Ventilatory pattern and respiratory muscle activation in normocapnic and hypercapnic COPD patients: preliminary analysis of an ongoing pilot study.

Introduction: In advanced COPD, hypercapnia may reflect impaired ventilatory control and increased recruitment of accessory muscles. The study of normocapnic and hypercapnic patients could provide insight into pathophysiological mechanisms and potential intervention. Aims: To compare ventilatory pattern, electromyographic activation of scalene (SC), intercostal (IC)muscles and central CO2 sensitivity to CO2 in normocapnic and hypercapnic COPD. Methods: Patients were classified as normocapnic (PaCO₂ ≤45 mmHg) or hypercapnic (PaCO₂ >45 mmHg). Ventilatory pattern (RR, Vt), SC and IC EMG activation were measured using Root Mean Square (% of maximum at Total Lung Capacity, drive = EMG/Ti, and total activation (minute) = % of maximum at Total Capacity × RR). Results: 19 patients were enrolled. No significant differences were observed in age (68 ± 7 vs 71 ± 8 years, p = 0.18), weight or BMI (p > 0.40). Differences in ventilatory pattern, EMG activation are described below. Conclusion: These findings suggest that hypercapnia in COPD is associated with a faster and shallower ventilatory pattern, increased EMG activity especially scalene and a decreases CO2 sensitivity. erjor;12/suppl_17/101/TB1 T1 TB1 Normocapnic Hypercapnic p value Number of patients 9 10 Respiratory Rate (rpm) 16 ± 4.22 21 ± 6.8 0.047 Tidal Volume (ml) 671 ± 191 476 ± 148 0.033 SC muscle activation (% Mx EMG) 15.8 ± 7.9 26 ± 12.5 0.034 SC muscle drive (EMG/ti) 9.7 ± 4.1 22.9 ± 14.6 0.039 Total SC activation (% Mx EMG x RR) 229 ± 95 549 ± 346 0.05 IC muscle activation (% Mx EMG) 12.02 ± 6.7 18.4 ± 8.8 0.128 IC muscle drive (EMG/ti) 7.8 ± 4.4 15.9 ± 8.1 0.024 Total IC activation (% Mx EMG x RR) 191 ± 107 378 ± 214 0.041