Abstract
The dynamic viscoelastic properties of sputum have been studied using the conventional dynamic method and the newly developed Raised Cosine Pulse (RCP) method. The sputum samples obtained fresh in the morning were stored at room temperature (about 20°C) in closed containers until use. Measurements were made within 4 hours of expulsion. Each test required only about 1.5 ml of sputum.
1. Conventional dynamic method. A thixotrometer (coaxial cylinder type) was used for the experiments. Dynamic viscosity (η′), storage modulus (G′) and loss modulus (G″) were obtained over a range from 10-2 to 100 rad/sec in angular frequency.
1-1) 13 sputum samples (mucoid 4, mucopurulent 3, purulent 6) were obtained from 11 patients with chronic obstructive lung disease (COLD). Measurements were carried out at 37°C. All samples showed similar frequency dependence. With an increase in frequency, η′ decreased linearly and steeply, but G', on the other hand, increased slowly.
1-2) The effect of expectorants on the viscoelasticity of sputum was examined by adding them to purulent sputum samples. The measurements were carried out at 25°C. (a) After adding 20 % N-acetyl-L-cysteine the samples were then subjected to shear at 5.0 rpm for 10 minutes. The values of G″ revealed only slight decreases, but the values of G' showed extreme reduction. (b) With 0.2% bromhexine, no significant decrease was observed in dynamic viscoelasticity. (c) In 10 and 30 minutes after adding 0.5% seaprose-S, the values of G′ and G″were found greatly. decreased.
2. RCP method. Rheopexy-Analyzer was used for the experiments. 11 sputum samples (mucoid 5, purulent 6) were obtained from 8 patients with COLD. Measurements were carried out at 37°C. The values of dynamic viscoelasticity obtained were over the range from 10-3 to 100 rad/sec in angular frequency, and were roughly in agreement with those obtained by the conventional dynamic method in almost all samples. A peak of G″ which indicated a relaxation region near 10-1 rad/sec was observed more evidently in purulent sputa than in mucoid sputa. In 4 samples of purulent sputa, the value of G′ and G″ showed a sequential decrease during 60 minutes. The dynamic mechanical behavior obtained from sputa has been predicted with a mechanical model combining Maxwell and Voigt elements in a series.
