Researchers with the U.S. Autonomic Disorders Consortium have shown a simple, bedside test can help spot underlying neurological disorders like Lewy body dementia (LBD) in people who have orthostatic hypotension (OH).
When a healthy person changes from a sitting position to a standing position, their heart rate automatically rises and their blood pressure remains stable. This is how the body responds to gravitational stress and the increased effort required to continue sending blood to the brain. For people with OH, their blood pressure falls when they stand up, because the nerves that activate the squeezing of the blood vessels aren’t working correctly. This may result in dizziness or even fainting. OH can be caused by medications, anemia or dehydration.
When OH is caused by a neurological disorder like LBD, it’s called neurogenic OH. Typically, physicians measure the change in blood pressure and heart rate between sitting and standing to determine if OH is neurogenic or non-neurogenic. Until now, however, the specific degree of change in heart rate associated with neurogenic OH have not been systematically studied. Guidelines to differentiate between neurogenic and non-neurogenic OH were based on consensus of expert clinical experience, not on scientific data.
In a recent study, researchers assessed 24 people with non-neurogenic OH and 378 people with neurogenic OH. The neurogenic OH group included 96 people with multiple system atrophy, 13 with pure autonomic failure, 19 with dementia with Lewy bodies, and 96 with Parkinson’s disease, and 154 people who had OH plus subtle motor symptoms, REM sleep behavior disorder, or loss of smell. This last group was categorized as being in the “prodromal” stage of a Lewy body disorder, where only early warning signs are evident. None in the prodromal group had enough symptoms to support a specific diagnosis of Parkinson’s disease, multiple system atrophy or dementia with Lewy bodies.
The study compared changes in participants’ heart rate and blood pressure while laying on a tilting table, which mimics a change in position from laying prone to standing up. The study revealed that those with neurogenic OH were more likely to have a smaller rise in heart rate when upright, and a larger drop in blood pressure, compared to those with non-neurogenic OH.
Researchers used the data to develop a ratio that clinicians can use to compare blood pressure readings when a person is sitting, versus after standing for several minutes. The findings suggest that patient reports of fainting or dizziness when standing warrant a careful assessment of blood pressure and heart rate when lying flat and after standing up for several minutes. Early and accurate diagnosis of LBD may be aided by the detection of neurogenic OH.
