The mass spectrometric measurement of intramural carbon dioxide tension to assess the efficacy of interventions to limit myocardial ischemic injury

In this study the influence of myocardial ischemia on intramural carbon dioxide tension (PmCO₂) was measured directly with the mass spectrometer in open-chest, anesthetized dogs with repetitive 10 minute coronary artery occlusions separated by 45 minutes of reflow. During each occlusion regional myocardial blood flow was measured by the Xenon washout technique. In all dogs, the rise in PmCO₂ (ΔPmCO₂) with the first artery occlusion was consistently greater than with the second occlusion. Subsequently, in the dogs not receiving an intervention (controls), ΔPmCO₂ with the third occlusion was unchanged from the second occlusion. When propranolol, hyaluronidase, or nitroglycerin were administered individually prior to the third occlusion, ΔPmCO₂ fell significantly from its value during the (control) second occlusion, and the combination of the three caused an even more marked decline in ΔPmCO₂. In contrast, isoproterenol infused during the third occlusion caused ΔPmCO₂ to rise significantly. Blood flow to the ischemic area increased with hyaluronidase and was unchanged in the other groups. Therefore, (1) the mass spectrometric measurement of PmCO₂ can be used to assess the efficacy of interventions to limit ischemic injury; (2) propranolol, hyaluronidase, and nitroglycerin given alone reduce the rise in PmCO₂ whereas isoproterenol increases it; and (3) the combination of propranolol, hyaluronidase, and nitroglycerin exerts a markedly beneficial effect on myocardial ischemic injury, as reflected by a drastic diminution in the rise of PmCO₂.