Liquid breathing
Encyclopedia
Liquid breathing is a form of respiration
in which a normally air-breathing organism breathes an oxygen
-rich liquid
(such as a perfluorocarbon), rather than breathing air.
Perfluorochemical (perfluorocarbon) molecules have very different structures that impart different physical properties such as respiratory gas solubility, density, viscosity, vapor pressure, and lipid solubility. Thus, it is critical to select the appropriate PFC for a specific biomedical application, such as liquid ventilation, drug delivery, blood substitutes, etc. The physical properties of PFC liquids vary substantially; however, the one common property is their high solubility for respiratory gases. In fact, these liquids carry more oxygen
and carbon dioxide
than blood.
In theory, liquid breathing could assist in the treatment of patients with severe pulmonary
or cardiac
trauma, especially in pediatric cases. Liquid breathing has also been proposed for use in deep diving
and space travel
. Despite some recent advances in liquid ventilation, a standard mode of application has not been established yet.
Liquid breathing is sometimes called "fluid breathing", but this can be misleading, as normal atmospheric air is also a fluid
.
, heater, and pumps to deliver to, and remove from the lungs tidal volume
aliquots of conditioned perfluorocarbon (PFC). One research group led by Thomas H. Shaffer has maintained that with the use of microprocessor
s and new technology, it is possible to maintain better control of respiratory variables such as liquid functional residual capacity
and tidal volume during TLV, than with gas ventilation. Consequently, the total liquid ventilation necessitates a dedicated liquid ventilator
similar to a medical ventilator
except that it uses a breatheable liquid. Many prototypes are used for animal experimentations, but experts recommend continued development of a liquid ventilator
toward clinical applications.
(approximately 40% of Total Lung Capacity
(TLC)). Conventional mechanical ventilation
delivers tidal volume
breaths on top of it. This mode of liquid ventilation currently seems technologically more feasible than total liquid ventilation, because PLV could utilise technology currently in place in many neonatal intensive-care units (NICU) worldwide.
The influence of PLV on oxygenation, carbon dioxide removal and lung mechanics has been investigated in several animal studies
using different models of lung injury Clinical applications of PLV have been reported in patients with acute respiratory distress syndrome
(ARDS), meconium aspiration syndrome
, congenital diaphragmatic hernia
and respiratory distress syndrome
(RDS) of neonates. In order to correctly and effectively conduct PLV, it is essential to
If PFC liquid is not maintained in the lung, PLV can not effectively protect the lung from biophysical forces associated with the gas ventilator.
New application modes for PFC have been developed.
of perfluorohexane
with two anesthetic vaporizers calibrated for perfluorohexane has been shown to improve gas exchange
in oleic acid
-induced lung injury in sheep.
Predominantly PFCs with high vapor pressure
are suitable for vaporization
, significant improvement of oxygenation and pulmonary
mechanics was shown in adult sheep with oleic acid
-induced lung injury.
In surfactant
-depleted piglet
s, persistent improvement of gas exchange and lung mechanics was demonstrated with Aerosol-PFC.
The aerosol device is of decisive importance for the efficacy of PFC aerosolization, as aerosolization of PF5080 (a less purified FC77) has been shown to be ineffective using a different aerosol device in surfactant-depleted rabbits. Partial liquid ventilation and Aerosol-PFC reduced pulmonary inflammatory response.
every 10 meters to over 1,000 bar at the bottom of the Mariana Trench
. Diving becomes more dangerous as depth increases, and deep diving presents many hazards
. All surface-breathing animals are subject to decompression sickness
, including aquatic mammal
s and free-diving
humans (see taravana
). Breathing at depth can cause nitrogen narcosis
and oxygen toxicity
. Ascending after breathing at depth can cause air embolism
s, burst lung, and collapsed lung
.
Special breathing gas mixes
such as trimix or heliox
ameliorate the risk of decompression illness
but do not eliminate it. Heliox further eliminates the risk of nitrogen narcosis but introduces the risk of helium tremors
below 500 feet (152 meters). Atmospheric diving suit
s maintain body and breathing pressure at 1 bar, eliminating most of the hazards of descending, ascending, and breathing at depth. However, the rigid suits are bulky, clumsy, and very expensive.
