PURPOSE: Dynamic hyperinflation (DH) causes exercise limitation and exertional dyspnea in patients with COPD. Exertional desaturation (ED) also occurs commonly in COPD and multiple mechanisms have been postulated to cause ED. However, neither routine pulmonary function testing nor imaging predicts ED accurately. In this study, we evaluated the relationship between DH and ED during six-minute walk testing (6MWT).
METHODS: ED and DH were measured in patients with stable COPD who did not require supplemental oxygen. SpO2 was measured by continuous pulse oximetry during 6MWT. ED was defined as a decline in SpO2 (delta SpO2) ≥ 4%. DH was determined by measuring inspiratory capacity (IC) before and after the 6MWT using a hand held spirometer. The change in IC (delta IC) is an indirect measure of increased end expiratory lung volume and, therefore, indicates the presence of DH. DH was defined as delta IC ≥ 0.1L. DH and ED were correlated with routine pulmonary function tests and other clinical variables.
RESULTS: 32 males with mean age, FEV1%, and DLCO% predicted of 65, 49% and 50% respectively were studied. Delta SpO2 correlated with delta IC (r=0.44, p=0.012) and age (r=0.36, p=0.046) by univariate analysis; whereas on multivariate regression analysis, only delta IC was retained. ED did not correlate with FEV1, FVC, FEV1/FVC, FEF25-75, RV, ERV, DLCO% predicted, BMI, smoking duration, pre- or post-walk BORG score, and distance covered in 6MWT. DH strongly correlated with ED (x2=7.9, p=0.0048). On receiver operator curve analysis, DH had a robust AUC of 0.797 for predicting ED (sensitivity 86%/specificity 64%, p=0.0002).
CONCLUSIONS: DH correlates with ED in patients with stable COPD. ED did not correlate with routine pulmonary function tests or other clinical variables. Further studies are required to determine whether the presence of DH predicts ED and the pathophysiological mechanisms through which DH might cause ED.
CLINICAL IMPLICATIONS: Based upon our findings, reduction of DH may ameliorate ED in individuals with COPD and obviate the need for supplemental oxygen.
DISCLOSURE: The following authors have nothing to disclose: Muhammad Zafar, Wayne Tsuang, Laura Lach, William Eschenbacher, Ralph Panos
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