Effect of periodic thermal stimulus on heart rate in term newborn infant

We studied heart rate changes in 25 term infants aged 1-7 days in quiet sleep during periodic thermal stimulation of one foot to widen the range of frequencies previously studied by others and to develop spectral analysis methods to quantify responses to thermal and other periodic sensory stimuli. The stimulation frequency was 0.10 Hz in all babies and ranged from 0.05 to 0.15 Hz in some. At 0.10 Hz, there was 1) an increase in spectral power at the frequency of stimulation (P < 0.001), 2) a tendency for overall low-frequency power to increase, 3) a reduction in respiratory sinus arrhythmia (P < 0.025), and 4) attenuation in the response between the first and second minute of stimulation (P < 0.01). At other frequencies of stimulation, essentially similar results were obtained. Respiration and other types of periodic sensory stimulation may also entrain the heart rate; we raise the question of whether low-frequency oscillations in heart rate are in fact related to thermoregulation or are a nonspecific feature of integrative processes in the brain stem.