The acidemia-induced rightward shift of the oxyhemoglobin dissociation curve does not increase further at a pH < 6.4, and is, at such extreme acidemia, less pronounced than calculated by the commonly used equations. To obtain optimal tissue oxygenation in patients with severe circulatory failure and extreme metabolic acidosis, Pao2 should be > 250 torr (> 33.3 kPa).
INOEBRIOTSEN, R. and S. LERAAND. Dilatation of a medium-sizcd artery immediately after local changes of blood pressure and flow as meaJured by ultrasonic terhnique. Acta physiol. scand. 1970. 79. 552-558. The effect of changes in blood pressure and flow on the calibre of the medium-sized artery has been studied in model experiments with an a-v fistula on the femoral vessels in dogs, On opening of the fistula a large local fall of blood pressure proximal to the fistula and an increase in flow up to 1000 74has been found. With the use of an ultrasonic technique for measurement of arterial diameter-by which it was possible to measure changes in the diameter in the order of 0.001 mm-we found an immediate increase, in the order of 10 %, in the diameter of the femoral artery on the opening of the a-v fistula. This increase remained as long as the fistula was patent. The results were identical in 5 dogs.The effect on the diameter of clamping the artery for some time, with consequent removal of the clamp, was examined in 5 dogs. Removal of the clamp itself resulted in only a small and temporary increase in the diameter of the artery. I t is concluded that the dilatation of the artery on opening of the fistula must be connected to the sudden increase in flow.
The myocardial potassium uptake during intracoronary isoproterenol stimulation was characterized in 12 anesthetized pigs. The beta-receptor subtype specificity and the effect of adenylate cyclase activation were determined. Potassium concentrations were continuously recorded by PVC-valinomycin minielectrodes in the left atrial cavity and in coronary sinus blood diverted through a shunt to the right atrium. The difference in potassium concentration between the left atrial cavity and coronary sinus, and the accumulated myocardial potassium uptake were calculated after computerized data sampling. By intracoronary drug infusion, changes in heart rate and systemic effects were minimized. Isoproterenol (0.6-0.8 microgram/min), a nonspecific beta-agonist, reduced coronary sinus potassium concentration transiently to a nadir of 0.28 (0.15-0.43) mM (median and 95% confidence interval) below control values (n = 12). The potassium uptake, which amounted to 140 (79-202) mumol/100 g tissue, corresponding to an intracellular potassium increase of about 3 mM, was abolished after selective beta 1-blockade by pafenolol. The specific beta 1-agonist dobutamine (40 micrograms/min) caused a similar potassium uptake before and after selective beta 2-blockade by ICI 118, 551. Salbutamol (2 micrograms/min), a specific beta 2-agonist, induced a minor potassium uptake of 4 (1-20) mumol/100 g, blocked by pafenolol. After nonselective beta-blockade by propranolol the adenylate cyclase stimulator forskolin caused a myocardial potassium uptake of similar magnitude to that of isoproterenol before beta-blockade. We conclude that a myocardial potassium uptake ensues during beta 1-adrenoceptor stimulation and adenylate cyclase activation.
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