Metronome-paced tachypnea test cutoff value for detecting dynamic hyperinflation in COPD: A diagnostic accuracy study

Dynamic hyperinflation (DH) is a key mechanism of exertional dyspnea in COPD, but cardiopulmonary exercise testing (CPET) is not universally available.

To determine the diagnostic accuracy and optimal absolute cutoff value of the metronome-paced tachypnea (MPT) test for detecting exercise-induced DH in patients with moderate COPD, using constant-load CPET as the reference standard.

This diagnostic accuracy study included 18 patients with moderate COPD. Patients underwent pulmonary function testing, symptom-limited incremental CPET, and two paired sessions, 21 days apart, each including MPT followed by constant-load CPET after approximately 30-60 min. DH on CPET was defined as an inspiratory capacity (IC) reduction ≥10% and/or ≥0.15 L. IC was measured at rest, after MPT, and at peak exercise. ROC curve analysis and the Youden index were used to determine the optimal post-MPT IC cutoff.

The MPT test showed good accuracy for identifying CPET-defined DH (AUC 0.862, 95% CI 0.675-0.963; p = 0.004). An IC decrease of 0.27 L after MPT was the optimal cutoff, with 94.7% sensitivity and 75% specificity. Mean bias between MPTΔIC and CPETΔIC was -0.25 L. No significant correlation was observed between MPTΔIC and baseline airflow obstruction or static lung-volume markers.

The MPT test showed good diagnostic accuracy as a simple screening tool for detecting exercise-induced DH in COPD. An absolute IC decrease ≥0.27 L after MPT may represent a potentially useful cross-sectional screening threshold, although further validation is needed before it can be interpreted as a definitive longitudinal threshold.