Marked fetal acidosis and specific changes in power spectrum analysis of fetal heart rate variability recorded during the last hour of labour.

OBJECTIVE: To assess whether intrapartum acidosis affects specific components of fetal heart rate variability. DESIGN: Prospective clinical study. SETTING: Twelve Nordic delivery units. SUBJECTS: Fetal heart rate variability was studied in 334 fetuses divided into two groups according to cord pH value: the acidotic group (cord arterial pH < 7.05 at birth, n= 15) and the control group (cord arterial pH > or =7.05 at birth, n= 319). METHODS: In spectral analysis of fetal heart rate variability, frequencies were integrated over the total frequency band (0.04-1.0 Hz), low-frequency band (0.04-0.15 Hz) and high-frequency band (0.15-1.0 Hz). We also calculated the low-to-high frequency ratio. MAIN OUTCOME MEASURES: The spectral bands of fetal heart rate variability were compared between the acidotic and control fetuses. RESULTS: We found that during the last hour of monitoring, baseline fetal heart rate gradually decreased, whereas total, low-frequency and high-frequency fetal heart rate variability initially increased but then, near the delivery, decreased in the acidotic fetuses when compared with the controls. Low-to-high frequency ratio was greater in the acidotic group during the whole study period (P= 0.002). Cord artery pH was inversely associated with total fetal heart rate variability (P < 0.001), low-frequency fetal heart rate variability (P < 0.001) and low-to-high frequency ratio (P= 0.004). CONCLUSIONS: Marked fetal acidosis was associated with frequency-specific changes in fetal heart rate variability as reflecting the compensation ability of autonomic nervous activation during the last hour of labour.

Ramipril Enhances Autonomic Control in Essential Hypertension: A Study Employing Spectral Analysis of Heart Rate Variation.

We estimated the effect of an angiotensin-converting enzyme inhibitor, ramipril, on the sympathetic and parasympathetic input to the sinoatrial node of hypertensive patients using spectral and time domain analysis of heart rate variation (HRV). The heart rate of patients with essential hypertension was recorded during spontaneous breathing at rest and during controlled deep breathing. The periodic HRV was quantified at low-frequency (0.025--0.075 Hz), mid-frequency (0.075--0.125 Hz) and high-frequency (0.15--0.40 Hz) bands. Ramipril changed the balance of autonomic nervous system assessed by spectra: the parasympathetic tone increased (p < 0.05) and the sympathetic tone decreased (p < 0.01). There was an inverse correlation between the decrease in diastolic blood pressure and increase in the mid-frequency HRV, which is connoted with resetting of the baroreceptor reflex by ramipril. Thus, ramipril treatment was associated with improved autonomic control of the circulatory system.