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.

FIGURE 1

Operating lung volume. Box and whisker plots of operating lung volume during exercise, expressed as ratio of inspiratory capacity (IC) or expiratory reserve volume (ERV) divided by vital capacity (VC), in subjects according to presence or absence EFL in exercise. Box represents 25^th and 75^th centiles, with horizontal line representing median and x depicting mean value; dots are outliers.

FIGURE 2

ROC curves. Receiver operating characteristic curves illustrating sensitivity and specificity of (A) 12-s sprint MVV in denominator for peak ${\dot{V}}_E$/MVV, and (B) proxy measure for MVV viz. peak ${\dot{V}}_E$/30⋅FEV₁.