1217 CHARACTERIZATION OF RESTRICTIVE AND OBSTRUCTIVE DISEASES USING RELATIONS AMONG STATIC PULMONARY FUNCTION PARAMETERS

Abstract

We studied the relationships among residual volume (RV), total lung capacity (TLC) and vital capacity (VC) in 26 children with obstructive lung disease (CF), 20 children with chest wall restriction (kyphoscoliosis) and 14 adults with restrictive pulmonary disease (sarcoidosis or diffuse interstitial fibrosis). It was found that once restrictive or obstructive processes have progressed past their initial stages, distinct relations are established among RV/TLC, VC and TLC consistent with the following model. As restrictive processes progress, changes in RV are small relative to changes in TLC. Therefore, as a first approximation, RV can be taken as a constant, K₁, and RV/TLC≈K₁/(K₁+VC)≈K₁/TLC (i.e., RV/TLC is inversely related to VC and TLC). For obstructive processes, changes in TLC are relatively smaller than changes in RV so that TLC≈K₂ and RV/TLC≈(K₂-VC)/K₂ (i.e., directly related to VC). When RV/TLC was plotted against VC/(Pred.VC) or TLC/(Pred.TLC) these inverse and direct relations were clearly seen, demonstrating that in spite of an increase in RV/TLC in both groups, they were separable when related to VC or TLC. For patients in the “earlier” stages of the processes, a distinction appears to be more clearly established for RV/TLC vs TLC than for RV/TLC vs VC. This approach involves observing only two parameters, permits objective classification and longitudinal follow-up of processes involved in a disease and can be easily used in computer-based systems.

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