J. Craig Hartman

Influence of desflurane, isoflurane and halothane on regional tissue perfusion in dogs

The actions of desflurane, isoflurane and halothane on regional tissue perfusion were studied using radioactive microspheres in dogs chronically instrumented for measurement of arterial and left ventricular pressure, global (left ventricular dP/dtmax) and regional (percent segment shortening) contractile function, and diastolic coronary blood flow velocity. Systemic and coronary haemodynamics and regional tissue perfusion were measured in the conscious state and during anaesthesia with equihypotensive concentrations of desflurane, isoflurane, and halothane. All three volatile anaesthetics (P < 0.05) increased heart rate and decreased mean arterial pressure, left ventricular systolic pressure, and left ventricular dP/dtmax Myocardial perfusion was unchanged in subendocardial, midmyocardial, andsubepicardial regions by the administration of either dose of desflurane. No redistribution of intramyocardial blood flow (endo/epi ratio) was observed during desflurane anaesthesia. Although regional myocardial perfusion was reduced (P < 0.05) in a doserelated fashion by halothane and by isoflurane at high concentrations, redistribution of intramyocardial blood flow was not observed during halothane or isoflurane anaesthesia. All three volatile anaesthetics reduced blood flow to the renal cortex, but only desflurane produced a decrease in renal cortical vascular resistance. Hepatic blood flow decreased in response to halothane but not desflurane or isoflurane. Concomitant decreases in hepatic resistance were observed during administration of desflurane and isoflurane. Doserelated decreases in intestinal and skeletal muscle blood flow were observed during halothane and isoflurane but not desflurane anaesthesia. The results suggest that desflurane maintains myocardial, hepatic, intestinal, and skeletal muscle blood flow while halothane and isoflurane decrease regional tissue perfusion in these vascular beds to varying degrees during systemic hypotension in the chronically instrumented dog.RésuméCe travail étudie les effets du desflurane, de l’isoflurane et de l’halothane sur la perfusion régionale à l’aide de microsphères radioactives sur des chiens préparés à demeure pour mesures itératives de la tension artérielle et ventriculaire gauche, de la contractilité globale (dP/dtmax ventriculaire gauche) et régionale (index de raccourcissement segmentaire) ainsi que de la vélocité du débit coronarien diastolique. L’hémodynamique systémique et coronaire et la perfusion régionale ont été mesurées à l’état de conscience et pendant l’anesthésie avec des concentrations hypotensives équivalentes de desflurane, d’isoflurane et d’halothane. Les trois agents (P < 0,05) ont augmenté la fréquence cardiaque et diminué la tension artérielle moyenne et le dP/dtmax ventriculaire gauche. La perfusion myocardique est demeurée inchangée aux régions subendocardique, midendocardique et subépicardique pendant l’administration de desflurane. On n’observe pas de redistribution du débit intramyocardique (rapport endo./épi.) pendant l’anesthésie au desflurane. Bien que la perfusion régionale soit réduite (P < 0,05) de façon proportionnelle pour les concentrations élevées d’isoflurane et d’halothane, la redistribution de débit sanguin myocardique n’est pas observée pendant l’anesthésie avec ces agents. Alors que les trois agents volatils diminuent le débit sanguin au cortex rénal, seul le desflurane en diminue la résistance vasculaire. Le débit sanguin hépatique diminue sous halothane mais non sous isoflurane et desflurane. Une diminution simultanée des résistances hépatiques survient pendant l’administration de desflurane et d’isoflurane. Des baisses de débit sanguin à l’intestin et aux muscles squelettiques proportionnelles à la concentration sont observées pendant l’anesthésie à l’halothane et l’isoflurane mais ne surviennent pas sous desflurane. Ces résultats suggèrent le maintien par le desflurane des débits sanguins myocardique, hépatique, intestinal et musculaire alors que l’halothane et l’isoflurane diminuent la perfusion tissulaire régionale de ces lits vasculaires à différents degrés pendant l’hypotension systémique chez le chien.

