CLOSING VOLUME AND INHOMOGENEITY OF VENTILATORY MECHANICAL SYSTEM

  • 1 January 1976
    • journal article
    • research article
    • Vol. 12  (2) , 371-385
Abstract
The use of the closing volume to detect small airway lesions is based on physiological data : it would reflect a special and physiological distribution of the pulmonary inhomogeneity. This work discusses the closing volume as used to determine a pathological process, i.e., the relationship between the observed profile of closing volume and other functional parameters, whose abnormalities are likely to reflect the inhomogeneity of the ventilatory mechanical system. In 126 patients representing a wide range of pathological processes, the closing volume and the following functional parameters were calculated : the VC[vital capacity]/theoretical VC ratio, the RV [respiratory volume] measured by dilution method and by plethysmography, the FEV1.0[forced expiratory volume in 1 s]/VC ratio, the expiratory total pulmonary resistance (RPTE), the efficient resistance (~R), the airway resistance (Raw), the effective compliance (Ce) measured at the spontaneous respiratory frequency, and its variation in relation with respiratory frequency (f), and a distribution index of inspired gas. The procedure and the reproducibility of the closing volume measurements and the significance of the lack of phase IV during the closing volume estimation are discussed. The reasons which suggest that closing volume extent and inhomogeneity of the ventilatory mechanics have a parallel evolution are explained. The increase in distribution inhomogeneity of the pulmonary time constants (shown by the slope of the Ce variation in relation with F and gas distribution index) is concomitant with an increase in closing volume. Although the lack of phase IV does not have a univocal signficance (this is a limit to the utilization of the closing volume alone as a detection test) the quantification of the closing volume brings, as the Ce, f relation does, an original element, but the evaluation of Ce, f is more difficult to realize in practice.