The Influence of Acute Beetroot Juice Consumption on Cerebral Autoregulation during Orthostatic Stress
Authors: Zazulak Hannah E. , Reed Emma L. , Worley Morgan L. , Chapman Christopher L. , Schlader Zachary J. , Johnson Blair D. 
Published: April 2020

Beetroot juice (BRJ) supplementation improves cerebrovascular function during exercise. Breathing a mild hypercapnic gas transiently reduces cerebral autoregulation in healthy participants. However, it is unknown if acute BRJ consumption improves cerebral autoregulation while breathing a mild hypercapniac gas.PurposeWe tested the hypothesis that acute BRJ consumption improves cerebral autoregulation while breathing a mild hypercapnic gas during oscillatory lower body negative pressure (LBNP).MethodsEight healthy participants (age: 27±5 y, 3 F) completed a 5 min baseline (BL) followed by 6 min of LBNP intervals (30s at −70 mmHg, 30s at 0 mmHg) while breathing a mild hypercapnic gas (3% CO2, 21% O2, 76% N2). LBNP was performed pre (PRE) and 3 hours after consuming 500 mL of BRJ (BRJ). Mean arterial pressure (MAP), heart rate (HR), end‐tidal carbon dioxide tension (PETCO2), and middle cerebral artery blood velocity (MCAv) were continuously recorded. Cerebral vascular conductance (CVC) was calculated as MCAv divided by MAP. The magnitude of change in MAP, HR, PETCO2, MCAv, and CVC due to LBNP were calculated from the mean change from BL (Δ) obtained during each interval throughout the LBNP protocols. Cerebral autoregulation (i.e., gain and phase) was assessed throughout the LBNP protocols using Fourier transformation and is reported for BL and as the change from BL (Δ). Values are reported as Δ mean±SD.ResultsThere were no differences between conditions at BL for MAP (PRE: 99±8 vs. BRJ: 95±7 mmHg; P=0.10), HR (PRE: 65±9 vs. BRJ: 65±10 bpm; P=0.40), PETCO2 (PRE: 48±3 vs. BRJ: 49±3 mmHg; P=0.30), CVC (PRE: 0.86±0.18 vs. BRJ: 0.83±0.13 cm/s/mmHg; P=0.16) gain (PRE: 0.96±0.29 vs. BRJ: 0.93±0.22 cm/s/mmHg; P=0.31), or phase (PRE: 7±5 vs. BRJ: 10±6°; P=0.19). At BL, MCAv was lower with BRJ (PRE: 84±14 vs. BRJ: 79±11 cm/s; P<0.01). The ΔMAP during −70 mmHg did not differ with BRJ (PRE: −8±5 vs. BRJ: −6±6 mmHg; P=0.51). The ΔMAP did not differ from BL during 0 mmHg PRE (P=0.44) but the ΔMAP was greater during 0 mmHg with BRJ (PRE: 1±3 vs. BRJ: 4±2 mmHg; P=0.03). The ΔHR was greater during −70 mmHg with BRJ (PRE: 13±10 vs. BRJ: 16±11 bpm; P=0.05) but the ΔHR during 0 mmHg did not differ with BRJ (PRE: −5±4 vs. BRJ: −3±3 bpm; P=0.29). The ΔPETCO2 did not differ between PRE and BRJ during −70 mmHg (PRE: −3±1 vs. BRJ: −3±2 mmHg; P=0.91) or 0 mmHg (PRE: −1±1 vs. BRJ: −1±2 mmHg; P=0.91). ΔMCAv did not differ from BL or between PRE and BRJ during −70 mmHg (PRE: −5±18 vs. BRJ: −4±16 cm/s; P=0.76) and 0 mmHg (PRE: −2±14 vs. BRJ: −1±13 cm/s; P=0.76). The ΔCVC did not differ with BRJ during −70 mmHg (PRE: −0.01±0.11 vs. BRJ: −0.03±0.08 cm/s/mmHg; P=0.20) but was greater with BRJ during 0 mmHg (PRE: −0.07±0.05 vs. BRJ: −0.11±0.08 cm/s/mmHg; P=0.02). During LBNP, there were no differences between conditions for Δgain (PRE: −0.03±0.18 vs. BRJ −0.05±0.10 cm/s/mmHg; P=0.41) or Δphase (PRE: −1±5 vs. BRJ: −3±8.2°; P=0.34).ConclusionsThese preliminary data indicate that acute BRJ does not alter cerebral autoregulation during an orthostatic stressor while healthy participants breathed a mild hypercapnic gas. Further investigations are warranted to determine if chornic BRJ ingestion affects cerebral autoregulation.