350 THERMOREGULATORY FLUCTUATIONS IN SKIN BLOOD FLOW AND HEART RATE VARIABILITY IN INFANTS

Abstract

Dysfunction in the control of heart rate (HR) and/or body temperature may predispose infants to SIDS, but the connection between thermoregulation and HR control in infants is unknown.Spontaneous fluctuations in HR and skin blood flow (SBF), measured with laser Doppler, were investigated in newborn infants, and the investigation was repeated at three months. SBF was measured in the palms, where there are numerous arteriovenous anastomoses.Both newborn and three month old infants showed characteristic fluctuations in SBF, which were closely related to variations in HR. Sudden vasoconstrictions were accompanied by a diphasic HR response, consisting of an initial acceleration, probably caused by coactivation of cardiac and cutaneous nerve fibres, followed by a deceleration, probably caused by baroreceptor activity.In an earlier study on adult subjects, we have demonstrated a similar diphasic HR response. In adults, the secondary, baroreceptor-mediated bradycardia was transient, lasting only a few heart beats. In infants, however, the HR deceleration lasted longer, and closely followed the time course of the vasoconstriction.The different HR response in infants and adults may reflect maturation of the baroreceptor reflex. The ability of peripheral vasodilatation may be less well developed in infants, which makes HR more important in the regulation of blood pressure.