The pulmonary arterial wedge pressure may be elevated, at least in those locations in the pulmonary arterial system where the entire distal pulmonary venous bed is involved. The perfusion lung scan may show diffuse patchy abnormalities. Vasodilator therapy has been ineffective in pulmonary veno-occlusive disease and has induced acute pulmonary edema in some instances. Similar pathological changes, such as plexogenic arteriopathy, are seen in the pulmonary vessels. The high prevalence of Raynaud's phenomenon and of positive ANA titers in patients who otherwise appear to have primary pulmonary hypertension indicates that collagen vascular disease may be an important underlying factor more frequently than usually considered.
Pulmonary vasculitis occurs in a wide variety of the systemic vasculitides as well.
Some of these vasculitides, such as leukoclastic vasculitis and periarteritis nodosa, appear to result from deposition of circulating immune complexes in the pulmonary vessels. Others, such as Wegener's granulomatosis, more likely result from a cell-mediated immune reaction. Pulmonary vasculitis does not necessarily cause pulmonary hypertension, particularly in the initial active phase of the disease. Pulmonary hypertension is more likely to occur in the later healed phase, which is marked by obliterative intimal and perivascular fibrosis. Primary pulmonary hypertension has occurred in some patients with hemophilia who have received long-term therapy with factor VIII concentrates.