Heart rate variability in patients with obstructive sleep apnea.

Several studies found that breathing abnormalities like OSA or Cheyne-Stokes ventilation are related to periodic changes in heart rate [1,2]. The influences of OSA on HRV analyzed by power spectral analysis have not been investigated until now. The purpose of this study was, therefore, to assess changes in the power spectrum of HRV during episodes of OSA as compared to a normal breathing pattern. Methods: Nine male patients with OSA, between 38 to 72 years of age, were studied. Patients did not suffer from cardiovascular diseases and did not take any medication. Patients underwent polysomnography and were additionally monitored by Holter ECG recordins (ELA 2448+S2 recorder, ELA Medical, Munich. Germany). In each patient two 20-minute periods, one recorded when the patient was awake with a normal breathing pattern and one recorded during an OSA episode. were selected for spectral analysis The RR intervals were resampled at 4 tlz and aperiodic trends were eliminated by using third-order polynomial fits. In each episode, discrete Fourier transform was computed for three 50% overlapping segments using a Hanning window and the results were averaged. The area under the curve was calculated for HF power (0.15-0.4 Hz), LF power (0.04-0.15 Hz), VLF power (0.0033-0.04 Hz), and total power (I 0.4 Hz). The area under a sharp peak at 0.125 Hz due to the phase locked loop speed control of the ELA 2448+S2 recorder was subtracted from the area under the curve of the LF frequency band. Additionally, normalized units of power spectra components were calculated. Wilcoxon’s test for paired data was used for statistical analysis, and the data are reported as medians and ranges. A value of p < 0.05 was considered statistically significant. Results: During periodic breathing HRV measured by SD of RR intervals and by total power increased significantly. A sharp peak with a center frequency of 0.0196 ? 0.0032 Hz occurred in the VLF power spectrum component of RR intervals during OSA episodes, resulting in a marked increase in VLF power (Table I). Additionally, LF and HF power increased significantly during periodic breathing. When expressed as normalized units, VLF power showed a pronounced increase during OSA episodes. whereas LF power decreased signiticantly and HF power showed a trend towards reduced values. Abbreviations used: HF, high frequency; HRV, heart rate variability; LF. low frequency; NU, normalized units; OSA, obstnictive sleep apnea. SD. standard deviation; VLF, very low frequency. Table 1: Heart rate variability during normal breathing and during periodic breathing due to obstructive sleep apnea (Data are reported as medians and ranges, * = pC0.05 vs. control)