Oxygen consumption in subepicardial and subendocardial regions of the canine left ventricle. The effect of experimental acute valvular aortic stenosis.

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Abstract
Moderate and severe levels of experimental valvular aortic stenosis (VAS) were produced in anesthetized, open-chest dogs to determine the effects of VAS on subepicardial (EPI) and subendocardial (ENDO) blood flow, O2 extraction, and O2 consumption (MVO2). Regional flow was determined by microspheres, and O2 saturation and extraction were analyzed by a three-wavelength absorbance microspectrophotometric method. Left ventricular pressure-volume work increased by 49% in moderate and 135% in severe VAS. The ENDO:EPI flow ratio averaged 1.21 +/- 0.09 in controls and decreased to 0.90 +/- 0.16 in moderate and 0.89 +/- 0.09 in severe VAS, and coronary flow increased by 40% and 58%, respectively. O2 extraction increased with both moderate and severe VAS, with extraction being higher in the ENDO than the EPI. MVO2 increased more in severe VAS than in moderate VAS. The ENDO:EPI MVO2 ratios fell to 1.10 (moderate) and to 0.84 (severe) from 1.44 in controls. We conclude that the O2 supply and consequently the MVO2 became limited in the ENDO relative to that in the EPI by simultaneous limitation of the O2 extraction reserve and the blood flow to this region during the increased O2 requirements imposed by experimentally induced VAS.