Table1_Influence of rapidly oscillating inspired O2 and N2 concentrations on pulmonary vascular function and lung fluid balance in healthy adults.pdf

Introduction: Aircrew may experience rapidly oscillating inspired O2/N2 ratios owing to fluctuations in the on-board oxygen delivery systems (OBOG). Recent investigations suggest these oscillations may contribute to the constellation of physiologic events in aircrew of high-performance aircraft. Therefore, the purpose of this study was to determine whether these “operationally-relevant” environmental challenges may cause decrements in measures of pulmonary vascular physiology.
Methods: Thirty healthy participants (Age: 29 ± 5 years) were recruited and assigned to one of the three exposures. Participants were instrumented for physiologic monitoring and underwent baseline cardiopulmonary physiology testing (ground level) consisting of a rebreathe method for quantifying pulmonary blood flow (Qc), pulmonary capillary blood volume (Vc) and alveolar–capillary conductance (Dm). Ultrasound was used to quantify “comet tails” (measure of lung fluid balance). After baseline testing, the participants had two 45 min exposures to an altitude of 8,000 ft where they breathed from gas mixtures alternating between 80/20 and 30/70 O2/N2 ratios at the required frequency (30 s, 60 s, or 120 s), separated by repeat baseline measure. Immediately and 45 min after the second exposure, baseline measures were repeated.
Results: We observed no changes in Qc, Dm or Vc during the 60 s exposures. In response to the 30 s oscillation exposure, there was a significantly reduced Qc and Vc at the post-testing period (p = 0.03). Additionally, exposure to the 120 s oscillations resulted in a significant decrease in Vc at the recovery testing period and an increase in the Dm/Vc ratio at both the post and recovery period (p < 0.01). Additionally, we observed no changes in the number of comet tails.
Conclusion: These data suggest “operationally-relevant” changes in inspired gas concentrations may cause an acute, albeit mild pulmonary vascular derecruitment, reduced distention and/or mild pulmonary-capillary vasoconstriction, without significant changes in lung fluid balance or respiratory gas exchange. The operational relevance remains less clear, particularly in the setting of additional environmental stressors common during flight (e.g., g forces).

研究背景：空勤人员可能因机载供氧系统（On-Board Oxygen Delivery Systems, OBOG）的波动，出现吸入气中O₂/N₂比例快速振荡的情况。近期研究表明，此类振荡可能与高性能航空器空勤人员出现的一系列生理反应相关。因此，本研究旨在探究这些“任务相关”的环境应激是否会导致肺血管生理指标出现异常变化。
研究方法：本研究招募30名健康受试者（年龄：29±5岁），将其分配至3种暴露方案之一。为受试者安装生理监测设备，并开展地面环境下的基础心肺生理测试：采用重复呼吸法量化肺血流量（Pulmonary Blood Flow, Qc）、肺毛细血管血容量（Pulmonary Capillary Blood Volume, Vc）及肺泡毛细血管弥散量（Alveolar-Capillary Conductance, Dm）；利用超声检查量化“彗星征”（肺液平衡的检测指标）数量。基础测试完成后，受试者需在8000英尺海拔环境中接受两次各45分钟的暴露：期间吸入按指定频率（30秒、60秒或120秒）在80/20与30/70的O₂/N₂比例间交替的混合气体，两次暴露之间需重复开展基础测量。在第二次暴露结束即刻及45分钟后，分别再次进行基础指标测量。
研究结果：在60秒振荡暴露组中，Qc、Dm及Vc未出现显著变化。针对30秒振荡暴露组，测试后阶段受试者的Qc与Vc显著降低（p=0.03）。此外，120秒振荡暴露组的恢复测试阶段中，受试者的Vc显著降低，且测试后与恢复阶段的Dm/Vc比值均显著升高（p<0.01）。同时，彗星征数量未出现显著变化。
研究结论：本研究数据表明，吸入气浓度的任务相关变化可能引发急性（尽管程度较轻）的肺血管去募集、扩张度降低及/或轻度肺毛细血管血管收缩，且肺液平衡与呼吸气体交换无显著变化。但其任务相关性仍不明确，尤其是在飞行中常见的其他环境应激因素（例如重力加速度）存在的场景下。