Rate of Rise of Myocardial PCO2 during Early Myocardial Ischemia in the Dog

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We have investigated the rate of rise of myocardial Pco2(Pmco2) after coronary artery occlusion using a new method for this measurement. Previous studies of Pmcch have been limited by the slow response of the only available method, and no increase in Pmcoi prior to 3 minutes after occlusion has been found. We have implanted a miniature PcOj electrode, with a 63% response time of 14 seconds, into the left ventricle of 14 open-chest dogs. After abrupt coronary occlusion, Pmcoi began to rise in 13.6 ± 1.1 seconds in heparinized dogs and in 7.5 ± 0.7 seconds in unheparinized dogs. The subsequent magnitude of the increase in Pmco2was 24, 88, 171, and 222 mm Hg at 2, 5, 10, and 15 minutes after occlusion. The rate of rise of Pmco2was essentially linear from 1 minute to 10 minutes at a rate of 18.3 mm Hg/min. The rate of rise was slower during the first 30 seconds after occlusion (6.1 mm Hg/min) and also from 30 seconds to 1 minute (9.7 mm Hg/min). This rate of rise is much greater than that previously observed and reflects the severe myocardial acidosis developing during ischemia. A rise in Pmco, is one of the earliest metabolic changes that has been observed during myocardial ischemia. Ore Res 45:324-330, 1979

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