Intravital microscopic observations of 15-microm microspheres lodging in the pulmonary microcirculation
Wayne J E Lamm1, Susan L Bernard, Wiltz W Wagner
1Division of Pulmonary and Critical Care Medicine, University of Washington, Box 356522, Seattle, WA 98195, USA.
Abstract:
Vascular infusions of 15-microm-diameter microspheres are used to study pulmonary blood flow distribution. The sites of microsphere lodging and their effects on microvascular perfusion are debated but unknown. Using intravital microscopy of the subpleural surface of rat lungs, we directly observed deposition of fluorescent microspheres. In a pump-perfused lung model, approximately 0.5 million microspheres were infused over 30 s into the pulmonary artery of seven rats. Microsphere lodging was analyzed for the location in the microvasculature and the effect on local flow after lodging. On average, we observed 3.2 microspheres per 160 alveolar facets. The microspheres always entered the arterioles as singlets and lodged at the inlets to capillaries, either in alveolar corner vessels or small arterioles. In all cases, blood flow continued either around the microspheres or into the capillaries via adjacent pathways. We conclude that 15-microm-diameter microspheres, in doses in excess of those used in typical studies, have no significant impact on pulmonary capillary blood flow distribution.
Insights
This study observed 15-micrometer microsphere lodging in rat lungs. High doses of these microspheres did not significantly impact pulmonary capillary blood flow distribution.
Area of Science:
- Physiology
- Microcirculation Research
Background:
- Microsphere infusions are used to study pulmonary blood flow.
- The exact lodging sites and effects of microspheres on microvascular perfusion remain unclear.
Purpose of the Study:
- To directly observe the deposition of fluorescent microspheres in the pulmonary microvasculature.
- To determine the effect of microsphere lodging on local blood flow.
Main Methods:
- Intravital microscopy was used on the subpleural surface of rat lungs.
- Microspheres were infused into the pulmonary artery of a pump-perfused rat lung model.
- Microsphere location and impact on flow were analyzed post-lodging.
Main Results:
- Microspheres lodged at the inlets to capillaries, specifically in alveolar corner vessels or small arterioles.
- Blood flow continued around lodged microspheres or through adjacent pathways.
- An average of 3.2 microspheres were observed per 160 alveolar facets.
Conclusions:
- 15-micrometer microspheres, even at high doses, do not significantly alter pulmonary capillary blood flow distribution.
- Microspheres lodge in arterioles and do not impede overall blood flow in the studied model.
