科研之友
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摘要
Respiratory and cardiovascular responses to muscle mechanoreflex (passive calf stretch) and metaboreflex activation (local circulatory occlusion) were examined during inhalation of a hypercapnic gas mixture in four trials. These controlled for the effects of central command, metabolite sensitization of muscle afferents and hypercapnia-induced elevation of central respiratory drive. In an isokinetic dynamometer, with circulation through the right leg occluded by inflation of a thigh cuff, 13 participants either rested (control trial; CON) or plantarflexed their ankle at 50% maximal force for 1.5 min (voluntary exercise trial; EX). Thereafter, circulatory occlusion was maintained and the calf passively stretched before return to the resting position. Both trials were performed while breathing air, as well as while breathing a normoxic, hypercapnic (5% CO2) gas mixture (CO2 trial and CO2+EX trial). Hypercapnic gas inhalation increased baseline minute ventilation ((V)over dot), heart rate and mean arterial pressure (+27.67 +/- 1.74 l min(-1), +7 +/- 0.85 beats min(-1) and +13 +/- 3.41 mmHg, respectively; means +/- SEM) above control values (9.78 +/- 0.86 l min(-1), 62 +/- 2.3 beats min(-1) and 88 +/- 2.6 mmHg, respectively). Voluntary exercise further increased these variables from baseline during both trials (P %26lt; 0.05). During the continued circulatory occlusion after voluntary exercise, mean arterial pressure remained significantly elevated (P %26lt; 0.05). Minute ventilation returned to baseline during circulatory occlusion following exercise in the EX trial, but in the CO2+EX trial the (V)over dot remained elevated at end-exercise levels during this period (+7.12 +/- 1.13 l min(-1)). Passive stretch caused further increases in (V)over dot during CO2+EX and CO2 trials but not in CON and EX. These results indicate that in the absence of central command, either muscle metaboreflex and/or mechanoreflex activation stimulates ventilation during concurrent hypercapnia.
- 出版日期2012-2
