Effect of nitroglycerin and arterial hypertension on myocardial blood flow following acute coronary artery occlusion in the dog.

This study was designed to evaluate the effects of nitroglycerin and phenylephrine-induced arterial hypertension on regional myocardial blood flow in awake dogs with acute occlusion of the left circumflex coronary artery. Myocardial blood flow to four transmural layers from epicardium to endocardium was estimated with 7-9 micron radionuclide labeled microspheres in 1) the non-ischemic myocardium, 2) the central ischemic zone, and 3) the border zone separating ischemic from normally perfused myocardium. Measurements were repeated 1) during infusion of nitroglycerin, 0.

Transmural myocardial perfusion during restricted coronary inflow in the awake dog.

Phasic coronary flow and transmural myocardial perfusion were studied during coronary artery constriction in 10 dogs with electromagnetic flowmeters and hydraulic occluders on the left circumflex coronary artery. Regional blood flow was estimated using left atrial injections of radionuclide-labeled microspheres 9 micron in diameter. During control conditions, 14+/-0.

Effect of exercise on perfusion of collateral-dependent myocardium in dogs with chronic coronary artery occlusion.

Since the ability of mature intercoronary collateral channels to increase myocardial blood flow in response to drug-induced coronary vasodilation has been questioned, the present study was undertaken to evaluate the response of coronary collateral circulation to the stress of exercise. Studies were performed at rest and during two levels of treadmill exercise in six dogs a minimum of 6 mo after placement of an Ameroid constrictor on the left circumflex coronary artery. Regional myocardial blood flow was estimated in normally perfused anterior and predominantly collateral-dependent posterior left ventricular wall with left atrial injections of radio-nuclide-labeled microscheres 7-10 mum in diameter.

Relationship between blood flow to ischemic regions and extent of myocardial infarction. Serial measurement of blood flow to ischemic regions in dogs.

This study was designed to measure early sequential changes in blood flow to ischemic regions after acute coronary occlusion and to determine the relationship between blood flow and the extent of subsequent myocardial infarction. Initial studies were carried out on five dogs which verified using radioisotope-labeled microspheres, 7-10 mum in diameter, to measure changes in blood flow in small myocardial regions after acute coronary artery occlusions. Studies then were carried out on 11 awake dogs chronically prepared with dwelling catheters in the aorta and left atrium and occluders on the left circumflex coronary artery.

Local effects of acute cellular injury on regional myocardial blood flow.

This study was designed to examine local effects of acute cellular injury on regional myocardial blood flow. Studies were carried out in awake dogs chronically prepared with indwelling catheters in the aorta and left atrium and an occluder on the left circumflex coronary artery. Regional myocardial blood flow was measured by using 7-10-mum radioisotope-labeled microspheres after reestablishing inflow to a region subjected to a 2-h complete coronary occlusion.

Distribution of myocardial blood flow in the exercising dog with restricted coronary artery inflow.

The effect of a proximal coronary artery stenosis on transmural myocardial blood flow during exercise was studied in nine dogs with electromagnetic flowmeter probes and hydraulic occluders on the left circumflex coronary artery. Regional myocardial blood flow at rest and during treadmill exercise was estimated with radioactive microspheres 7-10 mum in diameter. Exercise studies were performed during unrestricted coronary artery inflow (control exercise) and during partial inflation of the occluder to a level which did not reduce flow at rest but which limited the increase in flow during exercise to 66 +/- 6% (mild restriction) or 44 +/- 3% (severe restriction) of the value during control exercise.

Transmural distribution of myocardial blood flow during systole in the awake dog.

This study was designed to quantitate transmural myocardial blood flow when coronary arterial inflow was limited to systole and during the subsequent reactive hyperemic response. Studies were performed in 10 awake dogs chronically prepared with electromagnetic flowmeters and pneumatic occluders on the left circumflex coronary artery. Intermittent coronary perfusion, confined to the interval of left ventricular systole or an equivalent period during diastole, was effected by an R wave-triggered solenoid valve connected to the occluder.

Effects of nitroglycerin on transmural myocardial blood flow in the unanesthetized dog.

This study was designed to determin the effect of nitroglycerin upon transmural distribution of myocardial blood flow in the awake dog during normal conditions and in the presence of ischemia-induced coronary vasodilation. Studies were performed in chronically prepared dogs with electromagnetic flowmeters and hydraulic occluders on the left circumflex coronary artery. Regional myocardial blood flow was estimated by using radionuclide-labeled microspheres, 7-10 mum in diameter, injected into the left atrium.

Neurogenic influences on the coronary vascular response to ischemia in the awake dog.

The influence of the nervous system on the response of the coronary vessels to ischemia was evaluated by observing the reactive hyperemia subsequent to a 10 second occlusion of the left circumflex coronary artery in 19 awake dogs. Sympathectomy produced by pretreatment with 6-hydroxydopamine, chronic total surgical cardiac denervation, beta-adrenergic blockade with propranolol, and alpha blockade with phentolamine did not significantly after the reactive hyperemic response. Thus cardiac denervation did not impair the ability of the coronary vasculature to respond to a brief ischemic stimulus.

Regional myocardial blood flow during graded treadmill exercise in the dog.

Regional myocardial blood flow was measured in nine dogs at rest and during three levels of treadmill exercise by using left atrial injections of 7-10-mum radioactive microspheres. At rest, heart rate was 76 plus or minus 3 beats/min (mean plus or minus SEM), mean left ventricular myocardial flow was 0.94 plus or minus 0.

Myocardial blood flow distribution during ischemia-induced coronary vasodilation in the unanesthetized dog.

This study was designed to determine whether coronary vasodilation distal to a flow-limiting coronary artery stenosis could result in redistribution of myocardial blood flow to produce subendocardial underperfusion. Studies were performed in 10 awake dogs chronically prepared with electromagnetic flow-meters and hydraulic occluders on the left circumflex coronary artery. Regional myocardial blood flow was measured using radionuclide-labeled microspheres, 7-10 mum in diameter, injected into the left atrium.

Regional myocardial blood flow in awake dogs.

The objectives of this study were to test the hypothesis in awake dogs that during control conditions endocardial vessels are maximally dilated and to determine whether variables introduced by general anesthesia and thoracotomy modify distribution of myocardial blood flow or impair capacity for augmentation of flow in response to a coronary vasodilator stimulus. Myocardial blood flow was measured in relatively small, 2-3 g, left ventricular epicardial and endocardial samples by using 7-10-mum radioisotope-labeled microspheres during control conditions and during infusion of adenosine in dosages which produced maximum increases in coronary blood flow. Measurements were made initially in awake resting animals and were repeated after pentobarbital anesthesia, thoracotomy, and pericardiotomy.