Breathing pattern and ventilatory response to exercise in chronic obstructive pulmonary disease

<bold>Background and Aim:</bold> Patients with chronic obstructive pulmonary disease (COPD) show a ventilatory limitation to exercise due to ventilatory inefficiency and dynamic hyperinflation (DH). Breathing pattern can be measured by T_I/T_TOT (inspiratory time/total time) and V_T/T_I (tidal volume/inspiratory time), that increase during exertional hyperpnea in healthy subjects. These parameters have never been studied in COPD, so we analysed them at rest and on exercise in a COPD cohort. <bold>Methods:</bold> We retrospectively enrolled stable COPD patients with a variable airflow obstruction. They all underwent spirometry and cardiopulmonary exercise testing on a cycle ergometer. <bold>Results:</bold> In 234 COPD patients (75 females; age range 41-89 years; BMI 27±5 kg/m²), T_I/T_TOT and V_T/T_I increased from 0.259±0.040 to 0.304±0.038 and from 854.1±229,6 ml/s to 2100±622.5 ml/s, respectively (p<0.05) during exercise. T_I/T_TOT and V_T/T_I at peak were both positively related (p<0.05) with VO_2peak (ml/min/kg) and maximal workload (Watt). T_I/T_TOT at rest and at peak showed a positive correlation (p<0.05) with the peak-rest difference in inspiratory capacity (ΔIC, in ml). Clustering patients according to the development of DH (ΔIC ≥150 ml), a T_I/T_TOT at peak ≤ 0.302 (AUC = 0.697, p<0.001; sensitivity: 0.705 specificity: 0.605) and a T_I/T_TOT at rest ≤ 0.266 (AUC = 0.620, p<0.05, sensitivity 0.585 specificity 0.612) significantly predicted the development of DH. <bold>Conclusions:</bold> T_I/T_TOT and V_T/T_I significantly increase during maximal exercise in COPD. T_I/T_TOT at both rest and peak significantly correlated with DH and also predicted its development. T_I/T_TOT and V_T/T_I may be useful measures of the ventilatory response to exercise in COPD.