Abstract
Orthostatic hypotension is a common clinical feature in the management of hypertension. Aging, antihypertensive agents, and diabetes mellitus are frequently involved in the cause and etiology of orthostatic hypotension in hypertensives. Here we proposed a new method for evaluating orthostatic hypotension.
We made an electrically driven head-up tilt (HUT) table controlled by computer. According to a white-noise approach, we randomly altered the tilt angle between 0–30° every 8 sec, while tonometrically measuring arterial pressure (AP) in 15 normal subjects (male, 28±7 years) and 5 patients with autonomic baroreflex failure (2 Parkison's disease, 2 multiple-system atrophy, 1 Shy-Drager syndrome). We repeated the same procedures after atropine (0.04 mg/kg, i.v.) and trimethaphan infusion (0.1 mg/kg/min, i.v.) to nullify autonomic effects in normal subjects. Based on an FFT algorithm, we calculated the frequency response of AP to the change in the HUT angle. Finally we computed an AP response to a sudden change in HUT angle from 0 to 90°, i.e., a step response of AP to HUT.
The estimated step response showed that, in normal subjects, a sudden HUT from 0 to 90° induced the initial AP fall by 25±6 mmHg in 10 sec, but such an AP drop was quickly suppressed to be 13±4 mmHg within 20 sec. On the other hand, AP monotonically fell by 108±19 mmHg without any rebound after atropine and trimethaphan. In patients with autonomic baroreflex failure, the sudden HUT yielded a rapid progressive fall in AP by 58±9 mmHg in 10 sec and by 82±18 mmHg in 30 sec.
In conclusion, these results revealed the quickness and magnitude of the direct effect of HUT on AP in humans, indicating that such an effect is quickly and effectively suppressed by normal baroreflex function. Our method is useful for a quantitative evaluation of orthostatic hypotension. (See Figure)
Am J Hypertens (2004) 17, 13A–14A; doi: 10.1016/j.amjhyper.2004.03.028
