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Biomedical subjects

M R Salem

Publications and source records attributed to M R Salem.

At least 73 records · Page 4Linked to original sources
PubMed1989

Influence of nifedipine on systemic and regional hemodynamics during adenosine-induced hypotension in dogs.

Previous pharmacologic studies indicating competitive interactions between adenosine and nifedipine at the adenosine vascular receptor suggest that adenosine may be a less effective hypotensive drug after pretreatment with nifedipine. This hypothesis was tested in 18 pentobarbital-anesthetized, open-chest dogs by evaluating the hypotensive effects and regional hemodynamic responses to 60-minute intravenous adenosine infusions before and after bolus injection of nifedipine (20 micrograms/kg, IV). Regional blood flow was measured with 15-microns radioactive microspheres. Before nifedipine, infusion of adenosine at a rate of 126 +/- 30 mumol/min caused a 50% reduction in mean aortic pressure that in the presence of no change in aortic blood flow was attributable to a proportional decrease in systemic vascular resistance. These systemic effects were associated with heterogeneous changes in regional blood flow; blood flow decreased in the renal cortex (-68%), pancreas (-50%), spleen (-77%), and skin (-61%); increased in the left (+112%) and right (+265%) ventricular myocardium; and did not change significantly in the duodenum, liver, skeletal muscle, or brain. Nifedipine did not alter the dose requirement or time course of the adenosine-induced hypotensive response or affect the associated systemic hemodynamic changes. Furthermore, nifedipine caused only minor alterations in the regional blood flow changes during adenosine-induced hypotension. Apparently the high plasma levels of adenosine required for controlled hypotension in the present study were sufficient to overcome the blocking influence of nifedipine at the adenosine vascular receptor. The study demonstrates that the hypotensive action of adenosine remains unimpaired after pretreatment with nifedipine.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine↗
PubMed1988

Regional hemodynamics and oxygen supply during isovolemic hemodilution in the absence and presence of high-grade beta-adrenergic blockade.

Studies were performed in 16 pentobarbital-anesthetized dogs to evaluate regional circulatory effects of isovolemic hemodilution in the absence (group 1) and presence (group 2) of high-grade beta-adrenergic blockade with propranolol. Regional blood flow measured with 15 microm radioactive microspheres was used to calculate regional oxygen supply. In group 1, hemodilution with 5% dextran (40,000 molecular weight) reduced arterial hematocrit and oxygen content by approximately one half and had heterogeneous effects on regional blood flows. Blood flow was unchanged in the renal cortex, liver, and spleen, and it increased in the pancreas, duodenum, brain, and myocardium; however, only in the brain and myocardium were increases in blood flow sufficient to maintain oxygen supply at baseline (pre-hemodilution) levels. In group 2, intravenous administration of propranolol (1 mg/kg) itself decreased blood flow in the spleen and myocardium and had no other regional effects. Hemodilution after propranolol caused regional circulatory changes that were essentially similar to those in the absence of propranolol. It is concluded that (1) during isovolemic hemodilution, oxygen supply to the brain and myocardium is maintained at the expense of oxygen supply to less critical organs, and (2) this pattern of regional circulatory response during hemodilution remains intact in the presence of high-grade beta-adrenergic blockade with propranolol.

Adrenergic beta-Antagonists↗
PubMed1988

Regional hemodynamics and oxygen supply during isovolemic hemodilution alone and in combination with adenosine-induced controlled hypotension.

