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

Abstract

Background: 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.

Methods: 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.

Results: 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.

Keywords: Breathing pattern; COPD; CPET; T(I)/T(TOT); V(T)/T(I).