A spatial hierarchical framework for the co-management of ecosystems in Canada and the United States for the upper Great Lakes region.

Over the past three decades, considerable effort has been invested in the development of complex and comprehensive ecosystem classifications and inventories in many parts of North America. Paralleling this has been an evolution in those hierarchical frameworks guiding the development and application of classifications. However, resource management agencies continue to grapple with the dilemma of applying multiple classification and inventory templates over large jurisdictions, especially as they attempt to address ecosystem management objectives. Given that Canada and the United States share ecosystems and that commitments have been made by all levels of government to make progress towards ecosystem-based approaches to management, there is a need to provide the proper tools. Comprehensive goals will not be achieved without collaboration and cooperation.This paper outlines the range of ecosystem classification approaches that exist in the Upper Great Lakes region. Canadian and American national hierarchical frameworks are briefly examined. Specific information needs and tasks are outlined which must be followed, independent of national boundaries, for the successful integration of planning and monitoring programs for large regional ecosystems.A general model is proposed for the development and application of an integrated, multi-scale and bi-national ecosystem classification, inventory and information system. This approach would facilitate data sharing and communication across jurisdictional boundaries.

Left-ventricular unloading by transvalvular axial flow pumping in experimental cardiogenic shock and during regional myocardial ischemia.

The efficacy of the transfemoral left-ventricular assist device Hemopump (HP; 21 Fr outer diameter) was examined in experiments with adult sheep in two different models of cardiogenic shock (tachycardia shock; ischemia shock), and during ventricular fibrillation. During tachycardia (high frequency pacing-induced; n = 14), HP assist led to a significant increase in cardiac output (from 2.2 to 2.8 liters/min), mean aortic pressure (from 47.6 to 65.6 mmHg), and myocardial perfusion pressure (from 25.5 to 59.0 mmHg). Simultaneously, a normalization of body oxygen-uptake (from 1.4 to 2.5 ml/min.kg), a decrease in myocardial oxygen consumption (from 6.1 to 4.8 ml/min.100 g), and a normalization of myocardial lactate metabolism were observed during HP assist. During regional myocardial ischemia (PTCA balloon occlusion of the proximal LAD (3.5 min; n = 12), HP assist led to significant decrease in LV end-diastolic pressure (from 21.1 to 12.1 mmHg), and increase in diastolic aortic pressure (from 58 to 67 mmHg) resulting in significant increase in coronary perfusion pressure. In the early reperfusion period, myocardial release of both lactate and potassium was significantly lowered with HP assist. During ventricular fibrillation (induced by electrical stimulation; n = 9), HP flow rates decreased from 2.5 (after 10 min) to 2.1 liters/min (after 30 min). Mean aortic pressures simultaneously decreased from 64.0 to 54.6 mmHg. Perfusion conditions were sufficient for maintenance of aerobic myocardial metabolism, but were borderline for peripheral circulation. Our hemodynamic and metabolic data demonstrate beneficial effects of cardiac assist with the Hemopump 21 Fr in both tachycardia-induced severe cardiogenic shock and during acute regional myocardial ischemia.(ABSTRACT TRUNCATED AT 250 WORDS)

Efficiency of the left ventricle assist device Hemopump in cardiac fibrillation.

We have examined in sheep the efficiency of the Hemopump during ventricular fibrillation. Circulatory arrest was induced by electrical stimulation and maintained for 30 min. Haemodynamic measurements were recorded continuously and blood samples were taken before, during and after fibrillation to determine total body and myocardial metabolic activity. All hearts were defibrillated successfully after 30 min of fibrillation. During fibrillation, the Hemopump sustained a mean arterial pressure of about 60 mm Hg with a blood flow rate of about 2.3 litre min-1. These perfusion conditions were sufficient for maintenance of aerobic myocardial metabolism, but with a borderline circulatory supply to the total organism.

Protective effects of the Hemopump left ventricular assist device in experimental cardiogenic shock.