Reduction of myocardial infarct size by ramiprilat is independent of angiotensin II synthesis inhibition

The angiotensin-converting enzyme inhibitor ramiprilat, the angiotensin II receptor antagonist losartan, angiotensin II, ramiprilat plus angiotensin II, or saline (N = 6 each group), were administered i.v. in anesthetized, open-chest rabbit preparations of acute myocardial ischemia. Animals were instrumented for measurement of systemic hemodynamics and left ventricular +dP/dtmax, then subjected to 30 min of left anterior descending coronary artery occlusion (marginal branch) followed by 2 h of reperfusion. Ramiprilat (50 micrograms/kg), losartan (10 mg/kg), or saline were administered prior to reperfusion, and angiotensin II (2.5 ng/kg per min) was infused 15 min prior to occlusion and throughout the remainder of the experiment. Losartan was supplemented (10 mg/kg) after 1 h of reperfusion. These non-hypotensive doses of ramiprilat and losartan were demonstrated to significantly antagonize the systemic pressor effects of i.v. challenge with angiotensin I (15% of control, maximum) and II (5% of control, maximum), respectively, for the duration of the experiment. Systemic hemodynamic and +dP/dtmax changes due to occlusion/reperfusion or drug administration were similar between treatment groups. Infarct size was measured post-experimentally using tetrazolium staining and is reported as a percent of area at risk. Infarct size/area at risk (%) was significantly lower in rabbits administered ramiprilat only (20 +/- 6%*) or ramiprilat plus angiotensin II (26 +/- 5%*), compared to those receiving saline (41 +/- 6%), angiotensin II (51 +/- 4%), or losartan (52 +/- 4%, mean +/- S.E.M., * P < 0.05). These data indicate that direct angiotensin II receptor stimulation or receptor antagonism does not alter the degree of myocardial necrosis.(ABSTRACT TRUNCATED AT 250 WORDS)

The role of bradykinin and nitric oxide in the cardioprotective action of ACE inhibitors

BACKGROUND The angiotensin-converting enzyme inhibitor ramiprilat has been previously demonstrated to protect myocardium from ischemia/reperfusion injury. The objective of these investigations was to examine the roles of bradykinin, angiotensin II, and nitric oxide in the cardioprotective effects of ramiprilat. METHODS Anesthetized, open-chest rabbits were instrumented for production of myocardial ischemia (30 minutes) and subsequent reperfusion (120 minutes), after which myocardial infarct size was measured. Animals were treated intravenously with either saline solution, ramiprilat (50 micrograms/kg), the bradykinin2 receptor antagonist HOE 140 (1 microgram/kg), ramiprilat + HOE 140, angiotensin II (2.5 ng.kg-1.min-1), the angiotensin II receptor antagonist losartan (20 mg/kg), ramiprilat + angiotensin II, the nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester (100 micrograms.kg-1.min-1), or ramiprilat + NG-nitro-L-arginine methyl ester. RESULTS Among all treatment groups myocardial infarct size was reduced significantly below saline control only by ramiprilat (-54%) and ramiprilat + angiotensin II (-37%). Pretreatment with HOE 140 or NG-nitro-L-arginine methyl ester abolished the cardioprotective effect of ramiprilat. Neither stimulation nor antagonism of angiotensin II receptors altered infarct size from the saline control level. Also, when isolated neonatal rat cardiomyocytes were exposed to hypoxia/reoxygenation, ramiprilat (100 mumol/L) and bradykinin (10 nmol/L) improved cell viability (approximately 60%), and the protective effect of both agents was reversed by administration of HOE 140 (10 mumol/L). CONCLUSIONS These results indicate that the in vivo cardioprotective effect of ramiprilat can be abolished by antagonizing bradykinin receptors or inhibiting nitric oxide synthase, and that the effect is not related to angiotensin II receptor activity. The potential bradykinin-sparing property of ramiprilat may promote increased bradykinin-stimulated nitric oxide production leading to cardioprotection. Part of the cardioprotective effects of ramiprilat/bradykinin/nitric oxide may occur locally as demonstrated by the in vitro results using isolated cardiomyocytes.

In vivo validation of a transit-time ultrasonic volume flow meter.

