Peripheral chemoreflex restrains skeletal muscle blood flow during exercise in participants with treated hypertension.

Abstract

We tested the hypothesis that in human hypertension, an increased tonicity/sensitivity of the peripheral chemoreflex causes a sympathetically mediated restraint of nutritive blood flow to the exercising muscles. Fourteen patients with treated hypertension (age 69 ± 11 years, 136 ± 12/80 ± 11 mmHg; mean ± SD) were studied under conditions of intravenous 0.9% saline (control) and low-dose dopamine (2 µg kg-1 min-1) to inhibit the peripheral chemoreflex, at baseline, during isocapnic hypoxic rebreathing and during rhythmic handgrip exercise (3 min, 50% maximum voluntary contraction). At baseline, dopamine did not change mean blood pressure (95 ± 10 vs. 98 ± 10 mmHg, P = 0.155) but increased brachial artery blood flow (59 ± 20 vs. 48 ± 16 ml min-1, P = 0.030) and vascular conductance (0.565 ± 0.246 vs. 0.483 ± 0.160 ml min-1 mmHg-1; P = 0.039). Dopamine attenuated the increase in mean blood pressure (∆3 ± 4 vs. ∆8 ± 6 mmHg, P = 0.007) to isocapnic hypoxic rebreathing and reduced peripheral chemoreflex sensitivity by 28 ± 37% (P = 0.044). Rhythmic handgrip exercise induced increases in brachial artery blood flow and vascular conductance (both P < 0.05 vs. rest after 45 s) that were greater with dopamine than saline (e.g. Δ76 ± 54 vs. Δ60 ± 43 ml min-1 and Δ0.730 ± 0.440 vs. Δ0.570 ± 0.424 ml min-1 mmHg-1, respectively, at 60 s; main effect of condition both P < 0.0001). Our results indicate that the peripheral chemoreflex is tonically active at rest and restrains the blood flow and vascular conductance increases to exercise in treated human hypertension. KEY POINTS: It was hypothesised that in human hypertension, an increased tonicity/sensitivity of the peripheral chemoreflex causes a sympathetically mediated restraint of nutritive blood flow to the exercising muscles. Treated patients with hypertension (n = 14) were studied under conditions of intravenous 0.9% saline (control) and low-dose dopamine (2 µg kg-1 min-1) to inhibit the peripheral chemoreflex. Low-dose dopamine reduced resting ventilation and peripheral chemoreflex sensitivity, and while mean blood pressure was unchanged, brachial artery blood flow and vascular conductance were increased. Low-dose dopamine augmented the brachial artery blood flow and vascular conductance responses to rhythmic handgrip. These findings indicate that the peripheral chemoreflex is tonically active at rest and restrains the blood flow, and vascular conductance increases to exercise in treated human hypertension.