Changes in the interstitial pH of dog myocardium in response to local ischemia, hypoxia, hyper- and hypocapnia, measured continuously by means of glass microelectrodes.

Abstract

In open-chest dogs the pH changes of the myocardial interstitium were measured during local ischemia, hypoxia, hyper- and hypocapnia. Microglasselectrodes (Corning 0150) were inserted into the wall of the left ventricle. Simultaneously we recorded the local myocardial blood flow, the arterial blood pressure, the heart rate and the expiratory CO2 concentration. Local ischemia was produced by transient occlusion of the left descending coronary artery. In the ischemic region a decrease in pH occurred after 15–30 sec, the magnitude of which depended on the occlusion time, and on the extent of the ischemic region. When the occlusion time was short, the maximum decrease in pH was found after the release of blood flow. Mean values varied from about 0.1 pH (1 min occlusion) to 0.65 pH (30 min occlusion). After fibrillation the pH fell by 1.2 units (mean value) below the initial level. Hypoxia (10% for 5–13 min) was accompanied by an increase in pH by 0.05–0.1 units. After 2–3 min the pH reached a steady state or decreased again. After ventilation with sufficient O2 concentration an acidotic overshoot occurred (0.03-0.1 pH). When shifts in the interstitial pH similar to those during ischemia and hypoxia were produced by varying the arterialpCO2, no comparable changes in local blood flow and in the other parameters could be observed.