Studies were performed in ten pentobarbital-anesthetized, open chest dogs to evaluate regional circulatory effects of isovolemic hemodilution alone, and in combination with adenosine-induced controlled hypotension. Regional blood flow measured with 15-microns radioactive microspheres was used to calculate regional oxygen supply. Hemodilution with 5% dextran (40,000 molecular weight) reduced arterial hematocrit and oxygen content by approximately one-half and caused heterogeneous changes in regional blood flows; flow decreased in the spleen, was unchanged in the renal cortex, liver, skeletal muscle and skin, and increased in the duodenum, pancreas, brain and myocardium; however, only in the brain and myocardium were increases in flow sufficient to preserve oxygen supply. Intravenous infusion of adenosine reduced aortic pressure by 50% and reduced flow in most tissues (renal cortex, pancreas, liver, spleen, skin, and brain), with the result that oxygen deficits were produced or accentuated in these organs. The magnitude of flow reductions in the renal cortex (-73%) and cerebral cortex (-37%) were noteworthy. In the myocardium, direct coronary vasodilation by adenosine caused parallel increases in blood flow and oxygen supply to levels exceeding prevailing metabolic requirements. It is concluded that 1) during isovolemic hemodilution alone, oxygen supply to the brain and myocardium is maintained at the expense of oxygen supply to less critical organs and, 2) during combined isovolemic hemodilution and adenosine-induced hypotension, oxygen is oversupplied to the myocardium but undersupplied to the brain and kidney. These latter effects suggest the need for extensive clinical monitoring of patients in whom combined isovolemic hemodilution and adenosine-induced hypotension is utilized.

Adenosine↗
PubMed1988

Myocardial oxygen consumption and segmental shortening during selective coronary hemodilution in dogs.

Experiments were conducted in 33 open chest, anesthetized dogs to evaluate direct effects of hemodilution on myocardial oxygenation and contractile function. The left anterior descending coronary artery (LAD) was perfused selectively from a controlled pressure reservoir with either normal arterial blood or arterial blood diluted with lactated Ringer's solution. Systemic hemodynamic parameters were held stable. In the LAD bed, values were obtained for coronary blood flow (CBF) with an electromagnetic flowmeter, myocardial oxygen consumption (MVO2) using the Fick principle, and percentage segmental shortening (%SS), an index of local myocardial contractility, by sonomicrometry. Studies were conducted with LAD perfusion pressure (PP) set at control (100 mm Hg) and at 50% of that level to simulate coronary insufficiency (CI). CI abolished coronary reactive hyperemia after release of a 90-second occlusion, indicating exhausted vasodilator reserve capacity. With PP at control, reductions in LAD hematocrit to as low as 10% had no effect on MVO2 or %SS, because increases in blood flow were sufficient to offset induced falls in arteriovenous oxygen content difference. However, during CI, a more modest reduction in hematocrit to 17% caused reductions in both MVO2 and %SS, because of inadequate flow responses during hemodilution. The following conclusions can be made: 1) Extreme hemodilution is well tolerated by the normal heart with a stable work requirement and; 2) Relatively modest hemodilution may compromise myocardial oxygenation and contractile function when in the presence of exhausted or severely depleted vasodilator reserve capacity.

Animals↗
PubMed1988

Myocardial blood flow and oxygen consumption during isovolemic hemodilution alone and in combination with adenosine-induced controlled hypotension.

Recent reports have proposed combining isovolemic hemodilution and controlled hypotension to limit blood loss during surgery. Before such a technique can be considered for clinical use, it must be demonstrated that it does not endanger maintenance of adequate myocardial oxygenation. Accordingly, measurements of left ventricular myocardial blood flow and oxygen consumption were obtained during isovolemic hemodilution alone and in combination with adenosine-induced controlled hypotension in ten pentobarbital-anesthetized, open chest dogs with normal coronary circulation. Hemodilution to a hematocrit of 21.7% was produced by isovolemic exchange of whole blood for 5% dextran. In the presence of hemodilution, adenosine was infused intravenously at a rate sufficient to decrease mean aortic pressure to 51 mm Hg. Myocardial blood flow was measured with radioactive microspheres and used to calculate global left ventricular myocardial oxygen consumption and oxygen supply. Hemodilution alone increased aortic blood flow (+43%) but had no effect on aortic pressure, left atrial pressure, heart rate, or left ventricular dP/dtmax; an increase in myocardial blood flow (+130%) maintained oxygen supply and consumption at the baseline level. Adenosine-induced hypotension during hemodilution decreased heart rate (-35%), left ventricular dP/dt max (-28%), and aortic blood flow (-14%). These systemic responses were accompanied by reduced myocardial oxygen consumption (-29%) and increased myocardial blood flow (+54%) and myocardial oxygen supply (+72%). These latter effects resulted in reduction in the coronary arteriovenous oxygen content difference and in an attendant rise in coronary sinus Po2 (+66%), which are signs of luxuriant myocardial perfusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine↗
PubMed1985

Cardiac electrophysiologic effects of pancuronium.

