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.