Effect of oral high frequency oscillation.

Laros et al. state probably on the basis of experience in one patient that oral high frequency oscillation (OHFO) combined with forced expiration manoeuvres on tracheobronchial clearance is disappointing in patients with flaccid lungs. Their letter to the editor suggests that our conclusions, meaning that OHFO combined with forced expiration manoeuvres is inefficient, could not be made because the pulmonary compliance of our patients is unknown. Although we did not measure the compliance, it is hard to believe that patients with this minor degree of airway obstruction have flaccid lungs. Other lung function data, like TLC, FRC, RV or the different between FEV 1 and FIV1, as indications for flaccid lungs, did support this. After OHFO there was no increase in TLC or RV, measured by body plethysmography and helium-equilibration method. The method used by Laros et al. is different from the method used in our study. The influence of the oral cavity can be important because of its flaccidity, as stated by Laros. Since our method is so different from the one used by Laros, and since there is no circumstantial evidence for flaccid lungs in our patients, we believe that our conclusions remain valid. Besides the method described by Laros et al. seems not to be applicable in patients on a daily outpatient basis.