Lung volume dependence of respiratory function in rodent models of diabetes mellitus

BACKGROUND: Diabetes mellitus causes the deterioration of smooth muscle cells and interstitial matrix proteins, including collagen. Collagen and smooth muscle cells are abundant in the lungs, but the effect of diabetes on airway function and viscoelastic respiratory tissue mechanics has not been characterized. This study investigated the impact of diabetes on respiratory function, bronchial responsiveness, and gas exchange parameters. METHODS: Rats were allocated randomly to three groups: a model of type 1 diabetes that received a high dose of streptozotocin (DM1, n = 13); a model of type 2 diabetes that received a low dose of streptozotocin with a high-fat diet (DM2, n = 14); and a control group with no treatment (C, n = 14). Forced oscillations were applied to assess airway resistance (Raw), respiratory tissue damping (G), and elastance (H). The arterial partial pressure of oxygen to the inspired oxygen fraction (PaO(2)/FiO(2)) and intrapulmonary shunt fraction (Qs/Qt) were determined from blood gas samples at positive end-expiratory pressures (PEEPs) of 0, 3, and 6 cmH(2)O. Lung responsiveness to methacholine was also assessed. Collagen fibers in lung tissue were quantified by histology. RESULTS: The rats in groups DM1 and DM2 exhibited elevated Raw, G, H, and Qs/Qt, compromised PaO(2)/FiO(2), and diminished airway responsiveness. The severity of adverse tissue mechanical change correlated with excessive lung collagen expression. Increased PEEP normalized the respiratory mechanics, but the gas exchange abnormalities remained. CONCLUSIONS: These findings indicate that diabetes reduces airway and lung tissue viscoelasticity, resulting in alveolar collapsibility that can be compensated by increasing PEEP. Diabetes also induces persistent alveolo-capillary dysfunction and abnormal adaptation ability of the airways to exogenous constrictor stimuli.