The cutaneous R-pulse interval: its application as a clinical measure of neonatal cardiovascular function.

The time interval from the onset of the R wave of the ECG to the onset of the cutaneous capillary pulse wave, i.e., cutaneous R-pulse interval or RPIc, was evaluated in 21 full-term and 22 preterm infants as a measure of cardiovascular function. RPIc showed a significant linear relationship with birth weight (r = .58, p less than .001) and gestational age (r = .62, p less than .001) for healthy infants. At similar gestational ages, the sick infants showed a significant prolongation of RPIc when compared to their healthy counterparts (mean prolongation 18.5 msec, p less than .01). The infusion of calcium gluconate, an inotropic agent, consistently and significantly shortened the RPIc from its preinfusion value (p less than .01). In 7 infants, simultaneous measurement of intra-aortic R-pulse interval accompanied parallel changes in RPIc. These preliminary observations suggest that continuous monitoring of RPIc may provide a reliable noninvasive measure of neonatal cardiovascular function.