Circulation, Vol 84, 1049-1057, Copyright © 1991 by American Heart Association
CT Ting, CY Chou, MS Chang, SP Wang, BN Chiang and FC Yin
BACKGROUND. Resistance, pulse wave velocity, and wave reflections have been
shown to be increased in patients with essential hypertension compared with
normotensive controls. These alterations are completely normalized by
nitroprusside infusion but exacerbated during beta- adrenergic blockade,
suggesting an enhanced smooth muscle tone that is in part modulated by
adrenergically mediated vasodilation. The present study was performed to
examine the extent to which this apparently enhanced smooth muscle tone is
a result of alpha-adrenergically mediated vasoconstriction. METHODS AND
RESULTS. Age-matched normotensive and hypertensive Chinese subjects were
instrumented with catheter-tipped micromanometers and an electromagnetic
flow velocity sensor positioned in the ascending aorta. Aortic impedance
and wave reflection properties were obtained from Fourier analysis of the
pressure and flow signals during baseline conditions, after beta- blockade
with propranolol (0.15 mg/kg i.v.), and after alpha-blockade with
intravenous phentolamine (range, 15-80 mg) that was sufficient to either
normalize blood pressure or produce a pressure that could not be further
lowered. Compared with normotensives, in the baseline state, hypertensives
had elevated resistance (1,962 versus 1,268 dyne.sec/cm5, p less than
0.001), total power (1,893 versus 1,568 mW, p less than 0.08), reflected
pressure wave component (25.6 versus 13.5 mm Hg, p less than 0.001), ratio
of reflected to forward wave (0.65 versus 0.42, p less than 0.001), and
pulse wave velocity as determined from the frequency of the first
zero-crossing of impedance phase angle (4.6 versus 3.5 Hz, p less than
0.03). During combined alpha- and beta- adrenergic blockade, blood pressure
decreased into the normal range (from 162/103 to 131/87 mm Hg) but was
still somewhat higher than that in the normotensive subjects. Resistance
(1,914 dyne.sec/cm5, p less than 0.03), reflected wave (19.5 mm Hg, p less
than 0.01), and ratio of reflected to forward wave (0.61, p less than
0.001) were, however, persistently elevated above normal values.
CONCLUSIONS. alpha- Adrenergically mediated vasoconstriction cannot account
for all of the hemodynamic alterations seen in essential hypertension.
ARTICLES
Arterial hemodynamics in human hypertension. Effects of adrenergic blockade
Department of Medicine, Veterans General Hospital, Taiwan, Republic of China.
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