Determining pulmonary resistance to gas flow during sinusoidal pressure wave mechanical ventilation

Standard techniques for measuring pulmonary resistance (RP) to gas flow in newborn infants yield results that are widely dispersed and difficult to interpret. The purpose of this study is to describe and evaluate a new improved method for determining RP which utilizes a sinusoidal pressure wave generator. Measurements of respiratory flow rate and transpulmonary pressure were made in cats 1) breathing spontaneously, 2) mechanically ventilated with a time-cycled pressure-limited ventilator, and 3) mechanically ventilated with a sinusoidal pressure wave delivered to the airways. RP values were calculated using 2 methods: 1) at midinhalation (RPI) and midexhalation (RPE), and 2) at iso-volume times during inhalation and exhalation (RP(iso-V)). During spontaneous breathing, RP values were 65 +/- 16 (mean +/- SE), 90 +/- 23 and 78 +/- 27 cm H2O/L . sec for RPI, RPE, and RP(iso-V), respectively. Mechanical ventilation yielded RP values of 35 +/- 4 and 124 +/- 26 cm H2O/L . sec for RPI and RPE, respectively. During sinusoidal airway pressure ventilation, standard errors were reduced; PP values were 33 +/- 4, 54 +/- 6, and 42 +/- 4 cm H2O/L . sec for RPI, RPE, and RP(iso-V), respectively. The use of the sinusoidal pressure wave generator smoothed the pressure-flow data and improved the quality of RP determinations. Coefficients of variation were reduced by 45%. The methods used are simple to apply and may make the determination of RP in ICU patients more practical.