PULMONARY HISTIOCYTOSIS-X - PULMONARY-FUNCTION AND EXERCISE PATHOPHYSIOLOGY

Pulmonary histiocytosis X (PHX) is a diffuse, smoking-related lung dis ease characterized pathologically by bronchocentric inflammation, cyst formation, and widespread vascular abnormalities and physiologically by exercise limitation. The major mechanism underlying exercise impair ment 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 elas tic recoil: 12 subjects had an elevated coefficient of elastic recoil with 11 demonstrating a predominant pattern of restriction, and 10 sub jects had normal elastic recoil and relatively normal lung function. E xercise performance was severely limited in both subgroups (workload 5 3 +/- 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 (DL(CO), bas eline VD/VT, exercise VD/VT) were abnormal. Strong correlations betwee n overall exercise performance (% predicted V overdot O(2)max) and ind ices of vascular involvement were present: DL(CO) (r = 0.68, p = 0.000 4), baseline VD/VT (-0.65, 0.001), exercise VD/VT (-0.67, 0.0004). Sim ilar correlations were found when exercise performance was measured by maximal workload achieved. We conclude that (1) subjects with PHX pre sent with either normal or predominantly restrictive pulmonary physiol ogy and that (2) exercise impairment is common and appears to reflect pulmonary vascular dysfunction.