How to discriminate between hibernating and stunned myocardium.

AIM: The aim of the present study was to examine if it is possible to discriminate between hibernating and stunned myocardium in vivo by determining the ratio between diastolic and systolic coronary arterial inflow and by measuring oxygen saturation in draining coronary venous blood. METHODS: Experiments were performed in 32 open chest pigs anesthetized with sodium pentobarbital. In 11 pigs hibernation was induced in a part of the left ventricular myocardium by reducing flow in the mid-left anterior descending coronary artery (LAD) to about 60% of baseline flow. In 12 pigs stunning was induced by occluding mid-LAD twice for 10 min with a 30 min interval. In 9 pigs (control group) coronary flow was not manipulated. RESULTS: We found, at comparable degrees of regional dysfunction, that the ratio between diastolic and systolic flow in stunned myocardium remained unaltered, but fell from about 2 to 1 in hibernating myocardium. Furthermore, coronary venous oxygen saturation decreased from about 30% to 17% in blood draining hibernating myocardium, but remained statistically unaltered in blood draining stunned myocardium. CONCLUSION: We conclude that it is possible to discriminate between hibernating and stunned myocardium by measuring phasic coronary arterial blood flow and oxygen saturation in blood draining the region in question. During hibernation only, the diastolic flow component of coronary arterial inflow is reduced and the coronary venous oxygen extraction increased.

Cardiac fibrinolytic capacity is markedly increased after brief periods of local myocardial ischemia, but declines following successive periods in anesthetized pigs.

BACKGROUND: Fibrinolysis in blood is mainly reflected by the activities of tissue plasminogen activator (tPA) and of plasminogen activator inhibitor-1 (PAI-1). The effect of myocardial ischemia on their activities in the coronary circulation is, however, not established. OBJECTIVES: With an improved experimental model, we therefore examined the effect of a brief period of myocardial ischemia on their activities. Furthermore, the consequences of repeated periods of ischemia, mimicking the situations in patients with unstable angina, were investigated. METHODS: In six anesthetized pigs, we occluded the distal left anterior descending coronary artery (LAD) four times for 10 min with 40 min intervals and determined the activities of tPA and PAI-1 in arterial and coronary venous blood. By simultaneously recording LAD flow, we could estimate cardiac release of these factors at baseline conditions and during reperfusion. RESULTS: Neither net cardiac release of PAI-1 nor alterations in plasma PAI-1 levels were demonstrated during the experiment. However, a significant net release of tPA activity of 10.4 +/- 3.2 IU mL(-1) (P < 0.005) was recorded during baseline conditions. During reperfusion following the first period of ischemia, the cardiac release of tPA activity increased to a peak of 103 +/- 30-fold baseline release, but declined progressively after repeated periods of ischemia. After the fourth period, tPA release did not exceed an estimated baseline accumulation during ischemia and early reperfusion. CONCLUSIONS: In this porcine model, a substantial local increase in fibrinolytic capacity was observed after brief periods of ischemia, but declined subsequently by repeated periods of ischemia.

Coronary reactivity in the porcine heart after short lasting myocardial ischaemia: effects of duration of ischaemia and myocardial stunning.

STUDY OBJECTIVE: The aim was to characterise reactive hyperaemia and endothelium dependent (ADP) and independent (adenosine) vasodilatation after ischaemic periods of increasing duration, and in the stunned myocardium. DESIGN: The left anterior descending coronary artery was occluded 5-7 cm distal from its origin for consecutive periods of 2, 2, 5, 10, and 2 min separated by 30 min of reperfusion. Coronary flow was continuously measured by Doppler flowmetry proximal to the occlusion site. ADP and adenosine were infused into the left coronary artery proximal to the flowprobe. EXPERIMENTAL MATERIAL: 11 domestic pigs, weight 25-36 kg, were used. MEASUREMENTS AND MAIN RESULTS: In the stunned myocardium maximal reactive hyperaemia after 2 min of ischaemia was preserved, whereas all other variables describing reactive hyperaemia were diminished: time to maximal hyperaemia by 40% (p less than 0.01), duration of hyperaemia by 44% (p less than 0.001), volume of hyperaemia by 53% (p less than 0.001), and repayment of flow debt by 43% (p less than 0.001). The vasodilating effects of ADP and adenosine (dose-response curves) were not altered after development of stunning. CONCLUSIONS: Preserved maximal hyperaemia and vasodilation during ADP and adenosine infusion, but reduced volume of hyperaemia, indicate normal coronary reactivity but diminished release in the stunned myocardium of the vasodilator(s) responsible for the prolonged postischaemic flow increase.

