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Capillary recruitment and heterogeneity of perfused capillary distribution in dog myocardium
1Department of Physiology and Biophysics, UMDNJ Robert Wood Johnson Medical School, Piscataway 08854-5635.
Insights
Researchers estimated functional diffusion distances in dog hearts by tracking fluorescent dye in capillaries. Unlabeled capillaries suggest a potential blood flow reserve, particularly under stress.
Area of Science:
- Cardiovascular Physiology
- Myocardial Microcirculation
Background:
- Understanding capillary perfusion is crucial for assessing myocardial oxygen supply.
- Functional diffusion distances are influenced by the distribution of actively perfused capillaries.
Purpose of the Study:
- To estimate functional diffusion distances in dog myocardium.
- To characterize the distribution of perfused capillaries under varying conditions.
Main Methods:
- Injected fluorescent dye into the coronary circulation of anesthetized dogs.
- Analyzed frozen myocardial sections using fluorescence microscopy and silver staining.
- Quantified labeled vs. total capillary density via morphometry.
Main Results:
- A single pass of dye in normoxia labeled 60-66% of capillaries, with a near-random distribution.
- Maximal distances to labeled capillaries increased by 50% compared to total capillaries.
- Multiple passes or asphyxia labeled 76-79% of capillaries, approaching the total capillary bed's ordered pattern.
Conclusions:
- Unlabeled capillaries in normoxia may represent a spatially heterogeneous blood flow reserve.
- Capillary recruitment increases with repeated dye passes or during asphyxia.
- These findings have implications for understanding myocardial oxygenation and reserve capacity.
Abstract:
To estimate functional diffusion distances, the distribution of perfused capillaries was calculated in dog myocardium. A fluorescent dye was injected via a femoral vein in 6 anesthetized, open-chest dogs, and passed once through the coronary circulation (23 +/- 3 s). In 6 animals the dye circulated 4-20 min. In 6 animals the dye circulated for one pass following 2-3 min of asphyxia. The heart was then removed and frozen. Frozen sections from the left ventricule were cut, illuminated to excite the dye to fluoresce, and photographed. They were then stained by silver methenamine to mark all capillaries. The density of all capillaries was compared to that of capillaries containing fluorescent label. The distributions of capillaries were estimated by morphometry. In one pass of the normoxic coronary circulation, 66(+/- 4 SE)% of subepicardial and 60(+/- 4)% of subendocardial capillaries were detectably labeled. Their distribution approached a random pattern, and maximal distances to the nearest labeled capillary were lengthened by 50% compared to all capillaries. With multiple passes of the dye, or with asphyxia 76-79% of the capillaries were detectably labeled and their distribution approached the ordered pattern of the total capillary bed. We speculated that the unlabeled capillaries represented a spatially heterogeneous blood flow reserve.