Predictive value of 24-hour ambulatory blood pressure monitoring in the diagnosis of autonomic dysfunction

The usefulness of noninvasive ambulatory blood pressure monitoring (24-hour ABP) in the evaluation and management of clinical hypertension is well established, however, its utility in autonomic dysfunction is uncertain. To determine the operating characteristics of three variables of 24-hour ABP to identify autonomic dysfunction in patients presenting with orthostatic hypotension. Cross-sectional. 50 consecutive patients undergoing diagnostic testing for orthostatic hypotension were included in the study. All patients underwent 24-hour ABP, beat-to-beat analysis of blood pressure changes during a Valsalva manuevere and 80-degree head-up tilt. The diagnostic utility of diurnal pattern reversal, post-prandial hypotension and heart rate variability were examined. Several operating characteristics were examined, including sensitivity and specificity. In general, presence of post-prandial hypotension showed the best operating characteristics (e.g., sensitivity= .85 false positives = .15). Whereas definitive diagnosis of autonomic dysfunction involves a battery of diagnostic tests, this preliminary data suggests that the presence of postprandial hypotension as assessed by 24-hour ABP may be a more sensitive predictor of autonomic dysfunction that diurnal pattern reversal of heart rate variability.