Metronome-Paced Incremental Hyperventilation May Predict Exercise Tolerance and Dyspnea as a Surrogate for Dynamic Lung Hyperinflation During Exercise

BACKGROUND: Dynamic lung hyperinflation (DLH) has been evaluated based on decreased inspiratory capacity (IC) during exercise load. However, this is not routinely done in clinical practice. We have developed a convenient method of metronome-paced incremental hyperventilation (MPIH) and reported its usefulness. In the present study, we compared these two methods for evaluating DLH and examined whether our MPIH method can be used to predict DLH during exercise. METHODS: DLH was measured by MPIH and constant load exercise (CLE) in 35 patients with stable COPD. DLH was defined as the most decreased IC (IC(lowest)) and the most decreases in IC from IC at rest (−IC(lowest)), and we compared between these two methods. RESULTS: The IC(lowest) in CLE and the −IC(lowest) in MPIH were significantly lower in emphysema-dominant COPD than in emphysema-nondominant COPD. Both IC(lowest) and −IC(lowest) showed significant correlations between the two methods (r = 0.67, p < 0.01 and r = 0.44, p < 0.01, respectively). The endurance time of CLE was significantly correlated with IC(lowest) following MPIH (r = 0.62, p < 0.01) but not with that obtained by the CLE method. Furthermore, the IC(lowest) of MPIH was more significantly correlated with endurance time in emphysema-dominant COPD. Weak but significant correlations between the −IC(lowest) obtained by each method and maximum modified Borg scale were observed (MPIH: r = 0.38, p = 0.02; CLE: r = 0.37, p = 0.03). CONCLUSION: The MPIH method may be a convenient method to predict exercise tolerance and dyspnea as a clinically useful synergic screening surrogate for DLH during exercise.