[Power spectral analysis on heart rate variability of hypoxaemia in fetal lambs]

To analyze the effect of hypoxaemia on heart rate variability (HRV) in fetal lambs by means of power spectrum, the intrauterine surgical operations were performed at 116-125 gestational days in 7 lambs. Arterial catheter was inserted in the fetal femoral artery and sent to aorta abdominalis, and blood pressure was recorded continually on tape recorder. The microspheres were injected via the arterial catheter to block the micrangium of placenta, thus making an animal model of fetal hypoxaemia. The fetal blood sample was drawn through the catheter for blood gas analysis. In terms of the heart beat variability power spectral density, there were four consistent components, namely 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). Integrated peaks in the power spectrum were compared before and after administration of microsphere. The spectral power in the L frequency components was significantly increased (0.07 +/- 0.01 vs. 0.21 +/- 0.03, P<0.01), and the spectral power in the H frequency components was significantly reduced (0.53 +/- 0.1 vs. 0.27 +/- 0.05, P<0.05). There was no significant difference in M and VL. The times of microsphere injection were related to fetal blood pH (r=0.585, p<0.01), PCO2 (r=0.5, p<0.05) and PO2 (r=0.75, P<0.01). The results clearly demonstrate the association between change of power spectrum of heart rate variability and the effect of hypoxia of the fetus in labour.