 48 hours of life.