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_2m 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.

Sputum samples from 25 consenting CF subjects were analyzed by rheology tests (elastic modulus G and zero shear viscosity η₀) and Low Field Nuclear Magnetic (LF-NMR) resonance (T_2m). MCI/CCI were calculated from the rheological parameters. The average mesh-size (ξ) of the sputum structure was then evaluated by rheology/LF-NMR, together with FEV₁ for each patient.

There was an inverse correlation between G and η₀ versus T_2m, indicating that a worsening of the lung condition (T_2m-FEV₁ drop) is paralleled by an increase in sputum viscoelasticity (G and η₀) favoring mucus stasis/inflammation. A direct correlation was also observed between T_2m and MCI/CCI, showing that T_2m provides information as to airway mucus clearing. Moreover, there was a direct correlation between T_2m and the average sputum mesh size (ξ).

We demonstrated a correlation between T_2m (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_2m depends on mucus solid concentration and nanostructure.