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Query: UMLS:C0151744 (myocardial ischemia)
 31,282 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

To assess the effects of moderate potassium cardioplegia (37 mEq/l KCl) on the severity of myocardial ischemia during arrest and on post arrest ventricular function, 32 isolated, isovolumic feline hearts were studied before, during and 1 hour after ischemic arrest. Normothermia (37 degrees C) was maintained in the remaining 16 hearts, eight without KCl and eight with KCl. Hypothermia (27 degrees C) was maintained in the remaining 16 hearts, eight with KCl and eight without KCl. Myocardial oxygen (PmO2) and carbon dioxide tensions (PmCO2) were measured by mass spectrometry. Maximum developed intraventricular pressure (max DP) and max dP/dt were used as indices of performance. Compared with normothermic or hypothermic arrest alone, the addition of potassium cardioplegia resulted in a significant reduction in the peak PmCO2 measured during the arrest period. Hypothermia alone resulted in morphologic evidence of improved myocardial preservation and a significant reduction in peak PmCO2 compared with normothermia. Post arrest ventricular function was best with the combination of hypothermic arrest and potassium cardioplegia (max DP = 96 +/- 6% of control and max dP/dt = 99 +/- 5% of control). These data suggest that the beneficial effects of postassium cardioplegia and 27 degrees hypothermia are additive, and that reduction in myocardial ischemia as evidenced by a reduction in peak PmCO2 correlated with improvement in ventricular performance in the post arrest period and with preservation of myocardial structure.
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PMID:Effect of potassium cardioplegia on myocardial ischemia and post arrest ventricular function. 30 60

This study was conducted to determine whether low level exposure to carbon monoxide would increase myocardial ischemia associated with acute myocardial infarction. An hour after coronary artery ligation, eleven anesthetized dogs underwent five sequential respiratory exposures to 5,000 ppm carbon monoxide, producing mean blood carboxyhemoglobin levels of 4.9% to 17.0%. Ischemia, as indicated by the amount of S-T segment elevation in epicardial electrocardiograms, increased significantly at the lowest carboxyhemoglobin level and increased further with increasing carbon monoxide exposure. These changes occurred in the absence of altered heart rate, blood pressure, left atrial pressure, cardiac output, or blood flow to ischemic myocardium. Flow to non-ischemic myocardium increased with carbon monoxide exposure, the percentage increase being approximately double the increase in carboxyhemoglobin level. Thus, low level exposure to carbon monoxide can significantly augment ischemia in acute myocardial infarction, apparently through a reduction in oxygen supplied to ischemic tissue. The data suggest that hypoxia induced by carbon monoxide exposure is more severe than can be accounted for by a simple reduction in oxygenated hemoglobin.
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PMID:Augmentation of myocardial ischemia by low level carbon monoxide exposure in dogs. 47 72

This study was undertaken to investigate the effects of graded coronary constriction on regional gas tensions of the myocardium. In 12 open chest dogs, tissue carbon dioxide (PtCO2) and oxygen (PtO2) tensions were measured simultaneously in outer and inner layers of the myocardium using a mass spectrometer. In normal condition, higher PtO2 and lower PtCO2 were observed in outer layer than in inner layer. With application of coronary constriction, increase in PtCO2 and decrease in PtO2 were observed in both layers of the myocardium, but the response to the ischemic stimuli by applying coronary constriction in inner layer was different from that in outer layer. Severe coronary constriction, more than 90% in its diameter, was necessary to produce significant changes in both gas tensions in both layers of the myocardium. Decrease in PtO2 was found in the condition of less severe coronary constriction and to be greater in inner layer than in outer layer of the myocardium. In terms of the changes in PtCO2, inner layer was also more susceptible to the ischemic stimuli than outer layer. The greater and earlier elevation of PtCO2 in inner layer than in outer layer is regarded as one of the possible mechanisms of the reduction of myocardial contraction in the early stage of myocardial ischemia.
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PMID:Effects of graded coronary constriction on regional oxygen and carbon dioxide tensions in outer and inner layers of the canine myocardium. 71 21

