Little data is available about the pathophysiological mechanisms of unexplained dyspnea and their clinical meaning. Consecutive patients with unexplained dyspnea underwent prospective standardized cardiopulmonary exercise testing with echocardiography (CPETecho). Patients were grouped as having normal exercise capacity (peak VO₂ > 80% with respiratory exchange [RER] > 1.05), reduced exercise capacity (peak VO₂ ≤ 80% with RER > 1.05), or a submaximal exercise test (RER ≤ 1.05). From 307 patients, 144 (47%) had normal and 116 (38%) reduced exercise capacity, and 47 (15%) had a submaximal exercise test. Patients with reduced versus normal exercise capacity had significantly more mechanisms for unexplained dyspnea (2.3±1.0 vs 1.5±1.0, respectively; p<0.001). Exercise PH (42%), low heart rate reserve (51%), low stroke volume reserve (38%), low diastolic reserve (18%), and peripheral muscle limitation (17%) were most common. Patients with more mechanisms for dyspnea displayed poorer peak VO₂ and had an increased risk for cardiovascular hospitalization (p=0.002). Patients with unexplained dyspnea display multiple coexisting mechanisms for exercise intolerance, which relate to the severity of exercise limitation and risk of subsequent cardiovascular hospitalizations.

关于不明原因呼吸困难的病理生理机制及其临床意义的资料很少。连续患有不明原因呼吸困难的患者接受了前瞻性标准化心肺运动测试和超声心动图 (CPETecho)。患者被分组为具有正常运动能力（峰值 VO ₂ > 80%，呼吸交换 [RER] > 1.05），运动能力降低（峰值 VO ₂≤ 80%，RER > 1.05），或次最大运动试验（RER ≤ 1.05）。在 307 名患者中，144 名（47%）运动能力正常，116 名（38%）运动能力降低，47 名（15%）运动能力低于极限。与正常运动能力相比，运动能力降低的患者出现不明原因呼吸困难的机制明显更多（分别为 2.3±1.0 和 1.5±1.0；p<0.001）。运动 PH (42%)、低心率储备 (51%)、低每搏输出量储备 (38%)、低舒张储备 (18%) 和外周肌肉受限 (17%) 是最常见的。具有更多呼吸困难机制的患者表现出较差的峰值 VO ₂并且心血管住院的风险增加（p=0.002）。原因不明的呼吸困难患者表现出多种运动不耐受的共存机制，这与运动受限的严重程度和随后的心血管住院风险有关。