Oscillatory resistance measured during noninvasive proportional assist ventilation

Setting proportional assist ventilation (PAV) requires the measurement of p atient resistance and elastance. To avoid patient sedation/paralysis or the use of an esophageal balloon, noninvasive PAV is indirectly set by the "ru naway" method or in accordance with patient comfort. The aim of this study was to ascertain whether the forced oscillation technique (POT) applied by the ventilator during noninvasive PAV is useful in assessing patient respir atory resistance. Nasal PAV was applied to 14 patients with severe chronic obstructive pulmonary disease. During PAV a modified ventilator applied a 5 -Hz pressure oscillation to noninvasively assess POT resistance (Rrs). Lung resistance (R-L) was measured in seven of the patients by using an esophag eal balloon. Moreover, measurements were also performed in five of the pati ents when PAV was applied through the mouth. Rrs was close to R-L both duri ng nasal (Rrs = 8.9 +/- 3.1, R-L = 9.0 +/- 2.6; cm H2O (.) s/L; n = 7, p > 0.05) and mouth (Rrs = 5.6 +/- 2.1, R-L = 5.8 +/- 1.4; cm H2O (.) s/L; n = 5, p > 0.05) breathing. Rrs was slightly greater than the maximum value of flow assistance applied during the setting of PAV (FAmax): 11.1 +/- 5.4 and 9.5 +/- 2.9 cm H2O (.) s/L, respectively (n = 14, p > 0.05), both variable s being significantly correlated (r = 0.72, p < 0.05). POT applied by the P AV ventilator allowed the assessment of patient resistance. These results s uggest that POT could be useful in setting PAV flow assistance and in autom atically and continuously updating this setting in accordance with patient resistance.