Oxygen transport

Oxygen transport - The major function of the heart, lungs and circulation is the provision of oxygen (and other nutrients) to the various organs and tissues of the body. During this process, carbon dioxide and other metabolic waste products are removed. The rate of supply and removal should match the specific metabolic requirements of the individual tissues. This requires adequate oxygen uptake in the lungs, global matching of delivery and consumption, and regional control of the circulation.

Oxygen transport of the Respiratory System

Oxygen transport Cycle Labeled Diagram

Failure to supply sufficient oxygen to meet the metabolic requirements of the tissues is the cardinal feature of circulatory failure or ‘shock’, and optimisation of tissue oxygen delivery and consumption is the goal of resuscitation. Atmospheric oxygen moves down a partial pressure gradient from air, through the respiratory tract, from alveoli to arterial blood and is then transported in the circulation to the capillary beds and cells, diffusing into the mitochondria and being utilised at cytochrome a 3 Clinically important points to note in the management of a critically ill patient are that:

The movement of oxygen from • the left ventricle o the systemic tissue capillaries is referred to as oxygen delivery (DO 2), and is the product of cardiac output (flow) and arterial oxygen content (CaO

2). The latter is calculated from CaO2 = Hb × arterial oxygen saturation of haemoglobin (SaO2) × 1.34. By increasing cardiac output, arterial oxygen saturation or haemoglobin concentration, DO 2 will be increased.

• The regional distribution of oxygen delivery is also vital. If skin and muscle receive high blood flows but the splanchnic bed does not, the gut will become hypoxic even if overall DO 2 is high.
• The movement of oxygen from tissue capillary to cell occurs by diffusion and depends on the gradient of oxygen partial pressures, diffusion distance and the ability of the cell to take up and use oxygen. Thus microcirculatory, tissue diffusion and cellular factors, as well as DO 2, influence the oxygen status of the cell.