A bedside test that measures heart rate in relation to blood pressure after standing may help doctors determine if a patient has neurologic disease, according to a study published online on February 5, 2018 in the Annals of Neurology.
When standing up abruptly, it is natural for blood pressure to drop slightly and then bounce back to normal, and for heart rate to increase temporarily. If the body fails to bounce back, blood pressure can stay abnormally low, a condition called orthostatic hypotension (OH). This may be caused by dehydration and anemia but it can also occur when neurologic conditions such as Parkinson disease, Lewy body dementia, or multiple system atrophy affect the way the nervous system controls blood pressure, also known as “neurogenic OH.”
In the past, doctors have noticed that patients with neurogenic OH have little or no change in heart rate when their blood pressures drop, while patients with OH from other causes usually experience a spike in heart rate. This difference, they realized, could be used as a clue to diagnose neurologic disease.
To distinguish neurogenic from non-neurogenic OH, researchers at the New York University School of Medicine sought to pinpoint the difference in heart rate change in relation to blood pressure drop after standing between the two groups. They studied 402 patients with OH from major clinics across the United States, 378 of whom had neurogenic OH and 24 of whom had OH due to other causes. They put the patients on a tilting table, which simulates going from lying down to standing up, and measured changes in blood pressure and heart rate.
Researchers found that patients with neurogenic OH had twice the fall in blood pressure but only one-third the increase in heart rate compared to those with non-neurogenic OH. They determined that a ratio of change of heart rate to change of blood pressure of less than 0.5 would make a good cutoff to distinguish neurogenic from non-neurogenic OH.
“Our results show that neurogenic OH can be diagnosed accurately based on the reduced increase in [heart rate] in relation to the fall in [blood pressure],” the authors write. Patients with OH who test positive using this method will require additional screening for underlying neurologic disease. A limitation to this study is that postural changes were conducted with a tilt table, which is a good approximation of going from a lying position to a standing position but may differ from active standing.