NMR determination of myocardial pH in vivo: separation of tissue inorganic phosphate from blood 2,3-DPG

Myocardial infarction in a canine model monitored by two-dimensional 31P chemical shift spectroscopic imaging

We have developed a closed chest animal model that allows noninvasive monitoring of cardiac high energy phosphate metabolism before, during, and for at least 3 weeks after a myocardial infarction. Ten beagles underwent 2 h of coronary occlusion followed by 3 weeks of reperfusion. Myocardial high energy phosphates from 12-ml voxels were noninvasively tracked using 31P two-dimensional chemical shift imaging. Gadolinium enhanced 1H MRI identified the zone at risk, and radioactive microspheres assessed regional blood flow and partition coefficients. Occlusion of the left anterior descending coronary artery produced infarcts that were 13.7+/-8.8% (mean+/-SD) of the left ventricular volume. Rapid changes in the phosphocreatine and inorganic phosphate levels were observed during occlusion, whereas adenosine triphosphate levels decreased more slowly. All metabolites recovered to base-line levels 2 weeks after occluder release. Multiple inorganic phosphate peaks in the infarct voxel spectra indicated that more than one metabolically compromised tissue zone developed during occlusion and reperfusion. Microsphere data indicating three distinct blood flow zones during ischemia and reperfusion (<0.3, 0.3-0.75, and >0.75 ml/min/g) supported the grouping of pH values into three distinct metabolic distributions.

Haemodynamic and metabolic effects in diabetic ketoacidosis in rats of treatment with sodium bicarbonate or a mixture of sodium bicarbonate and sodium carbonate

To examine factors determining the haemodynamic and metabolic responses to treatment of diabetic ketoacidosis with alkali, groups of anaesthetised and ventilated rats with either diabetic ketoacidosis (mean arterial pH 6.86-6.96, mean arterial blood pressure 63-67 mm Hg) or hypovolaemic shock due to blood withdrawal (mean pHa 7.25-7.27, mean arterial blood pressure 36-41 mm Hg) were treated with sodium chloride ('saline'), sodium bicarbonate or 'Carbicarb' (equimolar bicarbonate plus carbonate). In the diabetic ketoacidosis series, treatment with either alkali resulted in deterioration of mean arterial blood pressure and substantial elevation of blood lactate, despite a significant rise in myocardial intracellular pH determined by 31P-magnetic resonance spectroscopy. These effects were accompanied by falling trends in the ratios of myocardial phosphocreatine and ATP to inorganic phosphate. Erythrocyte 2,3-bisphosphoglycerate was virtually absent in animals with diabetic ketoacidosis of this severity and duration. In contrast, in shock due to blood withdrawal, infusion of saline or either alkali was accompanied by a transient elevation of mean arterial blood pressure and no significant change in the already elevated blood lactate; erythrocyte 2,3-bisphosphoglycerate was normal in these animals. The effect of alkalinization in rats with severe diabetic ketoacidosis was consistent with myocardial hypoxia, due to the combination of very low initial erythrocyte 2,3-bisphosphoglycerate, alkali-exacerbated left shift of the haemoglobin-oxygen dissociation curve and artificial ventilation. No evidence was found for any beneficial effect of 'Carbicarb' in either series of animals; 'Carbicarb' and sodium bicarbonate could be deleterious in metabolic acidosis of more than short duration.

Magnetic resonance imaging and spectroscopy of the human heart

Magnetic resonance imaging and spectroscopy have a great potential both for clinical cardiac diagnostics and for research in cardiac physiology, metabolism and disease. At the present time, cardiac MRI already is the method of choice in several clinical conditions, especially in imaging central vasculature and intra- and paracardiac masses. With the recent development of contrast agents and ability to measure both flow velocities and flow volume, the cardiac MRI is likely to have a profound role in evaluating coronary arterial disease as well as valvular heart disease. The limitations due to long imaging times of cardiac MRI-studies are likely to be overcome with the development of ultrafast imaging techniques in the near future. On the other hand, cardiac MRS is still a research tool, which needs technical improvements before it can be widely utilized in clinical work. However, attempts to this aim are highly justified, when the possibility that MRS will provide metabolic information of the heart is considered and bearing in mind, that MR-magnets with sufficient field strength for MRS are increasingly in use in most modern hospitals. The role of magnetic resonance imaging (MRI) and spectroscopy (MRS) in the evaluation of heart diseases is still evolving. Some clear indications for clinical use of cardiac MRI have already become apparent, whereas cardiac MRS is still confined to research applications. The current paper consists of a review of the role of MRI for cardiovascular diagnosis together with a review of the currents status of cardiac MRS.