Each year there are over 30,000 heart operations in the United Kingdom. These are possible because of the development of an artificial heart-lung bypass machine.

During the operation, the machine takes over from the heart and continues to pump blood around the body. It also oxygenates the blood and removes waste carbon dioxide. It is not unusual for the heart to be stopped for several hours during major surgery with the patient being kept alive by a heart-lung bypass machine.

The machine takes de-oxygenated blood from the heart's right atrium. This drains into a reservoir and is then passed through an oxygenator. Here, it comes into contact with a series of thin, permeable membranes. These separate the blood from the oxygen and allow gas exchange to take place. Oxygen crosses the membrane by diffusion and enters the red blood cells. Carbon dioxide moves in the other direction and is removed.

The oxygenated blood is then pumped at high pressure back into the aorta to continue its journey around the body and keep all the cells supplied with oxygen.

A heart-lung bypass machine can be used for major operations but it could not be used to keep a patient alive who has a long-term lung problem or while their lungs are recovering from some form of damage. Also, an artificial ventilator will not be of any use if the patient's lungs are unable to take in the oxygen required.

To try and solve this problem, the University of Pittsburgh Medical Center, in the United States, is developing an artificial lung that can sit inside a blood vessel and oxygenate blood as it moves past a series of porous membrane tubes attached to an external oxygen supply.

Called the Intravenous Membrane Oxygenator (IMO), it is intended to treat patients with life-threatening lung problems. This could be due to some form of trauma or it could be used with patients who have lung infections like pneumonia. Their lungs cannot take in sufficient oxygen and the IMO is designed to add extra oxygen to the blood before it gets to the patient's lungs. In this way the damaged lungs are assisted until they are able to recover.