Mortality was most closely associated with right ventricular hemodynamic function and can be characterized by means of an equation using three variables: mean pulmonary artery pressure, mean right atrial pressure, and cardiac index. Such an equation, once validated prospectively, could be used as an adjunct in planning treatment strategies and allocating medical resources.

Pulmonary arterial hypertension (PAH) includes various forms of pulmonary hypertension of different etiology but similar clinical presentation and functional derangement. Histopathological vascular changes in all forms of PAH are qualitatively similar but with quantitative differences in the distribution and prevalence of pathological changes in various portions of the pulmonary vascular bed. The documentation of these topographic variations in the response of the pulmonary vasculature to injury may be important to understand the pathogenesis of the various subsets of PAH. To standardize the precise histopathological documentation of the pulmonary vasculopathy in PAH we propose a histopathological classification that includes both the predominant segment of the pulmonary vasculature affected and the possible coexistence of pathological changes in other vascular segments.

Qualitative and quantitative studies were performed on pulmonary blood vessels in lung tissue obtained by biopsy, pneumonectomy, or autopsy from 58 patients in the Registry of Primary Pulmonary Hypertension sponsored by the Heart, Lung, and Blood Institute of the National Institutes of Health. In 49 patients (84%), the hypertensive vascular disease involved predominantly or exclusively muscular pulmonary arteries and arterioles. In the present study, the histopathologic nature and extent of hypertensive pulmonary vascular lesions are described in 58 patients from the NHLBI Registry.

Two plasma proteins, vitamin D-binding protein (actin monomer sequestrant) and gelsolin (actin polymer severing), have been found in association with actin in plasma from ill humans and during experimental injury. In vitro, these are the only plasma proteins that display a high affinity for actin. We infused increasing amounts of globular actin intravenously to rats to evaluate its disposition in plasma and tissues. Intravascular filament formation, microthrombi, and endothelial injury were observed, especially in the pulmonary circulation. These pathological changes were not observed when the globular actin in the infusate had been preincubated with the vitamin D-binding protein in vitro. Complexes of actin with both proteins were found in the plasma, suggesting a saturable, plasma actin-binding system in vivo. Our findings suggest that in vivo saturation of these proteins' actin-binding capacities may serve as a paradigm for pulmonary vascular disorders seen during widespread tissue trauma and cell lysis.

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