Characterization of a respiratory triggered nebulizer for surfactant drug delivery in newborns

The respiratory system has an essential role in the life of an individual, and it is therefore necessary for his condition to be optimal. This system begins to develop from the first weeks of pregnancy and then gradually completes until the last periods of gestation. However, there are cases of premature births, due to several factors, that involve the birth of newborns before the full maturity of the respiratory system, with more or less severe conditions depending on the degree of prematurity. This condition of immaturity of the respiratory system can lead to a condition in which a substance of fundamental importance for respiratory functions is not enough: the surfactant. The latter has surfactant properties and creates, at the level of the alveoli, thin films that combat surface pressure to prevent alveoli from collapse. A lack of surfactant leads to breathing difficulties that can be fatal, and generally, such a condition requires the need for mechanical ventilation to help the subject in respiratory functions. Assisted ventilation is supported by surfactant replacement therapy, in which exogenous surfactant administration is performed. This is usually done by endotracheal procedure, but since it is an invasive and risky technique, nebulization is a good alternative. There are several nebulization devices, and in particular, this study focuses on the analysis of the particles produced by a pulmonary surfactant nebulizer, in relation to several other nebulization devices. Precisely, the study aims to conduct a comprehensive evaluation of the nebulizer’s performance, in terms of particle velocity and size distributions, evaluated according to the change of two test parameters: the pressure of compressed air and the blowing time. A special measurement setup has been created to carry out the acquisitions with the nebulizer, which are studied through an algorithm generated to automate the acquisition of particle velocity and diameter. The analysis showed that a good combination of parameters is a pressure of 3 bar and a blowing time of 0.3 s. However, although the combination is the best among those considered, the result is not yet optimal to consider the system suitable for spraying surfactant for therapy, since the particles produced are too large and slow. There are particles with an average speed of 0.39 m/s and a diameter of about 0.3 mm, still too large to reach the lower airways, therefore the alveoli, for which a diameter of 1-5 µm is necessary.