Dyspnea On Exertion In Deployed Veterans: Deconditioning Or Underlying Dysfunction?

PURPOSE: We previously reported higher dyspnea on exertion (DOE) among non-treatment-seeking Veterans deployed to post-9/11 conflicts in Southwest Asia. While DOE etiology is complex, it is commonly assumed that DOE indicates low cardiorespiratory fitness or deconditioning. However, DOE often isn’t solely attributable to deconditioning, and it remains unclear if DOE arises from cardiorespiratory deconditioning or exercise intolerance due to an underlying cardiorespiratory condition in deployed Veterans. Thus, we compared cardiorespiratory fitness between deployed Veterans and non-deployed controls. METHODS: Deployed Veterans (‘DV’, n = 25) and non-deployed controls (‘Controls’, n = 11) underwent CPET using the Bruce treadmill protocol. Indirect calorimetry and perceptual rating scales were used to measure rate of oxygen consumption (V̇O2), rate of carbon dioxide production (V̇CO2), minute ventilation (V̇E), heart rate (HR), perceived exertion (RPE; Borg 6-20 scale), and perceived breathlessness (RPB; Borg 0-10 scale). Valid effort required two or more of: 1) peak respiratory exchange ratio ≥ 1.1, 2) peak HR ≥ 85% of age-predicted max, 3) V̇O2 plateau (< 2.1 ml/min/kg change), 4) RPE ≥ 17, or 5) blood lactate reaching sex- and age-based thresholds. Percent predicted values were calculated per Bruce et al. (1973). Mann-Whitney U tests compared deployed and non-deployed controls at a significance of p < 0.05. RESULTS: No significant differences were detected in age (DV vs. Controls, 36 ± 8 vs. 31 ± 8 yrs; p = 0.11), height (172.0 ± 10.2 vs. 172.3 ± 9.8 cm; p = 0.99), weight (85.12 ± 22.79 vs. 79.66 ± 11.33 kg; p = 0.58), or BMI (28.6 ± 5.6 vs. 26.8 ± 3.4 kg/m2; p = 0.37). At peak exercise, RPB was significantly higher among DV (5.2 ± 1.7) than Controls (3.8 ± 0.9) (p < 0.01). No significant group differences were detected in absolute V̇O2peak (2.88 ± 0.68 vs. 3.13 ± 0.74 L/min; p = 0.22), or V̇O2peak as a percent of predicted (100 ± 19 vs. 110 ± 31; p = 0.34). CONCLUSION: Deployed Veterans report significantly higher breathlessness at peak exercise despite a normal V̇O2peak, suggesting DOE may not solely stem from deconditioning but potentially unrecognized factors contributing to respiratory burden. Further research is needed to identify specific contributing factors. Supported by: VA ORD I21RX001079