Quantitative Variation Of Blood Pressure Dynamics During Sleep Apnea
Sleep Apnea is one of the major sleep disorders characterized by complete cessation or decline in breathing for about 10s or more during sleep, thereby adversely affecting the quality of sleep. Studies show that about 6 % of the US adult population suffers from obstructive sleep apnea, which in turn plays a major role in the development of hypertension, heart failure, stroke and is also responsible for reduced performance in everyday activities due to lack of quality sleep. In this study the physiological response to sleep apnea were determined using beat to beat blood pressure in both healthy subjects and sleep apnea patients. During simulated study, two protocols were used which varies on the inter breath hold intervals and are named as protocol A and protocol B. The study was conducted for both the sitting and supine posture of the subjects. The features extracted are: systolic and diastolic pressure values, pulse pressure, mean arterial pressure, slope of the waveform trend and area under the pressure waveform. Using these metrics, the physiological variations during both simulated and actual apnea are determined and the results indicate a significant rise in blood pressure during apnea episodes. In addition to the systolic, diastolic and mean arterial pressure, some of the new metrics like area under the blood pressure waveform and the slope of systolic and diastolic trend proved to be significant features in detecting apnea. For sitting A, the mean and standard deviation for area are 85.95 ± 24.69 mmHg-s (breath hold) and 75.58 ± 20.57 mmHg-s (baseline) and for systolic slope, the values are 0.59 ± 0.38 mmHg/s during breath hold and -0.01 ± 0.29 mmHg/s during baseline. Similarly mean values of these metrics during breath holds were higher for other protocols used. From the sleep apnea study the mean values obtained for area are 79.45 ± 22.25mmHg-s (normal breathing), 82.05± 22.30 mmHg-s (apnea), 81.77± 23.15 mmHg-s (hypopnea) and for systolic slope: -0.11± 0.03 mmHg/s (normal breathing), 0.6 ±0.07 mmHg/s (apnea), 0.04± 0.006 mmHg/s (hypopnea). This shows that area under pressure waveform and the slope or the rate of rise of the blood pressure are good indicators to distinguish between apnea events.