Does tilting from horizontal to 60° upright elicit a different plasma norepinephrine response in patients with severe essential hypertension compared to normal subjects?
Patients with severe essential hypertension exhibit a blunted neuroadrenergic response (insignificant rise in plasma norepinephrine) to orthostatic stress compared to normal subjects.
A significant increase in the plasma concentration of norepinephrine on tilting 19 normal subjects from the horizontal to 60° upright is described. Evidence that this represents an increased neuroadrenergic activity to maintain cerebral circulation despite the peripheral pooling of blood has previously been reported. When 9 subjects with severe essential hypertension were similarly tilted, the rise in plasma norepinephrine concentration was insignificant. This may indicate a diminished neuroadrenergic activity in essential hypertension due to compensatory reflexes from the baroreceptor regions.
Hickler et al. (Tue,) studied this question.