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1 Internal Medicine, University of Rome, Rome, Italy
2 Physiology, WSU, Detroit, Michigan, United States
3 Institute of Health and Sport Sciences, University of Tsukuba, Tsukuba, Ibaraki, Japan
4 Surgery, Wayne State University, Detroit, Michigan, United States
5 Laboratory for Human performance Research, Osaka International University, Moriguchi, Osaka, Japan
6 Department of Physiology, Wayne State University, Detroit, Michigan, United States
* To whom correspondence should be addressed. E-mail: doleary{at}med.wayne.edu.
In heart failure (HF) there is a reduced baroreflex sensitivity at rest and, during dynamic exercise, there is enhanced muscle metaboreflex activation (MRA). However, how the arterial baroreflex modulates HR during exercise is unkown. We tested the hypothesis that spontaneous baroreflex sensitivity (SBRS) is attenuated during exercise in HF and that MMR activation further depresses SBRS. In 7 conscious dogs we measured HR, cardiac output, and left ventricular systolic pressure at rest and during mild and moderate dynamic exercise before and during MRA (via imposed reductions of hindlimb blood flow) before and after induction of HF (by rapid ventricular pacing). SBRS was assessed by the sequences method. In control, SBRS was reduced from rest with a progressive resetting of the baroreflex stimulus-response relationship in proportion to exercise intensity and magnitude of MRA. In HF, SBRS was significantly depressed in all settings however, the changes with exercise and MRA occurred with a pattern similar to the control state. As in control, the baroreflex stimulus-response relationship showed an intensity- and MMR-dependent rightward and upward shift. The results of this study indicate that HF induces an impairment in baroreflex control of HR at rest and during exercise, although the effects of exercise and MRA on SBRS occurs with a similar pattern as in control, indicating the persistence of some vagal activity.
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