The objective of this investigation was to validate a transit-time ultrasound blood flow metering system in vivo. Implanted chronically and acutely on the ascending aorta of the dog, the transit-time flow probe determined varying flow rates simultaneously with measurements made by the electromagnetic flow metering method. The transit-time technique was also compared to two methods in which blood was collected volumetrically by either graduated cylinder (ascending aorta/dog) or pump withdrawal (abdominal aorta/cat). Statistical analysis of the results provided evidence that the transit-time ultrasound method measured in vivo blood flow rate no differently than the electromagnetic or pump withdrawal techniques, however, transit-time determinations of blood volume were 10% below that indicated by graduated cylinder collection. With transit time represented on the y-axis, three linear regressions of all paired blood flow measurements were calculated yielding the following slopes (delta y/delta x) and regression coefficients (r), respectively: electromagnetic (1.00, 0.98), graduated cylinder (0.85, 0.93), and pump withdrawal (0.93, 1.00). The results validate the transit-time ultrasound system used in the present investigation as an accurate method capable of measuring blood flow in both acutely and chronically instrumented animal preparations.

Steal-prone coronary circulation in chronically instrumented dogs : isoflurane versus adenosine

The influence of isoflurane and adenosine on left ventricular myocardial blood flow was investigated in dogs chronically instrumented for measurement of systemic and coronary hemodynamics, regional myocardial contractile function (with ultrasonic sonomicrometers), and myocardial perfusion (by the radioactive microsphere method). An Ameroid constrictor was implanted on the left circumflex coronary artery to produce a progressive stenosis that gradually reduced vascular reserve of the distal perfusion territory. The depletion of reserve was evaluated by daily monitoring of the hyperemic response to adenosine. A stenosis of moderate severity was considered present when left circumflex reserve was attenuated by approximately 60-70%. During left circumflex stenosis development, the left anterior descending coronary artery was totally occluded for 2 min each hour eight times daily with a hydraulic occluder to stimulate coronary collateral development over a period of 9-13 days. Contractile dysfunction during and flow debt repayment after each brief occlusion were used to monitor coronary collateral development. After stenosis and collateral development had occurred, the left anterior descending coronary artery was permanently occluded to simulate a condition of multivessel coronary artery disease with enhanced collateral development. In separate groups of experiments, hemodynamics and myocardial perfusion were measured before and after administration of adenosine (0.54 and 1.08 mg/min) or isoflurane (1.1 and 1.9%, end-tidal) and in the presence of either agent during adjustment of diastolic aortic pressure and heart rate to control levels. Total left anterior descending coronary artery occlusion in the presence of a moderate left circumflex stenosis produced an increase in mean arterial and left ventricular end diastolic pressures. Isoflurane decreased arterial pressure, left ventricular systolic pressure, and positive rate of increase of left ventricular pressure (dP/dt50) without altering heart rate. Administration of the high concentration of isoflurane reduced blood flow in normal areas and in regions distal to the partial (from 1.05 +/- 0.10 to 0.76 +/- 0.11 ml.min-1.g-1) or total coronary occlusion (from 0.64 +/- 0.10 to 0.41 +/- 0.11 ml.min-1.g-1). However, when arterial pressure and heart rate were restored to levels present in the conscious state, perfusion in all zones was maintained at control levels (1.06 +/- 0.11 for the stenotic and 0.69 +/- 0.12 ml.min-1.g-1 for the occluded region). Ratios of transmural blood flow between occluded and normal or occluded and stenotic zones were not different from the conscious state during a constant aortic pressure and heart rate.(ABSTRACT TRUNCATED AT 400 WORDS)

Alterations in Collateral Blood Flow Produced by Isoflurane in a Chronically Instrumented Canine Model of Multivessel Coronary Artery Disease

