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Distribution of bronchial blood flow was measured in unanesthetized sheep by the use of two modifications of the microsphere reference sample technique that correct for peripheral shunting of microspheres: 1) A double microsphere method in which simultaneous left and right atrial injections of 15-microns microspheres tagged with different isotopes allowed measurement of both pulmonary blood flow and shunt-corrected bronchial blood flow, and 2) a pulmonary arterial occlusion method in which left atrial injection and transient occlusion of the left pulmonary artery prevented delivery to the lung of microspheres shunted through the peripheral circulation and allowed systemic blood flow to the left lung to be measured. Both methods can be performed in unanesthetized sheep. The pulmonary arterial occlusion method is less costly and requires fewer calculations. The double microsphere method requires less surgical preparation and allows measurement without perturbation of pulmonary hemodynamics. There was no statistically significant difference between bronchial blood flow measured with the two methods. However, total bronchial blood flow measured during pulmonary arterial occlusion (1.52 +/- 0.98% of cardiac output, n = 9) was slightly higher than that measured with the double microsphere method (1.39 +/- 0.88% of cardiac output, n = 9). In another series of experiments in which sequential measurements of bronchial blood flow were made, there was a significant increase of 15% in left lung bronchial blood flow during the first minute of occlusion of the left pulmonary artery. Thus pulmonary arterial occlusion should be performed 5 s after microsphere injection as originally described by Baile et al. (1).(ABSTRACT TRUNCATED AT 250 WORDS)

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The present study was designed to evaluate the distribution of bronchial blood flow to major airways and peripheral lung and to quantitate lung edema during a 2-h histamine infusion (2 micrograms.kg-1.min-1) in unanesthetized sheep. By the use of radioactive microspheres, the blood flow to trachea and to tracheal cartilage, smooth muscle, and mucosa/submucosa was determined along with measurements of blood flow to different sized airway segments and the systemic blood flow to lung parenchyma. Histamine greatly increased blood flow to medium-sized (5- to 10-mm-diam) central airways in which blood flow increased 5-10 times base line, whereas in small (1- to 5-mm-diam) central airways the increase was 10-15 times. Blood flow in tracheal mucosa/submucosa increased six times base line, but in tracheal smooth muscle the increase was only three times base line, and in cartilage it remained at base line. Most of the systemic blood flow to the lung perfuses less than 1-mm-diam peripheral airways, and these airways demonstrated less vasodilation during histamine infusion. Mean blood flow to whole-lung parenchyma (whole lung minus trachea) was only two times base line during histamine infusion. Water content of trachea and main stem bronchi was significantly increased after histamine. Histopathologic findings after histamine infusions included congestion and edema of airways with only minor effects noted in alveoli. We conclude that histamine is a potent and selective vasodilator of bronchial vessels and particularly affects blood flow to central airways and to airway mucosal/submucosa.(ABSTRACT TRUNCATED AT 250 WORDS)

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