Magnitude of myocardial potassium changes during acute alterations in pacing frequency in the in situ pig heart.

A transient loss of potassium from cardiac tissue during increments in stimulation frequency has been found in different isolated preparations, but there is no agreement as to the magnitude and time course of this loss. In the present study myocardial potassium balance was determined during changes in heart rate in pigs with an intact circulation. The left azygos vein, which drains into the coronary sinus in this species, was cannulated and a shuntline to the right atrium established. Coronary sinus blood was thus continuously drawn from the shunt by a pump, without admixture of systemic venous blood, and myocardial release and uptake of potassium were determined before, during, and after periods of pacing tachycardia. A transient mean(SEM) loss of potassium (13.0(5.6) mumol X 100 g-1 or about 0.25 mumol per beat change in heart rate) occurred during the first 90 s after increasing heart rate by a mean(SEM) of 53(4) beats X min-1. By discontinuing pacing heart rate returned to control values (mean(SEM) -43(7) beats X min-1), and myocardial potassium uptake ensued (mean(SEM) 9.8(3.3) mumol X 100 g-1 or 0.23 mumol per beat change in heart rate). The peak changes in coronary sinus potassium concentrations occurred 30 s after heart rate). The potassium lost during the periods of pacing tachycardia represented only about 0.2% of total myocardial potassium, equivalent to a reduction in intracellular potassium concentration of 0.3 mmol X litre-1. Since intracellular sodium and calcium concentrations are closely linked to the potassium concentration, the observed changes in potassium concentrations, although small, may be related to the positive inotropic effect of pacing tachycardia (the positive staircase phenomenon).

Relationship between ST-segment elevation and local tissue flow during myocardial ischaemia in dogs.

The relationship between electrocardiographic ST-segment changes and local tissue flow recorded from idential sites in the myocardium was determined by inserting platinum electrodes into the left ventricular wall of anaesthetized dogs. Local myocardial blood flow was measured during graded coronary constriction by recording tissue hydrogen desaturation rate. In the detection of ischaemic ST-segment elevation, intramural recordings proved to be more sensitive than corresponding epicardial recordings. Significant ST-segment elevation could only be detected by reducing local myocardial flow below 50% of control; by further reduction ST-segment elevation increased in proportion to the reduction in myocardial flow. Thus, significant myocardial ischaemia might exist without electrocardiographic alterations.

Reduced prostaglandin release from the stunned porcine heart--significance for attenuated reactive hyperaemia.

