An ultrasound imaging method for in vivo measurement of tracheal elasticity

The mechanical properties of trachea can reflect the bio-function and may represent the changes of compliances and stifinesses of airway. Therefore, the difference of airway mechanical properties between the normal people and the patients with airway disease can be observed in clinic. The objective of this paper is to determine the trachea elasticity of normal people by non-invasive ultrasound imaging method in statistic pressure. The measurement was involved 9 normal subjects (age from 23 to 40, 4 males and 5 females) and 2 patients (age from 23 to 40, 2 males). A Threshold Positive Expiratory Pressure device (Threshold PEP, New Jersey, USA) was used to provide positive expiratory pressure therapy. All subjects were asked to breathe through a mouthpiece. Then, 5 different loads of PEP were applied to the range from 0 cmH₂O to 20 cmH₂O and in a scale of 5 cmH₂0. A clinical ultrasound system ( Terason 2000 Burlington, MA, USA) with a 7 MHz transducer for measuring the mean diameter of trachea anteroposterior and transverse from thyroid cartilage and suprosternal notch. Finally, the ultrasound imaging was captured and analyzed by calculating the elasticity, Young´s Modulus, which was taking the ratio of stress over strain. The Intra-class correlation coefficients were employed to verify the reliablity for the experiment. Our result shows that the elasticity of normal subject tracheal were in the range of 145~981kPa, the abnormal subject were in the range of 69~108kPa, and the Intra-class correlation coefficients were in the range 0.8~0.99. In this study, we demonstrate the use of ultrasound imaging for measuring airway mechanical property and we also observed significant difference of the stress to strain experiments between normal subject and abnormal subject. This paper provides a new approach to measure the elasticity of human tracheal in real time, patient-friendly way.