Post-Exercise Nasal Patency, Spirometry, and CBCT-Derived Lund–Mackay Scores in Competitive Swimmers: A Multivariate Analysis

Background/Objectives: Competitive swimmers present simultaneously with supranormal lung function and a high prevalence of upper-airway structural pathology. This study examined whether CBCT-quantified sinus mucosal burden and post-exercise peak nasal inspiratory flow (PNIF) are related, and whether their combination with spirometry identifies distinct ventilatory subgroups, in competitive swimmers. Methods: Twenty-nine competitive swimmers (18 male, 11 female; age 20.7 ± 2.8 yr) underwent nasal endoscopy (n = 29), CBCT with Lund–Mackay (LM) scoring (n = 20), bilateral PNIF at rest (T3) and ≤60 s post-sprint (T4), spirometry (FVC, FEV1, PEF, FEF25–75; GLI-2012 norms), and a 30 s maximal tethered sprint (Fmax, N). Principal component analysis (PCA) and hierarchical cluster analysis were applied to ΔPNIF, LM score, resting spirometry, and Fmax. Results: LM score and ΔPNIF were not significantly correlated (Spearman ρ = 0.32; p = 0.17). PCA yielded two components (63.1% of variance) that did not cleanly separate a mucosal-reactivity dimension from ventilatory reserve: LM score loaded together with Fmax on the second component, while ΔPNIF loaded moderately on both components. Hierarchical clustering identified three subgroups (silhouette coefficient 0.38), but none combined reduced ΔPNIF with elevated LM score; the subgroup with the highest mean LM score (n = 7) showed the highest mean ΔPNIF (+29.3 L/min) of the three. Resting spirometry was supranormal throughout (FEV1% 115.3 ± 14.2%) and did not differ between subgroups. Exercise-induced bronchodilation was pronounced across the cohort (ΔFEV1 +9.6 pp; d = 0.84), and tethered force (Fmax) was the sole correlate of World Aquatics performance (r = 0.560; p = 0.002). Conclusions: In this cohort, CBCT-derived sinus mucosal burden and post-exercise nasal decongestion were not significantly associated, and clustering did not identify a subgroup analogous to a “dysfunctional” ventilatory–sinonasal phenotype. Post-exercise PNIF and resting spirometry appear to capture largely independent aspects of exercise physiology in competitive swimmers, but neither, alone or combined with LM score, discriminated a distinct clinical subgroup in this sample. Tethered force remains the strongest correlate of competitive performance identified.