Overview
Clinical Meaning
The clinician evaluating orthostatic hypotension must perform comprehensive autonomic nervous system assessment and differentiate the underlying etiology for targeted management.
The clinician evaluating orthostatic hypotension must perform comprehensive autonomic nervous system assessment and differentiate the underlying etiology for targeted management. Autonomic function testing includes: cardiovagal function (heart rate response to deep breathing -- normally varies by 15+ bpm; Valsalva ratio normally above 1.5), adrenergic function (BP response to Valsalva maneuver -- Phase II should show minimal BP decline in healthy individuals; Phase IV should show BP overshoot above baseline; absence of Phase IV overshoot indicates impaired adrenergic function), and sudomotor function (quantitative sudomotor axon reflex test QSART -- reduced sweat output indicates postganglionic sympathetic cholinergic dysfunction). The Composite Autonomic Severity Score (CASS) integrates these results into a standardized severity grading (0-10). For neurogenic OH specifically, supine and upright plasma norepinephrine levels are diagnostic: central autonomic failure (MSA, PAF) shows low supine NE (below 100 pg/mL) that fails to rise adequately with standing; peripheral autonomic failure (diabetic, amyloid) shows low supine NE with absent standing increase; intact autonomic system shows supine NE 200-400 pg/mL with doubling upon standing. The clinician prescribes pharmacological therapy, manages the supine hypertension paradox, evaluates for treatable...
