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Biomedical subjects

F C White

Publications and source records attributed to F C White.

At least 73 records · Page 4Linked to original sources
PubMed1979

Ischemic myocardial injury after exercise stress in the pressure-overloaded heart.

Systemic hemodynamics and regional myocardial blood flows were determined in 18 miniswine during the development of pressure-overload hypertrophy induced by supravalvular aortic constriction. Nine miniswine served as control animals. Regional myocardial blood flows were measured at rest and during exercise stress with radioactive microspheres after 2 days and 1 month of aortic constriction. Exercise stress, causing the heart rate to increase to 85% of its maximum, was imposed twice weekly for 5 minutes on 13 pressure-overloaded animals to elicit differences between the control and experimental groups that might not occur at rest. At rest, regional myocardial blood flows of pressure-overloaded animals were similar to those of control animals. When exercise stress was imposed after 2 days and 1 month of pressure overload, endocardial blood flows decreased 45% below control exercise levels, although epicardial blood flows were unchanged. During the first 2 weeks of pressure overload epicardial and endocardial electrocardiograms showed S-T segment elevation with exercise stress but not at rest. Postmortem examinations after 1 month of pressure overload showed significant histologic evidence of myocardial injury, namely, fibrosis, which was subendocardially located. These findings indicate that the pressure-overloaded heart is at risk for ischemic injury, particularly during the early, uncompensated stage.

Animals↗
PubMed1978

Regional redistribution of myocardial blood flow after coronary occlusion and reperfusion in the conscious dog.

Early and late changes in regional myocardial blood flow distribution within the left circumflex coronary arterial bed after occlusion and after occlusion and reperfusion were compared with the extent of myocardial tissue necrosis. Radiolabeled microspheres, 15 micrometer, were used to study regional myocardial blood flow in conscious dogs at 5 minutes, 2 and 6 hours and 1 month after coronary occlusion. Blood flow was measured in conscious dogs whose hearts were reperfused for 72 hours after 2,6 and 24 hours of occlusion. Blood flow was measured in four distinct transmural myocardial zones delineated by dye injections and gross infarct features of the occluded left circumflex coronary bed. After occlusion, myocardial flow was redistributed from deep layers to outer layers, and within 6 hours after occlusion collateral flow was increased to the outer zones in excess of redistributed flow. After reperfusion, blood flow greately increased to regions containing predominantly normal tissue, and flow was redistributed away from the necrotic zones. The indigenous collateral circulation was a major determinant of infarct size in the occluded and reperfused myocardium. The concept of a migrating and narrowing marginal zone is discussed.

Animals↗
PubMed1978

Effects of endurance exercise on coronary collateral blood flow in miniature swine.

Coronary collateral blood flow was measured in 7 miniature pigs, exercise trained (ET) for 10 mo by running about 35 km/wk, and in 10 sedentary control pigs (SC). In acute, open-chest preparations, radiolabeled (85SR, 141CE, or 51Cr) microspheres, 15 +/- 5 micron in diameter, were injected into the left atrium during each of three conditions: control (C), total occlusion of the left circumflex artery (TO), and TO plus mechanically elevated aortic pressure (TOP). Blood flow to the circumflex bed during control condition in ET and SC was 0.36 +/- 0.07 (SE) and 0.43 +/- 0.10 ml.g-1.min-1, respectively. During TO, circumflex flow in ET and SC fell to 0.05 +/- 0.01 and 0.06 +/- 0.01 ml.g-1.min-1, respectively. In the presence of TOP, left circumflex flow in ET and SC rose to 0.11 +/- 0.04 and 0.11 +/- 0.02 ml.g-1.min-1, respectively. Blood flow to the tissue bed of the left anterior descendens was the same in both groups of pigs under all conditions. Thus, 10 mo of endurance exercise training seems to have no effect on the development of coronary collaterals in the left ventricles of pig hearts.

Animals↗
PubMed1978

Myocardial infarction in the baboon: regional function and the collateral circulation.

