Noninvasive assessment of respiratory resistance in severe chronic respiratory patients with nasal CPAP

Noninvasive measurement of respiratory resistance during nasal ventilatory support could be useful to assess the mechanical status of the patient and to optimize the ventilator settings. The aim was to investigate whether the forced oscillation technique (FOT) applied through a nasal mask allows rel iable noninvasive estimation of respiratory resistance (Rrs) in patients wi th severe chronic respiratory disease, FOT Rrs (5 Hz) and lung resistance (RL) measured simultaneously from sponta neous breathing signals by an oesophageal balloon were compared in eight pa tients with chronic obstructive pulmonary disease and in sig patients with a restrictive ventilatory defect due to chest wall disease, Measurements we re performed in sitting and supine postures during application of nasal con tinuous positive airway pressure (CPAP): 4, 8 and 12 cmH(2)O in obstructive patients and 4 cmH(2)O in restrictive patients. In the restrictive patients Rrs and RL (in cmH(2)O.s.L-1) were virtually co incident: mean+/-SD, 12.6+/-6.1 and 11.6+/-6.6 (r=0.96) in sitting and 9.7/-3.1 and 10.2+/-3.3 (r=0.92) in supine posture, respectively, In the obstr uctive patients (CPAP = 4 cmH(2)O), Rrs slightly underestimated RL: mean+/- SD, 11.5+/-5.9 and 14.1+/-16.8 (r=0.92) in sitting and 15.0+/-9.8 and 21.1/-12.6 (r=0.96) in supine posture, respectively. Similar results were found at CPAP = 8 and 12 cmH(2)O. The results obtained in patients with resistance values in the range typica lly found in nasal ventilatory support suggest that forced oscillation tech nique could be valuable to noninvasively estimate a patient's respiratory m echanical resistance.