Bleomycin induced lung fibrosis increases work of breathing in the mouse.

Bleomycin induces a transient lung fibrosis in mice that has been used to investigate mechanisms related to idiopathic pulmonary fibrosis. Our aim was to determine a sensitive method for assessing lung function in bleomycin treated mice that correlated with the degree of lung fibrosis as measured by collagen immunohistochemistry. Bleomycin (2 U/kg) or saline was intratracheally microsprayed to male C57BL/6 mice under isoflurane anesthesia. Lung function (single compartment model, constant phase model, and work of breathing) was assessed using the flexiVent system, and after euthanasia lungs were inflated with formalin in situ for histological analysis. The lung fibrosis histopathology score for the bleomycin treated animals on day 21 was indicative of mild-to-moderate fibrosis (Saline treated control: 0 ± 0, Bleomycin treated: 4.9 ± 0.4). There were at least three large areas of fibrosis in the peribronchial alveolar regions of the lung, but less than 50% of each lung was affected by fibrosis. Although changes in lung function were less obvious, volume normalized dynamic work of breathing measured at 30 ml/kg tidal volume (Saline treated control: 9.2 ± 0.1 J/l, Bleomycin treated: 10.6 ± 0.3 J/l) and the oscillatory mechanics constant phase model parameter tissue elastance (H; Saline treated control: 31 ± 2 cm H(2)O/ml, Bleomycin treated: 38 ± 3 cm H(2)O/ml) were significantly increased on day 21. The work of breathing (r = 0.83) correlated slightly better with fibrosis histopathology score than H (r = 0.64). Work of breathing can detect decrements in lung function due to pulmonary fibrosis, correlates well with the amount of collagen in the lungs, and may be a more sensitive quantitative measure of efficacy for drugs being developed to treat pulmonary fibrosis.

Granulocytosis and increased adhesion molecules after resistive loading of the diaphragm.

Upregulation of endothelial cell adhesion molecules, followed by an influx of granulocytes and macrophages, can contribute to exertion-induced skeletal muscle injury. The purpose of this study was to quantify circulating leukocyte subsets, diaphragm injury and infiltrating leukocyte subsets, and surface expression of vascular cell adhesion molecule (VCAM)-1 and intracellular adhesion molecule (ICAM)-1 in the diaphragm after inspiratory resistive loading (IRL). Eight New Zealand white rabbits underwent 1.5 h of IRL and seven control rabbits underwent a sham procedure. Blood samples, taken at baseline and 2, 6, 12, 24, 48 and 72 h after the onset of IRL or sham, showed that band cell counts had increased at 6 h post-IRL. Point counting of haematoxylin and eosin-stained cross-sections, sampled at 72 h post-IRL, showed greater injury in diaphragms from IRL rabbits compared with controls. Immunohistochemical processing showed increased expression of ICAM-1 and VCAM-1, and higher granulocyte and macrophage counts in IRL diaphragms than control diaphragms. Macrophages were the predominant inflammatory cells. Increased intracellular adhesion molecule-1 and vascular cell adhesion molecule-1 expression, and infiltration of granulocytes and macrophages may contribute to inspiratory resistive loading-induced diaphragm injury.