Occlusion of the anterior descending coronary artery was produced in sedated baboons 7-15 days after implantation of a micromanometer and ultrasonic crystals for measurement of regional left ventricular dimensions in ischemic, marginal, and control segments. One minute after coronary occlusion (CO), ischemic segments exhibited a marked systolic bulge with wall thinning, and percent systolic shortening of marginal segments decreased. Over the ensuing weeks, there was a progressive increase of end-diastolic lengths in marginal and ischemic segments, whereas systolic shortening in these segments did not improve significantly. Control segments did not change. In control baboons, the coronary collateral index was 55 +/-25 (SE) compared to 560 +/- 74 in normal dogs. One month after CO, the collateral index was 543 +/- 144 in baboons compared to 6,685 +/- 716 in dogs, regions of normal tissue were seen in the infarct (14.2 +/- 2% of left ventricular mass). Minimal coronary collateral development in the baboon provides a likely explanation for differences from the dog in regional functional responses and in the character of the infarct.

Animals↗
PubMed1978

Characteristics of coronary blood flow and transmural distribution in miniature pigs.

The relationship between phasic systolic and diastolic coronary blood flow and its transmural distribution has been studied in 29 Yucatan miniature pigs at rest and during heavy exercise, with and without adenosine infusion (1.5 mg . kg-1 . min-1) and with and without a subtotal coronary artery occlusion. Altered factors that affected coronary flow included vascular resistance, perfusion pressure, myocardial oxygen demand, and extra-vascular pressure. The data indicate that, at rest, endomural perfusion is significantly dependent on diastolic blood flow. However, the ability of the myocardial vessels to autoregulate during systole as well as during diastole was clearly shown with the use of adenosine infusion. This ability to regulate flow intrinsically appeared to transcend the endocardial dependency on diastolic perfusion under certain stressful conditions, e.g., during heavy exercise, when the diastolic duration was significantly reduced. Systolic transmural perfusion may then become a significant factor in meeting the blood flow demands of the myocardium. However, due to gradients in vascular resistance, perfusion pressure, and oxygen demand, the coronary reserve of the epicardium appears to be greater than that of the endocardium under any condition.

Adenosine↗
PubMed1977

The effect of chronic hypoxemia on regional myocardial blood flow in the conscious dog after acute coronary artery occlusion.

Chronic hypoxemia was produced in 16 dogs by surgical transposition of the caudal vena cava to the left atrium to determine if chronic hypoxemia would alter the response of the myocardium to acute ischemia. An electromagnetic aortic flow probe, left atrial tube, and occlusive cuff on the left circumflex coronary artery were permanently implanted in 11 hypoxemic and 26 normal control dogs. The animals were studied in the conscious state after recovery from the surgery. Dogs with hypoxemia had a blood hematocrit value of 54.3 +/- 1.0% (SE), arterial PO(2) of 43.2 +/- 1.4 mm Hg, and 80.2 +/- 1.6% oxygen saturation. There was no difference from control animals in the ratio of left ventricular weight to body weight, but the right ventricular weight was significantly decreased in the hypoxemic dogs. Cardiac output from the left ventricle was twice that of the right ventricle. Aortic blood flow was 3.68 +/- 0.22 liters/min in hypoxemic animals and 2.64 +/- 0.19 liters/min in normal dogs. Myocardial blood flow measured with 15-mu diameter tracer microspheres was increased from 79 +/- 10 and 59 +/- 8 ml/100 g/min in left ventricular endocardial and epicardial halves, respectively, in normal dogs to 212 +/- 48 and 172 +/- 39 in dogs with chronic hypoxemia. There were no deaths in 10 hypoxemic dogs within 24 hours after complete circumflex coronary artery occlusion; 7 of 26 (27%) normal dogs died after circumflex coronary artery occlusion during the conscious state. Gross infarct size was extremely variable in both groups. Median infarct size was smaller in dogs with hypoxemia and was directly correlated with arterial PO(2) in hypoxemic dogs. There was a mild, but statistically not significant, increase in the anastomotic index of hypoxemic dogs compared with that of normal animals, suggesting that a metabolic adaptive change rather than increased collateral circulation may have been responsible for the decreased mortality and smaller infarct size in hypoxemic dogs.

Animals↗
PubMed1976

Regional myocardial blood flow during acute myocardial infarction in the conscious dog.

