Exhaled particle size and phospholipid composition of the respiratory tract lining fluid following moderate-intensity exercise in sub-zero conditions

Exercise-induced bronchoconstriction (EIB) commonly develops following prolonged exercise in cold, dry environments, but the acute mechanisms underlying airway responses to such environmental stressors remain poorly understood. Exhaled particle analysis offers a novel, non-invasive approach to assess respiratory tract lining fluid (RTLF) composition and may provide mechanistic insights into early airway responses before clinically detectable changes occur. This study investigated exhaled particle characteristics and lipid composition in response to moderate-intensity exercise in sub-zero conditions among healthy atopic and non-atopic individuals. Eighteen recreationally active participants (14 male) aged 29 ± 6 years, performed two moderate-intensity exercise trials (30 and 90 min duration) in a climate chamber set to -15°C. Participants provided exhaled particle (PEx) samples using the PExA® method, before and 30 min after each exercise trial. The PExA® device analysed particle mass and count across eight size bins (0.4 - 5 µm) and the collected PEx samples underwent lipidomic analysis to assess differences in the RTLF composition before and after exercise. Exercise induced a significant increase in smaller particles in PEx samples (0.4-0.7m; p < 0.01). Three lipid species were altered after the 30-min exercise trial, and 11 after 90-min exercise. Phosphatidylethanolamine PE(16:1_18:0) was the only lipid that consistently increased across both exercise durations (30 min: p = 0.023; 90 min: p = 0.044; g = 0.97). No significant differences in overall particle characteristics were observed between atopic and non-atopic participants, though three specific lipid species showed differential exercise responses between groups, including an oxidised phosphatidylcholine species PC(16:0_9:0;O) (p = 0.006, q = 0.59, g = 0.86). These results provide preliminary insight into airway surfactant responses to exercise in a cold climate and contribute to the growing understanding of how the PExA® method can be applied as a non-invasive tool for respiratory health assessment in an acute setting. .