Analysis of Baroreflex during 28-hour bed-rest with Fluid Loading
- Paper number
IAC-08.A1.2.1
- Author
Ms. Anna Grinberg, International Space University (ISU), Canada
- Coauthor
Dr. Richard Hughson, University of Waterloo, Canada
- Year
2008
- Abstract
Fluid volume depletion is suspected to be a major contributor to orthostatic hypotension during prolonged bed-rest and spaceflight. Significant reductions in blood and plasma volumes are known responses to spaceflight and bed-rest studies greater than 5 hours in duration. These reductions may degrade the sensitivity of the arterial baroreflex. NASA’s proposed fluid loading protocol seeks to replace lost plasma volume by ingestion of salt tablets and water. The dosage is 15 ml/kg salt with one 1-g salt tablet for each 125 ml of water over 2 hours. To examine the physiological effects of this fluid loading protocol on blood pressure regulation, 8 male subjects completed two 28-hour bed-rest sessions, with and without a period of fluid loading occurring between 25.5 and 27.5 hours. Their responses to orthostatic stress were examined before and after fluid bed-rest by simulating orthostasis in a lower-body negative-pressure (LBNP) box during a progressive test (0, -10, -20, -30, and -40 mmHg). Physiological parameters including R-R interval, systolic blood pressure, and plasma volume were monitored. Spectral analysis was employed to determine any changes in baroreflex sensitivity with bed-rest, and if these changes were restored with fluid loading. Spectral analysis examines the relationship between systolic blood pressure and R-R interval times by analyzing frequency trends of the signals in the mid-frequency band (0.07-0.14 Hz). Data will be analyzed using a two-way ANOVA, examining the effects of fluid loading and different levels of LBNP on blood pressure regulation.
- Abstract document
- Manuscript document
(absent)