STUDY OBJECTIVE: Since both reactive hyperaemia and membrane phospholipids are altered even after short lasting ischaemic periods, the release of PGE2 and PGI2 in the basal state and during early reperfusion was examined to determine whether it was changed in the stunned myocardium. The effect of prostaglandin synthesis inhibition on reactive hyperaemia was also examined. DESIGN: The distal left anterior descending coronary artery was occluded for brief periods and coronary flow was recorded by Doppler flowmetry. In subgroups: (1) a shunt was established draining the ischaemic region for determination of myocardial prostaglandin release associated with 2 min of ischaemia before and after a 10 min occlusion; (2) prostaglandin synthesis was blocked between two 2 min occlusions by infusing indomethacin into the left anterior descending artery; and (3) segment lengths were measured in the left anterior descending artery region subjected to consecutive periods of 2, 10, and 2 min of ischaemia, and in a control region. EXPERIMENTAL MATERIAL: 21 pentobarbitone sodium anaesthetised pigs, weight 21-30 kg, were used. MEASUREMENTS AND MAIN RESULTS: 30 min after the 10 min occlusion, systolic shortening was reduced by 38(18-57)% (median +95% confidence interval; p less than 0.05). Concomitantly, basal PGE2 and PGI2 release was reduced by 69(30-77)% (p less than 0.05) and 58(7-81)% (p less than 0.05), respectively. During early reperfusion after 2 min of ischaemia, PGE2 release was reduced by 53(17-86)% (p less than 0.05) after development of stunning, whereas PGI2 release remained unaltered. Blockade of prostaglandin synthesis did not affect reactive hyperaemia either in normal or in stunned myocardium. CONCLUSIONS: Prostaglandin release from the stunned myocardium is reduced. Since indomethacin did not affect reactive hyperaemia, the attenuated PGE2 release during early reperfusion in stunned myocardium cannot explain the concomitant reduction in reactive hyperaemia.

Frequency dependent myocardial potassium fluxes during beta adrenergic stimulation of intact pig hearts.

STUDY OBJECTIVE: The aim was to determine the frequency dependent myocardial potassium fluxes of intact pig hearts at control inotropy and during beta adrenergic stimulation. DESIGN - Atrial pacing rate was suddenly raised and decreased by 50 beats.min-1 at control inotropy and during infusion of isoprenaline, 2.5 nmol.min-1, into the left coronary artery. EXPERIMENTAL MATERIAL: Nine anaesthetised pigs (21-33 kg) were instrumented for electric pacing of the right atrium and metabolic and haemodynamic recordings. MEASUREMENTS AND MAIN RESULTS: Myocardial potassium balance was measured by PVC-valinomycin electrodes in the left atrial cavity and in a shunt (with flow meter) diverting blood from the coronary sinus to the right atrium. Isoprenaline raised net myocardial potassium flux following the change in pacing rate from 19(14-23) to 38(32-46) mumol.100 g-1.min-1 (median, 95% confidence interval, difference: p = 0.03). The corresponding myocardial potassium flux per beat increased from 0.38(0.29-0.45) to 0.80(0.63-0.97) mumol.100 g-1 (p = 0.03). Accumulated potassium flux increased from 9(8-11) to 17(11-27) mumol.100 g-1, respectively (p = 0.03). CONCLUSIONS: In intact hearts beta adrenergic stimulation doubles the frequency dependent myocardial potassium flux. This component constitutes 22-25% of the ouabain inhibitable potassium flux at both levels of inotropy.

ATP gated potassium channels in acute myocardial hibernation and reperfusion.

