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.

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Precise surgical excision of brain tumors depends on the surgeon's ability to accurately differentiate tumors from healthy brain tissues. We have developed an automated system integrated with biochips, an actuation unit, and electronics to measure the electrical resistivity of ex vivo human brain tissues for differentiating normal and tumor. The electrical resistivity of fresh (n = 48), formalin-fixed for one week (n = 48), and long-term (six months) formalin-fixed (n = 27) healthy human brain samples from different anatomical regions and tumor samples (glioma n = 6; fresh, formalin-fixed for one week, and formalin-fixed for six months) were measured using the automated system. The resistivity of glioma (22.4 ± 1.6 Ω.cm) was significantly lesser than the normal region (82 ± 3 Ω.cm) for fresh tissue samples (p = 5e-8). The trend of lower resistivity of glioma compared to normal was preserved after one week and six months of formalin fixation. We also report the effects of heterogeneity of normal brain tissue and formalin-fixation on the electrical properties of tissues. White matter regions were found to have higher resistivity compared to grey matter regions. The heterogeneity associated with grey matter regions was lower than the white matter regions. Formalin-fixation was observed to increase the magnitude of resistivity measured while retaining the observed trend across the different regions of the brain and tumors. The study shows that the electrical resistivity could potentially be used as an additional biomarker for delineating normal from the tumor.