Systolic Time Intervals in Newborn Infants

Systolic time intervals, calculated from the carotid artery pulse curve have been used for some time to assess left ventricular performance. Normal values have been established for adults and older children, but few investigations have been made on newborn infants, generally with partly contradictory results. Therefore a study has been undertaken in 29 normal newborn infants 1/2-119 hours old, and 9 infants 2-3 months old to establish normal values for different intervals. They were found to differ from those reported for adults and older children, most clearly seen in the relatively long preejection period (PEP). Statistically significant differences were found between the PEP of 20 infants below 47 hours of age and 9 infnats 2-3 months old: PEP 82 ms and 68 ms respectively. (p less than 0.01); the same is true of the quotient PEP/LVET (left ventricular ejection time), which was found to be 0.41 and 0.35 resp. (p less than 0.01). By adult standards this would mean impairment of left ventricular function. A possible explanation of this could be a difficulty for the left ventricle to cope with the systemic circulation during the first days of life even in normal newborns, a difficulty not fully compensated for even at 3 months of age.