The efficacy of the new cable-driven rotating left ventricular assist device Hemopump in cardiogenic shock was examined in experiments with adult sheep (n = 14; body weight 50-71 kg). Shock was induced by high frequency ventricular pacing. Aortic, pulmonary, central venous and left ventricular pressures as well as electromagnetic measurements of coronary blood flow were recorded continuously; cardiac output was measured by thermodilution technique. Blood samples for determination of oxygen content, electrolytes and lactate were taken under control conditions, in shock, and during pump intervention at different levels of pump speed. Vascular resistance, total body and myocardial oxygen consumption as well as myocardial uptake and release of lactate were calculated. High frequency pacing led to a significant decrease in cardiac output (from 3.8 +/- 0.8 to 2.2 +/- 1.6 l/min), mean aortic pressure (89.1 +/- 14.4 to 47.6 +/- 7.2 mmHg), and total body oxygen consumption (2.6 +/- 0.3 to 1.4 +/- 0.7 ml/min per kg), as well as myocardial release of lactate (arterial coronary-venous difference of lactate: 0.27 +/- 0.26 to -0.32 +/- 0.72 mmol/l). Hemopump assist in this condition resulted in a significant increase in cardiac output (to 2.8 +/- 0.6 l/min), mean aortic pressure (to 65.6 +/- 13.9 mmHg), and myocardial perfusion pressure (from 25.5 +/- 11.0 to 59.0 +/- 14.7), and led to nearly normal total body oxygen consumption (2.5 +/- 0.7 ml/min per kg), a decrease in myocardial oxygen consumption (from 6.1 +/- 2.1 in shock, to 4.8 +/- 1.7 ml/min per 100 g), and to normal arterial coronary-venous difference of lactate (0.24 +/- 0.26 mmol/l).(ABSTRACT TRUNCATED AT 250 WORDS)

Myocardial support and protection during regional myocardial ischemia using the Hemopump assist device.

A study was designed to quantify the influence of the Hemopump on myocardial metabolism in regional myocardial ischemias induced by repetitive balloon-occlusions (3.5 minutes) of the LAD in 12 sheep (b.w. 49-61 kg). In order to make immediate comparisons and obtain paired-couples, ischemias were carried out with and without the Hemopump in operation. An energetic unloading of the left ventricle was achieved by the Hemopump already under preocclusion conditions, reducing myocardial O2-consumption from 7.52 to 5.98 ml/min/100 g LV (= 20%) as well as lowering the LVEDP from 13.3 to 9.8 mmHg (p less than or equal to 0.01). During ischemia a clear increase of LVEDP (13.3 to 21.0 mmHg) occurs, which was prevented in the group with Hemopump-assist (9.8 to 12.1 mmHg). Combined with a sustained higher diastolic aortic pressure, a better myocardial perfusion pressure resulted. Energetic unloading and improvement of perfusion conditions might be the cause of the significantly lowered release of lactate and potassium. Due to theses fibrillation (n = 3) only occurred during occlusions without Hemopump-support. In summary, a significant reduction of the ischemic burden on the myocardium was found. Thus the Hemopump could be of benefit to patients who fail to be weaned from CPB or who are suffering from instable cardiovascular performance.

Transfemoral placement of the left ventricular assist device "Hemopump" during mechanical resuscitation.

The Hemopump is a new left-ventricular assist device (21 F diameter), which provides up to 3.5 L/min output after placement in the left ventricle via the femoral artery. We describe the first case in which the device was inserted during resuscitation. The patient developed untreatable sustained ventricular tachycardias/fibrillation 40 hours after coronary artery bypass grafting. After prolonged mechanical resuscitation (about 3 hours) as a last resort the Hemopump was inserted and rhythm and hemodynamics stabilized. In the following hours a decrease in aortic pressure pulsatility indicated, effective left ventricular support when the Hemopump was running. For short periods the patient had nonpulsatile aortic pressure wave forms, implying complete pump dependence. In this situation cardiac output was about 3.0 L/min, mean aortic pressure reached nearly 50 mmHg using high dosage of catecholamines. The patient remained pump-dependent and died due to untreatable ventricular fibrillation. There was no significant hemolysis during the 20 hours the Hemopump was running. Autopsy revealed no signs of thrombembolism, but intimal lesions of the A. iliaca and of the abdominal aorta with subsequent thrombus formation were demonstrated. In view of the experimentally proven benefit in cardiogenic shock and problems and risks caused by the insertion, future indications for clinical use of this new device are discussed.