Liquid breathing offers a third option, promising the mobility available with flexible dive suits and the reduced risks of rigid suits. With liquid in the lungs, the pressure within the diver's lungs could accommodate changes in the pressure of the surrounding water without the huge gas partial pressure exposures required when the lungs are filled with gas. Liquid breathing would not result in the saturation of body tissues with high pressure nitrogen or helium that occurs with the use of non-liquids, thus would reduce or remove the need for slow decompression
.
A significant problem, however, arises from the high viscosity
of the liquid and the corresponding reduction in its ability to remove CO2. All uses of liquid breathing for diving must involve total liquid ventilation (see above). Total liquid ventilation, however, has difficulty moving enough liquid to carry away CO2, because no matter how great the total pressure is, the amount of partial CO2 gas pressure available to dissolve CO2 into the breathing liquid can never be much more than the pressure at which CO2 exists in the blood (about 40 mm of mercury (Torr
)).
At these pressures, most fluorocarbon liquids require about 70 mL/kg minute-ventilation volumes of liquid (about 5 L/min for a 70 kg adult) to remove enough CO2 for normal resting metabolism. This is a great deal of fluid to move, particularly as liquids are generally more viscous than gases, (for example water is about 850 times the viscosity of air). Any increase in the diver's metabolic activity also increases CO2 production and the breathing rate, which is already at the limits of realistic flow rates in liquid breathing. It seems unlikely that a person would move 10 liters/min of fluorocarbon liquid without assistance from a mechanical ventilator, so "free breathing" may be unlikely.
. The first medical use of liquid breathing was treatment of premature babies and adults with acute respiratory distress syndrome (ARDS)
in the 1990s. Liquid breathing was used in clinical trials after the development by Alliance Pharmaceuticals of the fluorochemical
perfluorooctyl bromide, or perflubron for short. Current methods of positive-pressure ventilation can contribute to the development of lung disease in pre-term neonates, leading to diseases such as bronchopulmonary dysplasia
. Liquid ventilation removes many of the high pressure gradients responsible for this damage. Furthermore, perfluorocarbons have been demonstrated to reduce lung inflammation, improve ventilation-perfusion mismatch and to provide a novel route for the pulmonary administration of drugs.
In order to explore drug delivery techniques that would be useful for both partial and total liquid ventilation, more recent studies have focused on PFC drug delivery using a nanocrystal suspension. The first image is a computer model of a PFC liquid (perflubron) combined with gentamicin molecules.
The second image shows experimental results comparing both plasma and tissue levels of gentamicin after an intratracheal (IT) and intravenous (IV) dose of 5 mg/kg in a newborn lamb during gas ventilation. Note that the plasma levels of the IV dose greatly exceed the levels of the IT dose over the 4 hour study period; whereas, the lung tissue levels of gentamicin when delivered by an intratracheal (IT) suspension, uniformly exceed the intravenous (IV) delivery approach after 4 hours. Thus, the IT approach allows more effective delivery of the drug to the target organ while maintaining a safer level systemically. Both images represent the in-vivo time course over 4 hours. Numerous studies have now demonstrated the effectiveness of PFC liquids as a delivery vehicle to the lungs.
Clinical trials with premature infants, children and adults were conducted. Since the safety of the procedure and the effectiveness were apparent from an early stage, the US Food and Drug Administration
(FDA) gave the product "fast track" status (meaning an accelerated review of the product, designed to get it to the public as quickly as is safely possible) due to its life-saving potential. Clinical trials showed that using perflubron with ordinary ventilators
improved outcomes as much as using high frequency oscillating ventilation (HFOV). But because perflubron was not better than HFOV, the FDA did not approve perflubron, and Alliance is no longer pursuing the partial liquid ventilation application. Whether perflubron would improve outcomes when used with HFOV remains an open question.
In 1996 Mike Darwin
and Dr. Steven B. Harris proposed using cold liquid ventilation with perfluorocarbon to quickly lower the body temperature of victims of cardiac arrest
and other brain trauma to allow the brain to better recover.
