COMPUTER-ANALYSIS OF HEART-RATE VARIATION AND BREATHING MOVEMENTS IN FETAL LAMBS

A quantitive method for studying the frequency-specific relationships between heart rate (HR) and fetal breathing movements (FBM) was develo ped. The reactivity of periodic HR variation in relation to FBM was in vestigated by means of power spectral analysis. Seven fetal lambs were studied during the third trimester of gestation using a chronic anima l model. HR variability increased at the rate of FBM, as shown by an i ncrease of spectral density at > 0.35 Hz in the HR autospectrum and in the cross-spectrum of HR and respirogram, as well as by an increase i n the short-term variability index CVS. FBM were associated with the i ncreased HR variation in all but the lowest frequency bands (0-07-1.0 Hz), Although respiratory sinus arrhythmia was found, only 10 per cent of the total HR variability and 25 per cent of the joint-density of H R and respirogram appeared at > 0.35 Hz during FBM. The greatest varia tion in both the HR and respirogram spectra appeared at <0.07 Hz. Alth ough the low-frequency variability of HR and respirogram was simultane ous, it was on the whole not synchronised. The existence of multiple c ontrol systems that simultaneously link the cardiac and respiratory co ntrol mechanisms to each other in the fetal lamb is postulated.