The Effect of Torso Rotation on Blood Pressure Regulation during Tilt-Table Testing
- Paper number
IAC-07-A1.2.02
- Author
Dr. Marlene Grenon, McGill University, Canada
- Coauthor
Dr. Douglas Watt, Canada
- Year
2007
- Abstract
INTRODUCTION : Orthostatic intolerance (OI) continues to represent an important challenge after spaceflight. It is also known that changes in the vestibular system occur during spaceflight. Since the vestibular system is thought to be implicated in blood pressure (BP) regulation in animals and humans through the vestibulosympathetic reflexes, we hypothesized that an acute suppression of vestibular function would lead to an increase in OI during tilt-table testing (TTT). METHODS : Eight healthy male and female subjects with no history of syncope participated in the present study. Torso rotation (TR) was used to produce a partial and temporary suppression of vestibular function. False torso rotation (FTR), which provides the same amplitude and frequency of head rotation relative to the body as TR, but without significant rotation of the head relative to space, was used to control for the effect of physical activity by TR on BP regulation. TTT was used to assess OI. After 2.5 minutes in the supine position, the subjects were raised to an angle of 70 degrees which was maintained for 10 minutes during which BP and heart rate (HR) were measured. Each subject took part in two experimental sessions, designated A and B. Session A included control TTT, 30 minutes of normal activity, repeat control TTT, 30 minutes of TR and post-TR TTT. Session B was similar to except that TR was replaced by FTR. Drop in systolic or diastolic BP of more than 20 mm Hg was considered significant for OI, along with the presence of OI symptoms. RESULTS : No significant difference in episodes of OI were noted between control TTT and post-TR TTT. One subject experienced a significant drop in BP during the control and the post-TR TTT (event asymptomatic). A second subject experienced a drop in BP during the control TTT only (event asymptomatic). A third subject experienced a drop in BP during the post-TR TTT only (subject symptomatic). A fourth subject experienced a late drop in BP during the post-TR TTT (event asymptomatic). All other subjects experienced no changes in hemodynamics or symptoms with TTT. FTR did not significantly affect BP or HR control during TTT. CONCLUSIONS : Based on the present data, we can state that suppression of vestibular function using TR does not significantly affect BP regulation during head-up tilt, and does not lead to increase in OI.
- Abstract document