Dietary Sodium Manipulation And Cerebrovascular Reactivity During Isometric Handgrip Exercise: A Pilot Study

High dietary sodium (HS) is associated with cerebrovascular dysfunction and higher stroke risk. We previously found that HS for 10 days did not change cerebrovascular reactivity to high or low CO2 in young adults. However, it is unclear whether HS affects cerebrovascular reactivity during exercise. PURPOSE: The purpose of this study was to test the hypothesis that short-term dietary sodium (Na+) manipulation would not change middle cerebral artery blood velocity (MCAv) responses during isometric handgrip exercise (HG). METHODS: In a randomized crossover study, participants completed three 10-day conditions separated by ≥4 weeks: low Na+ (LS: 1000 mg/d), dietary guideline recommended Na+ (RS: 2300 mg/d), and HS (7000 mg/d). The diets were matched for calories, macronutrients, and potassium. We assessed right MCAv via transcranial Doppler, beat-to-beat blood pressure (BP) via finger photoplethysmography, and end-tidal CO2 (ETCO2) via capnography during supine rest (10 min) and HG at 40% of their maximum voluntary contraction (2 min). We assessed changes (Δ) from baseline to the final minute of HG in mean BP, mean MCAv, cerebrovascular conductance index (CVCi; mean MCAv/mean BP), and MCAv pulsatility index (PI; [peak MCAv - nadir MCAv]/mean MCAv). We compared changes between conditions with Friedman’s test. We present normally distributed data as mean ± SD and non-normal data as median [IQR]. We quantified differences with Kendall’s W effect size. RESULTS: We obtained triplicate data in 6 male adults (Age: 23 [1] years; body mass index: 25.0 ± 1.6 kg/m2). Increasing dietary Na+ increased urinary Na+ excretion (LS: 51 [37]; RS: 85 [45]; HS: 191 [100] mM/24 h; P = 0.03, W = 0.60). Baseline ETCO2, mean BP, MCAv, CVCi, PI, and relative HG intensity were not different between conditions (Ps ≥ 0.08). There were no differences in Δmean BP (LS: 12 ± 7, RS: 22 ± 6, vs. HS: 13 ± 12 mmHg; P = 0.22, W = 0.25), ΔMCAv (LS: 1.7 ± 6.9, RS: 11.5 ± 14.0, vs. HS: 7.1 ± 9.0 mmHg; P = 0.12, W = 0.36), ΔCVCi (LS: -0.07 ± 0.06, RS: -0.01 ± 0.12, vs. HS: 0.00 ± 0.10 mmHg; P = 0.61, W = 0.08), or ΔPI (LS: -0.23 ± 0.23, RS: -0.30 ± 0.20, vs. HS: -0.20 ± 0.15 P = 0.61, W = 0.08) between conditions. CONCLUSION: These pilot data indicate that short-term dietary sodium manipulation has a negligible effect on ΔCVCi and ΔPI, and a moderate effect on ΔMCAv during HG among healthy adults. Supported by: ATR (K01HL147998), MCB (K01HL164978), and JCW (K01HL160772) are supported by the National Institutes of Health. JCW is also supported by the American Heart Association (23CDA1037938).