Ventilation Heterogeneity in Never-smokers and COPD:
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RATIONALE AND OBJECTIVES: Pulmonary functional magnetic resonance imaging provides a way to quantify ventilation and its heterogeneity-a hallmark finding in chronic obstructive pulmonary disease (COPD). Unfortunately, the etiology and physiological meaning of ventilation defects and their relationship to pulmonary function and symptoms in COPD are not well understood. Another biomarker of ventilation heterogeneity is provided by the "poorly communicating fraction" (PCF), and is calculated as the ratio of total lung capacity to alveolar volume made using whole-body plethysmography. Our objective was to compare ventilation heterogeneity using hyperpolarized (3)He magnetic resonance imaging (MRI) and PCF measurements in elderly never-smokers and in ex-smokers with COPD. MATERIALS AND METHODS: One hundred forty-six participants (71 ± 8 years, range = 48-87 years) provided written informed consent including 45 elderly never-smokers (71 ± 6 years, range = 61-84 years) and 101 ex-smokers with COPD (71 ± 8 years, range = 48-87 years). During a single 2-hour visit, spirometry, plethysmography, and hyperpolarized (3)He MRI were acquired. The MRI-derived ventilation defect percent (VDP) and plethysmography measurements were acquired and PCF values were calculated. Linear regression, Pearson correlations, and Bland-Altman analysis were used to evaluate the relationships for PCF and MRI VDP. RESULTS: PCF (P < 0.001) and VDP (P < 0.001) were significantly increased with increasing COPD severity. There was a significant relationship for VDP and PCF (r = 0.68, P < 0.001) in all subjects and COPD subjects alone (r = 0.61, P < 0.001). Bland-Altman analysis showed that PCF and VDP were significantly different (mean bias = 9.7, upper limit = 32, lower limit = -13, P < 0.001), and in severe-grade COPD, PCF overestimates of VDP were significantly greater. CONCLUSIONS: In elderly never-smokers and in ex-smokers with COPD, PCF and VDP are moderately correlated estimates of COPD ventilation heterogeneity that may be reflecting similar pathophysiology.
