Combined use of rheology and portable low-field NMR in cystic fibrosis patients

Background: As most cystic fibrosis (CF) patients progress to respiratory failure, lung functionality assessment is pivotal. We previously developed a test that indirectly monitors airways (inflammation/functional test) by measuring the spin-spin relaxation time (T-2m) of the water hydrogens present in CF sputum. Here the T-2(m) significance in the monitoring of CF lung disease was further investigated by studying the correlation of T-2m with: 1) sputum viscoelasticity, 2) mucociliary clearability index (MCI)/cough clearability index (CCI) and 3) sputum average mesh-size. Methods: Sputum samples from 25 consenting CF subjects were analyzed by rheology tests (elastic modulus G and zero shear viscosity eta(0)) and Low Field Nuclear Magnetic (LF-NMR) resonance (T-2m). MCI/CCI were calculated from the rheological parameters. The average mesh-size (xi) of the sputum structure was then evaluated by rheology/LF-NMR, together with FEV1 for each patient. Results: There was an inverse correlation between G and eta(0) versus T-2m, indicating that a worsening of the lung condition (T-2m-FEv(1) drop) is paralleled by an increase in sputum viscoelasticity (G and eta(0)) favoring mucus stasis/inflammation. A direct correlation was also observed between T-2(m) and MCI/CCI, showing that T-2(m) provides information as to airway mucus clearing. Moreover, there was a direct correlation between T-2(m) and the average sputum mesh size (xi). Conclusions: We demonstrated a correlation between T-2(m )(measured in CF patient's sputum) and the sputum viscoelasticity/average mesh-size and with MCI/CCI, parameters related to airway mucus clearing. Thus, the present data strengthen the potential of our test to provide indirect monitoring of airway disease course in CF patients as T-2(m) depends on mucus solid concentration and nanostructure.