CO2 and coronary flow regulation.

These data indicate that the observed PCO2 change following an abrupt change in myocardial O2 consumption, occurs too slowly to participate in the initial adjustment in metabolic coronary flow change, which is essentially complete within 30 sec. Also, the magnitude of PCO2 response is insufficient to conclude that CO2 can provide the major cause of flow regulation. However, CO2 could act as a back-up regulator. These conclusions may be modified if further information becomes available.