A microelectrode examination of guinea pig left ventricular papillary muscle was performed to determine whether there was a direct effect of pancuronium on cardiac cells and, if so, to attempt to ascertain the mechanism of this effect. Electrical events were measured before and during superfusion with pancuronium, epinephrine, propranolol, and verapamil; alone and in various combinations. Pancuronium prolonged the duration of the action potential (AP); increased resting potential (Em), AP magnitude, and rate of rise of the AP (dV/dt); and resulted in spontaneity in 12% of the muscles. Epinephrine and pancuronium combined caused spontaneity in 80% of the muscles and oscillatory behavior. Additionally, this combination decreased AP magnitude, Em, and dV/dt in several preparations--a pattern of response similar to that seen in ouabain-treated myocardial cells under the influence of catecholamines. These changes were always reversed by verapamil or by perfusion with a drug-free medium, and were usually reversed by propranolol. The data suggest a combined pancuronium/epinephrine induced increase in cardiac membrane permeability to Ca2+.

Action Potentials↗
PubMed1981

Deliberate hypotension and anesthetic requirements of halothane.

Following determination of minimum alveolar anesthetic concentration (MAC) of halothane during normotension, 18 dogs were divided into three groups. Dogs in each group then received either pentolinium, trimethaphan, or sodium nitroprusside, and mean arterial pressure was decreased to 60% of control values for 1 hour. The MAC of halothane was determined during hypotension and then arterial pressure was returned to control values and MAC was redetermined at normotension. The MAC of halothane decreased significantly during hypotension in all three groups: in the pentolinium group from a control MAC of 1.2 +/- 0.14 (SEM) to a MAC of 0.7 +/- 0.11 during hypotension, in the trimethaphan group from a control MAC of 1.02 +/- 0.06 to a MAC of 0.72 +/- 0.07 during hypotension, and in the nitroprusside group from a control MAC of 1.02 +/- 0.07 to a MAC of 0.73 +/- 0.07 during hypotension. Upon return of mean arterial pressure to normotensive levels, MAC of halothane returned to control values in dogs given pentolinium and trimethaphan, but in dogs given nitroprusside MAC remained at the hypotensive value. There was no correlation between the changes in MAC and carotid blood flow or cardiac index. These data indicate that anesthetic requirements decrease during deliberate hypotension irrespective of the drug used to produce hypotension.

Anesthesia, Inhalation↗
PubMed1980

Anesthetic care of pediatric surgical patients.

Some technical aspects of intraoperative anesthetic care of pediatric surgical patients are discussed. Recent concepts of premedicant, anesthetic and muscle relaxant drugs as related to the pediatric patient are presented. Endotracheal intubation is an integral part of the pediatric anesthetic management. Adequacy of fluid and blood replacement is emphasized. Most current pediatric anesthetic systems incorporate the "T piece" principle. Maintenance of a near normal PaCO2 could be accomplished by allowing partial rebreathing during controlled ventilation. Current status of three useful techniques is presented: deliberate hypotension, hemodilution, and the rapid induction-intubation technique for children with a full stomach. Anesthetic considerations of special problems, such as neurosurgery or cardiac surgery and monitoring, are not discussed.

Anesthesia↗
PubMed1978

Haemodynamic responses to induced arterial hypotension in children.

Cardiovascular measurements were made in 12 children in whom arterial hypotension was induced with pentolinium and halothane. Propranolol was given to five patients who exhibited tachycardia. Measurements were made at the following stages: before induction of hypotension, 5 min after the administration of pentolinium, when a "dry" opening field was obtained, at the time of maximum hypotension and when arterial pressure had returned to 90% of the control values. The decrease in arterial pressure 5 min after the administration of pentolinium was accompanied by tachycardia, but there was no significant change in cardiac index and the operative field was congested. A substantial decrease in cardiac output occurred when a "dry" field was obtained.

Adolescent↗