Impact of age and blood pressure on the lower arterial pressure limit for maintenance of consciousness during passive upright posture in healthy vasovagal fainters: preliminary observations

Maintenance of consciousness importantly depends on systemic arterial blood pressure (BP) remaining above the lower pressure limit for cerebrovascular au- toregulation. This study evaluated the impact of age and baseline arterial blood pressure (BP) on the BP recorded at onset of syncope in otherwise healthy individu- als undergoing passive head-up tilt (HUT) testing for suspected vasovagal syncope. Since hypertension is thought to shift the lower autoregulation point to higher val- ues, and since older healthy patients tend to have higher BP than younger individu- als, 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 ¼ 17; Group 2: 25e59 years, n ¼ 18; and Group 3: R60 years, n ¼ 7. As ex- pected, baseline arterial systolic blood pressure of patients R60 years (162G37 mmHg) was significantly higher than in the other two groups (Group 1: !25 years, 116G15 mmHg; Group 2: 25e59 years, 128G12 mmHg). Further, the R60 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: R60 years, 61G15 mmHg, Group 2: 25e59 years, 58G6 mmHg, and Group 1: 54G16 mmHg) and were not statistically