Precapillary oxygenation contributes relevantly to gas exchange in the intact lung.

RATIONALE: Oxygen uptake is the elemental function of the lung. However, current understanding of this process has largely been derived from theoretical considerations and measurements of global pulmonary gas exchange.
OBJECTIVES: To report the direct visualization of pulmonary oxygen uptake in vivo and its use for the analysis of temporal and spatial oxygenation profiles along individual arteriovenous pathways in lungs of healthy and chronic hypoxic mice.
METHODS: A murine model for intravital microscopy of the breathing lung under sealed thorax conditions was combined with multispectral oximetry for two-dimensional oxygen saturation mapping. This combination allowed for visualization of the blood oxygenation process from pulmonary arterioles to capillaries and venules in two-dimensional oxygen saturation maps.
MEASUREMENTS AND MAIN RESULTS: Temporal and spatial oxygenation profiles revealed that oxygenation occurs within 100 milliseconds over a distance of approximately 130 μm in the pulmonary microvasculature of the anesthetized mouse. About 50% of total oxygen uptake takes place in precapillary arterioles of less than 30 μm in diameter before the blood enters the alveolar capillary bed. In chronic hypoxic mice, precapillary oxygenation was significantly attenuated as a result of the widened transarteriolar diffusion distance.
CONCLUSIONS: Oxygen saturation mapping in the intact lung yields unique insights into the temporal and spatial characteristics of pulmonary gas exchange in intact and diseased lungs. Precapillary gas exchange contributes importantly to blood oxygenation at rest, but is attenuated in remodeled lung arterioles, which may be of relevance in pulmonary hypertension.