title: Dynamic hyperinflation correlates with exertional oxygen desaturation in patients with chronic obstructive pulmonary disease.
abstract: BACKGROUND
  Dynamic hyperinflation (DH) causes exercise limitation and exertional dyspnea in patients with chronic obstructive pulmonary disease (COPD). Exertional desaturation (ED) also occurs commonly in COPD but neither routine physiologic parameters nor imaging predict ED accurately. In this study we evaluated the relationship between DH and ED during 6-min walk testing (6MWT).
  
  
  METHODS
  We measured ED and DH in patients with stable COPD. SpO2 was measured by continuous pulse oximetry during 6MWT. ED was defined as a decline in SpO2 (ΔSpO2) ≥4 %. DH was determined by measuring inspiratory capacity (IC) before and after the 6MWT using a handheld spirometer. DH was defined as ΔIC >0.0 L. We correlated DH and ED with clinical and pulmonary physiologic variables by regression analysis, χ (2), and receiver operator curve (ROC) analysis.
  
  
  RESULTS
  Thirty males [age = 65 ± 9.4 years, FEV1 % predicted = 48 ± 14 %, and DLCO % predicted = 50 ± 21 % (mean ± SD)] were studied. ΔSpO2 correlated with ΔIC (r = 0.49, p = 0.005) and age (r = 0.39, p = 0.03) by univariate analysis; however, only ΔIC correlated on multivariate regression analysis (p = 0.01). ΔSpO2 did not correlate with FEV1, FVC, FEF25-75, RV, DLCO % predicted, BMI, smoking, BORG score, or distance covered in 6MWT. DH strongly correlated with ED (p = 0.001). On ROC analysis, DH had an area under the curve of 0.92 for the presence of ED (sensitivity = 90 %; specificity = 77 %, p < 0.001).
  
  
  CONCLUSIONS
  Routine pulmonary function test results and clinical variables did not correlate with ED in patients with stable COPD. Dynamic hyperinflation strongly correlates with exertional desaturation and could be a reason for this desaturation.
authors.affiliation: Cincinnati VAMC, Cincinnati, OH, USA.
authors.forename: Muhammad Ahsan
authors.initials: MA
authors.lastname: Zafar
authors.forename: Wayne
authors.initials: W
authors.lastname: Tsuang
authors.forename: Laura
authors.initials: L
authors.lastname: Lach
authors.forename: William
authors.initials: W
authors.lastname: Eschenbacher
authors.forename: Ralph J
authors.initials: RJ
authors.lastname: Panos
mesh_terms: D000368:Aged; D016009:Chi-Square Distribution; D004417:Dyspnea / Q000097:blood / Q000209:etiology / Q000503:physiopathology; D005080:Exercise Test; D017079:Exercise Tolerance; D005541:Forced Expiratory Volume; D006801:Humans; D001239:Inhalation; D008168:Lung / Q000503:physiopathology*; D008297:Male; D008450:Maximal Midexpiratory Flow Rate; D008875:Middle Aged; D015999:Multivariate Analysis; D010092:Oximetry; D010100:Oxygen / Q000097:blood*; D005082:Physical Exertion; D011237:Predictive Value of Tests; D029424:Pulmonary Disease, Chronic Obstructive / Q000097:blood / Q000150:complications / Q000503:physiopathology*; D012372:ROC Curve; D013147:Spirometry; D014797:Vital Capacity
chemical_list: D010100:Oxygen