ABSTRACT
Maintenance of consciousness importantly depends on systemic arterial blood pressure (BP) remaining above the lower pressure limit for cerebrovascular autoregulation. This study evaluated the impact of age and baseline arterial blood pressure (BP) on the BP recorded at onset of syncope in otherwise healthy individuals undergoing passive head-up tilt (HUT) testing for suspected vasovagal syncope. Since hypertension is thought to shift the lower autoregulation point to higher values, and since older healthy patients tend to have higher BP than younger individuals, we hypothesized that even among healthy individuals HUT-induced syncope would occur at higher BP in older compared with younger subjects. Three groups of otherwise healthy individuals who had positive HUT were identified: Group 1: <25 years, n=17; Group 2: 25-59 years, n=18; and Group 3: > or =60 years, n=7. As expected, baseline arterial systolic blood pressure of patients > or =60 years (162+/-37 mmHg) was significantly higher than in the other two groups (Group 1: <25 years, 116+/-15 mmHg; Group 2: 25-59 years, 128+/-12 mmHg). Further, the > or =60 age group tolerated upright posture for a longer period before syncope than did younger patients. However, despite a trend for BP at syncope to increase with age, differences were small (Group 3: > or =60 years, 61+/-15 mmHg, Group 2: 25-59 years, 58+/-6 mmHg, and Group 1: 54+/-16 mmHg) and were not statistically significant. Thus, in generally healthy individuals, age and baseline BP has only a minor effect on the lower limit of BP necessary for maintenance of consciousness. On the other hand, higher baseline BP provides older individuals a greater blood pressure 'reserve' for maintenance of consciousness compared with younger subjects.