OBJECTIVE: ATP gated potassium (KATP) channels and adenosine are of crucial importance in coronary blood flow regulation and activation of KATP channels and adenosine receptor stimulation protect against infarction and development of stunning. The aim of this study was to test the hypothesis that opening of KATP channels and adenosine receptor stimulation are involved in perfusion-contraction matching, in acute hibernation, and in recovery after reperfusion. METHODS: 30 isolated piglet hearts (2-10 d old) and 20 isolated rabbit hearts were studied. The isolated piglet hearts were perfused with modified Krebs Henseleit (KH) solution enriched by washed human red blood cells; the isolated rabbit hearts were perfused with modified KH buffer. The effects of the KATP channel opener aprikalim (1 microM), the KATP channel antagonist glibenclamide (30 microM), and the adenosine receptor antagonist 8-(p-sulphophenyl)theophylline (SPT, 300 microM) on 2 h of low flow (10%) ischaemia and 1 h reperfusion were compared with saline in the piglet hearts. The effects of aprikalim (1 microM), glibenclamide (30 microM), and saline during 90 min of low flow (10%) ischaemia followed by 1 h reperfusion were also examined in the isolated rabbit hearts. RESULTS: At constant coronary flow aprikalim reduced perfusion pressure from 53(SEM 5) to 25(1) mm Hg (p < 0.001) in piglet hearts and from 55(5) to 39(5) mm Hg (p < 0.05) in rabbit hearts. Glibenclamide increased perfusion pressure from 47(5) to 61(6) mm Hg (p < 0.01) in piglet hearts and from 45(4) to 81(5) mm Hg (p < 0.001) in rabbit hearts. SPT increased perfusion pressure from 55(6) to 67(6) mm Hg (p < 0.05) in piglet hearts. Left ventricular systolic pressure remained unchanged in both models. During stepwise reductions in coronary flow a parallel stepwise reduction in left ventricular systolic pressure was observed in all groups. At 2 h of low flow ischaemia systolic pressure was 39(4)%, 37(5)%, 41(4)%, and 37(3)% of control for hearts treated with saline aprikalim, glibenclamide, and SPT, respectively. During the low flow period systolic pressure and MVO2 stabilised. An almost identical pattern occurred in rabbit hearts. After 30 min of recovery of piglet hearts left ventricular systolic pressure increased to 78(5)% (saline), 74(5)% (aprikalim), 84(5)% (glibenclamide), and 77(4)% (SPT) of control. The recovery as percentage of control in rabbit hearts was 63(11) (saline), 69(8) (aprikalim) and 56(13) (glibenclamide). CONCLUSION: Coronary vascular tone is highly responsive to KATP channel modulation and adenosine receptor blockade. KATP channels do not modulate either perfusion-contraction matching or acute hibernation and functional recovery during reperfusion in the red blood cell perfused piglet heart or the crystalloid perfused rabbit hearts. Moreover, adenosine receptor antagonism does not affect these phenomena in piglet hearts.

Significance of right atrial function during right sided inotropic stimulation of pig hearts in situ.

Cardiac adjustments to inotropic stimulation of the right side of the heart were examined in anaesthetised, open chest pigs by calcium chloride infusion (80 mumol.min-1) into the right coronary artery. At stable haemodynamic conditions and at constant heart rate, right ventricular (RV) pre-ejection segment length increased by 4.6 (2.7-7.2) % (median, 95 % confidence interval) (p less than 0.01), RV end diastolic pressure rose from 5.3 (3.4-7.7) to 6.0 (3.6-8.8) mm Hg (p less than 0.05), and stroke volume rose by 6.8 (4.2-10.8) % (p less than 0.001). When the effect of right atrial contraction on RV filling was excluded by simultaneous pacing of atria and ventricles, the RV pre-ejection segment length no longer increased, and stroke volume rose by only 3.5 (0.1-9.5) % (p less than 0.05) during right side inotropic stimulation. Right atrial inotropic stimulation improves right ventricular filling, and may cause redistribution of blood from the systemic to the pulmonary circulation. This redistribution would raise the pulmonary vascular pressures, and thereby also improve left ventricular filling. The improved right ventricular filling partly accounts for the rise in RV output.

Cardiac adaptation to one hour of mild regional low flow ischaemia in the pig.

OBJECTIVE: The aim was to determine the cardiac consequences of a 1 h period of mild regional low flow ischaemia in the pig heart. METHODS: In eight pentobarbitone sodium anaesthetised pigs (weight range 23-38 kg), the mid left anterior descending coronary artery was constricted by a hydraulic occluder. Transmural coronary blood flow (Doppler flowmetry) was reduced to approximately 70% of control for 1 h. After complete release of the occluder cardiac function was monitored for 2 h. Left ventricular segment lengths were continuously recorded in the region subjected to low flow ischaemia and in a control region supplied by the circumflex artery. RESULTS: After 1 h with a 28(SEM 3)% reduction in coronary blood flow, the systolic shortening index decreased from 100 to 68(7) (p < 0.001). This index transiently normalised upon reperfusion. Thereafter it declined, reaching a nadir of 72(5) at 1.25 h of reperfusion, and subsequently improved to 82(6) at 2 h of reperfusion. CONCLUSIONS: Normalisation of local myocardial function appears during the first minutes of reperfusion after 1 h of mild low flow ischaemia and is followed by a period of stunning.

