Longitudinal assessment of lung function in patients with pectus excavatum (PE)

Background: In PE patients, treatment often leads to subjective improvements of exercise capacity and dyspnoea. Objective changes in lung function, in contrast, are often lacking. We hypothesized that respiratory system reactance (Xrs) assessed at high lung volumes by the forced oscillation technique (FOT) would be more sensitive than conventional lung function tests to the respiratory pathophysiology of PE. Our aim was to investigate if, in PE patients treated by non-surgical vacuum bell therapy, longitudinal changes in Xrs are related to changes in chest wall deformity. Methods: 31 PE patients (mean(SD) age=13(3) years) underwent FOT at 5 Hz, spirometry and body plethysmography at 3-6 months intervals for the duration of the treatment. FOT was performed during spontaneous breathing followed by a slow vital capacity manoeuvre. Xrs was evaluated during tidal inspiration and expiration (X INSP, X EXP ) and at TLC (X TLC ). The association between lung function and chest wall deformity was assessed by multilevel linear regression and adjusted for height and weight if appropriate. Results: At baseline, patients had a mean(95%CI) FEV1 = 93(87,98)%pred, FEV1/FVC = 89(87,90)%, RV/TLC = 29(26,31)%, TLC = 94(89,98)%pred, X INSP = -1.2(-1.5,-0.9) cmH 2 O*s/L, X EXP = -1.4(-1.7,-1.0) cmH 2 O*s/L and X TLC = -2.2(-2.6,-1.8) cmH 2 O*s/L. FEV1 and FEV1/FVC presented a weak but significant decrease over time. Within each patient, depth of deformity was significantly associated with X TLC (p=0.001, R 2 =0.21) but not with either X INSP , X EXP , spirometric or plethysmografic parameters. Conclusion: Our results suggest that chest wall deformity may be associated with reduced chest wall compliance detected by FOT only at higher lung volumes.