PATHOPHYSIOLOGIC CORRELATIONS IN LYMPHOID INTERSTITIAL PNEUMONIA

Effective alveolar volume, diffusing capacity for carbon monoxide (DCO sb), volume-corrected diffusing capacity (DNA), static lung compliance (Cst), and lung distensibility were measured in 16 sheep seropositive for maedi-visna virus (MW) immediately before they were killed. Lungs were inflation-fixed, and the left lung was randomly sampled for morp hometric analysis. The total lung weight, total fixed lung volume, vol ume densities of tissue (Vvt) and air (Vva), and the alveolar surface density were measured and correlated with the physiologic measurements . The density of surface forces could not account for the variation in the distensibility of the lungs, indicating that tissue-related force s may be important in determining lung distensibility in lymphoid inte rstitial pneumonia (LIP) associated with MVV infection. Possible sourc es of tissue-related forces are the contractile tissue associated with lung parenchyma, airways, or vasculature. When DCOsb was corrected fo r volume, a strong negative correlation with Vvt was noted, indicating that factors distinct from lung-volume reduction are important in lim iting gas exchange in LIP associated with MVV infection. More sheep de monstrated abnormal DNA values than any other physiologic measurement, with reduced values being apparent even in sheep considered clinicall y normal and with little or no morphometric evidence of lung disease. Measurements of diffusing capacity are thus considered the most sensit ive functional index of disease progression.