The actions of isoflurane and adenosine on left ventricular myocardial perfusion during a total occlusion of the left anterior descending coronary artery and concomitant stenosis of the left circumflex coronary artery were investigated in dogs chronically instrumented for measurement of systemic and coronary hemodynamics, regional myocardial contractile function (via ultrasonic sonomicrometers), and myocardial blood flow (via the radioactive microsphere technique). An Ameroid constrictor was implanted on the left circumflex coronary artery to produce a slowly progressive stenosis that gradually depleted the coronary reserve of the distal vascular bed. The reductions in reserve were evaluated by daily measurement of baseline left circumflex coronary blood flow velocity and the hyperemic response to injection of adenosine. At a stage of moderate or severe left circumflex stenosis development, the left anterior descending coronary artery was totally occluded via a hydraulic occluder to simulate multivessel coronary artery disease, and control measurements of hemodynamics, regional contractile function, and myocardial blood flow were completed. In separate groups of experiments, either adenosine (0.64 and 1.28 mg/min) or isoflurane (1.6-1.8 and 2.3-2.5%, end-tidal) was administered and measurements remade during steady state hemodynamic conditions. Finally, diastolic aortic pressure and heart rate were adjusted to levels present in the control state during administration of adenosine or isoflurane, and additional measurements were recorded. Isoflurane reduced mean arterial pressure, left ventricular systolic pressure, and the rate of increase of left ventricular pressure at 50 mmHg (positive dP/dt50) without change in heart rate. Administration of isoflurane decreased blood flow in normal, stenotic, and occluded regions; however, when arterial pressure and heart rate were restored to levels present in the conscious state, myocardial perfusion in all regions was maintained at control levels. Ratios of flow between occluded and normal or stenotic zones remained unchanged from the conscious state during a constant aortic pressure and heart rate. Similar results were obtained in dogs with either a moderate or severe left circumflex coronary artery stenosis. In contrast, adenosine produced a dose-related decrease in collateral flow and occluded-to-normal or occluded-to-stenotic zone flow ratio. The results of this investigation indicate that adenosine but not isoflurane redistributes blood flow away from collateral-dependent myocardium to other regions in a chronically instrumented canine model of multivessel coronary artery disease.(ABSTRACT TRUNCATED AT 400 WORDS)

Ramiprilat attenuates hypoxia/reoxygenation injury to cardiac myocytes via a bradykinin-dependent mechanism.

