Water ingestion as prophylaxis against syncope.
BACKGROUND
Water ingestion raises blood pressure substantially in patients with perturbed autonomic control and more modestly in older subjects. It is unclear whether prophylactic water drinking improves orthostatic tolerance in normal healthy adults.


RESULTS
Twenty-two healthy subjects, 18 to 42 years of age, with no history of syncope underwent head-up tilt-table testing at 60 degrees for 45 minutes or until presyncope or syncope occurred. In their initial test, participants were randomized to either 16 oz (473 mL) of water drinking 5 minutes before tilt-table testing or tilt-table testing alone, with the alternative in a second test on a different day. During the first 30 minutes of tilt, 8 of 22 subjects without water experienced presyncope but only 1 of 22 who had ingested water (P=0.016). Water drinking attenuated the heart rate increase associated with tilt (P<0.001) while accentuating the increase in total peripheral resistance (P=0.012). The average time study participants tolerated head-up tilt was 26% longer after water (41.1+/-8.1 versus 32.6+/-14.3 minutes, mean+/-SD), with a pairwise mean difference of 8.5+/-14.0 minutes (95% CI, 2.3 to 14.7 minutes; P=0.011).


CONCLUSIONS
Water enhances tolerance of upright posture. The effect of water is mediated by increased peripheral vascular resistance. Water ingestion may constitute a simple and effective prophylaxis against vasovagal reactions in healthy subjects, such as those associated with blood donation.
Lu
Chih-Cherng
CC
Autonomic Dysfunction Center, Vanderbilt University School of Medicine, Nashville, Tenn 37232-2195, USA.
Diedrich
André
A
Tung
Che-Se
CS
Paranjape
Sachin Y
SY
Harris
Paul A
PA
Byrne
Daniel W
DW
Jordan
Jens
J
Robertson
David
D
D000293:Adolescent; D000328:Adult; D018592:Cross-Over Studies; D004295:Dihydroxyphenylalanine / Q000097:blood; D005260:Female; D006339:Heart Rate / Q000187:drug effects; D006801:Humans; D007022:Hypotension / Q000188:drug therapy / Q000503:physiopathology / Q000517:prevention & control; D008297:Male; D011187:Posture / Q000502:physiology; D012016:Reference Values; D013575:Syncope / Q000097:blood / Q000517:prevention & control*; D018667:Tilt-Table Test; D016896:Treatment Outcome; D014867:Water / Q000494:pharmacology*
D014867:Water; D004295:Dihydroxyphenylalanine