Ventilatory Limitation of Exercise in Pediatric Subjects Evaluated for Exertional Dyspnea

Abstract

Purpose: Attribution of ventilatory limitation to exercise when the ratio of ventilation ( ${\dot{V}}_E$ ) at peak work to maximum voluntary ventilation (MVV) exceeds 0.80 is problematic in pediatrics. Instead, expiratory flow limitation (EFL) measured by tidal flow-volume loop (FVL) analysis - the method of choice - was compared with directly measured MVV or proxies to determine ventilatory limitation. Methods: Subjects undergoing clinical evaluation for exertional dyspnea performed maximal exercise testing with measurement of tidal FVL. EFL was defined when exercise tidal FVL overlapped at least 5% of the maximal expiratory flow-volume envelope for > 5 breaths in any stage of exercise. We compared this method of ventilatory limitation to traditional methods based on MVV or multiples (30, 35, or 40) of FEV₁. Receiver operating characteristic curves were constructed and area under curve (AUC) computed for peak ${\dot{V}}_E$ /MVV and peak ${\dot{V}}_E$ /x⋅FEV₁. Results: Among 148 subjects aged 7-18 years (60% female), EFL was found in 87 (59%). Using EFL shown by FVL analysis as a true positive to determine ventilatory limitation, AUC for peak ${\dot{V}}_E$ /30⋅FEV₁ was 0.84 (95% CI 0.78-0.90), significantly better than AUC 0.70 (95% CI 0.61-0.79) when 12-s sprint MVV was used for peak ${\dot{V}}_E$ /MVV. Sensitivity and specificity were 0.82 and 0.70 respectively when using a cutoff of 0.85 for peak ${\dot{V}}_E$ /30⋅FEV₁ to predict ventilatory limitation to exercise. Conclusion: Peak ${\dot{V}}_E$ /30⋅FEV₁ is superior to peak ${\dot{V}}_E$ /MVV, as a means to identify potential ventilatory limitation in pediatric subjects when FVL analysis is not available.

Keywords: children; dyspnea; exercise; flow limitation; flow-volume curve; ventilation.