Assessing the Effect of Hypertension on Baroreflex in Response to Head-Up Tilt Position

Abstract

In this study, time and frequency domain analyses were applied to evaluate the relationship between arterial blood pressure and mean heart rate signals acquiring from healthy subjects and hypertension patients both in supine and head-up tilt positions to evaluate the effect of posture change on baroreflex. 11 hypertension patients (50.1±10.3 years) and 11 healthy subjects (58.4±8.4 years) were included in this study. Results revealed that the mean arterial blood pressure (MABP) values of hypertension patients in response to posture changes were maintained (average BP; supine: 104.7±20.2mmHg, tilt: 104.8±19.0 mmHg). However, MABP values in healthy subjects were become higher in head-up tilt position (average BP; supine: 88.3±8.2 mmHg, tilt: 95.3±11.7 mmHg). Both of MABP values of healthy subjects in supine and head-up tilt positions were significantly lower than those in hypertension patients (p<0.05). In the results of baroreflex using time domain analysis, cardiac-baroreceptor sensitivity (BRS) values in healthy subjects were significantly higher (p<0.05) than those in hypertension patients in both supine and head-up tilt positions (average BRS value; healthy (supine: 7.3; tilt: 6.4), Hypertension (supine: 6.1; tilt: 5.6)). On the other hand, BRS reduced in response to head-up tilt in both healthy and hypertension subjects. However, it showed significant difference (p<0.05) in healthy group only. It might indicate hypertension could affect baroreflex function. The value of α index estimated in frequency domain indicated the significant difference (p<0.05) in hypertension group in response to headup tilt (supine: 11.3; tilt: 7.5). Hence, it might indicate the effect of hypertension on autonomic nervous system. By the results, it can show the difference of time and frequency approaches. Moreover, baroreflex in hypertension patients might be affected in response to posture changes using time and frequency domain approaches. By the results, these noninvasive approaches can be tools to exam baroreflex in clinical practices.