Cardiovascular deconditioning during space flight and the use of saline as a countermeasure to orthostatic intolerance

Results are reported of trials with oral hydration by astronauts before reentry of the Orbiter. The experiments were run to evaluate hydration as a means of offsetting the loss of lower body negative pressure experienced after several days in space. The rehydration was carried out by 17 astronauts who ingested salt tablets and water prior to the end of the first eight STS mission orbital phases; nine astronauts abstained. Pulse and blood pressure data were collected from 1-2 hr post landing. Measurements were also made of the extent of cardiac deconditioning and the response to orthostatic stress (standing). Ingestion of the salt tablets reduced the heart rate response to stress an average of 29 percent. The statistical significance of the difference has encouraged adoption of the salt tablet countermeasure as an operational procedure by Shuttle astronauts.