Pulmonary histiocytosis X: pulmonary function and exercise pathophysiology.

Pulmonary histiocytosis X (PHX) is a diffuse, smoking-related lung disease characterized pathologically by bronchocentric inflammation, cyst formation, and widespread vascular abnormalities and physiologically by exercise limitation. The major mechanism underlying exercise impairment in this disease has not been previously defined. Spirometry, lung volumes, lung mechanics, and exercise physiology were performed on 23 patients with PHX. Two subgroups were identified on the basis of elastic recoil: 12 subjects had an elevated coefficient of elastic recoil with 11 demonstrating a predominant pattern of restriction, and 10 subjects had normal elastic recoil and relatively normal lung function. Exercise performance was severely limited in both subgroups (workload 53 +/- 3%). Abnormalities of ventilatory function and gas exchange were present but did not appear to be exercise-limiting in the majority of subjects. Indices reflecting pulmonary vascular function (DLCO, baseline VD/VT, exercise VD/VT) were abnormal. Strong correlations between overall exercise performance (% predicted VO2max) and indices of vascular involvement were present: DLCO (r = 0.68, p = 0.0004), baseline VD/VT (-0.65, 0.001), exercise VD/VT (-0.67, 0.0004). Similar correlations were found when exercise performance was measured by maximal workload achieved. We conclude that (1) subjects with PHX present with either normal or predominantly restrictive pulmonary physiology and that (2) exercise impairment is common and appears to reflect pulmonary vascular dysfunction.