Changes in myocardial carbon dioxide (PmCO2) and oxygen tension (PmO2) measured by mass spectrometry have been shown to reflect quantitatively progressive degrees of regional myocardial ischemia associated with stepwise reduction in coronary blood flow. The present study utilized mass spectrometry to assess the severity of regional myocardial ischemia developing during atrial pacing in the presence of a flow-limiting proximal critical coronary artend subendocardial layers was measured by the radioactive microsphere technique. Application of a "critical stenosis" resulted in a 6-mmHg decrease in PmO2 and a 17-mmHg increase in PmCO2 in the region of the myocardium supplied by the stenosed vessel. The addition of atrial pacing resulted in a 3-mmHg further decrease in Pmo2 and a 40-mmHg further increase in PmCO2. In the region of myocardium supplied by the critically stenosed vessel MBF increased in the subepicardial layer, but decreased or remained unchanged in the subendocardial layer. The failure of myocardial blood flow to increase in deeper myocardial layers in response to the increased myocardial oxygen demand of atrial pacing would provide a mechanism for the development of subendocardial ischemia in the presence of a critical coronary stenosis.
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PMID:Effects of atrial pacing on regional myocardial gas tensions with critical coronary stenosis. 83 20

Myocardial carbon dioxide tension and intramyocardial S-T segment voltage have previously been shown to provide useful quantitative indexes of the severity of regional myocardial ischemia. This study was designed to determine if (1) changes in intramyocardial S-T segment voltage and myocardial gas tensions, with the addition of atrial pacing, could be used to assess the functional significance of a coronary stenosis, and (2) if changes in S-T voltage recorded in intramyocardial electrodes proved a more sensitive indicator of ischemia than changes recorded in epicardial electrodes. In 12 open chest dogs, a variable constrictor and an electromagnetic flow probe were placed on the proximal left circumflex coronary artery. Myocardial carbon dioxide and oxygen tensions were recorded with mass spectrometry and unipolar intramyocardial S-T segment voltage with multicontact plunge electrodes. Intramyocardial S-T voltage and myocardial carbon dioxide tension showed parallel increases with atrial pacing in the presence of subcritical, critical and supercritical coronary stenoses. In the presence of a critical stenosis, S-T segment changes recorded in deepr myocardial layers were of greater magnitude than those recorded near the epicardial surface. These findings suggest that the severity of myocardial ischemia can be assessed by measuring intramyocardial S-T voltage or myocardial gas tensions at resting and paced heart rates. They also suggest that intramyocardial S-T voltage is a more sensitive indicator of the severity of pacing-induced myocardial ischemia than epicardial S-T changes. Application of this technique to patients undergoing coronary revascularization could allow intraoperative determination of the functional significance of questionable angiographic lesions and a more rational approach to the assignment of priorities to individual arteries when multiple bypasses are being considered.
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PMID:Functional significance of coronary arterial stenoses assessed by regional changes in intramyocardial S-T segment voltage and myocardial gas tensions with atrial pacing. 84 37

A portable carbon monoxide detector (catalytic electrode) was used to record carbon monoxide concentrations in enclosed public facilities, including night clubs, bars, restaurants, stores, hospitals, and public transit vehicles. The highest concentrations of carbon monoxide were found in night clubs, where evening indoor readings averaged 13.4 ppm, which was 4.1 +/- 1.5 ppm higher than outdoor readings. In one poorly ventilated establishment, values ranged from 20 to 40 ppm, with substantial gradients around the room. Adequate ventilation and screening of restaurant employees for ischemic heart disease should prevent problems from cigarette-induced build-up of carbon monoxide. Unfortunately, much lower concentrations of other constituents of smoke cause symptoms and changes of pulmonary function in the nonsmoker. If carbon monoxide is used as an indicator of cigarette smoke accumulation, concentrations should not exceed ambient readings by more than 5 ppm.
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PMID:Cigarette smoke in enclosed public facilities. 84 10

In a previous study from this laboratory, regional myocardial ischemia developed distal to a critical coronary stenosis in the fibrillating heart on cardiopulmonary bypass when myocardial perfusion was non-pulsatile. To assess the effect of pulsatile perfusion on the development of the fibrillation-induced ischemia, 10 dogs were placed on total cardiopulmonary bypass with the heart in the vented fibrillating state. A critical stenosis was applied to the left anterior descending artery (LAD). Pulsatile perfusion with a pulse pressure of 35 mm Hg and a pulse rate of 100/min was produced by a new method developed in this laboratory. During the 2 hours of bypass, ischemia in the LAD-supplied myocardium was assessed by changes in intramyocardial oxygen (PmO2) and carbon dioxide (PmCO2) tensions and by regional arterial-coronary venous lactate difference. With linear perfusion, regional ischemia in the LAD myocardium had been evidenced by a low PmO2 (8 +/- 3 mm Hg), a high PmCO2 (170 +/- 25 mm Hg) and regional lactate production (9.2 +/- 4.2 mg/100 ml). In contrast with pulsatile perfusion intramyocardial gas tensions remained stable during the 2 hours on bypass (PmO2 = 21 +/- 3 mm Hg, PmCO2 = 65 +/- 5 mm Hg, P less than 0.05 vs linear flow study) and lactate consumption was demonstrated (+17.7 +/- 2.9 mg/100 ml, P less than 0.001 vs linear flow group). With linear perfusion, myocardial blood flow to the LAD area had decreased 56 +/- 8% in the subendocardial layer and 46 +/- 7% in the subepicardial layer. In the dogs receiving pulsatile flow during bypass, regional LAD blood flow remained unchanged over the 2-hour bypass period and was significantly higher than the flow with linear flow (P less than 0.05). These data indicate that fibrillation-induced regional myocardial ischemia distal to a critical stenosis can be prevented by maintaining pulsatile perfusion during cardiopulmonary bypass.
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PMID:Regional ischemia distal to a critical coronary stenosis during prolonged fibrillation--improvement with pulsatile perfusion. 88 25

