Spectral analysis of heart rate variability (HRV) during overnight polygraphic recording was performed in 11 healthy subjects. The total spectrum power, power of the VLF, LF and HF spectral bands and the mean R-R were evaluated. Compared to Stage 2 and Stage 4 non-REM sleep, the total spectrum power was significantly higher in REM sleep and its value gradually increased in the course of each REM cycle. The value of the VLF component (reflects slow regulatory mechanisms, e.g. the renin-angiotensin system, thermoregulation) was significantly higher in REM sleep than in Stage 2 and Stage 4 of non-REM sleep. The LF spectral component (linked to the sympathetic modulation) was significantly higher in REM sleep than in Stage 2 and Stage 4 non-REM sleep. On the contrary, a power of the HF spectral band (related to parasympathetic activity) was significantly higher in Stage 2 and Stage 4 non-REM than in REM sleep. The LF/HF ratio, which reflects the sympathovagal balance, had its maximal value during REM sleep and a minimal value in synchronous sleep. The LF/HF ratio significantly increased during 5-min segments of Stage 2 non-REM sleep immediately preceding REM sleep compared to 5-min segments of Stage 2 non-REM sleep preceding the slow-wave sleep. This expresses the sympathovagal shift to sympathetic predominance occurring before the onset of REM sleep. A significant lengthening of the R-R interval during subsequent cycles of Stage 2 non-REM sleep was documented, which is probably related to the shift of sympathovagal balance to a prevailing parasympathetic influence in the course of sleep. This finding corresponds to a trend of a gradual decrease of the LF/HF ratio in subsequent cycles of Stage 2 non-REM sleep.
In order to evaluate the influence of the respiratory cycle on the EEG, we compared the power spectral analysis of the EEG performed by fast Fourier transformation during inspirium and exspirium in 10 healthy subjects. The measurement was performed during spontaneous breathing and then during eupnoe (0.25 Hz), bradypnoe (0.1 Hz) and tachypnoe (0.5 Hz) paced by a metronome. In the course of spontaneous breathing and bradypnoe, there was an increase in the delta power and in the total power in the anterior temporal region during inspirium in comparison with exspirium. The eupnoe was characterized by an inspiratory decrease in the delta power in the parietal region and in the total power in the frontal region. The tachypnoe resulted in a decrease of the beta power in the central region and a decrease of the theta power in the posterior temporal and in the occipital region during inspirium. In comparison of the EEG in eupnoe, bradypnoe and tachypnoe, a decrease of spectral power of all spectral bands was found except for delta during faster breathing frequencies and vice versa with a significant difference which wa
s found mostly between bradypnoe and tachypnoe, less frequently between eupnoe and tachypnoe.