Harms C A, Babcock M A, McClaran S R, Pegelow D F, Nickele G A, Nelson W B, Dempsey J A
John Rankin Laboratory of Pulmonary Medicine, Department of Preventive Medicine, University of Wisconsin, Madison 53705, USA.
J Appl Physiol (1985). 1997 May;82(5):1573-83. doi: 10.1152/jappl.1997.82.5.1573.
We hypothesized that during exercise at maximal O2 consumption (VO2max), high demand for respiratory muscle blood flow (Q) would elicit locomotor muscle vasoconstriction and compromise limb Q. Seven male cyclists (VO2max 64 +/- 6 ml.kg-1.min-1) each completed 14 exercise bouts of 2.5-min duration at VO2max on a cycle ergometer during two testing sessions. Inspiratory muscle work was either 1) reduced via a proportional-assist ventilator, 2) increased via graded resistive loads, or 3) was not manipulated (control). Arterial (brachial) and venous (femoral) blood samples, arterial blood pressure, leg Q (Qlegs; thermodilution), esophageal pressure, and O2 consumption (VO2) were measured. Within each subject and across all subjects, at constant maximal work rate, significant correlations existed (r = 0.74-0.90; P < 0.05) between work of breathing (Wb) and Qlegs (inverse), leg vascular resistance (LVR), and leg VO2 (VO2legs; inverse), and between LVR and norepinephrine spillover. Mean arterial pressure did not change with changes in Wb nor did tidal volume or minute ventilation. For a +/-50% change from control in Wb, Qlegs changed 2 l/min or 11% of control, LVR changed 13% of control, and O2 extraction did not change; thus VO2legs changed 0.4 l/min or 10% of control. Total VO2max was unchanged with loading but fell 9.3% with unloading; thus VO2legs as a percentage of total VO2max was 81% in control, increased to 89% with respiratory muscle unloading, and decreased to 71% with respiratory muscle loading. We conclude that Wb normally incurred during maximal exercise causes vasoconstriction in locomotor muscles and compromises locomotor muscle perfusion and VO2.
我们假设，在最大摄氧量（VO₂max）运动期间，呼吸肌对血流量（Q）的高需求会引发运动肌血管收缩并损害肢体血流量。七名男性自行车运动员（VO₂max为64±6 ml·kg⁻¹·min⁻¹）在两个测试阶段中，分别在自行车测力计上以VO₂max强度完成了14次持续2.5分钟的运动试验。吸气肌做功情况分为以下三种：1）通过比例辅助通气机减少；2）通过分级阻力负荷增加；3）不进行干预（对照）。测量了动脉（肱动脉）和静脉（股动脉）血样、动脉血压、腿部血流量（Qlegs；热稀释法）、食管压力和摄氧量（VO₂）。在每个受试者以及所有受试者中，在恒定的最大工作速率下，呼吸功（Wb）与Qlegs（呈负相关）、腿部血管阻力（LVR）和腿部VO₂（VO₂legs；呈负相关）之间存在显著相关性（r = 0.74 - 0.90；P < 0.05），并且LVR与去甲肾上腺素溢出之间也存在显著相关性。平均动脉压不会随Wb的变化而改变，潮气量或分钟通气量也不会改变。与对照相比，Wb变化±50%时，Qlegs变化2 l/min或为对照的11%，LVR变化为对照的13%，氧摄取没有变化；因此VO₂legs变化0.4 l/min或为对照的10%。总VO₂max在负荷时不变，但在卸载时下降9.3%；因此，VO₂legs占总VO₂max的百分比在对照时为81%，呼吸肌卸载时增加到89%，呼吸肌负荷时降至71%。我们得出结论，最大运动期间正常产生的Wb会导致运动肌血管收缩，并损害运动肌灌注和VO₂。
