Muscle metaboreflex and cerebral blood flow regulation in humans: implications for exercise with blood flow restriction

Abstract

We investigated the effect of activating metabolically sensitive skeletal muscle afferents (muscle metaboreflex) on cerebral blood flow and the potentially confounding influence of concomitant changes in the partial pressure of arterial carbon dioxide. Eleven healthy males (25 ± 4 yr) performed submaximal leg cycling exercise on a semirecumbent cycle ergometer (heart rate: ∼120 beats/min), and assessments were made of the partial pressure of end-tidal carbon dioxide (PetCO2 ), internal carotid artery blood flow (ICAQ) and conductance (ICACVC), and middle cerebral artery mean blood velocity (MCAvm) and conductance index (MCACVCi).The muscle metaboreflex was activated during cycling with leg blood flow restriction (BFR) or isolated with postexercise ischemia (PEI). In separate trials, PetCO2 was either permitted to fluctuate spontaneously (control trial) or was clamped at 1 mmHg above resting levels (PetCO2 clamp trial). In the control trial, leg cycling with BFR decreased PetCO2 (Δ-4.8 ± 0.9 mmHg vs. leg cycling exercise) secondary to hyperventilation, while ICAQ, ICACVC, and MCAvm were unchanged and MCACVCi decreased. However, in the PetCO2 clamp trial, leg cycling with BFR increased both MCAvm (Δ5.9 ± 1.4 cm/s) and ICAQ (Δ20.0 ± 7.8 ml/min) and attenuated the decrease in MCACVCi, while ICACVC was unchanged. In the control trial, PEI decreased PetCO2 (Δ-7.0 ± 1.3 mmHg vs. rest), MCAvm and MCACVCi, whereas ICAQ and ICACVC were unchanged. In contrast, in the PetCO2 clamp trial both ICAQ (Δ18.5 ± 11.9 ml/min) and MCAvm (Δ8.8 ± 2.0 cm/s) were elevated, while ICACVC and MCACVCi were unchanged. In conclusion, when hyperventilation-related decreases in PetCO2 are prevented the activation of metabolically sensitive skeletal muscle afferent fibers increases cerebral blood flow.

Sex differences in the ventilatory and cardiovascular response to supine and tilted metaboreflex activation

“…; Edgell and Stickland ; Prodel et al. ). ETCO 2 is also reduced in women during PECO despite the absence of hyperventilation; however, tidal volume does increase slightly but significantly.…”

“…; Prodel et al. ). However, when hypocapnia was prevented by eucapnic clamping, and mean arterial pressure (and presumably sympathetic activity) remained elevated, there was no reduction in MCA conductance implying that cerebrovascular constriction during PECO was due to changes in CO 2 only (Braz et al.…”

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

“…It is believed that increased anaerobic energy production may evoke higher metaboreflex activity and, consequently enhance heart rate (HR) response, cardiac output, and ventilation ( ) to adequately supply O 2 to exercising muscle and remove the metabolites generated from the anaerobic metabolism [ 11 – 13 ]. As a result, this compensatory mechanism produced by local hypoxia, together with a reduced venous return characteristic of BFR training, may overload central components of the cardiorespiratory system and lead to improvement in [ 14 , 15 ]. Furthermore, Egan et al [ 8 ] showed that higher blood lactate ([La - ] net ) accumulation, indicating greater contribution of the anaerobic metabolism, can result in significantly higher metabolic stress and consequently enhance mitochondrial biogenesis synthesis, a local factor which can also induce greater .…”

Increase of cortical cerebral blood flow and further cerebral microcirculatory effects of Serelaxin in a sheep model

“…Moreover, despite much work in recent years, the regulation of CBF is still incompletely understood (8,36). It can be assessed by laser Doppler flowmetry, which, based on the noninvasive quantification of blood flow velocity (16), allows to differentiate areal-dependent changes of microperfusion in the cortex and subcortex.…”