What is the difference in orthostatic hypotension caused by autonomic dysfunction and that caused by hypovolemia during a tilt table test?
In most autonomic neuropathies associated with orthostatic hypotension, failure of vascular reflexes to increase sympathetic outflow to splanchnic and muscular vasculature results in a drop in both systolic and diastolic pressures.
However, there is no increase in plasma Norepinephrine (hypoadrenergic response).
Conversely, in orthostatic hypotension secondary to hypovolemia, plasma Norepinephrine increases excessively in response to standing (hyperadrenergic response).
In orthostatic hypotension secondary to generalized sympathetic failure, a drop in systolic blood pressure is not associated with reflex tachycardia, whereas in orthostatic hypotension secondary to hypovolemia or deconditioning, with intact sympathetic nerves, reflex tachycardia is prominent.
A fall in systolic pressure alone is most likely caused by a non-neurologic disturbance (e.g., hypovolemia).