The technology came to be called gas/liquid ventilation (GLV), and was shown able to achieve a cooling rate of 0.5° C
per minute in large animals. It has not yet been tried in humans.
Most recently, hypothermic brain protection has been associated with rapid brain cooling. In this regard, a new therapeutic approach is the use of intranasal perfluorochemical spray for preferential brain cooling. The nasopharyngeal (NP) approach is unique for brain cooling due to anatomic proximity to the cerebral circulation and arteries. Based on preclinical studies in adult sheep, it was shown that independent of region, brain cooling was faster during NP-perfluorochemical versus conventional whole body cooling with cooling blankets. To date, there have been four human studies including a completed randomized intra-arrest study (200 patients). Results clearly demonstrated that prehospital intra-arrest transnasal cooling is safe, feasible and is associated with an improvement in cooling time.
s. Forces applied to fluids are distributed as omnidirectional pressures. Because liquids cannot be practically compressed, they do not change density under high acceleration such as performed in aerial maneuvers or space travel. A person immersed in liquid of the same density as tissue
has acceleration forces distributed around the body, rather than applied at a single point such as a seat or harness straps. This principle is used in a new type of G-suit
called the Libelle G-suit, which allows aircraft pilots to remain conscious and functioning at more than 10 G acceleration by surrounding them with water in a rigid suit.
Acceleration protection by liquid immersion is limited by the differential density of body tissues and immersion fluid, limiting the utility of this method to about 15 to 20 G.
Extending acceleration protection beyond 20 G requires filling the lungs with fluid of density similar to water. An astronaut totally immersed in liquid, with liquid inside all body cavities, will feel little effect from extreme G forces because the forces on a liquid are distributed equally, and in all directions simultaneously. However effects will be felt because of density differences between different body tissues, so an upper acceleration limit still exists.
Liquid breathing for acceleration protection may never be practical because of the difficulty of finding a suitable breathing medium of similar density to water that is compatible with lung tissue. Perfluorocarbon fluids are twice as dense as water, hence unsuitable for this application. On the other hand, although perfluorochemicals are denser than water, lung tissue floats within the PFC filled lungs, and if the lungs are not over-filled, there is no compromise in pulmonary or systemic blood flow. Therefore, if the astronaut is immersed in liquid and their lungs are filled with liquid PFC, they should not experience adverse effects, in spite of the almost twofold density difference. Based on interviews with adult patients that experienced partial liquid ventilation, when they became conscious they were unaware that 20-30 ml/kg of PFC was in their lungs during recovery.
Respiration (physiology)
'In physiology, respiration is defined as the transport of oxygen from the outside air to the cells within tissues, and the transport of carbon dioxide in the opposite direction...
in which a normally air-breathing organism breathes an oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
-rich liquid
Liquid
Liquid is one of the three classical states of matter . Like a gas, a liquid is able to flow and take the shape of a container. Some liquids resist compression, while others can be compressed. Unlike a gas, a liquid does not disperse to fill every space of a container, and maintains a fairly...
(such as a perfluorocarbon), rather than breathing air.
Perfluorochemical (perfluorocarbon) molecules have very different structures that impart different physical properties such as respiratory gas solubility, density, viscosity, vapor pressure, and lipid solubility. Thus, it is critical to select the appropriate PFC for a specific biomedical application, such as liquid ventilation, drug delivery, blood substitutes, etc. The physical properties of PFC liquids vary substantially; however, the one common property is their high solubility for respiratory gases. In fact, these liquids carry more oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
and carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
than blood.
In theory, liquid breathing could assist in the treatment of patients with severe pulmonary
Human lung
The human lungs are the organs of respiration in humans. Humans have two lungs, with the left being divided into two lobes and the right into three lobes. Together, the lungs contain approximately of airways and 300 to 500 million alveoli, having a total surface area of about in...
or cardiac
Human heart
The human heart is a muscular organ that provides a continuous blood circulation through the cardiac cycle and is one of the most vital organs in the human body...
trauma, especially in pediatric cases. Liquid breathing has also been proposed for use in deep diving
Underwater diving
Underwater diving is the practice of going underwater, either with breathing apparatus or by breath-holding .Recreational diving is a popular activity...
and space travel
Human spaceflight
Human spaceflight is spaceflight with humans on the spacecraft. When a spacecraft is manned, it can be piloted directly, as opposed to machine or robotic space probes and remotely-controlled satellites....