Release of endothelin from the porcine heart after short term coronary artery occlusion.

OBJECTIVE: Endothelin is increased in plasma following myocardial infarction. Whether brief periods of myocardial ischaemia not leading to myocardial infarction increase plasma endothelin is not known. Thus, the present study was designed to examine cardiac endothelin balance in association with a 10 min coronary artery occlusion followed by reperfusion. METHODS: Venous blood was selectively sampled from the transiently ischaemic myocardium using a shunt between the anterior interventricular vein and the right atrium in eight pentobarbitone anaesthetised pigs. Flow in the shunt was measured with a Doppler flow probe. Arterial blood was drawn from the aortic arch. Plasma endothelin was measured using an Endothelin 1-21 specific [125I] assay system. This assay system has no cross reactivity with big endothlin. RESULTS: A net cardiac endothelin uptake of 0.7(0.3-1.4) fmol.min-1 x g-1 (median, 95% confidence interval) in the control period shifted to a net release during the first 10 min of reperfusion. The release reached a maximum of 2.8(0.4-6.0) fmol.min-1 x g-1 after 1.5 min of reperfusion. Cardiac venous endothelin concentration increased from 3.4(2.5-4.8) to 4.4(3.6-6.9) and 4.4(3.6-6.6) fmol.ml-1 at 1.5 and 5 min of reperfusion, respectively (p < 0.001 for both). Arterial endothelin concentration decreased from 4.8(3.9-6.1) to 2.7(2.4-4.3) fmol.ml-1 at 10 min of reperfusion (p < 0.001). CONCLUSION: Endothelin is released from the heart for several minutes during reperfusion following a brief coronary artery occlusion.

Alterations in plasma endothelin during passage through the left heart chambers before and after brief myocardial ischaemia.

OBJECTIVE: Although the lung can both produce and extract endothelin, its role in regulating plasma endothelin is not settled. Whether the endocardium is able to affect plasma endothelin is also unknown. The first aim of this study was to examine if endothelin concentration in plasma changes when passing through the pulmonary circulation or the left heart chambers. A marked decrease in endothelin concentration has been shown to occur in the aortic arch during early reperfusion following a 10 min mid left anterior descending coronary artery occlusion. A second aim was therefore to investigate whether this decrease was due to removal of endothelin in the pulmonary circulation or through the left heart chambers. METHODS: In seven open chest, pentobarbitone anaesthetised pigs blood was obtained from the pulmonary artery, the left atrium, and the aortic arch at control conditions and at 10 and 20 min reperfusion following a 10 min coronary occlusion. Endothelin measurements were performed using an endothelin 1-21 specific [125I] assay system (RPA 555). RESULTS: At control conditions there was no difference in endothelin concentration in blood obtained from the pulmonary artery [3.9 (2.7-5.2) fmol.ml-1, median (95% confidence interval)] and the left atrium [3.8 (2.8-5.8) fmol.ml-1], whereas there was a significantly higher endothelin concentration in the aortic arch [4.9 (3.8-7.2) fmol.ml-1]. At 10 min reperfusion following the 10 min coronary occlusion there was still no difference in endothelin concentration between the pulmonary artery [4.3 (2.8-6.0) fmol.ml-1] and the left atrium [4.1 (2.7-5.7) fmol.ml-1]. However, in contrast to the increase observed before myocardial ischaemia, the endothelin concentration was significantly reduced in the aortic arch [2.8 (2.4-4.4) fmol.ml-1] compared to the left atrium. At 20 min reperfusion, all endothelin concentrations had returned to preischaemic values. CONCLUSIONS: These findings suggest a role for the left heart chambers in regulating the endothelin concentration in blood entering the aorta.

