Page 10, Architecture of the Circulation, Dr. D. Penney

Cardiac output distribution

As discussed earlier, skeletal muscle, abdominal viscera, and the kidneys each receive about 25% of the cardiac output at rest (Figure 7.05). The heart receives approximately 4% of cardiac output and brain about 3-fold more. The heart, however, accounts for 11% of whole body O2 consumption, producing a low coronary venous p02 (34 mmHg) and a large A-V O2 difference. This contrasts with the kidney which uses only 7% of the total O2 consumed, producing a higher renal vein pO2 (56 mmHg) and a small A-V 02 difference. The skin which is partially dead and is usually at lower than core body temperature is an even more extreme example of the pattern seen in the kidney.

Please note that venous 02 content can only be derived from venous p02 by making reference to the hemoglobin-oxygen association-dissociation curve, since the relationship between p02 and blood oxygen content (ml/dl) is non-linear.