. Despite some recent advances in liquid ventilation, a standard mode of application has not been established yet.
Liquid breathing is sometimes called "fluid breathing", but this can be misleading, as normal atmospheric air is also a fluid
Fluid
In physics, a fluid is a substance that continually deforms under an applied shear stress. Fluids are a subset of the phases of matter and include liquids, gases, plasmas and, to some extent, plastic solids....
.
| gas solubility | |
| Oxygen | 33-66 mL / 100 mL PFC |
| Carbon dioxide | 140-166 mL / 100 mL PFC |
| vapor pressure | 0.2-400 torr |
| density | 1.58-2.0 g/mL |
| viscosity | 0.8-8.0 cS |
Approaches
Because liquid breathing is still a highly experimental technique, there are several proposed approaches.Total liquid ventilation
Although total liquid ventilation (TLV) with completely liquid-filled lungs can be beneficial, the complex liquid-filled tube system required is a disadvantage compared to gas ventilation - the system must incorporate a membrane oxygenatorMembrane oxygenator
A membrane oxygenator is a device used to add oxygen to, and remove carbon dioxide from the blood. It can be used in two principal modes: to imitate the function of the lungs in cardiopulmonary bypass , and to oxygenate blood in longer term life support, termed extracorporeal membrane oxygenation,...
, heater, and pumps to deliver to, and remove from the lungs tidal volume
Tidal volume
Tidal volume is the lung volume representing the normal volume of air displaced between normal inspiration and expiration when extra effort is not applied.Typical values are around 500ml or 7ml/kg bodyweight.-Mechanical Ventilation:...
aliquots of conditioned perfluorocarbon (PFC). One research group led by Thomas H. Shaffer has maintained that with the use of microprocessor
Microprocessor
A microprocessor incorporates the functions of a computer's central processing unit on a single integrated circuit, or at most a few integrated circuits. It is a multipurpose, programmable device that accepts digital data as input, processes it according to instructions stored in its memory, and...
s and new technology, it is possible to maintain better control of respiratory variables such as liquid functional residual capacity
Functional residual capacity
Functional Residual Capacity is the volume of air present in the lungs, specifically the parenchyma tissues, at the end of passive expiration...
and tidal volume during TLV, than with gas ventilation. Consequently, the total liquid ventilation necessitates a dedicated liquid ventilator
Liquid ventilator
A liquid ventilator is similar to a medical ventilator except that it should be able to ensure reliable total liquid ventilation with a breatheable liquid...
similar to a medical ventilator
Medical ventilator
A medical ventilator can be defined as any machine designed to mechanically move breatheable air into and out of the lungs, to provide the mechanism of breathing for a patient who is physically unable to breathe, or breathing insufficiently....
except that it uses a breatheable liquid. Many prototypes are used for animal experimentations, but experts recommend continued development of a liquid ventilator
Liquid ventilator
A liquid ventilator is similar to a medical ventilator except that it should be able to ensure reliable total liquid ventilation with a breatheable liquid...
toward clinical applications.
Partial liquid ventilation
In contrast, partial liquid ventilation (PLV) is a technique in which a PFC is instilled into the lung to a volume approximating functional residual capacityFunctional residual capacity
Functional Residual Capacity is the volume of air present in the lungs, specifically the parenchyma tissues, at the end of passive expiration...
(approximately 40% of Total Lung Capacity
Lung volumes
Lung volumes and lung capacities refer to the volume of air associated with different phases of the respiratory cycle. Lung volumes are directly measured...
