This study aimed to investigate the changes in blood viscosity, pulmonary hemodynamics, nitric oxide (NO) production, and maximal oxygen uptake ($\dot{\mathrm{V}}{\mathrm{O}}_2\text{max}$) during a maximal incremental test conducted in normoxia and during exposure to moderate altitude (2,400 m) in athletes exhibiting exercise-induced hypoxemia at sea level (EIH). Nine endurance athletes with EIH and eight without EIH (NEIH) performed a maximal incremental test under three conditions: sea level, 1 day after arrival in hypoxia, and 5 days after arrival in hypoxia (H5) at 2,400 m. Gas exchange and oxygen peripheral saturation (SpO₂) were continuously monitored. Cardiac output, pulmonary arterial pressure, and total pulmonary vascular resistance were assessed by echocardiography. Venous blood was sampled before and 3 min after exercise cessation to analyze blood viscosity and NO end-products. At sea level, athletes with EIH exhibited an increase in blood viscosity and NO levels during exercise while NEIH athletes showed no change. Pulmonary hemodynamics and aerobic performance were not different between the two groups. No between-group differences in blood viscosity, pulmonary hemodynamics, and $\dot{\mathrm{V}}{\mathrm{O}}_2\text{max}$ were found at 1 day after arrival in hypoxia. At H5, lower total pulmonary vascular resistance and greater NO concentration were reported in response to exercise in EIH compared with NEIH athletes. EIH athletes had greater cardiac output and lower SpO₂ at maximal exercise in H5, but no between-group differences occurred regarding blood viscosity and $\dot{\mathrm{V}}{\mathrm{O}}_2\text{max}$. The pulmonary vascular response observed at H5 in EIH athletes may be involved in the greater cardiac output of EIH group and counterbalanced the drop in SpO₂ in order to achieve similar $\dot{\mathrm{V}}{\mathrm{O}}_2\text{max}$ than NEIH athletes.

本研究旨在调查血液粘度、肺血流动力学、一氧化氮 (NO) 产生和最大摄氧量的变化。$\dot{\mathrm{五}}{\mathrm{○}}_2\text{最大限度}$) 在常氧环境中进行的最大增量测试期间和暴露于中等海拔 (2,400 m) 的运动员在海平面 (EIH) 表现出运动诱发的低氧血症。9 名 EIH 和 8 名没有 EIH (NEIH) 的耐力运动员在以下三种条件下进行了最大增量测试：海平面、到达缺氧 1 天和到达 2,400 米缺氧 (H5) 后 5 天。气体交换和氧外周饱和度（SpO ₂) 被持续监控。通过超声心动图评估心输出量、肺动脉压和总肺血管阻力。在运动停止前和运动停止后 3 分钟采集静脉血，以分析血液粘度和 NO 终产物。在海平面上，患有 EIH 的运动员在运动期间表现出血液粘度和 NO 水平的增加，而 NEIH 运动员则没有变化。肺血流动力学和有氧运动表现在两组之间没有差异。在血液粘度、肺血流动力学和$\dot{\mathrm{五}}{\mathrm{○}}_2\text{最大限度}$到达后1天发现缺氧。在 H5 时，与 NEIH 运动员相比，EIH 的运动表现出较低的总肺血管阻力和较高的 NO 浓度。EIH 运动员在 H5 的最大运动量时心输出量更大，SpO ₂更低，但在血液粘度和$\dot{\mathrm{五}}{\mathrm{○}}_2\text{最大限度}$. EIH 运动员在 H5 观察到的肺血管反应可能与 EIH 组更大的心输出量有关，并抵消了 SpO ₂的下降，以实现类似的$\dot{\mathrm{五}}{\mathrm{○}}_2\text{最大限度}$比 NEIH 运动员。