An intubation catheter integrated with flow sensors and smart actuators for characterizing airflow patterns in stenosed trachea: an objective guide for CAO management

Abstract Stenosis reduces the effective lumen area in the tracheal and bronchial segments of the airway anatomy. Loss in patency due to obstruction increases resistance to airflow; thus, severe narrowing is often associated with morbidity and mortality. Etiologies such as congenital tracheal stenosis, tracheomalacia, laryngeal and subglottic stenosis, atresia are few among the many pathologies causing major airway obstruction and respiratory distress. Diagnosis of such anomalies is usually based on clinical suspicion due to the non-specificity of the associated clinical symptoms. Visual assessment using conventional bronchoscopy or radiography images from CT scan for precisely locating obstruction site is highly subject to clinician’s expertise. Characterizing airflow patterns in stenosed airway calls for newer diagnostic tools that can effectively quantify changes in airflow due to construction sites. Our work presents a steerable intubation catheter that can quantitatively measure air velocity across various segments of the tracheobronchial tree. The catheter consists of a three-layer flexible printed circuit board integrated with micro-electro-mechanical system-based thermal flow sensors and a pair of sub-millimeter helical shape memory actuators. Flow distribution is measured in excised sheep tracheal tissues at 15, 30, 50, 65, and 80 l min −1 for normal and stenosed conditions. Even a 10% reduction in lumen area generated unique peaks corresponding to the obstruction site; thus, the catheter can locate stenosis at the precritical stage. For 50% tracheal obliteration, the sensor closest to stenosis showed a 2.4-fold increase in velocity when tested for reciprocating flows. Thus, flow rate scales quadratically with reducing cross-section area, contributing to increased airflow resistance.