Adrenergic and vagal baroreflex sensitivity in autonomic failure.

BACKGROUND: The baroreflex is responsible for maintaining a stable blood pressure (BP) despite changes in body positions and fails in many autonomic disorders. The baroreflex regulates BP by changing the heart rate (vagal component) and total peripheral resistance (adrenergic component). Baroreflex sensitivity is widely used to quantify the vagal component of the reflex, but the adrenergic component is not quantifiable in the autonomic laboratory. OBJECTIVES: To develop and validate an index of adrenergic baroreflex sensitivity. DESIGN: We validated this index with microneurographically recorded muscle sympathetic nerve discharges generated by the Valsalva maneuver and verified it against groups of patients with graded severities of adrenergic failure. RESULTS: Adrenergic baroreflex sensitivity relates BP recovery time to the preceding decrease in BP evoked by the Valsalva maneuver. This index showed a graded and highly significant impairment in 3 groups of patients, (1) those with orthostatic hypotension (n = 26), (2) those with borderline orthostatic hypotension (n = 34), and (3) those with impaired reflex vasoconstriction without orthostatic BP change (n = 24), when compared with an age- and sex-matched control group (n = 29). Adrenergic baroreflex sensitivity better tracked the severity of adrenergic failure than the vagal component of baroreflex sensitivity and provides a much needed index to quantify total peripheral resistance changes in patients with adrenergic failure. CONCLUSIONS: The 2 indices of baroreflex sensitivity separately evaluate the vagal and adrenergic components of the baroreflex. Combined, they provide an index of composite or global baroreflex function.

Evaluation of orthostatic hypotension: relationship of a new self-report instrument to laboratory-based measures.

OBJECTIVE: To compare measured autonomic deficits (composite autonomic severity score [CASS]) with a brief self-report scale we developed to measure severity of symptoms of orthostatic hypotension. PATIENTS AND METHODS: Patients were recruited in 2 phases: from August to October 2002 and in April 2004. All patients underwent full evaluation in the autonomic laboratory, from which a CASS of autonomic deficits was derived. Patients also completed the 5-item self-report Orthostatic Grading Scale, which inquires about symptoms of orthostatic intolerance due to orthostatic hypotension (eg, severity, frequency, and interference with daily activities). RESULTS: Of 145 patients, 97 (67%) had orthostatic hypotension. The 5-item scale demonstrated strong internal consistency (coefficient alpha=.91). Patients with orthostatic hypotension had significantly higher scores on each questionnaire item and CASS subscores than those without orthostatic hypotension. The scale items correlated significantly with each of the CASS subscores, maximally with the CASS adrenergic subscore. CONCLUSIONS: Orthostatic hypotension is not the only cause of reduced orthostatic tolerance, and some patients may have orthostatic hypotension but be asymptomatic. Results of this study indicate that this 5-item questionnaire is a reliable and valid measure of the severity of symptoms of orthostatic hypotension and that it can supplement laboratory-based measures to provide a rapid, more complete clinical assessment. This questionnaire would also be useful as a brief screening device for orthostatic intolerance to aid physicians in identifying patients who may have orthostatic hypotension.