Transient oxygen uptake during myocardial reactive hyperemia in the dog

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Abstract
Uptake of O2 during myocardial hyperemia (MRH) following occlusions of 2.5-30 s was studied in 9 anesthetized open-chest dogs by continuous measurement of left anterior coronary blood flow and anterior coronary vein O2 saturation with electromagnetic flowmeter and fiber-optic catheters, respectively. The ratio of excess O2 uptake to debt multiplied by 100% was defined as the O2 repayment ratio (RR) and varied between -50% and +150% (mean 78%). Application of a steady-state Fick formula, results in a profound overestimate of the RR (70-400%, mean 295%). RR is severely distorted by the venous catheter system, and true RR in MRH is even lower than was found. Comparing these results with steady-state exercise autoregulation leads to the following conclusions: chemical kinetic limitations in O2 release by red blood cells are excluded; a simple direct PO2 of O2 regulation of flow is unlikely; these results are consistent with a more complex integral O2 regulation or with the metabolic hypothesis.

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