A New Method and Device for Differentiating Elastic and Resistive Properties of the Respiratory System

Obstructive lung diseases can be caused by bronchi narrowing or loss of lung tissue elasticity or both. The aim of the work was to develop a new measurement method and an equipment which enables to evaluate the obstruction causes. This Added Compliance and Resistance Method (ACRM) determines the fundamental parameters of the respiratory system mechanics that are the total respiratory system compliance (Crs) and resistance (Rrs). Each case of obstruction can be characterized by the corresponding point location on the Rrs-Crs plane. ACRM was verified by means of experiments performed with the use of our artificial patient developed previously, a commercial spirometer and the developed equipment. ACRM was compared with forced spirometry being the fundamental screening method for diagnosis of obstructive lung diseases and basing on the forced expiratory volume in 1st second (FEV1). Spirometry could not distinguish between pulmogenic and bronchogenic causes of an obstruction. For example, the value of FEV1 did not enable to differentiate moderate, mild and no bronchial obstruction from severe, moderate and mild obstruction, respectively, accompanied with twice increase of Crs. On the other hand, a Crs fall increased FEV1, and thus FEV1 underestimated the bronchial obstruction severity if the severity was determined on the base of its value. In contrast, ACRM could determine the cause of an obstruction case and the higher the severity of the obstruction, the better the differentiation. Concluding, the proposed method should supplement the forced spirometry to determine the patient state more precisely.