The effect of water temperature on orthostatic tolerance: a randomised crossover trial.

Purpose: Bolus water drinking, at room temperature, has been shown to improve orthostatic tolerance (OT), probably via sympathetic activation; however, it is not clear whether the temperature of the water bolus modifies the effect on OT or the cardiovascular responses to orthostatic stress. The aim of this study was to assess whether differing water temperature of the water bolus would alter time to presyncope and/or cardiovascular parameters during incremental orthostatic stress.
Methods: Fourteen participants underwent three head-up tilt (HUT) tests with graded lower body negative pressure (LBNP) continued until presyncope. Fifteen minutes prior to each HUT, participants drank a 500 mL bolus of water which was randomised, in single-blind crossover fashion, to either room temperature water (20 °C) (ROOM), ice-cold water (0-3 °C) (COLD) or warm water (45 °C) (WARM). Cardiovascular parameters were monitored continuously.
Results: There was no significant difference in OT in the COLD (33 ± 3 min; p = 0.3321) and WARM (32 ± 3 min; p = 0.6764) conditions in comparison to the ROOM condition (31 ± 3 min). During the HUT tests, heart rate and cardiac output were significantly reduced (p < 0.0073), with significantly increased systolic blood pressure, stroke volume, cerebral blood flow velocity and total peripheral resistance (p < 0.0054), in the COLD compared to ROOM conditions.
Conclusions: In healthy controls, bolus cold water drinking results in favourable orthostatic cardiovascular responses during HUT/LBNP without significantly altering OT. Using a cold water bolus may result in additional benefits in patients with orthostatic intolerance above those conferred by bolus water at room temperature (by ameliorating orthostatic tachycardia and enhancing vascular resistance responses). Further research in patients with orthostatic intolerance is warranted.
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