Myoglobin oxygenation remains constant during the cardiac cycle

Oxygen saturation of myoglobin (Mb) during the cardiac cycle was recorded spectrophotometrically by incorporating fiber optics in the isolated rat heart perfused using the Langendorff procedure. Oxygen saturation of Mb was continuously measured from absorbancy increments at 581-592 nm of transmitted light through the left ventricular free wall. In addition, quantification in the Mb oxygen saturation induced by the change of wall thickness during cardiac cycle was assessed from the absorbance change at 568-592 nm, namely, dual wavelengths of two isosbestic points. The results show that to obtain actual Mb oxygen saturation the absorbance change induced by the change in the wall thickness has to be subtracted from the absorbance change of 581-592 nm and that the Mb oxygen saturation in a steady state determines the amount of subtraction. On the basis of these procedures, it was found that the myocardial Mb oxygen saturation and hence myocardial oxygen tension during pulsation in aerobic and anaerobic steady state did not vary during the cardiac cycle.