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Effect of isoproterenol on myocardial mechanical function and cyclic AMP content in the fetal rabbit
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with one fatality. Of these 15 patients, 14 demonstrated thallium redistribution and three had ST-T changes suggestive of ischemia during exercise testing. An abnormal thallium scan or thallium redistribution occurred in 47% and 38% of patients without and in 93% of patients with perioperative ischemic events. Of the former patients, there was a low-risk group characterized by absence of thallium redistribution and a persistent defect as well as an intermediate group having thallium redistribution of lesser magnitude than highrisk group, but a negative exercise test. Other preoperative factors that failed to indicate the likelihood of an ischemic event were rate-pressure product, diabetes, history of heart failure, history of angina, and total exercise time. Although the authors state that patients with less severe degrees of thallium redistribution, good exercise tolerance, and no other risk factors could be subjected to surgery when appropriate cardiac monitoring is used perioperatively, they did not evaluate specifically the use of hemodynamic monitoring nor the occurrence of intraoperative events such as hypertension or tachycardia, which might predispose to infarction in their series.
Wead WB, Cassidy SS, Coast JR, et al: Reflex cardiorespiratory responses to pulmonary vascular congestion. J Appl Physiol 6 2 : 8 7 0 - 8 7 9 , 1987 In a canine preparation with an isolated left lung, pulmonary hypertension to increase pulmonary transcapillary pressure to 30 mmHg did not change heart rate, systemic arterial pressure, or inspiratory muscle activity. Thus, it appears that pulmonary vascular congestion does not stimulate pulmonary C fibers sufficiently to evoke systemic hemodynamic or central inspiratory changes. Although the experimental preparation permitted examination of the reflex cardiovascular and central inspiratory responses caused solely by stimulation of the isolated left lung with expansion to 30 cm water, vascular congestion, or stimulation of nerve endings, the possibility of interruption of nerve pathways, nonperfusion of the left lung, and the absence of the normal variation of alveolar carbon dioxide tension may affect the findings.
Lundy EF, Kuhm JE, Kwon JM, et al: Infusion of five percent dextrose increases mortality and morbidity following six minutes of cardiac arrest in resuscitated dogs. J Crit Care 2:4-14, 1987 This study and the accompanying editorial by Yatsu, McKenzie, and Lockwood confirm previous observations on the deleterious effects of glucose administration during hypoxic/ischemic cerebral insults. In a canine model anesthetized with halothane and subjected to 6 minutes of ventricular fibrillation followed by open chest cardiac massage, dogs receiving lactated Ringer's infusions had minimal deficits compared with those receiving dextrose 5% in lactated Ringer's (LR) solution. Animals receiving LR were extubated within three hours of arrest and required less epinephrine for maintenance of an adequate hemodynamic state, Although hyperglycemia itself does not produce cerebral damage,
CAROLL. LAKE
augmented damage results from anaerobic glycolytic metabolism to lactate.
Okuda H, Nakanishi T, Nakazawa M, et al: Effect of isoproterenol on myocardial mechanical function and cyclic AMP content in the fetal rabbit. J M o l Cell C a r d i o l 1 9 : 1 5 1 - 1 5 7 , 1 9 8 7 The effects of isoproterenol, which activates betaadrenergic receptors, and the adenylate cyclase system were studied in an isolated rabbit heart system to determine the differences in mechanical effects in fetuses and newborns. As reported by others, the effects of isoproterenol were less in the fetal than in the newborn rabbit hearts. Although the myocardial cyclic adenosine monophosphate (AMP) concentrations after isoproterenol were greater in the fetus, the inotropic effects of dibutyryl cyclic AMP were less than in the newborn. Since it appears from this study that the process from beta receptor to cyclic AMP in fetal rabbits is equal or more responsive to isoproterenol than in newborns, the decreased inotropic response may result from age-related differences in the inotropic effects of calcium.
McPherson DD, Hiratzka LF, Lamberth WC, Brandt B, Hunt M, Marcus ML, Kerber RE: Delineation of the extent of coronary atherosclerosis by high-frequency epicardial echocardiography. N E n g l J M e d 3 1 6 : 3 0 4 - 3 0 9 , 1 9 8 7 Coronary angiography may underestimate the severity and extent of coronary disease. Using high-frequency epicardial echocardiography, the ratio of coronary arterial lumen to wall thickness was determined in 37 patients with normal coronary arteries or with atherosclerotic disease. The ratio in angiographically normal segments was less than normal in patients with documented coronary disease although there was considerable overlap with values in patients with angiographic disease at the site of evaluation. A statistically significant decrease from normal in the ratio occurred with angiographie disease at the site of evaluation. Thus, diffuse coronary atherosclerosis is often present in the angiographicaUy normal vessels of patients with discrete coronary stenoses. Because of the variability of coronary lesions (ranging from discrete protruding intraluminal lesions to diffusely thickened walls), the use of angiographically estimated percent stenosis frequently does not correlate with physiologic coronary obstruction.
