Real-Time Magnetic Resonance Imaging to Study Orthostatic Intolerance Mechanisms in Human Beings: Proof of Concept.

Background Discerning the mechanisms driving orthostatic symptoms in human beings remains challenging. Therefore, we developed a novel approach combining cardiac and cerebral real-time magnetic resonance imaging, beat-to-beat physiological monitoring, and orthostatic stress testing through lower-body negative pressure (LBNP). We conducted a proof-of-concept study in a patient with severe orthostatic hypotension. Methods and Results We included a 46-year-old man with pure autonomic failure. Without and during -30 mmHg LBNP, we obtained 3T real-time magnetic resonance imaging of the cardiac short axis and quantitative flow measurements in the pulmonary trunk and middle cerebral artery. Blood pressure was 118/74 mmHg during supine rest and 58/35 mmHg with LBNP. With LBNP, left ventricular stroke volume decreased by 44.6%, absolute middle cerebral artery flow by 37.6%, and pulmonary trunk flow by 40%. Conclusions Combination of real-time magnetic resonance imaging, LBNP, and continuous blood pressure monitoring provides a promising new approach to study orthostatic intolerance mechanisms in human beings.