SESSION TITLE: Allergy and Airway SESSION TYPE: Fellow Case Reports PRESENTED ON: 10/07/2018 10:45 AM - 11:45 AM INTRODUCTION: Abnormalities in the small airways in the lung may not be reflected in spirometry which is essentially an assessment of large airways. The small airways are the so-called "silent zone of the lung" but represent 75% of the airways because of multiple branching. Oscillometry (IOS) is a technique to assess airways more distal. We present a patient who had severe dyspnea with normal spirometry but with significant small airway abnormality induced by exercise (forced oscillometry technique). CASE PRESENTATION: This is a 70 year old male (BMI 34.2kg/m2) with a history of World Trade Center (WTC) exposure who presented with unexplained dyspnea at rest as well as with exertion. He reported that symptoms began after 9/11 and had progressively worsened. He was being treated with intermittent bronchodilators and inhaled steroids but was not compliant with therapy. Cardiac workup on admission revealed no acute cardiac or respiratory disease. Pulmonary function tests were performed on the day of admission. Spirometry revealed normal lung volumes and normal airflow (FEV1/FVC = 77%). Resistance assessed by oscillometry was abnormal (R5 7.09 cm H20/L/sec), suggesting small airway abnormality. Pulmonary function was repeated on the sixth day of hospitalization following treatment with standing bronchodilators. Oscillometry had nearly normalized at resting conditions (R5 5.29 cm H20/L/sec) and patient reported relief of dyspnea at rest. Exercising the patient (“fast walk”) brought on dyspnea and increased abnormality on oscillometry (R5 9.53 cm H20/L/sec). His symptoms were attributed to small airway abnormality with possible etiologies including WTC exposure, central circulatory congestion, and/or obesity with mass loading of thoracic cage. DISCUSSION: Findings of abnormal oscillometry in this patient are compatible with exercise-induced small airway abnormality despite relatively normal large airway function based on spirometry. This has been previously documented by Lee who found an increase in peripheral airways resistance with exercise despite normal large airway function in child asthmatics. Without assessment of distal airway function, etiology of this patient’s dyspnea would not have been diagnosed. CONCLUSIONS: In the evaluation of unexplained dyspnea, oscillometry can provide insight when spirometry is normal. When symptoms are exertional, testing during exertion can elicit abnormalities not demonstrable at rest. Testing the patient while symptomatic, such as with exercise, can uncover pathophysiology since isolated distal airway dysfunction can be a source of dyspnea both at rest and on exertion. Reference #1: Lee, J.H., Lee, Y.W., Shin, Y.S., Jung, Y.H., Hong, C.S., and Park, J.W. Exercise-induced airway obstruction in young asthmatics measured by impulse oscillometry. J Investig Allergol Clin Immunol. 2010; 20: 575–581. Reference #2: Oppenheimer, B. W., Goldring, R. M., Herberg, M. E., Hofer, I. S., Reyfman, P. A., Liautaud, S., . . . Berger, K. I. (2007). Distal Airway Function in Symptomatic Subjects With Normal Spirometry Following World Trade Center Dust Exposure. Chest, 132(4), 1275-1282. https://doi.org/10.1378/chest.07-0913. Reference #3: Soghier, I; Smith, D; Berger, KI; Goldring, RM; Oppenheimer, BW. "Dysfunction Of The Distal Airway And Alveolar Capillary Membrane (distal Lung Unit) During Steady State Exercise". American journal of respiratory & critical care medicine. 2016; 193: 2414752. DISCLOSURES: No relevant relationships by Kenneth Berger, source=Web Response No relevant relationships by Roberta Goldring, source=Web Response No relevant relationships by Sheeja Thomas, source=Web Response