Criteria for adequate oxygenation of isometric kitten papillary muscle

Papillary muscles were taken from the right ventricles of hearts excised from chloroform-anesthetized kittens. Progressive 100-mmHg stepwise decreases in superfusate oxygen 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 tensions development, it was concluded that complete oxygenation of the entire muscle cross section was achieved when bath PO2 was maximal. Accordingly, adequate muscle oxygenation during 95% O2 aeration occurred when temperature, stimulation rate, and mean muscle diameter were, respectively, 1) 37 degrees C, 30 beats/min, and 0.89 +/- 0.06 mm; 2) 30 degrees C, 30 beats/min, and 0.94 +/- 0.02 mm; and 3) 30 degrees C, 12 beats/min, and 1.15 +/- 0.09 mm. On the other hand, adequate oxygenation at either 30 or 37 degrees C was not demonstrable when rate was 60 beats/min and muscle diameter exceeded 0.60 mm. We conclude that very low stimulation rates are required for oxygen sufficiency unless the papillary muscle is extremely thin.