Low-frequency respiratory rhythms in infants during the first six months of life.

The aim of the study was to investigate characteristics of low-frequency components in respiration. Sixteen healthy term infants were examined from the first day up to the 6th month of life. The respirogram, instantaneous respiratory frequency and respiratory amplitude of undisturbed segments of quiet sleep phases and periodic breathing (PB) were analysed via fast Fourier transformation. The peak frequency (PF) in the low-frequency range (0.04-0.2 Hz) was determined. PF for PB ranged from 0.056 to 0.1 Hz. Further, low-frequency rhythms (LFR) of the respirogram, which were stable during the recordings as well as during development, were found ranging from 0.045 to 0.067 Hz. The LFR of the respirogram is correlated with rhythmic changes in the relationship between inspiratory and expiratory amplitudes. The frequency of the LFR was significantly lower than that of the PB. The data indicate that LFR and PB are low-frequency respiratory rhythms which are separately controlled and perform independently.