(TLC)). Conventional mechanical ventilation
Mechanical ventilation
In medicine, mechanical ventilation is a method to mechanically assist or replace spontaneous breathing. This may involve a machine called a ventilator or the breathing may be assisted by a physician, respiratory therapist or other suitable person compressing a bag or set of bellows...
delivers tidal volume
Tidal volume
Tidal volume is the lung volume representing the normal volume of air displaced between normal inspiration and expiration when extra effort is not applied.Typical values are around 500ml or 7ml/kg bodyweight.-Mechanical Ventilation:...
breaths on top of it. This mode of liquid ventilation currently seems technologically more feasible than total liquid ventilation, because PLV could utilise technology currently in place in many neonatal intensive-care units (NICU) worldwide.
The influence of PLV on oxygenation, carbon dioxide removal and lung mechanics has been investigated in several animal studies
Animal studies
Animal studies is a recently recognized field in which animals are studied in a variety of cross-disciplinary ways. Scholars from fields as diverse as: art history, anthropology, biology, film studies, geography, history, psychology, literary studies, museology, philosophy, and sociology; and from...
using different models of lung injury Clinical applications of PLV have been reported in patients with acute respiratory distress syndrome
Acute respiratory distress syndrome
Acute respiratory distress syndrome , also known as respiratory distress syndrome or adult respiratory distress syndrome is a serious reaction to various forms of injuries to the lung....
(ARDS), meconium aspiration syndrome
Meconium aspiration syndrome
Meconium aspiration syndrome is a medical condition affecting newborn infants. It occurs when meconium is present in their lungs during or before delivery...
, congenital diaphragmatic hernia
Congenital diaphragmatic hernia
Congenital diaphragmatic hernia is a congenital malformation of the diaphragm. The most common type of CDH is a Bochdalek hernia; other types include Morgagni's hernia, diaphragm eventration and central tendon defects of the diaphragm...
and respiratory distress syndrome
Respiratory distress syndrome
There are two forms of respiratory distress syndrome:* ARDS, which is acute respiratory distress syndrome* Infant respiratory distress syndrome , which is a complication of premature birth, also known as hyaline membrane disease Also, respiratory distress can mean:* Shortness of breath*...
(RDS) of neonates. In order to correctly and effectively conduct PLV, it is essential to
- properly dose a patient to a specific lung volume (10-15 ml/kg) to recruit alveolar volume and
- redose the lung with PFC liquid (1-2 ml/kg/hr) to oppose PFC evaporationEvaporationEvaporation is a type of vaporization of a liquid that occurs only on the surface of a liquid. The other type of vaporization is boiling, which, instead, occurs on the entire mass of the liquid....
from the lung.
If PFC liquid is not maintained in the lung, PLV can not effectively protect the lung from biophysical forces associated with the gas ventilator.
New application modes for PFC have been developed.
PFC vapor
VaporizationVaporization
Vaporization of an element or compound is a phase transition from the liquid or solid phase to gas phase. There are three types of vaporization: evaporation, boiling and sublimation....
of perfluorohexane
Perfluorohexane
Perfluorohexane or tetradecafluorohexane, is a fluorocarbon. It is a derivative of hexane in which all of the hydrogen atoms are replaced by fluorine atoms. It is used in one formulation of the electronic cooling liquid/insulator Fluorinert for low temperature applications due to its low boiling...
with two anesthetic vaporizers calibrated for perfluorohexane has been shown to improve gas exchange
Gas exchange
Gas exchange is a process in biology where gases contained in an organism and atmosphere transfer or exchange. In human gas-exchange, gases contained in the blood of human bodies exchange with gases contained in the atmosphere. Human gas-exchange occurs in the lungs...
in oleic acid
Oleic acid
Oleic acid is a monounsaturated omega-9 fatty acid found in various animal and vegetable fats. It has the formula CH37CH=CH7COOH. It is an odorless, colourless oil, although commercial samples may be yellowish. The trans isomer of oleic acid is called elaidic acid...
-induced lung injury in sheep.
