Analysis of cardiovascular responses to head-up tilt testing

Abstract

Introduction: Head-up tilt (HUT) testing is a widely accepted tool in the clinical evaluation of patients presenting with episodic loss of consciousness. The test has assumed its importance in aviation environment, where a single episode of unconsciousness in-flight may have a catastrophic outcome. To rule out this, HUT is carried out in all cases of syncope as a part of aeromedical evaluation. The present study was undertaken to analyze the CVS response to HUT conducted over a period of 11 years at the Department of Space and Environmental Physiology at the Institute of Aerospace Medicine. Material and Methods: A total of 168 subjects had undergone HUT testing from 2002 to 2012. The testing equipment was a standard tilt table with a foot board support for the feet and restraint system at the level of chest, waist, and ankle to support the body during tilting. The testing protocol consisted of passive tilting to an angle of 70° from the horizontal position for 45 min in all the cases. The physiological parameters consisting of heart rate (HR) and blood pressure from the database were analyzed to understand the CVS response to HUT. Results: Out of the total 168 patients, 147 (88.5%) cases showed normal response. Twenty-one (12.5%) cases showed abnormal response. Out of the cases showing abnormal response, 14 cases had syncope with frank loss of consciousness and could not maintain the postural tone. The remaining seven cases showed postural orthostatic tachycardia syndrome (POTS), where the HR increased by more than 30 beats per minute. Conclusion: A retrospective analysis of 168 cases with history of syncope, in a period of 11 years, revealed an abnormal cardiovascular response to HUT in 12.5% of cases. The abnormal physiological responses were mostly consistent with syncope and POTS.