The exercise pressor reflex and chemoreflex interaction: cardiovascular implications for the exercising human

Abstract

Key points Although the exercise pressor reflex (EPR) and the chemoreflex (CR) are recognized for their sympathoexcitatory effect, the cardiovascular implication of their interaction remains elusive. We quantified the individual and interactive cardiovascular consequences of these reflexes during exercise and revealed various modes of interaction. The EPR and hypoxia‐induced CR interaction is hyper‐additive for blood pressure and heart rate (responses during co‐activation of the two reflexes are greater than the summation of the responses evoked by each reflex) and hypo‐additive for peripheral haemodynamics (responses during co‐activation of the reflexes are smaller than the summated responses). The EPR and hypercapnia‐induced CR interaction results in a simple addition of the individual responses to each reflex (i.e. additive interaction). Collectively, EPR:CR co‐activation results in significant cardiovascular interactions with restriction in peripheral haemodynamics, resulting from the EPR:CR interaction in hypoxia, likely having the most crucial impact on the functional capacity of an exercising human. Abstract We investigated the interactive effect of the exercise pressor reflex (EPR) and the chemoreflex (CR) on the cardiovascular response to exercise. Eleven healthy participants (5 females) completed a total of six bouts of single‐leg knee‐extension exercise (60% peak work rate, 4 min each) either with or without lumbar intrathecal fentanyl to attenuate group III/IV afferent feedback from lower limbs to modify the EPR, while breathing either ambient air, normocapnic hypoxia (SaO2 ∼79%, PaO2 ∼43 mmHg, PaCO2 ∼33 mmHg, pH ∼7.39), or normoxic hypercapnia (SaO2 ∼98%, PaO2 ∼105 mmHg, PaCO2 ∼50 mmHg, pH ∼7.26) to modify the CR. During co‐activation of the EPR and the hypoxia‐induced CR (O2‐CR), mean arterial pressure and heart rate were significantly greater, whereas leg blood flow and leg vascular conductance were significantly lower than the summation of the responses evoked by each reflex alone. During co‐activation of the EPR and the hypercapnia‐induced CR (CO2‐CR), the haemodynamic responses were not different from the summated responses to each reflex response alone (P ≥ 0.1). Therefore, while the interaction resulting from the EPR:O2‐CR co‐activation is hyper‐additive for blood pressure and heart rate, and hypo‐additive for peripheral haemodynamics, the interaction resulting from the EPR:CO2‐CR co‐activation is simply additive for all cardiovascular parameters. Thus, EPR:CR co‐activation results in significant interactions between cardiovascular reflexes, with the impact differing when the CR activation is achieved by hypoxia or hypercapnia. Since the EPR:CR co‐activation with hypoxia potentiates the pressor response and restricts blood flow to contracting muscles, this interaction entails the most functional impact on an exercising human.

Invasive Assessment of Hemodynamic, Metabolic and Ionic Consequences During Blood Flow Restriction Training

“…During exercise, mechanical and/or metabolic stress can induce systemic adjustments within the cardiovascular system, which is called exercise pressor reflex (Spranger et al, 2015 ; Wan et al, 2020 ). The present findings support the occurrence of the exercise pressor reflex as unilateral biceps curls with 30% of the 1RM resulted in elevations of HR, SBP and DBP compared to baseline even in CON.…”

The carotid bodies exercise control over active expiration but not peak performance during high‐intensity treadmill running

“…However, there are many additional changes in arterial blood chemistry, arising during intense exercise, which provide substrates for enhanced chemoafferent input from the carotid bodies to the brainstem circuits that govern respiratory timing and motor outflow, which are relevant to exercise-induced hyperpnoea. pressure responses to exercise were reported in humans (Wan et al, 2020). Synergistic interaction between the muscle metaboreflex and the central chemoreflex has been shown in humans using post-exercise cuff occlusion to activate muscle afferents (Alghaith, Balanos, Eves, & White, 2019).…”

One and one is not always two: hypo‐ and hyper‐additive effects of the chemoreflex during exercise

“…In this issue of the Journal, Wan et al (2020) have provided an important advance to the model of cardiovascular control and have exceeded the 'useful' designation in fine form! Their careful and clever approach has provided new information about how the EPR and CR interact during exercise and exert influences on cardiovascular regulation.…”

“…There is accumulating evidence to show that the CR plays an important role in cardiovascular control during exercise in health (Stickland et al 2011;Wan et al 2020). It should now be clear that the activation of the CR, along with the type of activation, should be considered within a 'useful' model of cardiovascular control during dynamic exercise.…”

“…Physical training is a cornerstone of patient management and unravelling the complexities of EPR:CR interactions may lead to more specific and effective exercise interventions and rehabilitation strategies for CHF patients (Marcus et al 2015), although much additional work is required. The work of Wan et al (2020) demonstrates the importance of including chemoreceptors when creating a framework to understand the physiological adjustments to exercise. Their work highlights the need to appreciate the integrative nature of whole-body exercise in healthy humans Perspectives J Physiol 598.12 as well as other states such as CHF and metabolic disorders (Limberg, 2018).…”