the individual hosts response to the MAC after After exposure? all, these are not called atypical mycobacteria for exposure or nothing. John M. Embil, MD, FRCPC C.P.W. Warren, MB, FRCPC Department of Medicine University of Manitoba Health Sciences Centre Winnipeg, Manitoba, Canada References 1 Embil J, Warren P, Yakrus M, et al. Pulmonary illness 2 3 4 5 6 7 associated with exposure to Mycobacterium avium complex in hot tub water: hvpersensitivitv pneumonitis or infection? Chest 1997; 111:813-16 Kahana LM, Kay JM, Yakrus MA, et al. Mycobacterium avium complex infection in an immunocompetent young adult related to hot tub exposure. Chest 1997; 111:242-45 Lynch DA, Rose CS, Way D, et al. Hvpersensitivitv pneumo¬ nitis: sensitivity of high-resolution CT in a population-based 159:469-72 study. AJR 1992; Schuyler M, Cormier MY. The diagnosis of hypersensitivity Chest 1997; 111:534-36 pneumonitis. Prince DS, Peterson DD, Steiner RM, et al. Infection with avium complex in patients without predispos¬ Mycobacterium ing conditions. N Engl J Med 1989; 321:863-68 due to Rosenzweig DY. intracellulare-avium Pulmonary7 mycobacterial infections clinical fea¬ complex: Mycobacterium tures and course in 100 consecutive cases. Chest 1979; 75:115-19 Teirstein AS, Damsker B, Kirsclmer PA, et al. Pulmonary7 infection with Mycobacterium avium-IntraceUulare: Diagno¬ sis, clinical patterns, treatment. Mt Sinai J Med 1990; 57: 209-15 Scully RE, Mark EJ, McNeely WF, et al. Case 6-1996: case records of the Massachusetts General Hospital. New Engl J Med 1996; 334:521-26 9 Coleman A, Colby TV. Histologic diagnosis of extrinsic allergic alveolitis. Am J Surg Pathol 1988; 12:514-18 8 Pulmonary Vascular Involvement in Pulmonary Histiocytosis X workload achieved=0.884-(0.0088XVdA^t at rest)-(0.002X residual volume) + (0.0044XDco); r2=0.73]. We concluded that the functional limitation in activity7 these patients experience, as reflected by diminished exercise performance, may be due in large part to pulmonary vascular involvement by the disease process. As yet, there have been no therapeutic trials with interventions aimed at vasodilation as a primary treatment for this condition. Our experience and that of Harari et al suggest that this might be a useful avenue to pursue. Robert S. Crausman, MD, FCCP Memorial Hospital of Rhode Island Pawtucket, Rhode Island Talmadge E. King, Jr, MD, FCCP National Jewish Medical and Research Center Denver References 1 Harari S, Brenot F, Barberis M, et al. Advanced pulmonary histiocytosis X is associated with severe pulmonar)7 hyperten¬ sion [letter]. Chest 1997; 111:1142-43 2 Travis WD, Borok Z, Roum JH, et al. Pulmonary7 Langerhans cell granulomatosis (histiocytosis X): a clinicopathologic study of 48 cases. Am J Surg Pathol 1993; 17:971-86 3 Crausman RS, Jennings CA, Tuder RM, et al. Pulmonary histiocytosis X: pulmonary function and exercise pathophysiol¬ ogy. Am J Respir Crit Care Med 1996; 153:426-35 Usefulness of Walking Test for Arterial Oxygen Desaturation Screening in General Population To the Editor: To the Editor: We read with interest the communication by Harari et al (April 1997)1 regarding their finding of pulmonary hypertension nally, linear regression analysis demonstrated that these param¬ eters (Vd/Vt and Deo) together explained 55% (partial r2=0.55) ofthe variability in exercise performance ofthe group [maximum in a group of severely affected patients with pulmonar)7 histiocytosis X (PHX) who had been referred for lung transplantation. Their the importance findings are intriguing and add to data indicating of the pulmonary vascular involvement in this disease. Vascular involvement has frequently been described pathologically in PHX. Travis and coworkers2 found evidence of vascular involve¬ ment in 80% of biopsy specimens. The pathophysiologic signifi¬ cance of this vascular involvement has received little attention. We reported the pulmonary7 function and exercise performance of a cohort (n=23) of less severely affected patients with PHX.3 The group demonstrated normal lung volume (total lung capac¬ ity, 90% predicted) and mildly altered spirometry7 (FEV1 77% predicted, FEV1/FVC 80%) with a disproportionate reduction in diffusing capacity for carbon monoxide (Deo, 59% predicted). The exercise performance for the group was reduced (workload at maximum exercise, 54% predicted) with an abnormal dead space to tidal volume ratio (41%, at rest), which failed to fall with exercise (41%, at peak exercise). This combination of a low Deo and abnormal physiologic dead space ventilation (Vd/Vt) strongly suggest the presence of pulmonary vascular abnormalities. Fi= = 1714 Downloaded From: http://journal.publications.chestnet.org/ on 10/28/2014 Patients with COPD often are hypoxic during exercise, even though they are not hypoxic at rest,1 and this exercise-induced hypoxemia may lead to pulmonary7 hypertension and heart fail¬ ure.2 The early diagnosis of exercise-induced hypoxemia may facilitate early use of appropriate therapeutic approaches which, in turn, may improve the patient's quality of life and prognosis. To evaluate the frequency of exercise-induced hypoxemia in an apparently healthy population, a 3-min walking test with simul¬ taneous measurement of oxygen saturation by pulse oximetry was performed by7 360 subjects during a medical health examination. No subject had a previous history of lung disease or abnormalities on chest radiography. During the walking test, each subject was equipped with a pulse oximeter and was encouraged to walk as fast as possible. None of the subjects had hypoxemia before the exercise test. Forty-one (11.4%) subjects developed oxygen desaturation disclosed that, during the walking test. Further investigation among these 41 subjects, there were 24 with COPD, 2 with arthritis rheumatoid-associated lung disease, 1 with diffuse causative panbronchiolitis, and 4 with severe scoliosis. The factor of exercise-induced hypoxemia could not be clarified in 10 subjects. The Hugh-Jones score and the pulse oxygen saturation at rest3 were not significantly different between subjects with and without oxygen desaturation (Table 1). Communications to the Editor