Inspiratory Muscle Fatigue and Pulmonary Deposition–Perfusion Imaging Predict Sleep Dysfunction in Long COVID: Evidence From MTC Scintigraphy and FIT Performance Metrics

ABSTRACT Background Post-COVID-19 syndrome may impair respiratory function, inspiratory muscle performance, and sleep quality; however, the interaction between inspiratory muscle fatigue, regional deposition/perfusion, and sleep disturbances remains unclear. Objective To analyze associations between inspiratory muscle fatigue, pulmonary radiopharmaceutical activity, and sleep disturbances in symptomatic and asymptomatic post-COVID-19 individuals. Methods This cross-sectional study included 33 post-COVID-19 individuals classified as symptomatic (n=23) or asymptomatic (n=10) according to symptom severity. Inspiratory muscle performance was assessed using maximal inspiratory pressure (MIP), sustained maximal inspiratory pressure (SMIP), and the inspiratory fatigue index (FIT) obtained from an incremental respiratory resistance test. Sleep was assessed by actigraphy, the Pittsburgh Sleep Quality Index (PSQI), and the Epworth Sleepiness Scale (ESS). Pulmonary aerosol deposition and perfusion were assessed by gamma scintigraphy using ⁹⁹ᵐTc-DTPA and ⁹⁹ᵐTc-MAA, respectively; total radiopharmaceutical activity was quantified for both lungs combined and for the right and left lungs separately. Results Symptomatic individuals had lower MIP (73 [37] vs 114 [22.50] cmH₂O), SMIP (502 [222] vs 935.50 [215] PTU), and FIT (22.30 [9.20] vs 46.25 [20.28]; all p<0.001). Total aerosol deposition (327.16 [232.97] vs 618.26 [187.88] Kct) and total lung perfusion (765.66 [269.94] vs 1046.94 [447.41] Kct) were reduced. PSQI (9 [5] vs 6.50 [6]; p=0.006) and ESS (12 [5] vs 4 [4]; p=0.003) were worse. FIT correlated with total aerosol deposition (r=0.93; p<0.001). Conclusions Long COVID is associated with reduced inspiratory muscle performance, impaired ventilation/perfusion, and worse sleep, supporting FIT and pulmonary scintigraphy as potential functional markers for assessment and rehabilitation monitoring.