Predominantly PFCs with high vapor pressure
Vapor pressure
Vapor pressure or equilibrium vapor pressure is the pressure of a vapor in thermodynamic equilibrium with its condensed phases in a closed system. All liquids have a tendency to evaporate, and some solids can sublimate into a gaseous form...
are suitable for vaporization
Aerosol-PFC
With aerosolized perfluorooctanePerfluorooctane
Perfluorooctane, also known as octadecafluorooctane, is a fluorocarbon liquid—a perfluorinated derivative of the hydrocarbon octane. Under the name PF5080 it is sold by 3M as part of their Fluorinert range of heat transfer fluids. It can be a good substitute for insulating oil in high...
, significant improvement of oxygenation and pulmonary
mechanics was shown in adult sheep with oleic acid
Oleic acid
Oleic acid is a monounsaturated omega-9 fatty acid found in various animal and vegetable fats. It has the formula CH37CH=CH7COOH. It is an odorless, colourless oil, although commercial samples may be yellowish. The trans isomer of oleic acid is called elaidic acid...
-induced lung injury.
In surfactant
Surfactant
Surfactants are compounds that lower the surface tension of a liquid, the interfacial tension between two liquids, or that between a liquid and a solid...
-depleted piglet
Domestic pig
The domestic pig is a domesticated animal that traces its ancestry to the wild boar, and is considered a subspecies of the wild boar or a distinct species in its own right. It is likely the wild boar was domesticated as early as 13,000 BC in the Tigris River basin...
s, persistent improvement of gas exchange and lung mechanics was demonstrated with Aerosol-PFC.
The aerosol device is of decisive importance for the efficacy of PFC aerosolization, as aerosolization of PF5080 (a less purified FC77) has been shown to be ineffective using a different aerosol device in surfactant-depleted rabbits. Partial liquid ventilation and Aerosol-PFC reduced pulmonary inflammatory response.
Diving
Gas pressure increases with depth, rising 1 barBar (unit)
The bar is a unit of pressure equal to 100 kilopascals, and roughly equal to the atmospheric pressure on Earth at sea level. Other units derived from the bar are the megabar , kilobar , decibar , centibar , and millibar...
every 10 meters to over 1,000 bar at the bottom of the Mariana Trench
Mariana Trench
The Mariana Trench or Marianas Trench is the deepest part of the world's oceans. It is located in the western Pacific Ocean, to the east of the Mariana Islands. The trench is about long but has a mean width of only...
. Diving becomes more dangerous as depth increases, and deep diving presents many hazards
Diving hazards and precautions
Divers face specific physical and health risks when they go underwater or use high pressure breathing gases. Some of these conditions also affect people who work in raised pressure environments out of water, e.g...
. All surface-breathing animals are subject to decompression sickness
Decompression sickness
Decompression sickness describes a condition arising from dissolved gases coming out of solution into bubbles inside the body on depressurization...
, including aquatic mammal
Aquatic mammal
Aquatic and semi-aquatic mammals are a diverse group of mammals that dwell partly or entirely in bodies of water. They include the various marine mammals who dwell in oceans, as well as various freshwater species, such as the Platypus and the European Otter.-Groups:* Order Sirenia: Sirenians**...
s and free-diving
Free-diving
Freediving is any of various aquatic activities that share the practice of breath-hold underwater diving. Examples include breathhold spear fishing, freedive photography, apnea competitions and, to a degree, snorkeling...
humans (see taravana
Taravana
Taravana is a disease often found among Polynesian island natives who habitually dive deep without breathing apparatus many times in close succession, usually for food or pearls. These free-divers may make 40 to 60 dives a day, each of 30 or 40 metres .Taravana seems to be decompression sickness....
). Breathing at depth can cause nitrogen narcosis
Nitrogen narcosis
Narcosis while diving , is a reversible alteration in consciousness that occurs while scuba diving at depth. The Greek word ναρκωσις is derived from narke, "temporary decline or loss of senses and movement, numbness", a term used by Homer and Hippocrates...
and oxygen toxicity
Oxygen toxicity
Oxygen toxicity is a condition resulting from the harmful effects of breathing molecular oxygen at elevated partial pressures. It is also known as oxygen toxicity syndrome, oxygen intoxication, and oxygen poisoning...
