Dempsey Jerome A, McKenzie Donald C, Haverkamp Hans C, Eldridge Marlowe W
University of Wisconsin, Madison, WI.
University of British Columbia, Vancouver, BC, Canada.
Chest. 2008 Sep;134(3):613-622. doi: 10.1378/chest.07-2730.
This review addresses three types of causes of respiratory system limitations to O(2) transport and exercise performance that are experienced by significant numbers of active, highly fit younger and older adults. First, flow limitation in intrathoracic airways may occur during exercise because of narrowed, hyperactive airways or secondary to excessive ventilatory demands superimposed on a normal maximum flow-volume envelope. Narrowing of the extrathoracic, upper airway also occurs in some athletes at very high flow rates during heavy exercise. Examination of the breath-by-breath tidal flow-volume loop during exercise is key to a noninvasive diagnosis of flow limitation and to differentiation between intrathoracic and extrathoracic airway narrowing. Second exercise-induced arterial hypoxemia occurs secondary to an excessively widened alveolar-arterial oxygen pressure difference. This inefficient gas exchange may be attributable in part to small intracardiac or intrapulmonary shunts of deoxygenated mixed venous blood during exercise. The existence of these shunts at rest and during exercise may be determined by using saline solution contrast echocardiography. Finally, fatigue of the respiratory muscles resulting from sustained, high-intensity exercise and the resultant vasoconstrictor effects on limb muscle vasculature will also compromise O(2) transport and performance. Exercise in the hypoxic environments of even moderately high altitudes will greatly exacerbate the negative influences of these respiratory system limitations to exercise performance, especially in highly fit individuals.
这篇综述探讨了大量活跃的、健康状况良好的年轻人和老年人在氧气运输和运动表现方面呼吸系统受限的三种原因。首先，由于气道变窄、反应过度，或由于在正常最大流量-容积范围内叠加了过高的通气需求，运动期间可能会出现胸内气道的流量受限。在剧烈运动时，一些运动员在非常高的流速下也会出现胸外上气道变窄。运动期间逐次呼吸的潮气量-流量环检查是无创诊断流量受限以及区分胸内和胸外气道变窄的关键。其次，运动诱发的动脉血氧不足继发于肺泡-动脉氧分压差过度增大。这种低效的气体交换可能部分归因于运动期间脱氧混合静脉血的小的心内或肺内分流。静息和运动期间这些分流的存在可以通过使用生理盐水对比超声心动图来确定。最后，持续高强度运动导致的呼吸肌疲劳以及由此对肢体肌肉血管系统产生的血管收缩作用也会损害氧气运输和运动表现。即使在中等高度的低氧环境中运动，也会极大地加剧这些呼吸系统对运动表现的限制的负面影响，尤其是对健康状况良好的个体。