Maximum myocardial oxygen transport during anemia and polycythemia in dogs.

The purpose of this study was to determine the effect of hematocrit changes on coronary pressure-flow relations during maximum vasodilation to define the relative importance of changes in hemoglobin concentration, blood viscosity, and perfusion pressure in determining maximum myocardial oxygen transport. An anemic group and a polycythemic group of dogs were studied under halothane anesthesia at the hematocrit extremes and after serial exchange transfusions to intermediate hematocrits. Circumflex pressure-flow relations were generated at each hematocrit during maximum pharmacological vasodilation (adenosine 20 micrograms X kg-1 X min-1 or chromonar 8 mg/kg). Maximal coronary vascular conductance (incremental conductance) decreased in an approximately linear fashion with increasing hematocrit. Maximum myocardial oxygen transport showed an "inverted U-shape" relation to hematocrit with the peak occurring at or slightly above normal hematocrit. Hemoglobin concentration, viscosity, and perfusion pressure were all found to be physiologically important determinants of maximal myocardial oxygen transport. Given normal perfusion pressure, arterial oxygen saturation, and myocardial oxygen extraction, we found that maximum myocardial oxygen delivery greatly exceeds the level necessary to supply basal myocardial oxygen needs at all hematocrits studied.

Effects of pressure gradients between branches of the left coronary artery on the pressure axis intercept and the shape of steady state circumflex pressure-flow relations in dogs.

When steady state pressure-flow relations are studied in the circumflex coronary artery, pressure gradients develop between it and other branches of the left coronary artery. To assess the effects of these pressure gradients, we compared the pressure axis intercept and shape of steady state circumflex pressure-flow relations in the presence and absence of gradients after autoregulation was abolished, both in the beating heart and during long diastoles in dogs. We used peripheral coronary pressures and radionuclide-labeled microspheres to assess arterial collateral flow. In the beating heart, interarterial pressure gradients reduced the curvature at low circumflex pressures, and overestimated the mean pressure axis intercept by 7.8 mm Hg (P less than 0.05). The results were similar for the pressure-flow relations derived during long diastoles. This overestimation exaggerates the difference between the pressure axis intercept and coronary sinus pressure. The peripheral coronary pressure and microsphere results indicate that these effects are mediated largely by arterial collateral flow.

Arterial and venous coronary pressure-flow relations in anesthetized dogs. Evidence for a vascular waterfall in epicardial coronary veins.

The coronary circulation of anesthetized dogs was tested for the presence of vascular waterfalls by manipulating coronary arterial and coronary venous pressures. The left main coronary artery and the coronary sinus were cannulated, and relationships between coronary artery pressure, coronary sinus pressure, and coronary flow were studied. Experiments were conducted during diastolic arrests, under steady state conditions, in the absence of autoregulation. Relations of coronary flow to coronary sinus pressure at constant coronary artery pressure were consistent with the presence of a vascular waterfall in the coronary sinus. When the great cardiac vein was cannulated, relations of great vein flow to great vein pressure at constant coronary artery pressure were consistent with the presence of a vascular waterfall in the great vein, indicating that waterfall behavior can occur in epicardial veins other than the coronary sinus. In dogs on right heart bypass, with the coronary sinus and great vein uncannulated, the relationship between right atrial pressure and coronary sinus pressure showed a waterfall pattern, indicating that the waterfall is not an artifact of venous cannulation. In the right heart bypass experiments, venous waterfall behavior was seen in beating hearts as well as during diastolic arrests. We conclude that a vascular waterfall is present in epicardial coronary veins which can significantly influence coronary blood flow.

Emergency intravenous access through the femoral vein.

A study was undertaken to assess the efficacy and safety of femoral venous catheterization for resuscitation of critically ill patients in the emergency department setting. From May 1982 to April 1983, 100 attempts were made at percutaneous insertion of a large-bore catheter into the femoral veins of patients presenting to our emergency department in cardiac arrest or requiring rapid fluid resuscitation. Eighty-nine attempts were successful. Insertion was generally considered easy, and flow rates were excellent. The only noted complications were four arterial punctures and one minor groin hematoma. This study suggests that short-term percutaneous catheterization of the femoral vein provides rapid, safe, and effective intravenous access.

