1/f fluctuations in fetal breathing rates

Fluctuations in fetal breathing rates (FBRs) have been investigated using spectral analysis techniques. Fetal breathing movements were recorded with chronically implanted diaphragmatic EMG electrodes in fetal lambs. Burst-burst intervals were determined using a template recognition method. The distribution of FBR over a long time series can be approximated by log-normal distribution. The power spectral density was found to be inversely proportional to Fourier frequency below 0.06 Hz, suggesting long-range density modulation. Analysis in the time domain revealed that self-similarity is preserved over different time scales, and that bursts tend to be bunched in clusters within which intervals between bursts are roughly uniform. Sequential distribution histograms over short time series revealed multiple peaks that vary over time