"The evaluation of autonomic nervous system parameters using heart rate variability analysis in obstructive sleep apnea patients following CPAP treatment"

Patients diagnosed with obstructive sleep apnea syndrome (OSAS) following a lab-attended full polysomnography and who were prescribed continuous positive airway pressure (CPAP) therapy were included in this study. We aimed to evaluate the effects of regular treatment of OSAS with CPAP therapy on autonomic functions using heart rate variability(HRV) analysis. After an initial polysomnography, the patients who were prescribed CPAP were submitted to a control polysomnography with CPAP treatment in the sleep unit of our University hospital. Data from 21 patients(9 female, 12 male) between the ages of 35-75(mean age: 56.8 ± 8.8) were retrospectively reviewed. HRV parameters were recorded before and after the CPAP treatment. The patients with uncontrolled hypertension, chronic obstructive coronary disease, type 1 and type 2 diabetes mellitus, left ventricular hypetrophy assessed with echocardiography, serious valvular disease, liver kidney or thyroid disease, cardiomyopathies and left ventricular systolic dysfunction (LVEF:<%40) had been excluded from the study. ECG and heart rate data of the patients were recorded with the module ?rhythm analyzer? which is the trademark of Medcare Flaga Reyjkavik simultaneously with the polysomnography. HRV parameters were assessed by the ?HRV report module? of the system. HRV analysis was performed at the beginning of the sleep analysis with 10-minutes periods when the patient was awake and the breathing movements was regular. Thus, we aimed to exclude the artifical changes of HRV which were reported to be associated with abnormal thoracoabdominal movements (breathing effort) and apnea. The time and frequency-based analysis were used to evaluate of the heart rate variability. We observed a significant increase of the values of RR, SDNN, SDANN, rMSSD and pNN50 which are scales of time-based HRV analysis and after CPAP treatment compared to baseline recordings before initiation of treatment. Similarly the scale values of HF which is the frequency-based analysis considered to be the major determinant of parasympathetic (vagal) activity increased significantly after CPAP treatment. Heart rate measured with RR distance and accepted as an independent risk factor for cardiovascular mortality was observed to decrease significantly with CPAP treatment. In addition, the scales of time-based analysis were found correlated with the scales of frequency-based analysis statistically. The scales of time-based analysis were found correlated with each other statistically. The increase of variability and vagal activity observed with CPAP therapy may be one of the mechanisms at the basis of the favorable cardiovasculary effects of CPAP treatment in patients with OSAS. The results of our study suggest that the analysis of HRV which was not recommended to be performed during sleep to avoid artefacts related to repetitive apnoea episodes may be appropriate to be used when the patient is awake and the breathing was regular. HRV analysis is a cheap, practical and a painless non-invasive method compared to other methods evaluate the autonomic activity such as blood catecholamine assessment and peripheric sympathetic nerve activity measurements.