Free radical scavenging enzymes and G protein mediated receptor signalling systems in ischaemically preconditioned porcine myocardium.

OBJECTIVE: Increased antioxidant defence and altered G protein mediated receptor signalling systems could be expected in myocardial preconditioning. The myocardial antioxidant defence and the integrity of the G protein mediated receptor signalling systems were therefore examined in normal and preconditioned myocardium. METHODS: Preconditioning in the porcine heart was induced by two occlusions of the mid left anterior descending coronary artery for 10 min, with a 30 min reperfusion interval. Left ventricular biopsies were obtained from control and preconditioned regions 30 min after the last occlusion. RESULTS: In biopsies from the preconditioning region, neither the activities of superoxide dismutase of glutathione peroxidase, nor the content of malondialdehyde were changed. There were no alterations in either the number of receptors (beta adrenergic, muscarinic and endothelin receptors) or the amount of G proteins. Furthermore, the activity of adenylyl cyclase remained unchanged. CONCLUSIONS: No change in the antioxidant defence was demonstrated in preconditioned myocardium. This finding does not support the hypothesis that increased antioxidant defence could contribute to the cardioprotection of preconditioning. Additionally, an intact G protein mediated receptor signalling system was found in preconditioned myocardium with regard to beta adrenergic, muscarinic, and endothelin receptors.

Myocardial potassium uptake and catecholamine release during cardiac sympathetic nerve stimulation.

To determine whether sympathetic nerve stimulation induces a significant potassium uptake in the myocardium, the changes in myocardial potassium balance, catecholamine release, lactate uptake, and oxygen consumption were recorded in eight anaesthetised open chest pigs during electrical stimulation of the right intermediate cardiac nerve at 10 Hz. Potassium concentrations were continuously measured by polyvinylchloride valinomycin minielectrodes in arterial and coronary sinus blood. Potassium concentration in coronary sinus blood fell to a nadir 0.42(0.21-0.61) mmol.litre-1 below control values (median and 95% confidence interval) and resulted in a peak potassium uptake of 65(38-102) mumol.min-1 100 g-1 after 2.5(2.0-3.0) min, which correlated (r = 0.94, p less than 0.001) with cardiac noradrenaline release. Accumulated myocardial potassium uptake amounted to 139(82-241) mumol.100 g-1 when a stable potassium concentration difference between arterial and coronary sinus blood was reached after 5.5(4.25-6.50) min. Cardiac contractility (LV dP/dt), myocardial oxygen consumption, and lactate uptake rose from control to peak potassium uptake (p less than 0.001) by 140%, 158%, and 92% respectively. Coronary sinus blood noradrenaline and adrenaline concentrations rose significantly (p less than 0.01) from 58(44-87) pg.ml-1 at control to 2208(1159-5627) pg.ml-1 at peak uptake and from 15(11-19) pg.ml-1 to 85(64-230) pg.ml-1 respectively. Arterial noradrenaline increased from 29(19-41) pg.ml-1 to 374(176-640) pg.ml-1 and arterial adrenaline rose from 15(11-23) pg.ml-1 to 31(24-52) pg.ml-1 (p less than 0.001). It is concluded that sympathetic nerve stimulation induces a substantial myocardial potassium uptake in a dose dependent relation to cardiac noradrenaline release and alters the contractile and metabolic state of the heart substantially with only minor changes in arterial catecholamine concentration.

Oxygen free radical injury and Gs mediated signal transduction in the stunned porcine myocardium.

