Measurement of gastric blood flow with radioactive microspheres.

The validity of using radioactive microspheres (15 +/- 5-mum diameter) to measure gastric blood flow and its partition between gastric wall layers was investigated in anesthetized dogs with a chambered segment of gastric corpus. Total flow measured by a venous effluent technique demonstrated close correlation with microsphere-measured flow (r = 0.98, slope = 0.95) in 12 dogs given histamine, gastrin, or isoproterenol. In 12 histamine-stimulated dogs, mucosal flow measured by aminopyrine clearance and by microspheres also showed good agreement (r = 0.96, slope = 0.83). No evidence was found to indicate that microspheres altered hemodynamic or gastric function. In all experiments less than 1% of the total gastric radioactivity passed through arteriovenous shunts. The mucosa always contained a statistically adequate number of spheres (greater than 400), but the submucosa and muscularis frequently did not. Microspheres of all sizes mixed adequately in large arteries, but a significant difference was found in the distribution of 16- and 26 mum spheres between mucosa and submucosa, presumably because of streaming of the larger spheres past mucosal arteries. It was concluded that, with the techniques developed in our laboratory, microspheres could be a highly useful tool for quantitating gastric regional blood flow under a variety of experimental conditions.     

Regional cerebral blood flow measurement in rats with radioactive microspheres

The effect of the method of heart catheterization on the measurement of cerebral blood flow (CBF) with radioactive microspheres was evaluated during various experimental procedures in male Sprague-Dawley rats. Catheters were inserted into the left ventricle via the right carotid or right subclavian artery or directly into the left atrium for microsphere injections. CBF was measured in cerebral cortical and subcortical tissues under control anesthetized (70 % N₂O, 30 % O₂), hypoxic or hypercapnic test conditions. Under control conditions, CBF was similar in the right vs the left cerebral hemisphere in subclavian artery and atrial catheterized rats but was greater in the left vs the right cortex in carotid catheterized animals (p<.05). During hypoxia and hypercapnia CBF increased equally in both cerebral hemispheres in atrial catheterized rats. The increase in CBF was significantly attenuated in the cerebral hemisphere ipsilateral to carotid catheterization during hypoxia and hypercapnia, although the percentage increase in flow was similar in both hemispheres. The results indicate the limitations of measuring regional CBF changes under experimental test conditions in rats with a ligated carotid artery and suggest that atrial catheterization is the method of choice when comparable changes in CBF are desired in both cerebral hemispheres.     

Measurement of bronchial blood flow with radioactive microspheres in awake sheep

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)     

Regional trapping of microspheres in the lung compares well with regional blood flow

Microspheres (MS) are often used to measure the distribution of pulmonary blood flow in the assumption that the number of MS trapped in a region is proportional to blood flow. However, regional distribution of trapped MS has not been directly compared with regional blood flow in the lung. Regional trapping of MS was compared with regional flow of erythrocytes (RBC's) in isolated, perfused left lungs of dogs. Radioactivity from labeled MS and RBC's was measured by external detection using a gamma camera. We defined six regions of interest in the image of the left lateral surface of the lung: a dorsocaudal, a caudal, two ventral, an apical, and a central region. In each lung, regional trapping of MS was measured from the image of radioactivity obtained after slow injection of a suspension of MS into the arterial perfusion tubing. A radioactive bolus of labeled RBC's was injected during rapid imaging of the lung to obtain radioactivity vs. time curves from each region. The peaks of the regional radioactivity vs. time curves were used to estimate regional flows, though compensation had to be made for overlap of the washout and washin phases of the bolus of labeled RBC's. The results indicated that there were no differences in the regional distribution of MS compared with the regional distribution of RBC flow in isolated, perfused dog lungs.     

Measurement of carotid body blood flow in cats by use of radioactive microspheres

To resolve the controversy regarding carotid body blood flow, we used the radioactive microsphere technique for determination of tissue blood flow. We also measured the blood flow to several other tissues in the cat. Blood flow experiments were performed on 13 cats that were anesthetized, paralyzed, and mechanically ventilated with air. Different numbers of differently labeled 9-, 15-, and 25-micron microspheres were injected via a catheter into the left atrium. It was determined that one injection of 5 x 10(6) 15-micron microspheres was appropriate for the determination of carotid body blood flow. Flows to the carotid bodies and other organs by use of this protocol were as follows (ml.min-1.100 g-1, means +/- SE): carotid bodies, 1,417 +/- 143; adrenal glands, 406 +/- 89; left kidney, 355 +/- 69; right kidney, 375 +/- 74; heart, 201 +/- 39; liver 81 +/- 14; pancreas, 80 +/- 21; superior cervical ganglia, 62 +/- 9; carotid artery wall, 2.4 +/- 1.1. The blood flow to the carotid bodies was the highest for any organ. This measurement provides new evidence that tissue blood flow to the carotid body is very high. This high flow is consistent with the prompt physiological reflex functions of the carotid body.     

Testicular blood flow in monkeys as measured by xenon clearance and radioactive microspheres

Testicular blood flow was measured in monkeys using a 133xenon clearance technique and a 141cerium microsphere entrapment technique. The clearance procedure provided values that tended to be lower than those obtained using the microspheres, was technically less difficult, and has the advantage of being a clinical tool. The microsphere entrapment technique provides the simultaneous evaluations in numerous tissue sites but requires the removal of the tissues to be evaluated. The xenon clearance technique appears to be better suited for evaluations in nonhuman primates.     

Measurement of blood flow distribution by radioactive microspheres in the laying hen (Gallus domesticus)

• 1.1. Blood flow distribution was examined in 12 normothermic laying hens by microspheres injected via the brachial artery into the root of the aortic arch above the aortic valves.
• 2.2. Double reference sampling (brachial and sciatic) accounted for uneven microsphere distribution between upper and lower body arterial flows.
• 3.3. This easily accessible injection site yielded results comparable to those attained by left atrial injections.
• 4.4. Blood flow (ml/min g tissue) was highest in the spleen (8.2); intermediate in the brain, kidneys. adrenals, liver, follicles (1.1–3.1); below 0.5 in the skin. muscle, respiratory tract and post ovulatory follicle. Hyperthermia markedly changed this order.

     

Some applications of microspheres in flow cytometry

Microspheres of latex ranging from 0.1 to 10 microns in diameter are nowadays commercially available. Labelled with different fluorochromes, they are good standards to check the optical path and to calibrate flow cytometers. The kits available contain microspheres highly selected with a precise size and a narrow distribution, so as to allow an easy alignment of instruments. Mixed with the cell preparations, microspheres may be used as an internal standard, in order to compare samples from day to day. Phagocytic activity has been investigated after incubation of cells with fluorescent microspheres. Covalently bound to ligands such as antibodies, microspheres become a powerful and specific reagent to label cell surface antigens. The positive signal is enhanced, allowing the detection of poorly represented epitopes. This paper reviews some examples of these applications published in the flow cytometry field.