Sputum rheology and bacteriology in stable and exacerbated chronic obstructive pulmonary disease

<b>Background:</b> Mucous in the airway helps the clearance of pathogens and foreign particles. An acute exacerbation of chronic obstructive pulmonary disease (AECOPD) is often accompanied with increased sputum volume and purulence. However, the association between sputum rheology and disease state of COPD is not clear. We assessed sputum rheology during stable state and AECOPD. <b>Methods:</b> Sputa were collected from 51 consecutive patients with 90 visits during stable state, at exacerbation and 21 days after an exacerbation (AECOPD-follow-up). Dynamic rheology i.e. the elastic modulus G’, viscous modulus G’’, vector sum of viscosity and elasticity G* and the ration of the elastic modulus to viscous modulus tan δ were analyzed, using a cone-and-plate rheometer (Rheomuco, Rheonova France). <b>Results:</b> Among the enrolled subjects, the mean age was 66±1.2 years and 38/51 (75%) were males. The average FEV1 was 1.5±0.06 and FVC was 3.1±0.09. There was no significant difference in G’ (median 5.8 vs. 6.6 vs. 3.6; p=0.813), G’’ (median 1.4 vs. 1.5 vs. 1.2; p=0.839), G* (median 5.9 vs. 6.7 vs. 3.7; p=0.846) or tan δ (median 0.26 vs. 0.26 vs. 0.27; p=0.534) between stable state, AECOPD and AECOPD-follow up, respectively. There was no association with FEV1 or FVC and the various rheological parameters. In 57 cases, sputum was analysed using conventional microbiology. A positive result was obtained in 31/57 (54%) cases. There was no difference in the rheological parameters between positive and negative cases, nor was there a difference in the parameters dependent on the species of pathogen found. <b>Conclusions:</b> There is no clear association between sputum rheology and COPD sputum microbiology or disease states.