The Effect of Age on Exercise Blood Pressure Responses Following Short‐term Water Deprivation

Aging impairs regulation of body fluid homeostasis (attenuated thirst sensations, blunted anti‐diuretic hormone release, and reduced renal function) leading to a greater incidence of hypernatremia (elevated serum sodium concentrations ([sNa + ])). Previous studies suggest significantly greater increases in [sNa + ] following water deprivation (WD) in older adults (OA) compared to young adults (YA). This is problematic as data from animal models suggest a relation between plasma hypernatremia and exaggerated blood pressure (BP) responses during sympathoexcitatory stimuli. This is clinically relevant in humans because exaggerated BP responses to sympathoexcitatory stimuli is associated with greater future incidence of hypertension. However, it is unknown whether WD causes greater increases in [sNa + ] and consequently larger increases in BP responses during sympathoexcitatory stimuli in OA compared to YA. PURPOSE To test the hypothesis that WD causes greater increases in [sNa + ] and consequently larger increases in BP responses during exercise pressor reflex activation in OA compared to YA. METHODS Twenty‐five healthy YA (11F/14M; age: 25±1 yrs; BMI: 23±1 kg/m 2 ; screening BP: 108±2/59±2 mmHg) and eight healthy OA (7F/1M; age: 67±2 yrs; BMI: 23±1 kg/m 2 ; screening BP: 119±5/77±3 mmHg) completed two hydration conditions in random crossover fashion. A normal hydration control visit (CON; 23mL water/kg bodyweight/day for three days) and WD visit (stepwise reduction in water intake over three days followed by a 16h WD prior to testing) were separated by at least one week. Beat‐to‐beat BP was measured via finger photoplethysmography throughout a ten‐minute baseline, isometric handgrip exercise (HG; 30% MVC, two minutes), and post‐exercise ischemia (PEI; upper arm occlusion, three minutes). Changes in [sNa + ] and resting BP were analyzed using two‐way independent group ANOVAs (condition x age). Responses during the final minute of HG and all three minutes of PEI were each compared to the baseline period using a two‐way ANCOVA (condition x age, with resting brachial systolic BP as a covariate). Significance was set a priori at p<0.05. RESULTS Both age groups had higher [sNa + ] during WD compared to CON (YA: 141.3±0.5 vs. 142.6±0.5, OA: 142.2±1.0 vs. 143.1±0.8 mmol/L, condition: p=0.024, age: p=0.421, interaction: p=0.601). OA had higher resting BP than YA during both conditions (YA: 112±2 vs. 112±2, OA: 144±8 vs. 139±7 mmHg, condition: p=0.220, age: p<0.001, interaction: p=0.076). Systolic BP responses were not different between age groups or conditions during HG (YA: Δ15±2 vs. 17±2, OA: Δ18±7 vs. 16±2 mmHg, F(1,61)=0.539, p=0.708, partial η 2 =0.04), or PEI (YA: Δ14±2 vs. 17±3, OA: Δ23±6 vs. 20±2 mmHg, F(1,61)=0.331, p=0.567, partial η 2 =0.005; CON vs. WD mean±SEM for all results). CONCLUSION These preliminary data suggest that short‐term WD does not elicit larger increases in [sNa + ] or larger increases in BP responses during exercise pressor reflex activation in OA compared to YA. Support or Funding Information NIH Grant 1R01HL128388 (WBF & SDS), NIGMS P20GM113125, and University Doctoral Fellowship (JCW). This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .