NEWS: 20th May 2007
 
Oxygen Delivery

Oxygen delivery is a term used in medicine to describe the process of how oxygen is presented to the cells which need it for generating the energy which keeps us alive. If oxygen delivery is interrupted the cells will begin to suffer from lack of oxygen (known as hypoxia) and may, if the supply of oxygen is not restored, die.

The delivery of oxygen to cells can be thought of as consisting of two major components:

? The blood, which carries oxygen around the body attached to red blood cells within it.

? The heart, which pumps the blood through the circulatory system (the blood vessels) to where it is needed.

Blood is composed of many different types of cells suspended in a fluid component known as plasma. Of these cells the red blood cells are responsible for transporting oxygen, via molecules within them know as haemoglobin. As the red blood cells pass through the lungs they pick up oxygen and are then pumped towards their destination by the action of the heart. The amount of oxygen carried by the blood (known as its ?oxygen content?) depends primarily on two factors. How much oxygen is available in the air sacs of the lungs (the alveoli) for collection and how many red blood cells are circulating in the blood to carry it. As such, diseases of the lungs (e.g. pneumonia) and those which reduce the number of red blood cells (e.g. anaemia) will adversely affect oxygen delivery.

The pump for this system (the heart) must also be working effectively to ensure adequate oxygen delivery. Without the continuous action of the heart the oxygenated blood would not be transported to the tissues which require it. Heart failure and structural problems with the heart will lead to reduced oxygen delivery.

Oxygen delivery can be measured in critically ill hospital patients using complicated monitoring systems on the intensive care unit. It is possible to manipulate oxygen delivery in these patients in an attempt to improve their survival. The aim being to increase the amount of oxygen available to their tissues. Unfortunately this line of treatment is not always successful.

At high altitude oxygen delivery is reduced because of the reduced availability of oxygen in the air. Sudden exposure to extreme altitude would cause a dramatic and possibly fatal drop in oxygen delivery. However, slow exposure to altitude by gradual ascent allows adaptive processes to occur which are collectively known as acclimatisation. Our understanding of acclimatisation to date is that changes occur which together lead to an increase in oxygen delivery. For example we breathe harder and faster, our heart beats faster and the number of red blood cells increases. All of which restore a normal level of oxygen delivery to the tissues despite the lack of oxygen in the air.