OBJECTIVE: The aim was to investigate involvement of oxygen free radicals and any changes in the Gs mediated beta adrenergic signalling system of stunned porcine myocardium. METHODS: Myocardial stunning was induced in eight pentobarbitone anaesthetised pigs by brief occlusions of the distal left anterior descending coronary artery for periods of up to 10 min. Segment length function was measured in the ischaemic region and in a control region supplied by the circumflex artery. Left ventricular biopsies were obtained from the two regions 1 h after the last occlusion for ultrastructural and biochemical studies. Timolol has been used to prevent arrhythmia during ischaemia. RESULTS: At the time when biopsies were obtained, percent systolic shortening was reduced to 58% in the region subjected to ischaemia and was only minimally reduced in the control region. In the biopsies from the stunned region: (1) electron microscopy showed mild and reversible intracellular changes in the stunned myocardium; (2) the activities of superoxide dismutase and glutathione peroxidase were decreased by 66% and 52%, respectively; (3) the content of malondialdehyde was increased by 49%; (4) neither density nor affinity of beta adrenoceptors showed any changes; (5) there were no alterations in messenger RNA encoding for the alpha subunit of the stimulatory guanine nucleotide binding protein (Gs), demonstrated by northern and dot-blot hybridisations; (6) ELISA technique utilising a specific antipeptide antibody showed no quantitative change in Gs; (7) the activity of adenyl cyclase was unchanged. CONCLUSIONS: Even though the stunned porcine myocardium showed substantial evidence of free radical injury, the beta adrenergic signalling system was intact.

Endotoxemia alters splanchnic capacitance.

The splanchnic circulation constitutes a major portion of the total capacitance vasculature and may affect venous return and subsequently cardiac output during low output states. This study assessed the effects of rapid (10 microg/kg over 5 min) and slow (10 microg/kg over 60 min) induction of endotoxin (Escherichia coli) shock on splanchnic blood volume in 8 farm swine. Blood volume was measured by using Tc99m-labeled erythrocytes and radionuclide imaging. Baseline arterial pressure (MAP), central venous pressure (CVP), and liver, splenic, mesenteric and total splanchnic volumes were stable during the 30-min baseline. Approximately 30 min after the rapid endotoxin infusion, splenic volume decreased by 45%, whereas liver volume increased by 40% and MAP decreased by 60% (P < 0.01). The reduction in splenic volume occurred within 10 min of the endotoxin infusion, whereas liver volume changes occurred after MAP reduction. The slow endotoxin infusion also reduced splenic volume by approximately 50% (P = 0.05), whereas MAP declined by 30% (P < 0.05). However, the slow endotoxin infusion lowered liver volume (P < 0.05). Mesenteric volume was unaffected by the fast or slow endotoxin infusion. Total splanchnic volume was unaffected by the fast infusion but decreased by 37% in the slow infusion group (P < 0.05). In summary, E. coli endotoxin reduces splenic blood volume and increases liver blood volume after acute hypotension ensues. Endotoxin does not increase total splanchnic blood volume and may actually decrease total splanchnic volume in the absence of circulatory collapse. This endotoxin shock model is not associated with blood volume pooling in the splanchnic capacitance circulation.

Echocardiographic criteria for detection of postinfarction congestive heart failure in rats.

We evaluated postinfarction myocardial function in rats and determined echocardiographic criteria for congestive heart failure (CHF) using high performance echocardiography. Extensive myocardial infarction (MI) was induced in rats by left coronary occlusion. Sham-operated animals served as controls. Five weeks later, high-frame rate ( approximately 200 Hz), fully digitized, shallow-focus (10-25 mm), two-dimensional, M-mode and Doppler echocardiography was performed. A J-tree cluster analysis was performed using parameters indicative of CHF. Reproducibility was examined. The cluster analysis joined the animals into one Sham and two MI clusters. One of the MI clusters had clinical characteristics of CHF and elevated left ventricular end diastolic pressure. Among the echocardiographic variables, only posterior wall shortening velocity separated the failing and nonfailing MI clusters. We conclude that, by high frame rate echocardiography, it is possible to obtain high- quality recordings in rats. It is feasible to distinguish MI rats with CHF due to myocardial dysfunction from those without failure and to perform longitudinal studies on myocardial function.

