Submitted on October 11, 2007
Accepted on December 16, 2007
Spontaneous Baroreflex Control of Cardiac Output During Dynamic Exercise, Muscle Metaboreflex Activation and Heart Failure
Masashi Ichinose1, Javier A. Sala-Mercado2, Donal S O'Leary2*, Robert L Hammond2, Matthew Coutsos2, Tomoko K Ichinose3, Marco Pallante4, and Ferdinando Iellamo4
1 Faculty of Human Development, Kobe University, Kobe, Hyogo, Japan; Department of Physiology, Wayne State University, Detroit, Michigan, United States
2 Department of Physiology, Wayne State University, Detroit, Michigan, United States
3 Laboratory for Human performance Research, Osaka International University, Moriguchi, Osaka, Japan; Department of Physiology, Wayne State University, Detroit, Michigan, United States
4 Internal Medicine, University of Rome, Rome, Italy
* To whom correspondence should be addressed. E-mail: doleary{at}med.wayne.edu.
We have previously shown that spontaneous baroreflex-induced changes in heart rate (HR) do not always translate into changes in cardiac output (CO) at rest. We have also showed that heart failure (HF) decreases this linkage between changes in HR and CO. Whether dynamic exercise and muscle metaboreflex activation (via imposed reductions in hindlimb blood flow) further alter this translation in normal and HF conditions is unknown. We examined these questions using conscious, chronically instrumented dogs before and after pacing-induced HF during mild and moderate dynamic exercise with and without MRA. We measured left ventricular systolic pressure (LVSP), CO and HR and analyzed the spontaneous HR-LVSP and CO-LVSP relationships. In normal animals, mild exercise significantly decreased HR-LVSP (-3.08 ± 0.5 vs. -5.14 ± 0.6 beats min-1 mmHg-1 P 
0.05) and CO-LVSP (-134.74 ± 24.5 vs. -208.6 ± 22.2 ml min-1 mmHg-1 P 0.05). Moderate exercise further decreased both and in addition significantly reduced HR-CO translation (25.9 ± 2.8 vs. 52.3 ± 4.2 % P 0.05). Muscle metaboreflex activation at both workloads decreased HR-LVSP whereas it had no significant effect on CO-LVSP and the HR-CO translation. HF significantly decreased HR-LVSP, CO-LVSP, and the HR-CO translation in all situations. We conclude that spontaneous baroreflex HR responses do not always cause changes in CO during exercise. Moreover, muscle metaboreflex activation during mild and moderate dynamic exercise reduces this coupling. In addition, in HF the HR-CO translation also significantly decreases during both workloads and decreases even further with muscle metaboreflex activation.
