Abstract P393: Orthostatic Heart Rate-Blood Pressure Relationship Identifies Neurogenic Orthostatic Hypotension
Background: Neurogenic orthostatic hypotension (nOH) is a chronic disabling condition associated with significant morbidity and mortality. Currently, the diagnosis of nOH relies on impaired autonomic reflexes as determined by testing available only in specialized centers. Our objective was to test the hypothesis that a blunted heart rate (HR) increase in response to a given systolic blood pressure (SBP) fall will correctly diagnose nOH. Methods: We performed a retrospective study of nOH patients (studied in an inpatient environment off medications that can interfere with autonomic function) and control subjects. nOH was diagnosed on the basis of SBP fall ≥20 mmHg on standing associated with a decrease in SBP≥ 20 mmHg during phase 2 of the Valsalva maneuver and absence of phase 4 SBP overshoot. Controls had any SBP fall on standing but intact autonomic reflexes. Receiver operator characteristic curve (ROC) analysis was performed on the ratio of the changes from supine to 3 min standing in HR and SBP (ΔHR/ΔSBP). Results: We studied 171 nOH patients (66±1 years, males 61%, multiple system atrophy 42%, Parkinson disease 14%, pure autonomic failure 32% and undetermined 12%) and 53 controls (51±3 years, males 28%). nOH patients had a greater drop in standing SBP (-63±2 vs. -16±4 mmHg in controls; p<0.01) but a smaller increase in HR (13±1 vs. 18±1 bpm in controls; p<0.01). The ROC analysis at 95% Confidence Interval showed that a ΔHR/ΔSBP ratio <0.445 had a 81% specificity and 79% sensitivity in identifying nOH (AUC=0.86, p<0.01. Figure). Conclusions: Our study suggests that a simple ratio of ΔSBP/ΔHR <0.445 during a posture test in clinic can reliably identify patients with nOH.