Identifying the role of group III/IV muscle afferents in the carotid baroreflex control of mean arterial pressure and heart rate during exercise

Abstract

This study sought to comprehensively investigate the role of metabolically and mechanically sensitive group III/IV muscle afferents in carotid baroreflex responsiveness and resetting during both electrically evoked (EVO, no central command) and voluntary (VOL, requiring central command) isometric single-leg knee-extension (15% of maximal voluntary contraction; MVC) exercise. Participants (n = 8) were studied under control conditions (CTRL) and following lumbar intrathecal fentanyl injection (FENT) to inhibit μ-opioid receptor-sensitive lower limb muscle afferents. Spontaneous carotid baroreflex control of mean arterial pressure (MAP) and heart rate (HR) were assessed following rapid 5 s pulses of neck pressure (NP, +40 mmHg) or suction (NS, -60 mmHg). Resting MAP (87 ± 10 mmHg) and HR (70 ± 8 bpm) were similar between CTRL and FENT conditions (P > 0.4). In terms of spontaneous carotid baroreflex responsiveness, FENT did not alter the change in MAP or HR responses to NP (+13 ± 5 mmHg, P = 0.85; +9 ± 3 bpm; P = 0.99) or NS (-13 ± 5 mmHg, P = 0.99; -24 ± 11 bpm; P = 0.49) at rest or during either exercise protocol, which were of a remarkably similar magnitude to rest. In contrast, FENT administration reduced the exercise-induced resetting of the operating point for MAP and HR during both EVO (116 ± 10 mmHg to 100 ± 15 mmHg and 93 ± 14 bpm to 82 ± 10 bpm) and VOL (107 ± 13 mmHg to 100 ± 17 mmHg and 89 ± 10 bpm to 72 ± 10 bpm) exercise bouts. Together, these findings document that group III/IV muscle afferent feedback is critical for the resetting of the carotid baroreflex MAP and HR operating points, independent of exercise-induced changes in central command, but not for spontaneous carotid baroreflex responsiveness.

Sex differences in diaphragmatic fatigue: the cardiovascular response to inspiratory resistance

“…Recent work indicates that the interaction between pressor and carotid baroreflex control of HR and MAP may be additive and independent of central command (Hureau et al . ). It remains to be elucidated if attenuation of group III/IV afferent feedback compromises cardiovascular adjustments during exercise differently in men and women.…”

Blunted cardiovascular responses to exercise in Parkinson’s disease patients: role of the muscle metaboreflex

“…The BP response to exercise arises from the activation of central command and EPR; however, the arterial baroreflex also plays an important modulator role in this response (Fisher et al 2015;Raven et al 2006). During exercise, the arterial baroreflex is reset and remains operative throughout (Fadel 2008;Joyner 2006), a process that occurs at the onset of the exercise probably directed by activation of skeletal muscle sensory fibers (Degtyarenko and Kaufman 2006;Hureau et al 2018;Papelier et al 1997), which functionally allows the arterial baroreflex to buffer the exercise-induced elevations in MSNA and BP. In this sense, the blunted metaboreflex activation presented in patients with PD could result in an impaired exercise-induced arterial baroreflex resetting, which could become worse with disease progression given that a moderate correlation to disease stage and a strong correlation to disease duration were found relative to cBRS, but further studies will need to confirm this hypothesis.…”

Corticospinal excitability during fatiguing whole body exercise

“…Investigations attempting to decipher the role of group III/IV muscle afferents on corticospinal excitability during fatiguing whole body exercise have utilized a pharmacological approach to temporarily attenuate the activity of these muscle afferents. Lumbar intrathecal fentanyl, a μ-opioid receptor agonist, attenuates approximately 60% of group III and IV muscle afferent feedback from the legs (Amann et al, 2009; Hureau et al, 2018a) via the closing of N-type voltage-gated calcium channels (Estrada and Kaufman, 2018). While the attenuation of these afferents have implications on the regulation of cardiovascular, ventilatory, and fatigue responses to exercise (Amann et al, 2015), this section will focus on the role of group III/IV muscle afferent feedback as a mechanism influencing the excitability of the corticospinal pathway.…”