. Ascending after breathing at depth can cause air embolism
Air embolism
An air embolism, or more generally gas embolism, is a pathological condition caused by gas bubbles in a vascular system. The most common context is a human body, in which case it refers to gas bubbles in the bloodstream...
s, burst lung, and collapsed lung
Pneumothorax
Pneumothorax is a collection of air or gas in the pleural cavity of the chest between the lung and the chest wall. It may occur spontaneously in people without chronic lung conditions as well as in those with lung disease , and many pneumothoraces occur after physical trauma to the chest, blast...
.
Special breathing gas mixes
Breathing gas
Breathing gas is a mixture of gaseous chemical elements and compounds used for respiration.Air is the most common and only natural breathing gas...
such as trimix or heliox
Heliox
Heliox is a breathing gas composed of a mixture of helium and oxygen .Heliox has been used medically since the 1930s, and although the medical community adopted it initially to alleviate symptoms of upper airway obstruction, its range of medical uses has since expanded greatly, mostly because of...
ameliorate the risk of decompression illness
Decompression illness
Decompression Illness describes a collection of symptoms arising from decompression of the body.DCI is caused by two different mechanisms, which result in overlapping sets of symptoms. The two mechanisms are:...
but do not eliminate it. Heliox further eliminates the risk of nitrogen narcosis but introduces the risk of helium tremors
High pressure nervous syndrome
High-pressure nervous syndrome is a neurological and physiological diving disorder that results when a commercial diver or scuba diver descends below about while breathing a helium–oxygen mixture. The effects depend on the rate of descent and the depth...
below 500 feet (152 meters). Atmospheric diving suit
Atmospheric diving suit
An atmospheric diving suit or ADS is a small one-man articulated submersible of anthropomorphic form which resembles a suit of armour, with elaborate pressure joints to allow articulation while maintaining an internal pressure of one atmosphere...
s maintain body and breathing pressure at 1 bar, eliminating most of the hazards of descending, ascending, and breathing at depth. However, the rigid suits are bulky, clumsy, and very expensive.
Liquid breathing offers a third option, promising the mobility available with flexible dive suits and the reduced risks of rigid suits. With liquid in the lungs, the pressure within the diver's lungs could accommodate changes in the pressure of the surrounding water without the huge gas partial pressure exposures required when the lungs are filled with gas. Liquid breathing would not result in the saturation of body tissues with high pressure nitrogen or helium that occurs with the use of non-liquids, thus would reduce or remove the need for slow decompression
Decompression
Decompression has several meanings:* Decompression , the release of pressure and the opposition of physical compression* Decompression sickness, a condition arising from the precipitation of dissolved gases into bubbles inside the body on depressurization* Decompression , a procedure used to treat...
.
A significant problem, however, arises from the high viscosity
Viscosity
Viscosity is a measure of the resistance of a fluid which is being deformed by either shear or tensile stress. In everyday terms , viscosity is "thickness" or "internal friction". Thus, water is "thin", having a lower viscosity, while honey is "thick", having a higher viscosity...
of the liquid and the corresponding reduction in its ability to remove CO2. All uses of liquid breathing for diving must involve total liquid ventilation (see above). Total liquid ventilation, however, has difficulty moving enough liquid to carry away CO2, because no matter how great the total pressure is, the amount of partial CO2 gas pressure available to dissolve CO2 into the breathing liquid can never be much more than the pressure at which CO2 exists in the blood (about 40 mm of mercury (Torr
Torr
The torr is a non-SI unit of pressure with the ratio of 760 to 1 standard atmosphere, chosen to be roughly equal to the fluid pressure exerted by a millimetre of mercury, i.e., a pressure of 1 torr is approximately equal to 1 mmHg...
)).
At these pressures, most fluorocarbon liquids require about 70 mL/kg minute-ventilation volumes of liquid (about 5 L/min for a 70 kg adult) to remove enough CO2 for normal resting metabolism. This is a great deal of fluid to move, particularly as liquids are generally more viscous than gases, (for example water is about 850 times the viscosity of air). Any increase in the diver's metabolic activity also increases CO2 production and the breathing rate, which is already at the limits of realistic flow rates in liquid breathing. It seems unlikely that a person would move 10 liters/min of fluorocarbon liquid without assistance from a mechanical ventilator, so "free breathing" may be unlikely.
