fMRI in Postural Tachycardia Syndrome

Overview

Postural tachycardia syndrome (POTS) is one of the most common forms of chronic orthostatic intolerance in the United States. This is a disabling disorder characterized by an excessive increase in heart rate upon standing that is accompanied by symptoms such as dizziness and fatigue. One of the most under appreciated and bothersome symptoms of POTS is impaired cognition or "brain fog," which occurs to a level that interferes with daily activities such as work and education. Despite this high impact, the reasons why POTS patients have problems with cognition are not well understood. This project will test the overall hypothesis that "brain fog" in POTS is related to increased activation of cognitive brain regions during mental tasks when compared with healthy subjects, and that this activation is exacerbated by in the presence of orthostatic stress.

A randomized, double blind, crossover study will be conducted to determine if there are differences in resting brain structure and blood oxygen perfusion in postural tachycardia syndrome (POTS) compared with healthy subjects, and to identify the pattern of brain activation produced by cognitive testing under resting conditions and in the presence of a physical challenge mimicking orthostatic stress (lower body negative pressure, LBNP). This is an outpatient study that requires a screening visit in the Clinical Research Center within the Penn State Hershey Medical Center, and if eligible, two study visits in the Penn State Center for Nuclear Magnetic Resonance Imaging involving blood oxygen level dependent functional magnetic resonance imaging (BOLD-fMRI) and a cognitive test while lying in a magnetic resonance imaging (MRI) scanner with the lower body placed in the LBNP chamber. The LBNP chamber applies suction to the lower body to pool blood in the legs and physiologically mimic what happens when standing up. Blood pressure, heart rate, and oxygen saturation will be measured throughout the study. A scan will be performed while at rest to look at the structure and blood oxygen perfusion in the brain. The LBNP or sham pressure will then be initiated, with the order determined randomly and the other stress applied at the second study visit. Once the appropriate level of pressure is achieved, brain oxygen perfusion will be measured and subjects will be asked to complete one test of cognitive function. At the end of the cognitive test, brain oxygen levels will be measured and the testing will end. The time inside the MRI scanner at each study visit will be approximately 45 minutes.