5 years ago

Inorganic nitrate supplementation attenuates peripheral chemoreflex sensitivity but does not improve cardiovagal baroreflex sensitivity in older adults.

Bock, Bryan, Schneider, Ueda, Casey, Limberg, Hughes
Aging is associated with increased peripheral chemoreceptor activity, reduced nitric oxide (NO) bioavailability, as well as attenuation of cardiovagal baroreflex sensitivity (BRS), collectively increasing the risk of cardiovascular disease. Evidence suggests NO may attenuate peripheral chemoreflex sensitivity and increase BRS. Exogenous inorganic nitrate increases NO bioavailability via the nitrate-nitrite-nitric oxide pathway. Our hypothesis was that inorganic nitrate supplementation would attenuate peripheral chemoreflex sensitivity and enhance spontaneous cardiovagal BRS in older adults. We studied 13 older adults (67±3yrs) using a randomized, placebo-controlled crossover design with subjects' ingesting beetroot powder containing (BRA) or devoid of (BRP) nitrate and nitrite daily over four weeks. Spontaneous cardiovagal BRS was assessed over 15min of rest and was quantified using the sequence method. Chemoreflex sensitivity was assessed via ~5min of hypoxic (10% FiO2) exposure and reported as the slope of the relationship between oxygen saturation (%SpO2) and minute ventilation (L/min) or heart rate (HR, beats/min). Ventilatory responsiveness to hypoxia was reduced following BRA (-0.14±0.04 to -0.05±0.02 L/min/%SpO2, P=0.01) versus BRP (-0.10±0.05 to -0.11±0.05 L/min/%SpO2, P=0.80) with no differences in HR responsiveness (BRA: -0.47±0.06 to -0.33±0.04, BRP: -0.48±0.07 to -0.42±0.06 beats/min/%SpO2) between conditions (interaction effect P=0.41). Spontaneous cardiovagal BRS was unchanged following BRA and BRP (interaction effects P=0.69, 0.94, and 0.39 for all-, up-, and down-sequences, respectively) despite a reduction in resting systolic and mean arterial blood pressure in the experimental group (BRA) (P<0.01 for both). These findings illustrate that inorganic nitrate supplementation attenuates peripheral chemoreflex sensitivity without concomitant change in spontaneous cardiovagal BRS in older adults.

Publisher URL: http://doi.org/10.1152/ajpheart.00389.2017

DOI: 10.1152/ajpheart.00389.2017

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