Cardiac Baroreflex Sensitivity during Mild Hypercapnia Following Acute Beetroot Juice Consumption
Authors: Seymour Lauren E. , Fitts Triniti , Reed Emma L. , Worley Morgan L. , Schlader Zachary J. , Johnson Blair D. 
Published: April 2020

Introduction

Patients with obstructive sleep apnea often exhibit augmented arterial carbon dioxide tension (CO2) and autonomic dysfunction, which result in increased sympathetic activity and reduced baroreflex sensitivity. Beetroot juice (BRJ) is a popular nutraceutical that decreases resting sympathetic nerve activity and improves vascular function. However, the effects of acute BRJ consumption on cardiac baroreflex sensitivity (cBRS) in healthy individuals with elevated arterial CO2 is unknown.

Purpose

We tested the hypothesis that acute BRJ consumption will decrease cBRS during mild hypercapnia.

Methods

Thirteen healthy adults (age: 26±4 years; 5 females) participated in two oscillatory lower body negative pressure (OLBNP) protocols while breathing a mild hypercapnic gas (3% CO2; 21% O2; 76% N2) during one study visit. OLBNP protocols were completed before (PRE) and 3 hours after consuming 500 mL of beetroot juice (BRJ). After a 5 min resting baseline (BL), the OLBNP protocols consisted of alternating 30 s intervals between −70 mmHg and 0 mmHg for a total of 5 min. Blood pressure (finger photoplethysmography), heart rate (HR; ECG), and end‐tidal CO2 tension (PETCO2; capnography) were continuously recorded and mean values across the −70 mmHg and 0 mmHg intervals during OLBNP were calculated. The sequence method (WinCPRS) was used to calculate cBRS from the obtained beat‐to‐beat blood pressure and R‐R interval data at PRE and BRJ throughout the 5 min BL and 5 min of OLBNP. cBRS was represented by Up‐cBRS and Down‐cBRS sequences and overall cBRS gain.

Results

At BL, there were no differences in HR (PRE: 65±9 vs BRJ: 66±9 bpm; P=0.69), systolic blood pressure (SBP; PRE: 132±10 vs BRJ: 130±10 mmHg; P=0.17), diastolic blood pressure (DBP; PRE: 74±8 vs BRJ: 72±5 mmHg; P=0.14) and PETCO2 (PRE: 49±4 vs BRJ: 49±4 mmHg; P=0.45). At BL, mean arterial pressure (MAP) was lower with BRJ (96±8 vs 93±7 mmHg; P=0.01). At BL, there were no differences in Up‐BRS (PRE: 27±16 vs BRJ: 26±14 ms/mmHg; P=0.93), Down‐BRS (PRE: 22±11 vs BRJ: 20±9 ms/mmHg; P=0.65), or cBRS Gain (PRE: 17±8 vs BRJ: 19±8 ms/mmHg; P=0.18). During 0 mmHg of OLBNP, there were no differences in HR (PRE: 62±8 vs BRJ: 63±9 bpm; P=0.38), MAP (PRE: 98±7 vs BRJ: 97±6 mmHg; P=0.73), SBP (PRE: 133±7 vs BRJ: 133±10 mmHg; P=0.79), DBP (PRE 73±9 vs BRJ 74±5 mmHg; P=0.48), and PETCO2 (PRE 48±3 vs BRJ 48±4 mmHg; P=0.86). During −70 mmHg of OLBNP, there were no differences in DBP (PRE: 71±12 vs BRJ: 72±9 mmHg; P=0.48) or PETCO2 (PRE: 46±3 vs BRJ: 46±4 mmHg; P=0.86). During −70 mmHg of OLBNP with BRJ, HR was higher (77±10 vs 81±13 bpm; P<0.01), MAP was lower (90±10 vs 88±10 mmHg; P=0.01), and SBP was lower (123±13 vs 120±16 mmHg; P=0.01). During OLBNP, there were no differences in Up‐BRS (PRE: 15±8 vs BRJ: 16±8 ms/mmHg; P=0.94), Down‐BRS (PRE: 14±7 ms/mmHg vs BRJ: 13±5 ms/mmHg; P=0.65), or cBRS Gain (PRE 13±6 vs BRJ 11±6 ms/mmHg P=0.18).

Conclusions

Despite slight reductions in MAP following a single bolus of BRJ, there was no difference in cBRS in healthy participants while breathing a hypercapnic gas during an orthostatic challenge. Further research is warranted to determine the effects of chronic BRJ consumption on cBRS.