Relationships between respiratory and airway resistances and activity-related dyspnea in patients with chronic obstructive pulmonary disease

Abstract

Background: The aims of the study were: (1) to compare numerical parameters of specific airway resistance (total, sRawtot, effective, sRaweff and at 0.5 L {dot operator} s-1, sRaw0.5) and indices obtained from the forced oscillation technique (FOT: resistance extrapolated at 0 Hz [Rrs0 Hz], mean resistance [Rrsmean], and resistance/frequency slope [Rrsslope]) and (2) to assess their relationships with dyspnea in chronic obstructive pulmonary disease (COPD). Methods: A specific statistical approach, principal component analysis that also allows graphic representation of all correlations between functional parameters was used. A total of 108 patients (mean ± SD age: 65 ± 9 years, 31 women; GOLD stages: I, 14; II, 47; III, 39 and IV, 8) underwent spirometry, body plethysmography, FOT, and Medical Research Council (MRC) scale assessments. Results: Principal component analysis determined that the functional parameters were described by three independent dimensions (airway caliber, lung volumes and their combination, specific resistance) and that resistance parameters of the two techniques were not equivalent, obviously. Correlative analyses further showed that Rawtot and Raweff (and their specific resistances) can be considered as equivalent and correlated with indices that are considered to explore peripheral airways (residual volume (RV), RV/ total lung capacity (TLC), Rrsslope), while Rrsmean and Raw0.5 explored more central airways. Only specific resistances taking into account the specific resistance loop area (sRawtot and sRaweff) and Rrsslope were statistically linked to dyspnea. Conclusion: Parameters obtained from both body plethysmography and FOT can explore peripheral airways, and some of these parameters (sRawtot, sRaweff, and Rrsslope) are linked to activity-related dyspnea in moderate to severe COPD patients. © 2012 Mahut et al, publisher and licensee Dove Medical Press Ltd.