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Artificial lungs on the way—but don't hold your breath
THE LANCET
FEATURE
Artificial lungs on the way—but don’t hold your breath membrane lungs cannot be inserted ynical travellers have sometimes percutaneously and vessel cutdown is observed, “when in the developrequired. ing world, don’t drink the water; Intravascular membrane devices when in the developed world, don’t like the one designed at Pennsylvania breath the air”. Certainly, in many State University have several advandeveloped countries respiratory tages: because the catheter is inserted diseases are on the increase and directly into the bloodstream there is chronic lung disease is common. The no need for a pump to circulate the latter affects, in one form or another, blood through the device; lung resecan estimated 13 million Americans tion is not necessary; and the and causes about 75 000 US deaths patient’s skin and circulation need per year; in the UK about 4 million only be disturbed at one site to insert people are affected and the death rate the device, thus reducing the risk of is about 36 000 per year. For a patient with end-stage lung failure the only treatment currently available is lung transplantation. Although this operation is now relatively safe and successful, there are often problems in getting suitable donor organs and many people die while waiting in the queue. One solution to the organ shortage is to provide an alternative means of gas exchange. An ITAL fit for a pig (Keith Cook) Three strategies are being infection. Unfortunately, the largest considered: extracorporeal circuits, and most advanced model can intravascular gas-exchange, and exchange only about 40% of the intrathoracic lungs. basal adult metabolic requirement. In extracorporeal devices, gas One major problem with artificial exchange is achieved by use of small lungs that use microporous mempolypropylene micropororous fibres, branes as the gas-exchange surface is or a silicone rubber membrane—the that they can lose their ability to latter is best for longer-term use—or transfer gases within 4–6 hours of the a combination of the two materials. start of use. Consequently, various Extracorporeal membrane oxygenanew materials are being investigated tion and carbon dioxide removal, in an attempt to mimic as closely as however, require complicated circuits possible the gas-exchange function of and specialist medical and technical the human lung. In August last year, staff for patient monitoring. researchers at Tokyo Metropolitan Consequently researchers around the University, Japan, led by Prof Shoji world are investigating the possibility Nagaoka, reported the results of of designing implantable devices. experiments using a polyimide One type of implantable device is material with added fluorine. This the intravenous oyxgenator (IVOX), polymer is biocompatible and is suita device designed for insertion able for use in a small artificial lung straight into the blood stream. In that could be implanted. This polyFebruary last year, Michael Snider mer is 70 times better at exchanging and Kane High, scientists at oxygen than polydimethyl siloxane Pennsylvania State University which is widely used for long-term (Hershey, USA) described an artifiextracorporeal circulation; it is also cial lung of this type in which gas 100 times better at removing carbon exchange is achieved by use of a large dioxide. The use of this highly polynumber of microporous fibres merised film means that a machine extending in all directions from a only a few centimetres in size could catheter. The fibres are in contact exchange enough gas to support an with the lumen of the catheter which adult human being, an advance that contains one conduit to deliver 100% brings transplantable artificial lungs oxygen to the fibres and a second much closer to realisation. conduit to remove carbon dioxide. The latest advance in artificial This device can be readily adapted lungs was reported towards the end for percutaneous venous insertion of last year in the American Society of into the patient. By contrast, other Artificial Internal Organs Journal current designs of intravascular
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260
(1996; 42: 604–09) by a team of researchers at Northwestern University, Evanston, USA. The group is working on an artificial lung that can be implanted inside the chest cavity and attached directly to the pulmonary artery. Their device, called an implantable, intrathoracic artificial lung (ITAL), is intended to act as “transplant bridge” for patients awaiting lung transplantation and as a treatment for acute respiratory failure. At present, the Northwestern group have maintained lung function in a pig for 24 hours. The ITAL contains a bundle of microporous fibres that exchange oxygen for carbon dioxide. The oxygenated blood is then returned to the left atrium. It is also possible to adjust the device so that some blood continues through the impaired natural lungs. Keith Cook, a biomedical engineer and first author on the paper, explains that the new equipment offers a much higher delivery rate of oxygen and carbon dioxide than intravascular devices—the ITAL can supply the full gas-transfer requirements for a patient at rest. The ITAL is the first implanted device that has continued working for 24 h in an animal and, according to Robert Bartlett, professor of surgery at the University of Michigan, Ann Arbor, USA, a leading authority on artificial lungs, “This is an exceptional piece of work. This group are leading the pack right now”. But, Cook notes, “The major disadvantage is that ITAL is highly invasive, basically involving openchest surgery. It will probably be 5–10 years before we will see it in patients”. Another member of the research group, Lyle Mockros, professor of biomedical engineering, at Northwestern, is also concerned that it may be difficult to persuade a company to market ITAL commercially because of potential liability problems. However, in view of the extensive use of other invasive procedures in the USA, including the dramatic rise in the number of stenting procedures, the initial caution expressed by members of the Northwestern team may well be overcome, particularly if clinical testing is successful. David Jack
