The effects of a novel "fluid loading" strategy on cardiovascular and haematological responses to orthostatic stress.

Water drinking reduces the occurrence of syncope in healthy volunteers but the effects of hyperhydration are unknown. This study assessed the effects of combined creatine (Cr) and glycerol (Gly) induced hyperhydration on the cardiovascular and haematological responses to postural change. Subjects in all trials lay supine for 30 min before being tilted head-up to 70 degrees for a further 30 min or until the limit of their tolerance. Following 2 baseline trials, 19 subjects were matched for body mass and assigned to ingest either 20 g Cr and 2 g Gly kg(-1) body mass (BM) plus 2 l of water or 2 l of water alone (Pl) each day for 6 days and once more 5 h prior to the experimental trial. Subjects ingested 500 ml of water prior to all trials to ensure euhydration. During baseline trials, 3 subjects in the Cr/Gly group and 2 in the Pl group experienced presyncope during head-up tilt. Following Cr/Gly supplementation, BM increased by (mean +/- S.D.) 0.9 +/- 0.3 and total body water (TBW) increased by 0.7 +/- 0.2 l with no change in the Pl group. Cr/Gly supplementation resulted in a significant increase in systolic (11 mmHg) and diastolic (7 mmHg) blood pressure during head-up tilt with no change following Pl supplementation. Cr/Gly. Following Cr/Gly supplementation the number of subjects who became presyncopal was reduced from 3 to 1, with no change in the Pl group. These data suggest that hyperhydration mediated by Cr and Gly can enhance orthostatic tolerance in healthy individuals.