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Received April 7, 2004
Revised May 10, 2004
Accepted after revision June 25, 2004
1 University of California San Diego
2 University of North Texas Health Science Center
3 Copenhagen Muscle Research Centre
* To whom correspondence should be addressed. E-mail: dwray{at}ucsd.edu.
We sought to determine the dynamic relationship between carotid baroreflex (CBR)-mediated control and local control of the skeletal muscle vasculature during dynamic exercise. In twelve subjects (18-35 yrs), oscillatory NP (+40 Torr) was applied at 0.1 Hz (i.e. 5-sec on, 5-sec off) for five minutes to determine the degree of CBR control over heart rate (HR), arterial blood pressure (ABP), muscle sympathetic nerve activity (MSNA), femoral blood velocity (FBV), and skeletal muscle tissue oxygenation (TOm) at rest and during 7W dynamic knee-extension exercise. The TOm measurements of both the exercising (EL) and non-exercising leg (NEL) were evaluated. Fast Fourier transformation was performed on 5-min segments to calculate spectral power of the R-R interval, ABP, MSNA, FBV, and TOm time series, and the low-frequency (LF, 0.085-0.115 Hz) power spectra were compared to evaluate the degree of CBR-mediated entrainment for each variable. At rest, sinusoidal NP significantly increased LF spectral power of RRI, ABP, MSNA, and FBV. During exercise, sinusoidal NP provoked a similar increase in spectral power to rest for RRI and MSNA, while CBR-mediated changes in ABP and FBV were attenuated. Changes in spectral power of TOm during sinusoidal NP were similar between the EL and NEL at rest. However, during exercise the changes in TOm power were significantly less in the EL, while changes in the NEL were similar to rest. We have demonstrated simultaneous entrainment of all CBR efferent measurements, ranging from cardiac chronotropic effects to alterations at the level of the skeletal muscle microcirculation. Moreover, we have identified a significant and specific attenuation of end-organ responsiveness to CBR-mediated sympathoexcitation in the vasculature of the exercising muscle. However, despite a shift towards more predominant local control over the exercising muscle vasculature, systemic arterial blood pressure is well preserved.
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