| Abstract | Spectral analysis of heart rate variability is studied in 10 healthy growing premature infants to investigate the
changes in autonomic balance achieved as a function of changes in skin temperature. Heart rate is obtained
from ECG recordings and the power spectrum of beat-to-beat heart rate fluctuations is computed. The
infants maintain mean rectal temperature within 36.3-37.2 degrees C, while skin temperature changes. The
respiratory rate does not change at the different servocontrol set points. Heart rate is found to increase
slightly, but consistently. The low-frequency band (0.02-0.2 Hz), reflecting the interplay of the sympathetic
and parasympathetic tone and known to be maximum at the thermoneutral zone, is maximum at 35.5 and 36
degrees C and decreases gradually to a lower level at a servocontrol temperature of 36.5-37 degrees C. The
high-frequency band (0.2-2.0 Hz), coinciding with the respiratory peak and reflecting parasympathetic
activity, is significantly elevated at 36 degrees C (p < 0.01). The minimum low: high ratio, indicating the
minimum sympathetic-parasympathetic balance and possibly reflecting the most comfortable conditions,
occurs at 36 degrees C, although the differences are not statistically significant. Servocontrol skin
temperature may thus be adapted, and possibly selected at 36 degrees C for growing premature infants in an
attempt to achieve thermal comfort and more balanced autonomic activity. |