129Xenon-enhanced magnetic resonance imaging to understand particle exhalation from the human lung

Introduction: Particles are emitted from the lung lining liquid and exhaled with every breath. Particle exhalation has a large variability of two orders of magnitude between healthy subjects for unknown reasons. The aim of this study was to identify anatomical and physiological factors to better understand particle emission from the human lung. Methods: Ten healthy subjects underwent 129Xenon-enhanced magnetic resonance imaging (129Xe-MRI) and analysis of exhaled particles (PExA, Gothenburg, Sweden). Ventilation defect percentage (VDP), tissue-phase wall thickness (TP-WT) and uptake of xenon from the lung tissue into the blood (RBC-TP) was quantified from Xe-MRI and correlated with particle numbers (PexN) and particle mass (PexM). In addition, number and volume of breaths were recorded to derive PexN and PexM per breath. Results: PexN / breath and PexM / breath were positively correlated with VDP (r=0.66; p=0.053 and r=0.67; p=0.050, respectively), RBC-TP (r=0.74; p=0.02 and r=0.72; p=0.03, respectively), and to some extent TP-WT (r=0.51; p=0.16 and r=0.59; p=0.10, respectively) suggesting that the emission of particles from the human lung is dependent on multiple factors including ventilation defects, gas diffusion and partly alveolar wall thickness. Conclusion: 129Xe-MRI adds to our understanding of particle emission from the human lung, but the relevant driving factors for particle emission need to be further unraveled in order to conclusively understand the processes that affect particle emission from the human lung.