Functional patterns of healthy human respiratory dynamics by 3D MR spirometry

Functional pulmonary MRI can assess the pathophysiology of regional ventilation, provided that nominal ventilatory patterns are characterised as a baseline. This study investigates common features and their associated gravity dependence using 3D MR spirometry in freely breathing healthy volunteers. Repeated dynamic lung MR acquisitions were performed at 3 T on 25 healthy volunteers breathing freely in the supine and prone positions. Three-dimensional maps of tidal volumes (TV), peak expiratory flows (SPEF), expiratory flows at 25% of tidal volume (SEF25), and anisotropy deformation index (ADI) were inferred and normalised. Intra- and inter-volunteer reproducibility was evaluated using percentage differences (PD) and intraclass correlation coefficients (ICC), while gravity dependence was tested using a paired Wilcoxon test. Twenty-five volunteers (mean age, 45 years ± 17 standard deviation; 15 males) were included. Respiratory parametric maps are found spatially inhomogeneous throughout each volunteer's lung, with large coefficients of variation ranging between 30 and 63%. Yet, the main respiratory patterns are shared among volunteers with common features primarily governed by lung gravity dependence for TV, SPEF, and SEF25 (p < 0.05). Spirometry biomarkers are globally repeatable despite intrinsic physiological variabilities (median PD: 5.7-9.2%, ICC: 0.71-0.88), and fairly repeatable locally after normalisations (median PD: 11-19%, ICC: 0.78-0.90). 3D MR spirometry exhibits shared respiratory features between individuals with gravity dependence. Intra-volunteer repeatability and global accuracy were found, demonstrating the reliability of the technique. A new baseline is established for regional lung pathophysiology. Question Nominal ventilatory patterns in free breathing need to be characterised for regional pathophysiology. Findings Functional ventilatory maps showed significant inhomogeneity, but key patterns, primarily governed by gravity, were consistent across subjects. 3D MR spirometry demonstrated reliability despite physiological variability. Clinical relevance 3D MR spirometry is a reliable technique for absolute quantification of the regional ventilation and its dynamic. Nominal spatial patterns of the ventilation should be considered for assessing regional pathophysiology in free breathing.