Spectral Analysis of Heart
Rate Variability in Sleep
P. BUŠEK, J. VAŇKOVÁ, J. OPAVSKÝ1, J. SALINGER1,
S. NEVŠÍMALOVÁ
Department of Neurology, First Faculty of
Medicine, Charles University, Prague and 1Department
of Physiotherapy and Pain Management, Faculty of Physical
Culture, Palacky University, Olomouc, Czech Republic
Received May 20, 2004
Accepted November 15, 2004
On line available December 9, 2004
Summary
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.
Key words
Autonomic nervous system • Cardiac activity • Heart rate
variability • Orexin • Sleep
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