Severe pulmonary hypertension in histiocytosis X

Diminished exercise capacity in advanced pulmonary histiocytosis X does not appear to be related to ventilatory limitation but may be related to pulmo nary vascular dysfunction. Pulmonary hemodynamics and respiratory function were studied in 21 consecutive patients with advanced pulmonary histiocytos is X, and compared with parameters of patients with other severe chronic lu ng diseases (29 patients with chronic obstructive pulmonary disease and 14 patients with idiopathic pulmonary fibrosis). All patients with pulmonary h istiocytosis X displayed severe pulmonary hypertension: mean pulmonary arte rial pressure, 59 +/- 4 mm Hg; cardiac index, 2.6 +/- 0.8 L/min/m(2); and t otal vascular pulmonary resistance, 25 +/- 3 IU/m(2) (p < 0.05, as compared with patients with other chronic lung diseases). Pa-O2 was similar in the three groups, whereas FEV1 was lower in patients with other chronic lung di seases (p < 0.05). In contrast to other chronic lung diseases, the degree o f pulmonary hypertension was not related to variables of pulmonary function in pulmonary histiocytosis X. Histopathology was available for 12 patients with pulmonary histiocytosis X and revealed proliferative vasculopathy inv olving muscular arteries and veins, with prominent venular involvement. Two consecutive lung samples (taken before and after the occurrence of pulmona ry hypertension) were available for six patients with pulmonary histiocytos is X, and showed that pulmonary vasculopathy worsened, whereas parenchymal and bronchiolar lesions remained relatively unchanged. These results indica te that pulmonary hypertension in pulmonary histiocytosis X might be relate d to an intrinsic pulmonary vascular disease, in which the pulmonary circul ation is involved independent of small airway and lung parenchyma injury.