Continuous positive airway pressure improves respiratory mechanics and efficiency of neural drive in stable COPD: an exploratory study

BACKGROUND: Continuous positive airway pressure (CPAP) is a major treatment strategy for severe chronic obstructive pulmonary disease (COPD), especially with respiratory failure. However, it remains inconclusive whether CPAP affects respiratory mechanics and neural drive in stable COPD patients without respiratory failure. METHODS: Twenty-two COPD patients without respiratory failure received CPAP starting from 4 to 10 cmH(2)O in 1 cmH(2)O increments. Respiratory pattern, end expiatory lung volume (EELV), dynamic PEEPi (PEEPi(dyn)), airway resistance (Raw), pressure-time product of diaphragmatic pressure (PTPdi) and esophageal pressure (PTPeso), root mean square (RMS) of diaphragm electromyogram (EMGdi) and ratio of ventilation (Ve) to EMGdi (i.e., Ve/RMS) were measured before and at each level of continue positive airway pressure (CPAP). A subgroup analysis was performed between patients with and without inspiratory muscle weakness. RESULTS: Nineteen patients completed the treatment. The respiratory pattern improved significantly after CPAP. Raw, PTPdi, and Pdi decreased significantly. ΔEELV decreased at 4 cmH(2)O (P<0.05), but increased significantly at >8 cmH(2)O. PEEPi(dyn) decreased from 2.18±0.98 to 1.37±0.55 cmH(2)O. RMS increased while Ve/RMS improved significantly after CPAP (P<0.05). Besides, CPAP could significantly improve respiratory mechanics in patients with inspiratory muscle weakness. CONCLUSIONS: CPAP improves respiratory pattern, PEEPi, Raw, work of breathing and efficiency of neural drive in COPD patients without respiratory failure, but easily increases dynamic pulmonary hyperinflation. These effects on respiratory mechanics are significant in patients with inspiratory muscle weakness.