Continuous non-invasive monitoring to detect covert autonomic dysfunction in Parkinson's disease

Background: Lightheadedness on standing is a disabling symptom in Parkinson's disease associated with orthostatic hypotension and is thought to represent cardiovascular autonomic dysfunction. Traditional orthostatic blood pressures are normal in some patients with lightheadedness and other measures of cardiovascular dysautonomia can be insensitive. In this study, we used continuous non-invasive arterial pressure monitoring to measure beat-to-beat changes in blood pressure and heart rate on standing and during Valsalva as a potential marker of autonomic dysfunction. Methods: Subjects had a diagnosis of Parkinson's disease with or without documented orthostatic hypotension. Each participant underwent traditional measurement of orthostatic blood pressure and heart rate as well as measurement of beat-to-beat blood pressure and heart rate using continuous non-invasive arterial pressure monitoring during Valsalva maneuver and in response to standing. Orthostatic change in blood pressure and heart rate, and frequencies of normal and abnormal blood pressure responses to Valsalva maneuver were analyzed. Results: In subjects without documented orthostatic hypotension, there was a higher proportion of abnormal blood pressure responses to Valsalva in subjects with symptoms of lightheadedness or dizziness upon standing compared to those without symptoms (p=0.03). Additionally, the proportion of abnormal blood pressure responses during Valsalva observed in symptomatic subjects without orthostatic hypotension was indistinguishable from those with documented orthostatic hypotension (p=0.7). Conclusions: Our findings suggest that continuous non-invasive arterial pressure monitoring may be more sensitive than traditional measurement of orthostatic blood pressure to detect subtle cardiac dysautonomia in Parkinson's disease and helpful in the diagnosis of unexplained lightheadedness.