Regulation of blood pressure during exercise: Interactions between arterial baroreflex and muscle metaboreflex

 

Masashi Ichinose

Department of Business Administration, Meiji University, 1-9-1, Eifuku, Suginami, Tokyo, 168-8555 Japan

 

During heavy exercise, the arterial baroreflex (ABR) and the reflexes evoked by activation of those afferent nerve endings in the working skeletal muscles that are sensitive to metabolic changes (the so-called muscle metaboreflex) are hypothesized to be activated, and moreover to interact in ways that lead to modulation of the primary cardiovascular reflex responses.  For the past few years our group has been investigating the interaction between ABR and the muscle metaboreflex.  We have focused our efforts in identifying the effects of muscle metaboreflex activation on ABR-mediated beat-to-beat control over muscle sympathetic nerve activity (MSNA) in humans.  ABR control over MSNA (burst incidence, burst strength and total MSNA) was evaluated by analyzing the relationship between beat-to-beat spontaneous variations in diastolic arterial pressure and MSNA.  We have found that the modification of the ABR-mediated beat-to-beat control of MSNA that is seen during post exercise muscle ischemia (PEMI) induced muscle metaboreflex activation (i.e. resetting and an increase in sensitivity) could be a consequence of the alteration in ABR control of both the incidence and strength of the MSNA burst.  Furthermore, we have demonstrated that the ABR-mediated beat-to-beat control of MSNA is time-dependently modulated during the course of isometric exercise.  In addition, we have found that ABR control over MSNA is not uniform throughout a leg cycling exercise during which intensity is incrementally increased from very-mild to exhausting.  Interestingly, the modulation of ABR function that is seen during heavy and exhausting exercise is consistent with observations made during isometric exercise and PEMI (a time when the muscle metaboreflex is selectively activated).  We suggest that the modulations of ABR function during activation of muscle metaboreflex is one of the mechanisms for increasing, or maintaining, blood pressure at the required pressure and thereby contributes to the regulation of the cardiovascular system during exercise.

 

Key words: integrated circulatory regulation, sympathetic nervous system, peripheral reflexes