VARIATION OF EFFECTIVE COMPLIANCE WITH RESPIRATORY FREQUENCY - TEST OF INHOMOGENEITY OF VENTILATORY MECHANICAL SYSTEM

  • 1 January 1976
    • journal article
    • research article
    • Vol. 12  (2) , 349-369
Abstract
A decrease in effective compliance (Ce) with increase in respiratory frequency (f) is considered as representing an inhomogeneity in the distribution of the pulmonary time constants. The Ce variation in relation to f reflects the inadequacy of the first order linear mono-alveolar model usually used to describe the ventilatory mechanical properties. Such an assertion is widely accepted, but few attempts have been done to validate this point in patients and to determine the various components likely to affect the Ce, f relationship. In 171 patients, selected in order to sample different types of pulmonary lesions, the following functional parameters were calculated: VC[vital capacity]/theoretical VC ratio, RV [respiratory volume] by dilution method and by plethysmography, airway resistance and distribution index of inspired gas. The effective compliance and its variation with respiratory frequency were also calculated. After a discussion of the procedure and of the method used to express the compliance-frequency relationship (linear regression), it is shown that despite the elementary type of expression the relation is a good discriminative parameter. Its signification is discussed by analyzing results obtained in patients and by simulating a mathematical model of the ventilatory mechanics where the mechanical parameters are distributed. A negative slope of the compliance-frequency relationship probably expresses an important mechanical inhomogeneity. Taking into account the fact that the whole frequency-compliance relationship gives little information, in the face of an unpleasant test for the patients, a simplified procedure is proposed which is adapted to the usual practice.