Less-Than-Easy Breathing

Easter is this coming weekend for Christians and predominantly-Christian countries. To celebrate the resurrection of a religion's divine messiah, an anthropomorphic rabbit hops through suburbs, and on his journeys he hides candy and colored eggs. Yeah, no one ever said it had to make sense. And since Easter usually falls in April, it's become more of a celebration of spring, rather than a religious holiday. It's the beginning of the very brief time of the year where it's okay to wear pastel colors.

I can assure you that the Easter Bunny will be bypassing the researchers at Boston Children's Hospital, even though I'm sure he'll stop by to see the kids. Or, at least he'll be bypassing them if he has any respect for his laboratory rabbit comrades. Why?

Doctors there performed tracheal occlusions on rabbits. Half the rabbits were intravenously injected with a foam of micro particles encapsulating a core of pure oxygen gas. These rabbits' bloodstreams were able to deliver oxygen to tissues, while the other half that had not been injected choked to death--for science!

This discovery decreases the chance of brain damage or other organ damage to human patients who suffer acute hypoxemic conditions. Yay, science!

Intravenous delivery of respiration is a profound development, but alternative respiratory methods aren't new in concept. Liquid breathing, exchanging oxygen and carbon dioxide in the lungs via liquid medium, had been the stuff of science fiction for ages. Films such as The Abyss, Mission to Mars and Event Horizon, and TV programs such as Star Trek, SeaQuest and Seven Days all featured characters immersed in a liquid that facilitated CO2 and O2 exchange via the lungs.

But even during the production of these shows and movies, liquid respiration was at the forefront of medical technology. Currently, perfluorocarbons have proven to be the most reliable method of liquid breathing. PFCs have a surface tension similar to that of surfactant, a biological fluid which supports alveoli in the lungs. It also has a high density and oxygen is easily diffused through. Additionally, it has some anti-inflammatory properties. In fact, the scene from The Abyss, where a rat breathes while being immersed in PFCs, is real. Despite some initial panic, the rat lives without any injury.

Unfortunately, we can't quite just start throwing people into pools of PFCs. The best application for PFCs at the moment is through a therapy known as partial liquid ventilation. This technique requires the lungs to be filled about 40% with PFC, and then the patient is hooked up to a traditional medical ventilator. The PFC supports injured sections of the lung, while still diffusing oxygen. The PFC can also clean debris from alveoli to improve lung function.

Total immersion and total liquid ventilation share similar caveats. First, a membrane oxygenator must ensure that the entire PFC volume regularly exchanges its carbon dioxide for oxygen. The PFCs must be heated whenever they're not in the body, so there is significant energy expenditure. While there have been total ventilation prototypes of animals, no one has dared to construct one for humans, despite encouragement from many bioengineers.

So what could we use total ventilation technology for? For one, deep sea divers would be able to breathe PFCs instead of compressed air, or diving compounds such as heliox. Divers would need some mechanical assistance however, as the diaphragm isn't powerful enough to move liquids. This would eliminate the chance of the air embolisms, collapsed or burst lungs, and the bends. Total ventilation would also be used in space travel. Since liquids disperse g-forces across their entire volume in every direction, a person wearing a PFC suit would feel the effects of the g-forces across his or her whole body, as opposed to the contact points between harness, seat, and space suit. This would mean space travelers could withstand 20 G, whereas 10 G is enough for the typical person to blackout. If the astronaut is completely suspended in PFCs, he or she would be able to withstand more than 20 Gs. At the moment, PFCs remain unsuitable for this application. But a manned mission beyond Mars, if ever attempted, will likely require some form of this technology.

Anyway, this Easter always remember the backbone of future space empires may be built on the selfless sacrifices of rabbits.