Acute hydration status and micro-vascular function in healthy human volunteers (LB363)

Introduction: Water is critical for most physiological functions and dehydration can be pathological. There is evidence that long-term hydration impacts cardiac reactivity, however, there is little data on acute hydration status and micro-vascular function. Aim: To investigate whether hydration statusimpacts capillary blood flow and endothelial function in healthy human volunteers. Methods: Hydration status was measured in 20 subjects (45.1±7.4y; 9 M; 11 F) using osmometry for urine osmolality and dipstick for urine specific gravity (USG). Micro-vascular function was measured using controlled Laser Doppler Iontophoresis (Moor LDI), with acetylcholine (ACh) and sodium nitroprusside (SNP), delivered to dermal forearm vessels using graded currents (0µA x 5s; 40µA x 10s; 60 µA x 30s; 100 µA x 60s). Results: Mean urine osmolality was 271.5 mOsm/kg and mean USG 1006.9. No correlations were found (p>0.05) between urine osmolality and ACh or SNP at any current, using linear regression. Similarly, no correlation was found between USG and ACh. A small but significant relationship was found between USG and SNP at 40µA (p=0.048). Conclusion: Based on these results,it appears that acute hydration status may not be a strong predictor of micro-circulatory response to SNP and ACh. However, as SNP at 40 µA is correlated with USG, larger studies are needed to investigate further and explore whether USG is a more sensitive hydration marker in a micro-circulatory/endothelial context.