Breathing pattern and ventilatory response to exercise in patients with Chronic Obstructive Pulmonary Disease

Patients with Chronic Obstructive Pulmonary Disease (COPD) show ventilatory limitation to exercise due to dynamic hyperinflation (DH). Breathing pattern can be expressed by T_I/T_TOT (inspiratory time/total time) and V_T/T_I (tidal volume/inspiratory time). Both parameters significantly increase during exertional hyperpnea in healthy subjects, but they have never been studied in COPD. In a large cohort of COPD patients, we analysed T_I/T_TOT and V_T/T_I at rest and during maximal exercise.

We enrolled clinically stable COPD patients with wide degree of airflow obstruction. All participants underwent spirometry and cardiopulmonary exercise testing (CPET) on a cycle ergometer.

In 234 COPD patients (75 females; age range 41-89 years), T_I/T_TOT and V_T/T_I values significantly increased during exercise, from 0.259 ± 0.040-0.304 ± 0.038 and from 854.1 ± 229,6 ml/s to 2100 ± 622.5 ml/s respectively (p < 0.05). T_I/T_{TOT peak} and V_T/T_{I peak} were positively related (p < 0.05) with VO_2peak (ml/min/kg), maximal workload (Watt). T_I/T_{TOT peak}, but not V_T/T_{I peak} values showed a positive correlation (p < 0.05) with the peak-rest difference of inspiratory capacity (ΔIC, in ml). When related to minute ventilation T_I/T_TOT and V_T/T_I rest values in patients with DH (ΔIC ≥150 ml), compared with those without DH, did not differ between the two groups, though T_I/T_TOT, but not V_T/T_I values, significantly increased during exercise in patients without DH CONCLUSIONS: T_I/T_TOT and V_T/T_I values significantly increase during maximal exercise in COPD. T_I/T_TOT values were significantly correlated with dynamic hyperinflation. Our results suggest that T_I/T_TOT and V_T/T_I assessment may provide further information on exercise ventilatory limitation in COPD.