Relationship between plasma atrial natriuretic peptide concentrations and cardio-thoracic ratio during the early neonatal period.

Twenty-seven neonates were examined at 2.6 +/- 1.5 hours of age (stage 1) and 21 +/- 4.9 hours of age (stage 2) to clarify the relationship between cardio-thoracic ratio (CTR) on chest roentgenograms and plasma atrial natriuretic peptide (ANP) concentration. Among 22 infants who showed elevated plasma ANP, 14 had gained body weight (group A), while 8 other infants had lost weight (group B) at stage 2. The remaining 5 infants had decreased plasma ANP concentrations combined with weight loss at stage 2 (group C). All infants of group B had a patent ductus arteriosus. The plasma ANP concentration and CTR of groups A and B increased during the study period, while those of group C decreased. A linear relation was found between plasma ANP concentration and CTR in all cases (p less than 0.02). This study indicates that increased plasma levels of ANP are associated with an increased CTR.