Hemoglobin and Oxygen Delivery: Understanding the Arterial-Venous Difference

The amount of blood transporter (haemoglobin) to muscle arterial oxygen difference is inversely proportional.

- When transporting oxygen from the lungs to the peripheral tissues, the primary function of haemoglobin is to optimise oxygen delivery in response to varying levels of tissue oxygen demand.

- The rate of oxygen delivery is determined by several factors, and it is inversely related to the arteriovenous difference in PO2.

- An increase in blood flow increases oxygen delivery but not necessarily the A-V difference.

- Conversely, a diminished cardiac output not only reduces oxygen delivery but also increases the arteriovenous difference in oxygen tension.

The content of oxygen in a given volume of blood is determined solely by the haemoglobin concentration and oxygen saturation.

- The oxygen saturation of haemoglobin is influenced by PaO2, temperature and pH.

- In normal conditions, haemoglobin is almost completely saturated at PaO2 levels above 8 kPa.

- However, small changes in PaO2 at relatively low levels have relatively greater impact on oxygen content than similar changes at higher levels of PaO2.

- The oxygen carrying capacity of blood may be markedly reduced by alterations in haemoglobin concentration, e.g. in anaemia, or when there is altered haemoglobin structure as seen in certain abnormal haemoglobins.