Can Humans Breathe Liquid?
Breathe it in – the air around you is roughly 78% nitrogen, 21% oxygen, and 1% argon. During your lifetime, you'll inhale and exhale this life-giving mixture 672,768,000 times. Give the air around you a big hug.
But have you ever wondered if you can breathe liquid? Sci-Fi stories have repeatedly portrayed this possibility, most famously in James Cameron's deep sea action flick The Abyss. Can it actually be done?
In fact, it can, and it already has.
Before we elucidate how, it may help to understand why we can't breathe in, say, water or milk. It has less to do with the physical differences between those substances and air, and far more to do with the fact that they don't contain enough dissolved oxygen. Our lungs operate by pulling oxygen out of the air, and they can't extract enough out of most liquids because most liquids simply don't contain very much. There are some, however, that soak up oxygen like a sponge...
Research into liquid breathing dates back to the early 1900s, but it really kicked into high gear with the first synthesis of perfluorocarbons (PFCs) during the Manhattan Project in the 1940s. Scientists were searching for substances that resisted attack by reactive uranium compounds, when they stumbled upon PFCs. These compounds, made up of only carbon and fluorine, are inert, colorless, and odorless, with no apparent ill effects on the human body. What's more, they are extremely soluble to dissolved gases, capable of taking in more oxygen and carbon dioxide than blood.
This made scientists wonder if animals could breathe PFCs. In one of the earliest studies seeking to sate this curiosity, researchers submerged mice and cats in a PFC, finding that they breathed just fine for weeks. However, the animals suffered pulmonary damage from the long-term exposure, perhaps because carbon dioxide elimination was impaired – the animals couldn't exhale as effectively. Subsequent studies found that mechanical ventilation was required to resolve these ill effects. Essentially, a machine was needed to inhale and exhale the denser liquid for the lungs so carbon dioxide was removed in a timely manner.
Learning lessons from earlier animal trials, in 1989, doctors at the Temple University School of Medicine wondered if liquid breathing could help pre-term babies suffering from severe respiratory distress for whom all other treatments had failed. They partially filled the lungs of three subjects with PFC, noting some improvements in the babies' conditions. All three eventually died, however.
Seven years later, another team using refined liquid breathing techniques tried PFC liquid ventilation on 13 premature babies suffering from severe respiratory distress who were not expected to survive. Liquid breathing resulted in an improvement for a majority of the infants, potentially by stabilizing alveoli and reducing surface tension within the nascent lungs. Put more simply, the premies' lungs weren't ready for a gas environment, and PFC provided a nurturing bridge been amniotic fluid in the womb and outside air. Incredibly, eight of the infants survived at four-month follow-up.
Liquid ventilation has also been successfully attempted on critically ill adults with lung disorders.
Now that it's known that humans can breathe PFCs, the obvious question is why would we want to? Beyond stabillizing the lungs of newborns, medical trials haven't turned up any clear benefits. Hypothetically, liquid breathing could prevent deep divers from succumbing to "the bends" and protect astronauts from G-forces damaging the lungs, but PFCs are unsuitable for both of those applications, so a novel liquid medium will need to be invented first. Specifically tailored mechanical ventilators will also be required to cycle the fluid for proper oxygen and carbon dioxide exchange.
In short, breathing liquid is possible, but don't attempt it in order to impress the guests at your next dinner party.