POWER SPECTRAL-ANALYSIS FOR AUTONOMIC INFLUENCES IN HEART-RATE AND BLOOD-PRESSURE VARIABILITY IN FETAL LAMBS

Variability of R-R intervals and arterial blood pressure signals in ch ronically instrumented fetal lambs was analyzed by power spectral anal ysis based on an assumption of maximum entropy. There were four consis tent components, very low (VL, 0.01-0.025 cycle/beat), low (L, 0.025-0 .125 cycle/beat), middle (M, 0.125-0.2 cycle/beat), and high (H, 0.2-0 .5 cycle/beat), in the normal heart rate variability and blood pressur e spectra. Integrated peaks in the power spectrum were compared before and after the administration of sympathetic and parasympathetic block ades. beta-Sympathetic blockade reduced the spectral power in the VL a nd L frequency components. alpha-Sympathetic blockade reduced only the M frequency component in the spectrum of R-R interval variability. Pa rasympathetic blockade reduced the H and L frequency components in the R-R interval variability spectrum but increased these components in t he systolic blood pressure variability spectrum. The results clearly d emonstrate the association between fetal autonomic activity and change of power spectrum of heart rate and blood pressure variability.