Isolated rat neonatal cardiac myocytes were subjected to immersion in hypoxic (PO2 < 2 mm Hg), glucose-free Tyrodes solution for 5 h followed by concomitant reoxygenation and staining with the membrane-impermeant fluorophore, propidium iodide, in normoxic (PO2 > 150 mm Hg), serum-free culture media for 15 min in order to assess sarcolemmal damage indicative of myocyte viability due to hypoxia/reoxygenation injury. Prior to hypoxic exposure, cells were pretreated for 90 min with the angiotensin-converting enzyme inhibitor cyclopenta[b]pyrrole-2-carboxylic acid, 1-[2-[(1-carboxy-3-phenylpropyl)amino]-l-oxopropyl]octahydro-[2S-[1[R* (R*)]2 alpha, 3a beta, 6a beta]] (ramiprilat), concomitantly with ramiprilat and H-D-Arg-Arg-Pro-Hyp-Gly-Thi-Ser-D-Tic-Oic-Arg-OH (bradykinin B2 receptor antagonist HOE 140), the bioactive peptide Arg-Pro-Pro-Gly-Phe-Ser-Pro-Phe-Arg (bradykinin) or concomitantly with bradykinin and HOE 140. Hypoxia/reoxygenation injury to untreated control cardiac myocytes was characterized by a significant loss of sarcolemmal integrity measured at 75 +/- 4% of total cell fluorescence (mean +/- S.E., n = 42 cultures). Compared to propidium iodide staining of the above untreated control myocytes, those pretreated with 30 or 100 microM ramiprilat showed a significant reduction of propidium iodide staining to 45 +/- 9% and 40 +/- 8% (n = 9, P < 0.05) of untreated controls, respectively. Pretreatment with the protective concentrations of ramiprilat concomitant with 10 microM HOE 140 abolished the significant reduction in propidium iodide staining observed with ramiprilat alone. Similarly, pretreatment with 10 or 100 nM bradykinin significantly reduced propidium iodide staining to 35 +/- 5% and 60 +/- 10% (n = 6, P < 0.05) of the untreated hypoxic controls, respectively. In addition, concomitant pretreatment with protective concentrations of bradykinin and 10 microM HOE 140 also abolished the significant reduction in propidium iodide staining observed with bradykinin alone. The results indicate that the angiotensin-converting enzyme inhibitor ramiprilat has a protective effect on isolated cardiac myocytes exposed to hypoxia/reoxygenation and that this effect is most likely related to a local action of bradykinin on the cardiac myocyte via the activation of the kinin B2 receptor.Abstract Isolated rat neonatal cardiac myocytes were subjected to immersion in hypoxic (PO2 150 mm Hg), serum-free culture media for 15 min in order to assess sarcolemmal damage indicative of myocyte viability due to hypoxia/reoxygenation injury. Prior to hypoxic exposure, cells were pretreated for 90 min with the angiotensin-converting enzyme inhibitor cyclopenta[b]pyrrole-2-carboxylic acid, 1-[2-[(1-carboxy-3-phenylpropyl)amino]-1-oxopropyl]octahydro-[2S-[1[R∗(R∗)]2α,3aβ,6aβ]] (ramiprilat), concomitantly with ramiprilat and H- d -Arg-Arg-Pro-Hyp-Gly-Thi-Ser- d -Tic-Oic-Arg-OH (bradykinin B2 receptor antagonist HOE 140), the bioactive peptide Arg-Pro-Pro-Gly-Phe-Ser-Pro-Phe-Arg (bradykinin) or concomitantly with bradykinin and HOE 140. Hypoxia/reoxygenation injury to untreated control cardiac myocytes was characterized by a significant loss of sarcolemmal integrity measured at 75 ± 4% of total cell fluorescence (mean ± S.E., n = 42 cultures). Compared to propidium iodide staining of the above untreated control myocytes, those pretreated with 30 or 100 μM ramiprilat showed a significant reduction of propidium iodide staining to 45 ± 9% and 40 ± 8% (n = 9, P

Volatile anesthetics and regional myocardial perfusion in chronically instrumented dogs : halothane versus isoflurane in a single-vessel disease model with enhanced collateral development

The influence of halothane and isoflurane on regional myocardial blood flow was investigated in chronically instrumented dogs with a well developed coronary collateral circulation. Dogs were implanted with an Ameroid constrictor on the left anterior descending (LAD) coronary artery to produce slowly progressive coronary artery occlusion and collateral development. Contractile function in the collateral-dependent region was ascertained periodically during brief balloon cuff occlusion or during atrial pacing to characterize the degree of ongoing collateral development. Following documentation of enhanced collateral perfusion by the lack of contractile dysfunction during brief balloon cuff occlusion or atrial pacing at 50 days postimplantation, dogs were anesthetized (inhalation induction) with halothane (1.5% or 2.5%; n = 7) or isoflurane (2.0% or 3.0%; n = 8) using equihypotensive inspired concentrations of either agent. Radioactive microspheres were administered to measure regional myocardial perfusion during the conscious state and at stable hemodynamic states during both low and high concentrations of each volatile anesthetic. Myocardial blood flow during anesthesia was also determined following the adjustment of arterial pressure and heart rate to conscious levels by administration of phenylephrine and atrial pacing, respectively. Over the course of collateral development, balloon cuff-induced contractile dysfunction and pacing-induced contractile dysfunction in the collateral-dependent zone were reduced, indicating extensive collateral development. Halothane and isoflurane decreased global and regional indices of contractility and arterial pressure in a dose-dependent manner, but only isoflurane reduced coronary vascular resistance. Both anesthetics decreased myocardial perfusion within normal and collateral-dependent regions; however, flow was restored to levels found in the conscious state coincidental with control of arterial pressure and heart rate. Neither anesthetic alone, nor with concomitant control of arterial pressure and heart rate, produced a maldistribution of blood flow transmurally or between normal and collateral-dependent zones. The results suggest that both halothane and isoflurane, although decreasing major determinants of myocardial oxygen demand, do not unfavorably alter the regional distribution of coronary blood flow in a single-vessel disease model with enhanced collateral development.

