The influence of "sputum-like gel" viscosity on crackle characteristics ina mechanically ventilated porcine lung model

This study investigated the influence of airway secretion viscosity on the characteristics of crackle sounds produced using a mechanically ventilated porcine lung model, Aqueous ultrasonic methylene blue stained gel solutions of viscosity 100, 150 and 200 P were prepared and instilled into 15 isolat ed, mechanically ventilated per-cine lungs immersed in water, Sound signals recorded by a hydrophone before and after instillation of gel were subject ed to both fast Fourier transform and wave-form analysis. At the completion of sound recording, the main bronchi were dissected and the location of th e stained gel was photographically recorded. Wave-form analysis demonstrate d that expiratory phase crackle incidence and amplitude were both significa ntly higher than inspiratory phase data. This study demonstrates that crack le duration and amplitude are inversely related to gel viscosity and that e lectronic lung sound analysis can provide indirect evidence of sputum visco sity.