Respiratory devices airways resistance

In children, capsaicin spray was demonstrated to cause a severe bronchospasm and pulmonary edema (Winograd, 1977 Bdlmire et al, 1996). In the Billmire study, a 4-week-old infant was exposed to 5% pepper spray after discharge from a self-defense device. The infant suffered respiratory failure and hypoxemia, requiring immediate extracorporeal membrane oxygenation. Inhaled capsaicin causes an immediate increase in airway resistance (Fuller, 1991). This dose-dependent bronchoconstriction after capsaicin inhalation in humans is the same as that demonstrated in asthmatics and smokers (Fuller et al, 1985). The capsaicin-induced bronchoconstriction and release of substance P is due to stimulation of nonmyelinated afferent C-fibers. 

As shown from measurements in airway models or theories using modifications of the friction coefficients, the vast majority of the pressure drop across the entire lung occurs within the large airways, say 0 n 8. I us clinical evaluation of total airway resistance can miss diseases of the small airways whose diameters are less than 2 mm, the so-called silent zone of the network. Pressure drop measurements and models are also important for the design of ventilators and other respiratory assist or therapeutic devices that interface with lung mechanics. 

The underpressure created in the respiratory tract is the driving force for the airflow through an inhalation device. The attainable underpressure and the rate of the airflow both depend on the total resistance in the airways and inhaler. The pressure drop achieved during inhalation is furthermore a function of the anatomy of the lungs, the effort made by the patient, pathological factors and the presence of exacerbations (e.g. in case of asthma). 

Sleep therapy and respiratory care represent an additional class of applications in healthcare. Respirators, ventilators, and positive-pressure devices to allow airways to function properly are specific examples and require biocompatibilty. Respiratory masks and valves require chemical resistance and impact performance. PC-based blends are commonly used in applications in this space. 

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