CARDIAC SYMPATHOVAGAL BALANCE DURING SLEEP-APNEA EPISODES

The main acute cardiovascular effects of obstructive sleep apnea syndr ome (OSAS) are elevation of blood pressure and reflectory bradycardia, which are followed by an abrupt tachycardia on resumption of breathin g. This haemodynamic instability is related to hypoxemia and arousal, and may lead to increased risk from cardiac arrhythmias and sudden car diac death, as well as to the development of chronic arterial hyperten sion, in these patients. The aim of this study was to apply frequency domain analysis of heart rate variability (HRV) measured from continuo us electrocardiogram (ECG) recordings to evaluate how cardiac autonomi c function, and especially cardiac sympathovagal tone, changes during sleep apnea episodes. We identified 41 apneas leading to more than 4%- unit arterial oxygen desaturation in 12 patients (11 men, 1 women, age range 27-67 years). Frequency domain analysis of HRV was performed fr om ECG recordings using 4 min epochs starting 20 min before apnea bega n and lasting 20 min after the beginning of apnea. The mean (+/-SEM) f all in oxygen saturation during the apnea was 6.8+/-0.6%-units. While high frequency band (HF, reflects cardiac vagal activity) remained unc hanged, low frequency band (LF, mainly sympathetic activity) showed a constant increase, leading to significant change in the sympathovagal balance (LF/HF ratio). In conclusion, concordantly with previous perip heral sympathetic-nerve recordings, frequency domain analysis of HRV i s able to detect sympathetic activation during sleep apnea episodes, l eading to marked change in the sympathovagal balance.