INCREASED DEAD SPACE VENTILATION IN DYSPNEIC VETERANS WITH PRESERVED SPIROMETRY

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SESSION TITLE: Electronic Top Posters SESSION TYPE: Original Inv Poster Discussion PRESENTED ON: 10/08/2018 01:15 PM - 02:15 PM PURPOSE: Following deployment to Iraq and Afghanistan, Veterans frequently report respiratory symptoms that may be related to exposure to airborne hazards during deployment, yet spirometry is often within normal limits. In the presence of preserved spirometry, we previously reported an isolated reduction in diffusing capacity in this cohort at rest, but have not yet examined gas-exchange during exercise. We hypothesized gas-exchange abnormalities would be present during exercise among dyspneic Veterans with preserved spirometry, leading to increased physiological dead space (VD/VT). METHODS: We retrospectively reviewed 82 cases with preserved spirometry referred to our tertiary care clinic for dyspnea evaluation that underwent cardiopulmonary exercise testing (CPX). Complete pulmonary function testing and a progressive maximal CPX, with arterial blood gases at pre- and post-exercise, was performed in all Veterans on separate days. VD/VT was estimated breath-by-breath, graphically displayed, and classified as a progressive decrease (VD/VT-) or remains stable or increases during exercise (VD/VT+). Between-group (VD/VT+ vs. VD/VT-) comparisons were also performed. RESULTS: Approximately 51.2% of our sample demonstrated stable or increasing deadspace ventilation (VD/VT+) during maximal exercise. Groups were similar with respect to age, sex, body mass index, smoking history and self-reported respiratory symptoms and exposures (p < 0.05). Veterans with VD/VT+ had reduced exercise capacity (VD/VT+ vs. VD/VT-; VO2% predicted; 77.9±16.9% vs. 86.2±17.3, p = 0.030), ventilatory anaerobic threshold (% of VO2 peak, 50.2±11.7 vs. 57.6±11.2, p = 0.005), and greater ventilatory inefficiency (VE/VCO2 slope, 32.6±8.0 vs. 29.2±4.5, p = 0.023) in comparison to VD/VT-. Resting pulmonary function was similar between groups with the exception of diffusing capacity (DLCO % predicted; 82.8±13.3 vs. 90.9±15.9, p = 0.019) and a trend towards reduced total lung capacity (TLC % predicted; 91.0±11.0 vs. 95.6±11.4, p = 0.068). CONCLUSIONS: In our sample of dyspneic Iraq and Afghanistan veterans with preserved spirometry, more than 50% were unable to decrease physiological dead space from rest to peak exercise. Veterans exhibiting this type of pattern were also characterized by reduced exercise capacity and ventilatory efficiency during exercise, as well as reduced diffusing capacity at rest. Although these findings may suggest evidence for pulmonary vasculopathy, several mechanisms contribute to increased physiologic dead space and should be pursued in future research studies. CLINICAL IMPLICATIONS: Lung pathology from airborne hazards in Iraq and Afghanistan may initially present with exertional limitations, as evidenced by declining performance on standard military fitness test and exertional dyspnea. Early dynamic pulmonary evaluation, such as CPX, may be appropriate in at-risk individuals with unexplained dyspnea. DISCLOSURES: No relevant relationships by Ryan Butzko, source=Web Response No relevant relationships by Michael Falvo, source=Web Response No relevant relationships by Drew Helmer, source=Web Response No relevant relationships by Jacquelyn Klein-Adams, source=Web Response No relevant relationships by Ronaldo Ortiz-Pacheco, source=Web Response no disclosure on file for Anays Sotolongo