Does inspiratory behaviour affect the efficiency of non-invasive ventilation in COPD patients?

Non-invasive ventilation (NIV) is more and more used. Some failures of the technique have been reported, and efforts are needed to understand them. Collaboration (inspiratory behaviour) of the patient during NIV could play a role in the success of this technique. We have studied the influence of this one on the efficiency of NIV. While ventilating 10 stable chronic obstructive pulmonary disease patients with a nasal pressure support ventilation (PSV), we measured their flow and volume with a pneumotachograph and oesophageal and gastric pressures during three different respiratory voluntary behaviours: relaxed inspiration, active inspiratory effort and resisted inspiration. We showed that when compared with the relaxed inspiration: (a) Active inspiratory effort increases slightly minute ventilation from 14.8 +/- 4.7 to 15.41 +/- 4.19 during PSV 10/0 without change of breathing frequency but with an important increase of inspiratory work (W(OB)) from 14.47 +/- 9.43 to 28.55 +/- 25.35 J/min (P=0.008). PEEPi increases with active behaviour during PSV but not during BiPAP. (b) A resisted inspiration decreases inspiratory work (to 7.53 +/- 8.6 J/min) at the price of a decrease of the minute ventilation to 11.47 +/- 4.20 l/min (P=0.06). Results of ventilation, PEEPi and work parameters were identical during the bilevel pressure support (15/5 cm H2O). The aims of NIV being to increase ventilation and unload the inspiratory muscles, our results suggest that during NIV, a relaxed spontaneous breathing is preferable. These differences between the inspiratory behaviours could affect the expected benefits of PSV in acutely ill patients.