Increased number of myocardial blood flow measurements with radionuclide-labeled microspheres.

We evaluated the use of a least-squares radionuclide separation technique to allow an increased number of myocardial blood flow measurements with radionuclide-labeled microspheres in dogs. Two sets of labeled microspheres were studied: a set of eight labeled with 125I, 153Gd, 57Co, 51Cr, 113Sn, 85Sr, 95Nb, and 46Sc; and a set of nine in which 125I and 46Sc were replaced with 114In, 54Mn, and 65Zn. For each microsphere label the nuclide activities determined by least-squares separation compared favorably with those actually added to in vitro samples containing a fixed amount of the other nuclides in the set. For the set of eight radionuclide-labeled microspheres, myocardial flow measurements made with the least-squares separation technique and the reference sample method were usually within 15% and almost all within 20% of direct measurements of coronary venous outflow in a right heart bypass preparation. Serial left atrial injections of 15-micron microspheres totaling 48 X 10(6) caused no significant changes in systemic hemodynamics, regional myocardial flows, or coronary pressure-flow relations, whether the coronary bed was autorelating or vasodilated with chromonar. We conclude that at least nine myocardial blood flow measurements can be made in dogs with acceptable accuracy and without evidence of dysfunction due to embolization of the coronary vascular bed. With appropriate validation, this method should be applicable to other organs and animal models as well.

Direct measurement of left ventricular interstitial adenosine.

Characterization of adenosine's role as a regulator of coronary blood flow requires accurate measurement of endogenous adenosine concentration in the left ventricular (LV) interstitial compartment. Existing techniques for determining adenosine in this compartment are indirect, requiring the acceptance of major assumptions before conclusions can be drawn. We describe a new technique utilizing a LV epicardial diffusion well that allows us to make rapid, direct measurement of LV interstitial adenosine concentration, avoiding many problems inherent in existing techniques. Our results show adenosine concentrations of 555 pmol/ml in resting anesthetized dogs, indicating a resting adenosine level well within the vasoactive range. Further experiments using intramyocardial bolus injections of methylene blue dye and [8-14C]adenosine indicate that the epicardial well receives adenosine from a transmural distribution of LV interstitium and not from epicardial sources only. The transmural interstitial adenosine is transported via small lymphatics to the epicardial surface of the heart where diffusion occurs into the epicardial well. We also examined diffusion characteristics of the parietal pericardial membrane and found that the rate constant of adenosine diffusion for this and the visceral pericardium are of the same order of magnitude, indicating that the extensively used standard pericardial superperfusate method probably underestimates cardiac interstitial adenosine concentration by 50% or more. The influence of the parietal pericardium adequately explains why our resting adenosine concentrations using the epicardial well are higher than those recently reported using the standard pericardial superperfusate method.

Intrauterine cardiothoracic surgery: the fetal lamb model.

We have developed fetal lamb models of congenital cardiothoracic lesions that have been allowed to progress through birth for physiological study. Simulated lesions, simulated repairs, actual lesions, and actual repairs have been performed in this model. Sixty-two fetal lambs comprised the study group, including 48 in which models were created and 14 controls. Models included pulmonary stenosis, aortic stenosis, and diaphragmatic hernia. Gestational age ranged from 90 to 120 days (0.6 of normal gestation). In each pregnant ewe, laparotomy and hysterotomy were performed under general anesthesia, with care taken to avoid placental vessels. The foreleg was exposed, the appropriate anterior chest wall was isolated, and a thoracotomy was done. Thoracic or cardiac procedures then were performed under controlled transplacental anesthesia and perfusion. Following completion of the procedure, the fetal thoracotomy was closed, sterile antibiotic solution was placed in the amniotic sac, and the hysterotomy and laparotomy were closed. Subsequently the fetus either was allowed to progress to birth and infant study or underwent subsequent intrauterine repair and then was allowed to progress to birth and neonatal study. This fetal lamb model provides reproducible anatomical and pathophysiological lesions to facilitate the development of techniques for repair of such lesions in early infancy. Further, it offers the potential for developing methods of intrauterine cardiothoracic surgical repair.