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Fig. 3 | Respiratory Research

Fig. 3

From: Aerosol drug delivery to spontaneously-breathing preterm neonates: lessons learned

Fig. 3

a–c Illustrate different types of aerosol generators used to deliver aerosols to spontaneously-breathing premature-infants. Jet or pneumatic nebulizers use compressed gas to break up liquids into aerosols and incorporate baffles to filter large aerosol particles (a). Vibrating-membrane nebulizers consist of a membrane with 1000–7000 laser-drilled holes that vibrate at the top of the liquid reservoir thereby generating a mist of very fine droplets through the holes (b). The capillary aerosol generator (CAG) has been especially designed to deliver synthetic surfactant aerosols; this technology consists of a heated capillary through which surfactant is pumped and further dispersed as an aerosol (c). Medical aerosols usually conform to a log-normal particle size distribution (d); They are usually defined by their Mass Median Aerodynamic Diameter (MMAD) which determines the particle diameter at which half of the aerosolized drug mass lies below and half above the stated diameter. Particle size distribution is usually given as the Mass Median Diameter (MMD), which is not interchangeable with the MMAD. MMD is the output parameter in laser-diffraction experiments and considers the particles to be spherical and of unit density. It should be noted that the MMAD and MMD appear markedly shifted to the right in the distribution compared with the particle diameter mode, median, and mean of the absolute particle counts. a–c adapted from reference [79] and d adapted from reference [70]

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