Page 22, O2 Uptake, Exercise & Cor. Circ., Dr. D. Penney


Coronary Circulation (continued..):

Supplying oxygen to tissues and organs is a major function of the circulation and the reason that blood hemoglobin concentration is so high. Oxygen delivery, the total oxygen reaching a tissue, is a function of blood flow rate and oxygen content, where content is dependent upon percent saturation of the hemoglobin with oxygen, hemoglobin concentration, and maximal oxygen carriage per g of hemoglobin. Hemoglobin saturation in turn is a function of the hemoglobin-oxygen association-dissociation curve (ODC), a sigmoidal plot in which hemoglobin's affinity for oxygen is seen to vary widely as oxygen molecules attach/detach from the tetrameric molecule.

Hemoglobin concentration is a function of the activity of the hematopoietic system, normal values being 13-16 g/100 ml. Arterial blood is normally 96-98% saturated, but never 100% saturated. This is due to several factors:

  • shape of the ODC and particularly the low slope of the (upper) shoulder area of the curve
  • the pulmonary capillary PO2
  • the presence of methemoglobin and carboxyhemoglobin in the blood which do not carry oxygen, and
  • normal intra-pulmonary shunts.


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