Chapter-1 / Physiological Foundations - WHNLive Public Library

n respired again, the drop in respiration rateto the defici ncy phase being only approximately13 %. Th drop in the P02 level from6.5 to 1 mmHg (0.87 to 0.13 kPa) is directlyr f1 ted in the record in Fig. 102 below. In thearne figure above, the course of the pH in thebi arbonate-free Krebs-Ringer solution is reorded.The absolute values of respiration andfermentation of the myocardiac tissue arerelatively low, evidently as a result of celldamage due to the manipulations undertaken.De pite this, the remaining metabolism sufficesto allow us to see clearly in the solution, whichi kept buffer-free, the time-point of the pHreduction due to the start of ferm.mt.atiimetabolism. It can be seen from the recordi_in Fig. 102 that in the myocardiac t~'!IIUeamined, the sudden change to fermenta .metabolism occurs as soon as the P0 2 lew .the solution sinks to below 3.5 mmHg 0.46kPa). Roughly the same level is also fo d'other cell types. It can be deduced from thesudden transition to fermentation metabo'that even a relatively small improvement in eoxygen supply in the critical area of the tisis usually enough to bring about respirationmetabolism again, and thereby to eliminate thetissue over-acidification.1.4.5 Over-acidification of the tissueIn order to become better acquainted with theover-acidification by glycolysis (caused by 02deficiency), we chose as a model the myocardialtissue of the rat under simulation ofamyocardial infarction. The pH measurementswere implemented by P. G. Reitnauer in thesupply area of a coronary vessel, partiallyligated, with a movable pH glass electrode onthe beating rat heart [146].Wistar rats placed on a thermostatically controlledstage under ethyl urethane anesthesiawere tracheotomized, artificially respirated,thoracotomized and pericardiotomized. Theexposed, strongly beating heart seemed at firstto make measurement impossible, but wasbrought into a position as favorable as possiblefor the implementation of the ligature ormeasurement, by placing a nylon loop just alittle way below the surface of the outermostapex of the heart. A thread under a left ventricularcoronary branch was fed through themyocardium with a bent surgical needle, andmade into a loose loop, in order to trigger lateran experimental myocardial infarction. In orderto throttle the large vascular trunks, the hearthad to be turned upwards and the ligaturepositioned on its dorsal side. However, sinceit was difficult to manipulate the loop, nolying beneath the heart, during measurement,smaller vascular branches of the ventral side 0the left ventricle were also ligated according 0the individual shape of the coronaries. The"low-noise" pH measurement on the bearrat heart was made possible by very fmemicroelectrodes (Figs 103 and 104) [190 2which had been developed in our Institute formeasurements of the pH profIles of optimallover-acidified cancer micrometastases [189 192]. The largest diameter of the inserted part ofsuch an electrode was only approximatel200 JJ.m, so injuries critical to the heart fun ­tion were avoided. A miniaturized (Pt/Ag/AgCl/0.9 % NaCI in H 2 0) unit served as referenelectrode. For the measurement the referenand the indicator electrode were placed on theheart concentrically from both sides. fterfirm contact of the reference electrode with hsurface of the heart, there followed the in r­tion of the tip of the pH electrode in the upplarea of the coronary vessel branch prepared f rthe ligature, approximately 1 mm deep in hmyocardium. The position of the heartstabilized by the three point of contact apeloop, reference and pH electrode enoughFig. 03 Sch matic cross~tctiona pH micro lectrode