Carbon monoxide diffusion (DLCO), blood gas analysis at rest and after exercise, distribution of ventilation and perfusion by Xenon 133 were carried out in 43 hyperlipidemic patients, Fredrickson's types I, IIA, IIB, and IV. DLCO was significantly reduced in hypertriglyceridemic and to a lesser degree in hypercholesterolemic patients. A significant negative correlation was found between DLCO and triglyceride values. Significantly lower basal PaO2 values, which improved after exercise, were observed in both type IIA and type IV hyperlipemic patients. The ventilation/perfusion ratio distribution (V/Q) did not increase from the basal to the apical segments of the lungs in hyperlipidemic patients as it did in normals. The hypothesis of an alteration in pulmonary surface-active lipoprotein, directly related to hyperlipoproteinemia or indirectly caused by fat microembolism, may explain the reduced DLCO, the loss of V/Q gradient, and the decrease in PaO2 (which improves after exercise) observed in hyperlipemic patients. Disturbances in pulmonary gas exchange and PaO2 reduction could play an important role in the pathogenesis of both angina pain due to ischaemic heart disease, which is frequently observed in hyperlipemic patients, and the postprandial angina syndrome.
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PMID:Disturbances in pulmonary gaseous exchange in primary hyperlipoproteinemias. 101 88

Previous studies from this laboratory have demonstrated the usefulness of myocardial gas tensions as measured by mass spectrometry for the quantitative assessment of regional myocardial ischemia (Khuri et al., 1975a). Progressive increases in myocardial carbon dioxide tensions were noted when progressive reduction in coronary blood flow was created by means of a variable constrictor. The present study was designed to determine if changes in myocardial oxygen and carbon dioxide tension were greater in deep, compared to more superficial, myocardial layers. In eight anesthetized dogs, progressive reduction in circumflex coronary flow was associated with a progressive reduction in myocardial oxygen tension and a progressive increase in myocardial carbon dioxide tension and intramyocardial ST-segment voltage. Evidence of a transmural gradient in the severity of ischemia was present at all degrees of flow reduction. These results confirm the findings of previous metabolic studies, which demonstrated gradients in lactate and high-energy phosphates. Myocardial carbon dioxide tension, which can be monitored continuously by mass spectrometry, would appear to provide a useful means of quantitatively assessing changes in regional myocardial metabolism.
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PMID:Transmural gradients in myocardial gas tensions in regionally ischemic canine left ventricle. 103 74

Carboxyhaemoglobin (COHb) levels in tobacco smokers vary throughout the day since they are affected by the pattern of tobacco consumption and the rate at which COHb is eliminated. A method is described whereby a single COHb measurement together with a recent smoking history may be used to estimate the average COHb "boost" produced by each cigarette, the total daily carbon monoxide (CO) uptake from smoking, and the mean COHb level throughout the day. These three indices of tobacco smoke absorption were estimated in nine healthy cigarette smokers on different days, each set of three estimations being derived from separate COHb determinations. The indices were reasonably reproducible within the same person, and the differences between people were statistically highly significant (P less than 0-001). For example, the estimates of mean daily COHb level resulting from smoking ranged from 0-7% to 9-3% in smokers who smoked 15 to 40 cigarettes a day. These differences are sufficiently large to distinguish possible differences in the risk of developing diseases such as ischaemic heart disease which may result from the inhalation and absorption of tobacco smoke. The suggested indices also depend less on the time of the blood test and on the daily pattern of smoking than a COHb level alone. The ratio of the COHb boost to the CO yield of a cigarrette may reflect depth of inhalation more accurately than a smoker's self-assessment. Moreover there was little correlation between these two measures of inhalation in the nine subjects studied.
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PMID:Use of carboxyhaemoglobin levels to predict the development of diseases associated with cigarette smoking. 117 8


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