Evaluation of a method for assessing respiratory mechanics during noninvasive ventilation

Noninvasive assessment of respiratory resistance (Rrs) and elastance (Ers), which is not easy with conventional methods, could be useful in the optimi zation of pressure support ventilation, The aim of this study was to evalua te a simple noninvasive method (Delta-inst) of measuring Rrs during nasal p ressure support ventilation. Rrs and Ers (DeIta-inst) were computed from inspiratory mask pressure, flow and volume recorded during pressure support ventilation. The Delta-inst me thod was compared with the forced oscillation technique (FOT) in seven pati ents with chronic obstructive pulmonary disease (COPD) and in eight healthy subjects without and with added resistance (3.1 cmH(2)O .s .L-1). Rrs measured by Delta-inst (5.2+/-1.7, 7.2+/-0.5 and 6.9+/-1.2 cmH(2)O.s.L- 1) and by FOT (5.0+/-0.7, 7.6+/-0.9 and 8.1+/-2.7 cmH(2)O .s .L-1) in healt hy subjects without and with added resistance and COPD, respectively, were not significantly different (p>0.05). Rrs measured by both techniques showe d a significant coefficient of linear correlation (r=0.70 s) (p<0.01), in t he COPD patients, the variability of Delta-inst Rrs (30%) was greater than that of FOT Rrs (21%), The agreement between Ers obtained by Delta-inst and by FOT was less than that found for Rrs, Delta-inst is a noninvasive and simple method for reliably assessing resist ance. Therefore, it is useful for monitoring airway obstruction and is pote ntially helpful in adapting the settings for pressure support ventilation i n accordance,vith patient mechanics.