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1 Department of Physiology, Wayne State University, Detroit, Michigan, United States
2 Department of Physiology, Wayne State University, Detroit, Michigan, United States; Faculty of Human Development, Kobe University, Kobe, Ibaraki, Japan
3 Department of Physiology, Wayne State University, Detroit, Michigan, United States; Department of Surgery, Wayne State University, Detroit, Michigan, United States
4 Department of Physiology, Wayne State University, Detroit, Michigan, United States; Laboratory for Human performance Research, Osaka International University, Moriguchi, Osaka, Japan
5 Internal Medicine, University of Rome, Rome, Italy
6 Department of Surgery, Wayne State University, Detroit, Michigan, United States
* To whom correspondence should be addressed. E-mail: doleary{at}med.wayne.edu.
Hypoperfusion of active skeletal muscle elicits a reflex pressor response termed the muscle metaboreflex. Dynamic exercise attenuates spontaneous baroreflex sensitivity (SBRS) in the control of heart rate (HR) during rapid, spontaneous changes in blood pressure (BP). Our objective was to determine whether muscle metaboreflex activation (MRA) further diminishes SBRS. Conscious dogs were chronically instrumented to measure HR, cardiac output, mean arterial pressure and left ventricular systolic pressure (LVSP) at rest and during mild (3.2 km/h) or moderate (6.4 km/h @ 10%) dynamic exercise before and after MRA (via partial reduction of hindlimb blood flow). SBRS was evaluated as the slopes of the linear relationships (LRs) between HR and LVSP during spontaneous sequences of
3 consecutive beats when HR changed inversely vs. pressure (expressed as bpm/mmHg). During mild exercise, these LRs shifted upwards with a significant decrease in SBRS (-3.0 ± 0.4 vs. -5.2 ± 0.4, P < 0.05 vs. rest). MRA caused upward and rightward shifts of the LRs and decreases in SBRS (-2.1 ± 0.1, P < 0.05 vs. mild exercise). Moderate exercise shifted LRs both upward and rightward and SBRS significantly decreased (-1.2 ± 0.1, P < 0.05 vs. rest). MRA elicited further upward and rightward shifts of the LRs and reductions in SBRS (-0.9 ± 0.1, P < 0.05 vs. moderate exercise). We conclude that dynamic exercise resets the arterial baroreflex to higher BP and HR as exercise intensity increases. In addition, increases in exercise intensity as well as MRA attenuate SBRS.
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