[Pressure-flow relationship in the airways (author's transl)].

The perplexing features of the pressure-flow relationship in the pulmonary airways have been explained on the basis of a combined experimental-theoretical study. By systematically plotting the in vivo data on the pressure-flow relationship existing in the literature in a dimensionless manner (Moody diagram), we confirmed the results reported by Lisboa et al. [8] : contrary to the well-known theory of Jaffrin and Kesic [6], it appeared that under certain spontaneous breathing conditions Reynolds number is not the only parameter which governs the flow in the airways. We further confirmed this result using a cast of the central airways and a piston pump. The data showed that the pressure-flow relationship depended greatly on frequency, tidal volume and the physical properties of the gas used. After a systematic variation of these parameters, a dimensionless parameter epsilon, which depends importantly on local acceleration, was identified. This new parameter, together with those already identified (Re : Reynolds number; alpha : Womersley number), define the pressure-flow relationship in a given geometry during the course of a respiratory cycle. Implications of this theoretical knowledge on the measurement and interpretation of airway resistance are discussed.