A new approach to normalize myocardial temperature in the open-chest pig model.

To prevent unphysiological temperature fluctuations in the myocardium in the open-chest model, we constructed a thermocage. Five pigs under pentobarbital sodium anesthesia underwent repetitive left anterior descending (LAD) coronary artery occlusions. Myocardial temperature was measured without any thoracic temperature-controlling device and in the presence of either a heating lamp or the thermocage. Without any thoracic temperature-controlling device, the temperature at 5-mm myocardial depth was 1.28 +/- 0.33 degrees C below the intra-abdominal temperature (P < 0.05). During a proximal 5-min LAD occlusion, myocardial temperature decreased by 1.86 +/- 1.02 degrees C in the ischemic area (P < 0.05). Both the heating lamp and the thermocage abolished the difference between intra-abdominal and myocardial temperatures and prevented the decrease in myocardial temperature during ischemia. Only the thermocage minimized myocardial temperature fluctuations due to air currents and prevented epicardial exsiccation. We conclude that either a thermocage or a heating lamp may be used to normalize myocardial temperature in the open-chest pig model. However, the thermocage is superior to the lamp in minimizing temperature fluctuations and preventing epicardial exsiccation.

Simultaneous active compression-decompression and abdominal binding increase carotid blood flow additively during cardiopulmonary resuscitation (CPR) in pigs.

The effects of adding active compression-decompression and abdominal binding separately or combined to standard compression CPR was tested in a randomized cross-over design during ventricular fibrillation in eight pigs. The flow and pressure effects of the two techniques appeared to be additive with no interference between the two. Carotid blood flow increased 22% with active compression-decompression, 34% with abdominal binding and 59% with the combination compared to flow with standard compression. Peak antegrade carotid flow occurred in early systole with retrograde flow in early diastole and close to zero in late diastole with no profound alterations induced by active decompression or abdominal binding. Abdominal binding increased the intrathoracic pressure during the compression phase as estimated from the esophageal pressure, while active decompression caused a negative esophageal pressure during the decompression phase. Neither active decompression nor abdominal binding caused any changes in the coronary perfusion pressure, nor in the left ventricular transmural pressure except for a rise in mid-diastolic pressure with active decompression.

Effect of different compression--decompression cycles on haemodynamics during ACD-CPR in pigs.

The haemodynamic effects of variations in the relative duration of the compression and active decompression (4 cm/2 cm) during active compression-decompression cardiopulmonary resuscitation (ACD-CPR), 30/70, 50/50 and 70/30, were tested in a randomized cross-over design during ventricular fibrillation in seven anaesthetized pigs (17-23 kg) using an automatic hydraulic chest compression-decompression device. Duty cycles of 50/50 and 70/30 gave significantly higher values than 30/70 for mean carotid blood flow (32 and 36 vs. 21 ml min-1, transit time flow probe, cerebral blood flow (30 and 34 vs. 19, radionuclide microspheres), mean aortic pressure (35 and 41 vs. 29 mmHg) and mean right atrial pressure (24 and 33 vs. 16 mmHg). A higher mean aortic, mean right atrial and mean left ventricular pressure for 70/30 were the only significant differences between 50/50 and 70/30. There were no differences in myocardial blood flow (radionuclide microspheres) or coronary perfusion pressure (CPP, aortic-right atrial pressure) between the three different duty cycles. CPP was positive in both the early and late compression period and during the whole decompression period. The expired CO2 was significantly higher with 70/30 than 30/70 during the compression phase of ACD-CPR. Beyond that no significant differences in the expired CO2 levels were observed. In conclusion a reduction of the compression period to 30% during ACD-CPR reduced the cerebral circulation, the mean aortic and right atrial pressures with no effect on the myocardial blood flow of varying the compression-decompression cycle.