[Clinical application of the forced oscillation technique for titration of pressure support levels in chronic obstructive pulmonary disease patients during nasal noninvasive positive pressure ventilation].

OBJECTIVE

To study the use of oscillatory resistance (Rrs) and reactance (Xrs) to guide the settings of pressure level of ventilators in patients with severe chronic obstructive pulmonary disease (COPD) during noninvasive positive pressure ventilation (NPPV).

METHODS

Five Hz oscillatory inspiratory Rrs (R(re, in)) at different NPPV pressure levels in 8 patients were calculated and compared to inspiratory pulmonary resistance (R(L, in)) measured by means of oesophageal manometry. The difference between inspiratory and expiratory Xrs (deltaXrs) at different CPAP levels were also measured for each breathing cycle, which were subsequently analyzed and classified as flow-limited (EFL) or non-EFL by means of Mead-Whittenberger method. Then, the relationship among CPAP levels, the percentage of EFL breathing cycles at different CPAP levels and deltaXrs were analyzed and the threshold value of deltaXrs with maximum sensitivity and specificity to detect EFL were calculated.

RESULTS

The mean values of R(rs, in) and R(L, in) were (6.5 +/- 1.6) and (9 +/- 5) cm H2O x s(-1) x L(-1) (1 cm H2O = 0.098 kPa), respectively,r = 0.64, P < 0.01, but the agreement between these two resistances were poor and with a median of -2. 7 (-5.7 - 0.7)cm H2O x s(-1) x L(-1), and the limits of agreement ranged from -10.6 cm H2O x s(-1) x L(-1) to 4.9 cm H2O x s(-1) x L(-1). The linear regression equation of R(rs, in) to R(L, in) was R(L, in) = -1.62 + 1.69 R(rs, i), F = 109.6, P < 0.01. Increase in CPAP level resulted in decrease in deltaXrs and in numbers of EFL breathing cycles. The mean value of deltaXrs in EFL breathing cycles was significantly higher than that in NFL, and the threshold value of deltaXrs for detecting EFL was 1.83 cm H2O x s(-1) x L(-1), with a sensitivity of 94% and specificity of 97% respectively.

CONCLUSIONS

Although slightly underestimated, R(rs, in) is helpful to guide the settings of inspiratory positive airway pressure level, which will appropriately overcome the elevated pulmonary resistance, and the threshold value of deltaXrs, of end-expiratory pressure, which will eliminate the majority of EFL breathing cycles.