Joob AW, Dunn C, M i l l e r E D , e t a h Effect of left atrial to left femoral artery bypass and renin-angiotensin system blockade on renal blood flow and function during and after thoracic aortic occlusion. J Vasc Surg 5 : 3 2 9 - 3 5 , 1 9 8 7 The effects of a bolus dose (100/~g/kg) of enalaprilat (MK 422) were compared to left atrial to left femoral bypass and simple aortic clamping in 22 dogs. Enalaprilat, a converting enzyme inhibitor, was given at the time of aortic clamping. During aortic occlusion, urine output, renal blood flow, and glomerular filtration rate were zero in animals subjected to either unmodified aortic clamping or administration of
with one fatality. Of these 15 patients, 14 demonstrated thallium redistribution and three had ST-T changes suggestive of ischemia during exercise testing. An abnormal thallium scan or thallium redistribution occurred in 47% and 38% of patients without and in 93% of patients with perioperative ischemic events. Of the former patients, there was a low-risk group characterized by absence of thallium redistribution and a persistent defect as well as an intermediate group having thallium redistribution of lesser magnitude than highrisk group, but a negative exercise test. Other preoperative factors that failed to indicate the likelihood of an ischemic event were rate-pressure product, diabetes, history of heart failure, history of angina, and total exercise time. Although the authors state that patients with less severe degrees of thallium redistribution, good exercise tolerance, and no other risk factors could be subjected to surgery when appropriate cardiac monitoring is used perioperatively, they did not evaluate specifically the use of hemodynamic monitoring nor the occurrence of intraoperative events such as hypertension or tachycardia, which might predispose to infarction in their series.
Wead WB, Cassidy SS, Coast JR, et al: Reflex cardiorespiratory responses to pulmonary vascular congestion. J Appl Physiol 6 2 : 8 7 0 - 8 7 9 , 1987 In a canine preparation with an isolated left lung, pulmonary hypertension to increase pulmonary transcapillary pressure to 30 mmHg did not change heart rate, systemic arterial pressure, or inspiratory muscle activity. Thus, it appears that pulmonary vascular congestion does not stimulate pulmonary C fibers sufficiently to evoke systemic hemodynamic or central inspiratory changes. Although the experimental preparation permitted examination of the reflex cardiovascular and central inspiratory responses caused solely by stimulation of the isolated left lung with expansion to 30 cm water, vascular congestion, or stimulation of nerve endings, the possibility of interruption of nerve pathways, nonperfusion of the left lung, and the absence of the normal variation of alveolar carbon dioxide tension may affect the findings.
Lundy EF, Kuhm JE, Kwon JM, et al: Infusion of five percent dextrose increases mortality and morbidity following six minutes of cardiac arrest in resuscitated dogs. J Crit Care 2:4-14, 1987 This study and the accompanying editorial by Yatsu, McKenzie, and Lockwood confirm previous observations on the deleterious effects of glucose administration during hypoxic/ischemic cerebral insults. In a canine model anesthetized with halothane and subjected to 6 minutes of ventricular fibrillation followed by open chest cardiac massage, dogs receiving lactated Ringer's infusions had minimal deficits compared with those receiving dextrose 5% in lactated Ringer's (LR) solution. Animals receiving LR were extubated within three hours of arrest and required less epinephrine for maintenance of an adequate hemodynamic state, Although hyperglycemia itself does not produce cerebral damage,
CAROLL. LAKE
augmented damage results from anaerobic glycolytic metabolism to lactate.
Okuda H, Nakanishi T, Nakazawa M, et al: Effect of isoproterenol on myocardial mechanical function and cyclic AMP content in the fetal rabbit. J M o l Cell C a r d i o l 1 9 : 1 5 1 - 1 5 7 , 1 9 8 7 The effects of isoproterenol, which activates betaadrenergic receptors, and the adenylate cyclase system were studied in an isolated rabbit heart system to determine the differences in mechanical effects in fetuses and newborns. As reported by others, the effects of isoproterenol were less in the fetal than in the newborn rabbit hearts. Although the myocardial cyclic adenosine monophosphate (AMP) concentrations after isoproterenol were greater in the fetus, the inotropic effects of dibutyryl cyclic AMP were less than in the newborn. Since it appears from this study that the process from beta receptor to cyclic AMP in fetal rabbits is equal or more responsive to isoproterenol than in newborns, the decreased inotropic response may result from age-related differences in the inotropic effects of calcium.
McPherson DD, Hiratzka LF, Lamberth WC, Brandt B, Hunt M, Marcus ML, Kerber RE: Delineation of the extent of coronary atherosclerosis by high-frequency epicardial echocardiography. N E n g l J M e d 3 1 6 : 3 0 4 - 3 0 9 , 1 9 8 7 Coronary angiography may underestimate the severity and extent of coronary disease. Using high-frequency epicardial echocardiography, the ratio of coronary arterial lumen to wall thickness was determined in 37 patients with normal coronary arteries or with atherosclerotic disease. The ratio in angiographically normal segments was less than normal in patients with documented coronary disease although there was considerable overlap with values in patients with angiographic disease at the site of evaluation. A statistically significant decrease from normal in the ratio occurred with angiographie disease at the site of evaluation. Thus, diffuse coronary atherosclerosis is often present in the angiographicaUy normal vessels of patients with discrete coronary stenoses. Because of the variability of coronary lesions (ranging from discrete protruding intraluminal lesions to diffusely thickened walls), the use of angiographically estimated percent stenosis frequently does not correlate with physiologic coronary obstruction.
Joob AW, Dunn C, M i l l e r E D , e t a h Effect of left atrial to left femoral artery bypass and renin-angiotensin system blockade on renal blood flow and function during and after thoracic aortic occlusion. J Vasc Surg 5 : 3 2 9 - 3 5 , 1 9 8 7 The effects of a bolus dose (100/~g/kg) of enalaprilat (MK 422) were compared to left atrial to left femoral bypass and simple aortic clamping in 22 dogs. Enalaprilat, a converting enzyme inhibitor, was given at the time of aortic clamping. During aortic occlusion, urine output, renal blood flow, and glomerular filtration rate were zero in animals subjected to either unmodified aortic clamping or administration of