Effect of Short‐term Water Restriction on Blood Pressure Variability in Young Adults

Abstract

Water restriction causes an acute decline in plasma volume and subsequently elevates serum sodium and plasma osmolality. Rodent models demonstrate that elevated serum sodium and plasma osmolality increases blood pressure (BP) variability. This is important because elevated BP variability is an independent risk factor for adverse cardiovascular events. However, the effects of water restriction on BP variability in humans remains to be determined.PURPOSETo test the hypothesis that short‐term water restriction increases serum sodium and plasma osmolality and leads to greater BP variability in humans.METHODSYoung healthy adults (13M/11F, age: 25±1 yrs; BMI: 24±1 kg/m2; BP 107±2/60±1 mmHg) completed two three‐day‐long hydration protocols in randomized order, separated by at least one week. Women were tested in the early follicular phase of their menstrual cycle. Daily water intake for euhydration (EU) was 23 mL H2O/kg/day. Water intake for hypohydration (HYPO) consisted of a stepwise daily reduction in water intake, followed by a 16‐hour water abstention period prior to testing. Laboratory testing was conducted on day four of the protocols. Participants wore an ambulatory BP monitor and collected urine for urinalysis for 24 hours preceding each study visit. The ambulatory BP monitoring provides BP variability under free‐living conditions. Upon arrival to the laboratory, participants rested quietly in a dimly lit room in the supine position for ten minutes for the assessment of beat‐to‐beat BP variability via finger photoplethysmography under controlled conditions. The average real variability (ARV) index, the average of the absolute differences between all consecutive BP measurements, was determined. Standard deviation (SD) of BP was also determined.RESULTSHYPO led to higher plasma osmolality (290.6±1.0 vs. 287.7±1.0 mOsm/kg H2O, p<0.05), urine osmolality (707±42 vs. 470±32 mOsm/kg H2O, p<0.05), urine specific gravity (1.023±0.001 vs. 1.016±0.006, p<0.05) and thirst rating (7.0±0.4 vs. 2.7±0.6 on a 0–10 scale, p<0.05) compared to EU. Plasma volume declined (−5.4±1.3%) during HYPO compared to EU. Daytime ambulatory systolic BP variability was not different between HYPO and EU (ARV BP 9.1±0.4 vs. 10.0±0.6; SD BP 10.3±0.8 vs. 12.4±1.1, p>0.05 for both). Ambulatory mean and diastolic BP variability were not different between conditions (p>0.05). Beat‐to‐beat systolic BP variability was not different between HYPO and EU (ARV BP 2.0±0.1 vs. 1.9±0.1; SD BP 5.4±0.4 vs. 5.0±0.3, p>0.05 for both). Beat‐to‐beat mean and diastolic BP variability were also not different between conditions (p>0.05).CONCLUSIONThese preliminary data suggest that short‐term water restriction in young healthy adults does not increase ambulatory or beat‐to‐beat BP variability.Support or Funding InformationSupported by NIH Grant 1R01HL128388This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.