Criteria for adequate oxygenation of isometric kitten papillary muscle

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Abstract
Papillary muscles were taken from the right ventricles of hearts excised from chloroform-anesthetized kittens. Progressive 100-mmHg stepwise decreases in superfusate O2 partial pressure (PO2) from control (95% O2 aeration, PO2 620-650 mmHg) were produced, and subsequent changes in isometric active and resting tension were measured. If, under a given set of experimental conditions, the initial decrement in PO2 produced no decrease in active tension development, complete oxygenation of the entire muscle cross section was achieved when bath PO2 was maximal. Adequate muscle oxygenation during 95% O2 aeration occurred when temperature, stimulation rate and mean muscle diameter were, respectively, 37.degree. C, 30 beats/min and 0.89 .+-. 0.06 mm; 30.degree. C, 30 beats/min and 0.94 .+-. 0.02 mm; and 30.degree. C, 12 beats/min and 1.15 .+-. 0.09 mm. Adequate oxygenation at either 30.degree. or 37.degree. C was not demonstrable when rate was 60 beats/min and muscle diameter exceeded 0.60 mm. Very low stimulation rates are required for O2 sufficiency unless the papillary muscle is extremely thin.

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