Alveolar distribution of nebulized solution in health and lung injury assessed by confocal microscopy

Parenchymal distribution of nebulized drug in healthy and diseased lungs has not, as evident from a literature review, been well characterized. We use a vibrating mesh nebulizer to deliver fluorescein solution in vivo to healthy or intratracheal-lipopolysaccharide (LPS)-instilled anesthetized rats in dorsal recumbency, or ex vivo to the lungs of LPS-instilled rats. Following in vivo nebulization (healthy/LPS-instilled), we quantify fluorescein intensity distribution by confocal microscopy in standard locations on the surface of freshly isolated lungs. Following LPS instillation (in vivo/ex vivo nebulization), we quantify fluorescein intensity in visibly injured locations. In standard locations, there is uniform, low-intensity basal fluorescein deposition. Focal regions receive high deposition that is, in upper (cranial), middle, and lower (caudal) locations, 6.4 ± 4.9, 3.3 ± 3.0, and 2.3 ± 2.8 times greater, respectively, than average basal intensity. Following LPS instillation, deposition in moderately injured regions can be high or low; deposition in severely injured regions is low. Further, actively phagocytic cells are observed in healthy and LPS-instilled lungs. And LPS particularly impairs mechanics and activates phagocytic cells in the male sex. We conclude that a low level of nebulized drug can be distributed across the parenchyma excepting to severely injured regions.