Failure of vasodilator infusion to alter pulmonary diffusing capacity in systemic sclerosis

PURPOSE: Patients with systemic sclerosis (SSc) do not exhibit a normal increase in the diffusing capacity for carbon monoxide ([DL.sub.co]) on assuming the supine position. We sought to determine whether a potent prostacyclin derivative and vasodilator, iloprost, would reverse this defect. PATIENTS AND METHODS: Fourteen patients with SSc were enrolled in a randomized, double-blind, placebo-controlled study of iloprost. Patients were tested before and during 3 days of iloprost or placebo infusion with both upright and supine pulmonary function studies. RESULTS: The results of baseline pulmonary function studies including [DL.sub.co] were not significantly altered by iloprost. Furthermore, iloprost did not alter the abnormal postural [DL.sub.co] response. CONCLUSION: These results suggest that the pulmonary vascular defects seen in this group of patients are not a consequence of reversible pulmonary vasospasm.
Systemic sclerosis (SSc) is a connective tissue disease characterized by sclerosis (hardening) of the skin, gastrointestinal tract, lungs, heart, and kidneys. SSc is often complicated by lung disease, characterized by fibrosis, or fiber-like tissue formation, in the lungs and development of pulmonary hypertension, or increased pressures in the circulation of the lungs. Pulmonary hypertension is one of the main causes of death in SSc patients. Microscopic examination of the lung tissue has revealed thickening of the arterioles and narrowing of the vessel lumina, or inner cavity. SSc is associated with widespread vasospasm, or uncontrolled contraction of the blood vessels, and recurrent pulmonary vasoconstriction may lead to persistent pulmonary hypertension. Patients with SSc do not show the normal increase in lung diffusing capacity when changing from a sitting to a lying position. This may indicate the inability of the blood vessels within the lungs to distend, and may serve as an indicator of pulmonary vascular involvement in SSc patients with apparently normal lung function. The prostaglandin prostacyclin dilates blood vessels and has been shown to reduce pulmonary vascular resistance associated with pulmonary hypertension. Iloprost, an analog of prostacyclin, also dilates blood vessels and reduces pulmonary vascular resistance, but remains in the body for a longer duration as compared with prostacyclin. The ability of iloprost to dilate blood vessels may counteract possible vasospasm and restore the normal response in lung diffusing capacity in SSc patients. The effects of iloprost on lung diffusing capacity when changing from a sitting to a lying position were assessed in 14 patients with SSc. Before treatment, the patients did not show the normal increase in lung diffusing capacity when they went from a sitting to a lying position. Iloprost did not alter lung function or the abnormal response in lung diffusing capacity in these patients. These findings suggest that the defects of lung circulation in patients with SSc are unrelated to vasospasm of the lung blood vessels. (Consumer Summary produced by Reliance Medical Information, Inc.)