Vol 349 • January 25, 1997
FEATURE
Artificial lungs on the way—but don’t hold your breath membrane lungs cannot be inserted ynical travellers have sometimes percutaneously and vessel cutdown is observed, “when in the developrequired. ing world, don’t drink the water; Intravascular membrane devices when in the developed world, don’t like the one designed at Pennsylvania breath the air”. Certainly, in many State University have several advandeveloped countries respiratory tages: because the catheter is inserted diseases are on the increase and directly into the bloodstream there is chronic lung disease is common. The no need for a pump to circulate the latter affects, in one form or another, blood through the device; lung resecan estimated 13 million Americans tion is not necessary; and the and causes about 75 000 US deaths patient’s skin and circulation need per year; in the UK about 4 million only be disturbed at one site to insert people are affected and the death rate the device, thus reducing the risk of is about 36 000 per year. For a patient with end-stage lung failure the only treatment currently available is lung transplantation. Although this operation is now relatively safe and successful, there are often problems in getting suitable donor organs and many people die while waiting in the queue. One solution to the organ shortage is to provide an alternative means of gas exchange. An ITAL fit for a pig (Keith Cook) Three strategies are being infection. Unfortunately, the largest considered: extracorporeal circuits, and most advanced model can intravascular gas-exchange, and exchange only about 40% of the intrathoracic lungs. basal adult metabolic requirement. In extracorporeal devices, gas One major problem with artificial exchange is achieved by use of small lungs that use microporous mempolypropylene micropororous fibres, branes as the gas-exchange surface is or a silicone rubber membrane—the that they can lose their ability to latter is best for longer-term use—or transfer gases within 4–6 hours of the a combination of the two materials. start of use. Consequently, various Extracorporeal membrane oxygenanew materials are being investigated tion and carbon dioxide removal, in an attempt to mimic as closely as however, require complicated circuits possible the gas-exchange function of and specialist medical and technical the human lung. In August last year, staff for patient monitoring. researchers at Tokyo Metropolitan Consequently researchers around the University, Japan, led by Prof Shoji world are investigating the possibility Nagaoka, reported the results of of designing implantable devices. experiments using a polyimide One type of implantable device is material with added fluorine. This the intravenous oyxgenator (IVOX), polymer is biocompatible and is suita device designed for insertion able for use in a small artificial lung straight into the blood stream. In that could be implanted. This polyFebruary last year, Michael Snider mer is 70 times better at exchanging and Kane High, scientists at oxygen than polydimethyl siloxane Pennsylvania State University which is widely used for long-term (Hershey, USA) described an artifiextracorporeal circulation; it is also cial lung of this type in which gas 100 times better at removing carbon exchange is achieved by use of a large dioxide. The use of this highly polynumber of microporous fibres merised film means that a machine extending in all directions from a only a few centimetres in size could catheter. The fibres are in contact exchange enough gas to support an with the lumen of the catheter which adult human being, an advance that contains one conduit to deliver 100% brings transplantable artificial lungs oxygen to the fibres and a second much closer to realisation. conduit to remove carbon dioxide. The latest advance in artificial This device can be readily adapted lungs was reported towards the end for percutaneous venous insertion of last year in the American Society of into the patient. By contrast, other Artificial Internal Organs Journal current designs of intravascular
C
260
(1996; 42: 604–09) by a team of researchers at Northwestern University, Evanston, USA. The group is working on an artificial lung that can be implanted inside the chest cavity and attached directly to the pulmonary artery. Their device, called an implantable, intrathoracic artificial lung (ITAL), is intended to act as “transplant bridge” for patients awaiting lung transplantation and as a treatment for acute respiratory failure. At present, the Northwestern group have maintained lung function in a pig for 24 hours. The ITAL contains a bundle of microporous fibres that exchange oxygen for carbon dioxide. The oxygenated blood is then returned to the left atrium. It is also possible to adjust the device so that some blood continues through the impaired natural lungs. Keith Cook, a biomedical engineer and first author on the paper, explains that the new equipment offers a much higher delivery rate of oxygen and carbon dioxide than intravascular devices—the ITAL can supply the full gas-transfer requirements for a patient at rest. The ITAL is the first implanted device that has continued working for 24 h in an animal and, according to Robert Bartlett, professor of surgery at the University of Michigan, Ann Arbor, USA, a leading authority on artificial lungs, “This is an exceptional piece of work. This group are leading the pack right now”. But, Cook notes, “The major disadvantage is that ITAL is highly invasive, basically involving openchest surgery. It will probably be 5–10 years before we will see it in patients”. Another member of the research group, Lyle Mockros, professor of biomedical engineering, at Northwestern, is also concerned that it may be difficult to persuade a company to market ITAL commercially because of potential liability problems. However, in view of the extensive use of other invasive procedures in the USA, including the dramatic rise in the number of stenting procedures, the initial caution expressed by members of the Northwestern team may well be overcome, particularly if clinical testing is successful. David Jack
Vol 349 • January 25, 1997