Exercise-induced changes of the extracellular and the venous K+ concentrations ([K+]e, [K+]ven) were measured continuously in autoperfused dog gastrocnemii using PVC liquid membrane electrodes. O2 consumption (VO2), blood flow and performance of the muscles were also determined. The muscles were stimulated indirectly and isotonic tetanic contractions (0.2 s) were produced every 0.7 s for more than 45 min. 1. [K+]e started to increase immediately after the onset of exercise and reached a maximal value of 7.4 meq/l after 4 min of exercise, thereafter it decreased, reaching 5.3 meq/1 at the end of the 12 min exercise. After 6 min of recovery [K+]e became lower than the control level. [K+]ven reached maximal values of 5.0 meq/l after 30 s of exercise and thereafter decreased slowly to 3.8 meq/l at the end of exercise. Thus, a K+ gradient of up to 3 meq/l was observed between the interstitial space and the venous blood. About 30 s after the end of exercise a net K+ uptake of up to 0.3 mu eq per min per g was observed. 2. The K+ loss of the muscle fibres reached maximal values of 1.5 mu eq per min per g at 1.5 min after the onset of exercise. Total K+ loss was 7% during 12 min of exercise and 12.5% of intracellular K+ during 45 min of exercise. 3. The changes of [K+]e correlated closely with performance and VO2 during exercise but not during recovery. On the other hand, blood flow correlated with the changes of [K+]e during both exercise and recovery. These results support the hypothesis that changes of [K+]e of the working muscle might be an important factor regulating exercise hyperemia.
Experimental studies were carried out in 11 anesthetized pigs in order to compare the sensitivity of left ventricular ejection phase parameters as determined by quantitative angiocardiographic methods, for detection of mild or moderate ventricular dysfunction. The experimental setup implied various degrees of nonadequate muscular hypertrophy in relation to chronic volume overload by aortic insufficiency. Left ventricular stroke volume, flow, ejection fraction and mean circumferential fiber shortening did not demonstrate impairment of ventricular function reserve when studied in the resting state of the circulation, but became indicative to some degree by their abnormal pattern of response to acute afterload stress (angiotensin infusion). Mean normalized systolic ejection rate as well as normalized values of systolic ejection time were found to be the most sensitive indices of ventricular function in this study.
In open chest dogs up to 8 side branches of the R, circumflexus and descendens were embraced and could selectively be occluded. With a new developed method local myocardial length changes in the ischemic areas, and with H+-sensitive minielectrodes the interstitial H+-activities were measured. All changes which were observed during the 3-30 min lasting coronary artery occlusions (H+-increases to about 500 neq/1, increases of diastolic length, decreases of the contraction amplitude, ST-elevations) returned to preocclusion levels during reperfusion. LVP and dp/dt remained unchanged during ischemia and reperfusion.
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