Abstract
Carotid baroreceptors (CBR) are known to modulate muscle sympathetic nerve activity and vascular tone in humans (measured by microneurography, plethsmography, and ultrasound technology). However, CBR control of skeletal muscle microcirculatory blood flow is not well defined. Thus, near-infrared spectroscopy (NIRS) was employed to evaluate changes in muscle tissue oxygenation (TOm) as a reflection of microcirculatory blood flow. METHODS: Heart rate (HR), arterial blood pressure (ABP), and TOm were measured at rest and during 5-sec +40 mmHg neck pressure (NP, a CBR hypotensive stimulus) in 5 healthy volunteers. Blood flow responses are expressed as a percent of total labile signal (TLS) established by 3-minute suprasystolic leg occlusion. RESULTS: HR and ABP increased (P < 0.01) following NP, indicating a significant reflex response to carotid baroreceptor hypotension. All subjects experienced a significant attenuation in skeletal muscle TOm following NP (6.5 ± 1.0% change, P < 0.01), indicating a measurable reduction in skeletal microcirculatory blood flow. The time delay from NP stimulus to TOm response was 10.5 ± 1.4 sec. CONCLUSION: These data provide evidence of direct carotid baroreflex control of resting skeletal muscle microcirculatory blood flow in humans, and indicate that the time course for changes in TOm is similar to the published time constant for CBR mediated changes in ABP.
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