Revisited Physicochemical and Transport Properties of Respiratory Mucus in Genotyped Cystic Fibrosis Patients

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Abstract
We investigated the physicochemical and transport properties of sputum samples collected in physiotherapy from a well-documented group of 27 cystic fibrosis (CF) patients with identified CF genotypes. Sputum samples were characterized ex vivo for their water content, surface properties (surface tension and contact angle), rheologic properties (viscosity and elastic modulus), and transport properties (mucociliary and cough transport). These data were analyzed in relation to the clinical status of the patients (FEV1, FVC, Shwachman score, Brasfield score, nutritional status), their genotype, and the degree of infection of their sputa (leukocyte and Pseudomonas aeruginosa counts). We observed negative and significant correlations between mucociliary transport and elastic modulus of the patients' sputum (r = -0.63, p < 0.01), and between the cough transport and contact angle of the sputum (r = -0.81, p < 0.0001), respectively. The P. aeruginosa count was also significantly correlated with the sputum water content (r = -0.53, p < 0.02) as well as with the cough transport of the sputum (r = -0.62, p < 0.01). In CF patients with a sputum leukocyte count > 2,000/mm3, the sputum water content (p < 0.02), FEV1 (p < 0.05) and FVC (p < 0.02) were significantly lower than those of CF patients with a leukocyte count < or = 2,000/mm3. CF patients with a homozygous delta F 508 genotype had significantly greater values of sputum water content (p < 0.05), and cough-transport capacity (p < 0.05) than did heterozygous patients. No correlation was observed between the sputum properties and any of the clinical data. These results suggest that the control of infection should be emphasized in CF, since it can directly or indirectly modulate the degree of hydration, and therefore the physicochemical and transport properties, of airway secretions.