Application of carbon monoxide diffusing capacity in the mouse lung.

In the past decade the mouse has become the primary animal model of a variety of lung diseases. To assess various mechanisms underlying such pathologies, it is essential to make functional measurements that can reflect the developing pathology. In this regard, the diffusing capacity for carbon monoxide is a variable that directly reflects structural changes in the lung. Although measurement of single-breath diffusing capacity of the lung for carbon monoxide (DL(CO)) has also been previously reported in mice by a number of investigators, a number of technical issues have precluded routine and widespread use of this metric in mouse models. In the present report, we describe a means to quickly and simply measure a dimensionless variable closely related to the DL(CO) in mice, termed a diffusion factor for carbon monoxide (DF(CO)). The DF(CO) procedure involves a 9-s lung inflation with tracer gases in an anesthetized mouse, followed by a 1-min gas analysis time. We have tested the approach with two common models of lung pathology, elastase-induced emphysema and bleomycin-induced fibrosis. Results show a significant 15% reduction in DF(CO) in emphysema, and a 41% reduction in the fibrosis model. Repeat measurements within a mouse were found to be highly reproducible. This pulmonary function test can thus be used to detect structural changes with these pathological models. The method can also be used to measure changes in pulmonary blood volume, since the uptake of CO is highly dependent on this variable in addition to the gas exchange surface area.