Transverse diameter of the chest and of the heart of infants in the course of physiological cardiorespiratory adaptation.

The morphology of the lungs and heart was analysed in 824 newborn infants with normal cardiorespiratory adaptation. Under normal conditions, the air content of the lungs became satisfactory in the first 6--12 hours and normal in all cases after 24 hours. The values for the transverse diameter of the chest and heart were brought into correlation with birth weight, body length and gestational age. The transverse diameter of the chest and heart did not change during the early postnatal period (between 6--12 hours and 5 days). Both diameters were correlated with birth weight. The closest correlation was found in newborns under 1500 g, a varying one in those between 1500 and 2000 g and a close correlation in the category over 2000 g. The correlation of the two diameters with both length was linear and close, without any difference between the values obtained at different times of examination. A rather loose correlation was found between the transverse diameter of the chest and heart, and gestational age.