Regional myocardial blood flow was studied in the conscious dog at periods of 5 minutes to 4 days after occlusion of a major branch of the left coronary artery. Dogs were instrumented with aortic electromagnetic flow probes, occlusive cuffs on either the anterior descending or circumflex branch of the left coronary artery, and a left atrial Silastic catheter for injection of microspheres (15 +/- 5 mum) labeled with either 85Sr, 141Ce, or 51Cr. Microspheres were injected into 25 fully conscious dogs during three of the following time periods: control preocclusion and 0.1, 2, 6, 24, or 96 hours postocclusion. In the conscious dog, before occlusion, the endocardial half of the left ventricular myocardium received 28% more blood flow than the epicardial half. After sudden occlusion of a coronary artery branch, there was a marked reduction in blood flow as well as an alteration in distribution of blood flow within the ischemic tissue; blood flow was most severly reduced in the subendocardial center of the ischemic region, less so in the epicardial ischemic region, and least reduced in the marginal region of the infarct. Blood flow was increased to the nonischemic tissue. There was no change in this pattern of reduced blood flow by 6 hours postocclusion, but by 24 hours, flow was moderately increased to all areas except the central subendocardial core, and was further increased at 96 hours. Blood flow to the endocardial half of the left ventricular myocardium averaged 63 ml/100 g per min during the control period, was reduced to 12-18 ml/100 g per min at 0.1-6 hours in the ischemic region, increased to 29 ml/100 g per min at 24 hours, and to 48 ml/100 g per min by 96 hours. These findings indicate that there is a reversal of the flow ratio within ischemic myocardium with relative under-perfusion of the endocardial half of the wall, which is not corrected by 4 days. There is a modest increase of collateral blood flow to ischemic tissue by 24 hours and this increase is considerably augmented by 96 hours, apparently as a result of the growth and enlargement of collateral vessels.

Acute Disease↗
PubMed1975

Ventricular fibrillation threshold in acute myocardial infarction and its relation to myocardial infarct size.

The effect of myocardial infarct size on ventricular fibrillation threshold (VFT) was evaluated by determining changes in VFT during acute myocardial infarction and relating those changes to infarct size. Infarct size was estimated from gross measurement and from serial changes in serum CPK activity in 25 dogs. VFT reduction correlated well with gross infarct size (r=0.92). This suggests that the severity of electrical instability during AMI is related to the size of the developing infarct, and that appropriate therapeutic interventions to reduce infarct size during this time may also render the heart more electrically stable.

Animals↗
PubMed1975

Sampling and analysis of pesticides in the environment.

Environmental monitoring is now recognized as essential in areas of pesticide use in order to assess the impact of these pesticides on the environment. During the last two decades, advances in instrumentation in terms of detection limits and specificity, along with the growing expertise of residue chemists, have made reports of pesticide residue levels in the parts per billion range commonplace. Using this technical ability and carefully assessing the significance of the data obtained, pesticides can be used in a more efficacious manner with less possible damage to the environment.

Air Pollution↗
PubMed1972

Functional development of the coronary collateral circulation during coronary artery occlusion in the conscious dog.

We studied changes in the coronary collateral circulation during coronary artery occlusion in 14 conscious dogs by: a) determining simultaneous changes in peripheral coronary pressure (PCP) and retrograde flow (RF) after abrupt coronary artery occlusion; b) correlating these functional indices with quantitative anatomic indices (AI) of coronary collateral development (Menick et al: Am Heart J 82:503-510, 1971); and c) observing changes in these indices after repeated reocclusions of a coronary artery. These dogs were subjected to left circumflex coronary artery (LCCA) occlusions for 2 hours to 8 days; pressure tubes were implanted in the aorta and LCCA, the latter tube placed distal to an occlusive cuff for PCP and RF measurements. Afterwards the animals were sacrificed, their hearts injected with a modified Schlesinger's gelatin mass, and AI determined. During 2 to 24 hour LCCA occlusions (11 dogs) mean PCP rose to levels 50 to 80% of prevailing aortic pressure. During repreated 2- to 24-hour occlusions (2 dogs) in the same dog, the rate at which PCP rose increased. Retrograde flow was unchanged during 2- to 24-hour occlusions. Anatomic indices of these dogs were in the same range as those observed in unoccluded controls. When LCCA occlusion was maintained for more than 4 days (3 dogs), mean PCP rose during the first 24 hours and then remained stable; RF did not change until 4 days into occlusion and then increased. Anatomic indices of dogs occluded for more than 4 days were significantly greater (P < 0.001) than those of the 2- to 24-hour occlusion groups. Our study shows that: a) the early PCP rise after occlusion is not associated with an increase in RF, b) RF is a better index of collateral function and c) RF correlated well with the anatomic development of the collateral bed.

Animals↗