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