Perfluorocarbon liquid breathing is a method of respiration where an organism breathes an oxygen-rich liquid, specifically a perfluorocarbon, instead of air. This technique allows for gas exchange, enabling the uptake of oxygen and the release of carbon dioxide, even when the lungs are filled with fluid. Perfluorocarbons are synthetic liquids used for this purpose due to their unique properties that facilitate this unusual form of breathing.
How Perfluorocarbon Liquid Breathing Works
Perfluorocarbons facilitate gas exchange in the lungs due to their high solubility for respiratory gases, dissolving more oxygen and carbon dioxide than blood. For example, perflubron, a common perfluorocarbon, can carry over three times more oxygen than blood and approximately four times more carbon dioxide. This high gas solubility allows for adequate oxygen delivery and carbon dioxide removal.
Perfluorocarbons also have low surface tension. This property is similar to the natural surfactant in the lungs, which helps prevent the small air sacs (alveoli) from collapsing. When the lungs are filled with perfluorocarbon, the liquid replaces the air-liquid interface in the alveoli, reducing surface tension that can hinder gas exchange in injured lungs.
Perfluorocarbons are also denser than body fluids, nearly twice that of water. This density allows them to gravitate to the lower regions of the lungs, where collapse (atelectasis) often occurs in lung injury. By filling these collapsed areas, the perfluorocarbon acts like a liquid form of Positive End Expiratory Pressure (PEEP), helping to reopen and stabilize the alveoli. This allows the liquid to facilitate oxygen uptake and carbon dioxide release directly through the liquid medium.
Historical Development and Early Applications
The concept of liquid breathing has been explored for many decades, with initial investigations dating back to the early 1960s. In 1962, Johannes Kylstra conducted early experiments, demonstrating that mice could sustain gas exchange while spontaneously breathing oxygenated saline solution under high pressure. These pioneering studies laid the groundwork for further research into liquid ventilation.
A significant breakthrough occurred in 1966 when Leland Clark and Frank Gollan showed that mice could survive while submerged in perfluorocarbons under normal atmospheric pressure. This discovery was important because perfluorocarbons proved to be more effective and less toxic than saline solutions for sustaining respiration. Their work highlighted the potential of perfluorocarbons as a viable breathing medium.
Following these animal studies, the first human trials of perfluorocarbon liquid breathing were conducted in Philadelphia, Pennsylvania, in 1989. These early trials involved critically ill infants who were experiencing severe respiratory failure. Total liquid ventilation (TLV), where the lungs are completely filled with oxygenated perfluorocarbon, was administered using a gravity-assisted approach. While these infants showed initial improvements in lung function and gas exchange, they ultimately succumbed to their underlying conditions.
Medical Applications and Current Research
Perfluorocarbon liquid breathing, particularly in its partial liquid ventilation (PLV) form, is investigated for various medical conditions. PLV involves filling the lungs with a perfluorocarbon to about 40% of the total lung capacity, with conventional mechanical ventilation then delivering breaths on top of this liquid. This method is considered more technologically feasible than total liquid ventilation.
A primary area for its use is in pediatric medicine, especially for premature infants suffering from respiratory distress syndrome (RDS). Traditional positive-pressure ventilation methods can sometimes contribute to lung injury in these vulnerable neonates. Liquid ventilation can mitigate these high-pressure gradients and improve lung compliance and gas exchange in premature infants.
Beyond neonatal care, perfluorocarbon liquid breathing is also investigated for acute respiratory distress syndrome (ARDS) in adults. In ARDS, the lungs become stiff and inflamed, and perfluorocarbons can help by reducing inflammation, improving the distribution of air and blood flow, and acting as a lavage to clear debris from the airways. Research also explores perfluorocarbons for pulmonary drug delivery, where their properties allow for more uniform distribution of medications within diseased lungs.
Challenges and Considerations
Despite its potential, perfluorocarbon liquid breathing faces challenges that limit its widespread clinical use. A physiological hurdle is the high density and viscosity of perfluorocarbons compared to air. Perfluorocarbons are nearly twice as dense as water, meaning breathing muscles, like the diaphragm, must exert substantial effort to move the liquid. This increased work of breathing can be exhausting and problematic, especially for patients with compromised respiratory function.
Another physiological concern is the efficiency of carbon dioxide removal. While perfluorocarbons dissolve oxygen well, they are less efficient at clearing carbon dioxide, which can lead to a buildup of CO2 in the body (respiratory acidosis). This requires a high flow rate of breathing fluid that human lungs cannot sustain without assistance. The transition from liquid to gas breathing can also be complicated and potentially dangerous if not all the liquid is removed, leading to complications like pneumonia.
Logistically, implementing perfluorocarbon liquid breathing, particularly total liquid ventilation, requires complex specialized equipment. This includes a system with a membrane oxygenator, heaters to maintain the liquid at body temperature, and pumps to precisely deliver and remove the perfluorocarbon from the lungs. Such intricate systems are expensive and challenging to operate, preventing this technique from becoming a routine treatment in most clinical settings.