The effect of mild hypohydration on resting and reflex blood pressure regulation in healthy young and old adults
Date
2019
Authors
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Publisher
University of Delaware
Abstract
Arterial blood pressure (BP) dysregulation is associated with increased future risk of cardiovascular disease, the leading cause of death among adults in the United States. Indices of BP dysregulation include 1) high resting BP (i.e., hypertension), 2) high BP variability, and 3) exaggerated BP responses during exercise. Hypohydration is common among adults in daily life, is associated with future cardiovascular disease risk, and has greater incidence during aging. However, it is unknown whether hypohydration is a causative factor for BP dysregulation. Therefore, we sought to determine if acute hypohydration causes BP dysregulation. In randomized crossover fashion, 45 non-obese and non-hypertensive adults (35 young & 10 old adults with similar body mass index values and habitual physical activity levels) completed: 1) a normally hydrated control condition (CON) via a three-day protocol with prescribed water intake, and 2) a water deprivation condition (WD) via a stepwise reduction in water intake over three-days concluded with a 16-hour water abstention period. All experimental visits were separated by at least one week. No participants were currently taking any anti-hypertensive medications (inclusive of diuretics). Participants collected their urine and underwent ambulatory BP measurements throughout the 24-hour period preceding each experimental visit. On the day of the experimental visit we measured hydration biomarkers and brachial BP (automated oscillometric device). While participants lie quietly in the supine position, we continuously assessed heart rate (single-lead ECG), beat-to-beat BP (photoplethysmography), muscle sympathetic nerve activity (peroneal microneurography; 23 paired recordings), and common femoral artery blood flow (sonography) at rest and two minutes of isometric handgrip exercise. WD elicited mild hypohydration as evidenced by elevated plasma osmolality, urine osmolality and specific gravity, and thirst rating similarly among young and old adults. Despite mild hypohydration, WD did not increase: 1) resting or ambulatory daytime BP values, 2) resting or ambulatory BP variability, or 3) sympathetic or BP responses during handgrip exercise or the cold pressor test in either young or old adults. Together, our findings suggest that this model of acute mild hypohydration does not alter resting or reflex BP regulation in healthy young and old adults.