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Distribution of pulmonary and bronchial blood supply to airways measured by fluorescent microspheres
S L Bernard1, R W Glenny, N L Polissar
1Division of Pulmonary and Critical Care Medicine, University of Washington, and Veterans Affairs Medical Center, Seattle 98195, USA.
Abstract:
This study determined the relative contributions of systemic (bronchial) and pulmonary blood flow to the intraparenchymal airways >1 mm in diameter by using 15-mu m fluorescent microspheres and fluorescence microscopy in four dogs. Fluorescent microspheres of one color were injected into the inferior vena cava as a pulmonary blood flow marker, and fluorescent microspheres of another color were injected into the left ventricle as a systemic blood flow marker. After the second injection, the animals were killed and the lungs were excised and air dried at total lung capacity. The left lung was sliced into transverse planes and then sectioned into smaller blocks containing airways down to 1 mm in diameter. The blocks were then sectioned using a Vibratome and examined with a fluorescence microscope. Pulmonary and systemic blood flow markers were counted in airway walls, and the diameter of each airway was measured to determine the bronchial tissue volume. After a correction for the number of blood flow markers injected into each circulation, the average ratio of pulmonary to systemic blood flow markers seen in airway walls was 1:37, indicating that 97% of the blood supply to the intraparenchymal airways down to 1 mm in diameter was from the bronchial circulation. Furthermore, on the basis of a weighted least squares regression analysis, systemic (bronchial) blood flow per unit tissue volume increased as airway diameter decreased (P = 0.03).
Insights
The bronchial circulation supplies 97% of blood to airways larger than 1 mm. Systemic blood flow to airway tissue increases as airway diameter decreases.
Area of Science:
- Pulmonary and Cardiovascular Physiology
- Respiratory System Anatomy
Background:
- The intraparenchymal airways receive blood supply from both pulmonary and bronchial circulations.
- Understanding the relative contributions of these circulations is crucial for respiratory health research.
Purpose of the Study:
- To quantify the respective roles of systemic (bronchial) and pulmonary blood flow in supplying intraparenchymal airways greater than 1 mm in diameter.
Main Methods:
- Four dogs were used, with fluorescent microspheres injected into the inferior vena cava (pulmonary marker) and left ventricle (systemic marker).
- Lungs were excised, sectioned, and examined using fluorescence microscopy to count markers in airway walls.
- Airway diameter was measured to calculate bronchial tissue volume and blood flow ratios.
Main Results:
- A systemic to pulmonary blood flow marker ratio of 37:1 was observed in airway walls.
- This indicates that approximately 97% of the blood supply to airways down to 1 mm in diameter originates from the bronchial circulation.
- Systemic blood flow per unit tissue volume increased significantly as airway diameter decreased (P = 0.03).
Conclusions:
- The bronchial circulation is the predominant source of blood supply to larger intraparenchymal airways.
- Blood flow regulation in airways may vary with airway size, with smaller airways receiving proportionally more systemic blood flow.