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1 Department of Integrative Physiology and Cardiovascular Research Institute, University of North Texas Health Science Center, Fort Worth, Texas 76107; and 2 Copenhagen Muscle Research Center, Department of Anesthesia, Rigshospitalet, University of Copenhagen, DK-2200 Copenhagen, Denmark
We examined arterial baroreflex control of muscle sympathetic nerve activity (MSNA) during abrupt decreases in mean arterial pressure (MAP) and evaluated whether endurance training alters baroreflex function. Acute hypotension was induced nonpharmacologically in 14 healthy subjects, of which 7 were of high fitness (HF) and 7 were of average fitness (AF), by releasing a unilateral arterial thigh cuff after 9 min of resting ischemia under two conditions: control, which used aortic and carotid baroreflex (ABR and CBR, respectively) deactivation; and suction, which used ABR deactivation alone. The application of neck suction to counteract changes in carotid sinus transmural pressure during cuff release significantly attenuated the MSNA response (which increased 134 ± 32 U/14 s) compared with control (which increased 195 ± 43 U/14 s) and caused a greater decrease in MAP (19 ± 2 vs. 15 ± 2 mmHg; P < 0.05). Furthermore, during both trials, the HF subjects exhibited a greater decrease in MAP compared with AF subjects despite an augmented baroreflex control of MSNA. These data indicate that the CBR contributes importantly to the MSNA response during acute systemic hypotension. Additionally, we suggest that an impaired control of vascular reactivity hinders blood pressure regulation in HF subjects.
carotid baroreceptors; aortic baroreceptors; endurance training; neck suction
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