Induction of cyclic flow reduction in the coronary, carotid, and femoral arteries of conscious, chronically instrumented dogs: A model for investigating the role of platelets in severely constricted arteries

Under sterile conditions, dogs were instrumented for continuous measurement of hemodynamics, and an Ameroid constrictor was positioned around either the left carotid, left femoral, or left anterior descending coronary artery to produce slowly progressive narrowing of the vessel. Cyclic flow reduction (CFR) developed in the carotid artery in seven of nine dogs on day 5.1 +/- 0.8 (mean +/- S.E.M.) at a frequency of 6.7 +/- 0.6 cycles per 30 min. This phenomenon was abolished for 30 +/- 5 and 45 +/- 15 min with intravenous administration of 50 and 100 micrograms/kg, respectively of the thromboxane receptor antagonist, BM 13.505, 4-[2-(4-chloro-benzene-sulfonamide)-ethyl]-benzene acetic acid. Total carotid artery occlusion occurred on day 7.9 +/- 0.8. CFR developed in the femoral artery in one of three dogs on day 4 at a frequency of 7 cycles per 30 min and was abolished for 82 min after BM 13.505 (50 micrograms/kg i.v.). The vessel became totally occluded on day 7. Finally, CFR developed in the left anterior descending coronary artery in three of five dogs on day 9.3 +/- 4.9 at a frequency of 6.2 +/- 0.9 cycles per 30 min. CFR was abolished for 37 min after BM 13.505 (50 micrograms/kg i.v.) and for several hours after an oral dose of aspirin (650 mg). Total coronary occlusion was observed on day 17.4 +/- 2.6. The present results demonstrate that CFR can be induced in various arteries in conscious, chronically instrumented dogs by slowly progressive narrowing via Ameroid constrictors. This phenomenon may serve as a model for transient ischemic attack, claudication, and unstable angina. Because the conscious state is maintained, drug interactions with anesthetics are avoided. The usefulness of inhibitors of platelet aggregation in this model documents the potential benefit of such compounds in various vascular disease states.

Actions of isoflurane on myocardial perfusion in chronically instrumented dogs with poor, moderate, or well-developed coronary collaterals

The influence of isoflurane on myocardial perfusion (determined by the radioactive microsphere technique) in normal regions and areas distal to a left anterior descending (LAD) coronary artery occlusion was evaluated in dogs that were chronically instrumented for measurement of systemic and coronary hemodynamics and had varying degrees of coronary collateral development. In 17 dogs, an Ameroid constrictor was implanted on the LAD coronary artery to produce a slowly progressive occlusion that stimulated development of the collateral circulation. Collateralization was allowed to progress in three groups of dogs to a poor (3 ± 1 days), moderate (19 ± 4 days), or well-developed (50 days) stage postsurgery. After the indicated period of time had elapsed, the LAD coronary artery was occluded (via Ameroid constrictor and/or balloon cuff occluder). Radioactive microspheres were administered during the conscious state and at 2% and 3% inspired concentrations of isoflurane. A fourth set of microspheres was injected at 3% isoflurane with heart rate and blood pressure adjusted to conscious levels. Isoflurane produced equivalent changes in systemic hemodynamics in all groups, including an increase in heart rate and decreases in arterial pressure and left ventricular peak positive dP/dt. Regional contractile function of normal myocardium was reduced by isoflurane in all groups. Isoflurane (3%) significantly decreased subepicardial, subendocardial, and transmural blood flow in normal and collateral-dependent regions in all groups. Myocardial perfusion returned to levels present in the conscious state when arterial pressure and heart rate were adjusted to those levels present prior to induction of anesthesia. Neither the left ventricular transmural distribution nor the collateral-dependent to normal zone flow ratio was altered from conscious levels by isoflurane in any group with or without changes in blood pressure and heart rate. The results indicate that isoflurane does not redistribute coronary blood flow from collateral-dependent to normal regions in a single-vessel coronary artery disease model. The actions of isoflurane are also independent of the degree of coronary collateral development.