Increasing blood flow to exercising muscle attenuates systemic cardiovascular responses during dynamic exercise in humans

Abstract

Reducing blood flow to working muscles during dynamic exercise causes metabolites to accumulate within the active muscles and evokes systemic pressor responses. Whether a similar cardiovascular response is elicited with normal blood flow to exercising muscles during dynamic exercise remains unknown, however. To address that issue, we tested whether cardiovascular responses are affected by increases in blood flow to active muscles. Thirteen healthy subjects performed dynamic plantarflexion exercise for 12 min at 20%, 40%, and 60% of peak workload (EX20, EX40, and EX60) with their lower thigh enclosed in a negative pressure box. Under control conditions, the box pressure was the same as the ambient air pressure. Under negative pressure conditions, beginning 3 min after the start of the exercise, the box pressure was decreased by 20, 45, and then 70 mmHg in stepwise fashion with 3-min step durations. During EX20, the negative pressure had no effect on blood flow or the cardiovascular responses measured. However, application of negative pressure increased blood flow to the exercising leg during EX40 and EX60. This increase in blood flow had no significant effect on systemic cardiovascular responses during EX40, but it markedly attenuated the pressor responses otherwise seen during EX60. These results demonstrate that during mild exercise, normal blood flow to exercising muscle is not a factor eliciting cardiovascular responses, whereas it elicits an important pressor effect during moderate exercise. This suggests blood flow to exercising muscle is a major determinant of cardiovascular responses during dynamic exercise at higher than moderate intensity. integrated circulatory regulation; neural cardiovascular regulation; muscle metaboreflex DURING DYNAMIC EXERCISE, INCREASED skeletal muscle blood flow is essential to ensure an appropriate supply of O 2 to the active muscles and to remove the metabolic byproducts and generated heat. This exercise-induced skeletal muscle hyperemia is thought to be initially elicited by local mechanical and metabolic factors and to be modulated by neural cardiovascular regulatory mechanisms (8,41). Neural mechanisms also act to increase cardiac output (CO) and to redistribute blood flow from inactive regions to support the increase in skeletal muscle flow. This neural cardiovascular regulation is thought to be mediated by central command (41), as well as by feedback transmitted via afferent nerves (group III and IV fibers), innervating the working skeletal muscles, which are sensitive to mechanical (the so-called muscle mechanoreflex) and metabolic changes (the so-called muscle metaboreflex) (26,33,34,37,42), and are modulated via the arterial and cardiopulmonary baroreflexes (23,41,42).Reducing the blood flow to working muscles during dynamic exercise causes accumulation of metabolites within the active muscles and evokes muscle metaboreflex-mediated increases in sympathetic nerve activity, heart rate (HR), and systemic blood pressure (1,5,12,19,29,30,35,42). In addition, the reduced b...

Ventricular contraction and relaxation rates during muscle metaboreflex activation in heart failure: are they coupled?

“…The muscle metaboreflex is a negative feedback reflex which acts to lessen metabolite accumulation in the skeletal muscle by increasing total systemic blood flow (e.g. cardiac output) as well as arterial O 2 content via red blood cell mobilization (Coutsos et al., 2010; Crisafulli et al., 2003, 2011; Ichinose et al., 2010; Ichinose, Ichinose‐Kuwahara, Kondo, & Nishiyasu, 2015; O'Leary, Eric, Ansorge, & Collins, O'Leary & Augustyniak, 1998; Augustyniak et al., 2000; Sala‐Mercado et al., 2006; Sheriff, Wyss, Rowell, & Scher, 1987). In healthy subjects during relative ischaemia, when the levels of metabolites rise within the skeletal muscle they activate metabosensitive afferents.…”

Anaerobic metabolism induces greater total energy expenditure during exercise with blood flow restriction

“…By decreasing the availability of O 2 (reduced arterial and venous leg blood) to the exercising muscles and retaining the need for energy production to maintain muscle contraction, it is also plausible to suppose that cycling with BFR might increase cardiorespiratory response by metaboreflex [ 37 ] and/or by decreased venous return [ 6 , 29 ]. During BFR exercise the metabolic stress (e.g., [La - ], Pi, pH) will be increased [ 38 , 39 ] and stimulate metabolically sensitive group III and IV afferent nerve endings within the active muscle, eliciting a reflex increase in efferent sympathetic nerve activity and systemic arterial pressure, known as muscle metaboreflex [ 12 , 40 ], a reflex that significantly contributes to the autonomic cardiorespiratory response to exercise, as well as, increasing and HR [ 13 , 41 ].…”

“…The normal blood flow to exercising muscle during exercise at 40% of peak workload seems not to elicit cardiovascular responses, while exercise at 60% of peak workload can induce an important pressor effect [ 37 ]. Although both our exercise protocols were performed with mild intensity exercise (40% of power output at ), it seems LIE-BFR induced a great combination between intensity and local hypoxia to increase and HR, probably resulting from metaboreflex and reduced blood venous return.…”

Voluntary apnea during dynamic exercise activates the muscle metaboreflex in humans

“…In experiment 2, we measured LBF using Doppler ultrasound as previously described (30,54). Briefly, a Doppler ultrasound system (HDI 3500, ATL Ultrasound) equipped with a model L7-4 transducer probe (operating frequency: 4 MHz) was used to simultaneously measure two-dimensional common femoral artery diameter and mean blood velocity (MBV).…”