Medical treatment
The most promising area for the use of liquid ventilation is in the field of pediatric medicinePediatrics
Pediatrics or paediatrics is the branch of medicine that deals with the medical care of infants, children, and adolescents. A medical practitioner who specializes in this area is known as a pediatrician or paediatrician...
. The first medical use of liquid breathing was treatment of premature babies and adults with acute respiratory distress syndrome (ARDS)
Acute respiratory distress syndrome
Acute respiratory distress syndrome , also known as respiratory distress syndrome or adult respiratory distress syndrome is a serious reaction to various forms of injuries to the lung....
in the 1990s. Liquid breathing was used in clinical trials after the development by Alliance Pharmaceuticals of the fluorochemical
Fluorocarbon
Fluorocarbons, sometimes referred to as perfluorocarbons or PFCs, are organofluorine compounds that contain only carbon and fluorine bonded together in strong carbon–fluorine bonds. Fluoroalkanes that contain only single bonds are more chemically and thermally stable than alkanes...
perfluorooctyl bromide, or perflubron for short. Current methods of positive-pressure ventilation can contribute to the development of lung disease in pre-term neonates, leading to diseases such as bronchopulmonary dysplasia
Bronchopulmonary dysplasia
Bronchopulmonary dysplasia is a chronic lung disorder that is most common among children who were born prematurely, with low birthweights and who received prolonged mechanical ventilation to treat respiratory distress syndrome...
. Liquid ventilation removes many of the high pressure gradients responsible for this damage. Furthermore, perfluorocarbons have been demonstrated to reduce lung inflammation, improve ventilation-perfusion mismatch and to provide a novel route for the pulmonary administration of drugs.
In order to explore drug delivery techniques that would be useful for both partial and total liquid ventilation, more recent studies have focused on PFC drug delivery using a nanocrystal suspension. The first image is a computer model of a PFC liquid (perflubron) combined with gentamicin molecules.
The second image shows experimental results comparing both plasma and tissue levels of gentamicin after an intratracheal (IT) and intravenous (IV) dose of 5 mg/kg in a newborn lamb during gas ventilation. Note that the plasma levels of the IV dose greatly exceed the levels of the IT dose over the 4 hour study period; whereas, the lung tissue levels of gentamicin when delivered by an intratracheal (IT) suspension, uniformly exceed the intravenous (IV) delivery approach after 4 hours. Thus, the IT approach allows more effective delivery of the drug to the target organ while maintaining a safer level systemically. Both images represent the in-vivo time course over 4 hours. Numerous studies have now demonstrated the effectiveness of PFC liquids as a delivery vehicle to the lungs.
Clinical trials with premature infants, children and adults were conducted. Since the safety of the procedure and the effectiveness were apparent from an early stage, the US Food and Drug Administration
Food and Drug Administration
The Food and Drug Administration is an agency of the United States Department of Health and Human Services, one of the United States federal executive departments...
(FDA) gave the product "fast track" status (meaning an accelerated review of the product, designed to get it to the public as quickly as is safely possible) due to its life-saving potential. Clinical trials showed that using perflubron with ordinary ventilators
Medical ventilator
A medical ventilator can be defined as any machine designed to mechanically move breatheable air into and out of the lungs, to provide the mechanism of breathing for a patient who is physically unable to breathe, or breathing insufficiently....
improved outcomes as much as using high frequency oscillating ventilation (HFOV). But because perflubron was not better than HFOV, the FDA did not approve perflubron, and Alliance is no longer pursuing the partial liquid ventilation application. Whether perflubron would improve outcomes when used with HFOV remains an open question.
In 1996 Mike Darwin
Mike Darwin
Michael G. Darwin, also known as Michael Federowicz, was the president of the cryonics organization Alcor Life Extension Foundation from 1983 to 1988, and Research Director until 1992...
and Dr. Steven B. Harris proposed using cold liquid ventilation with perfluorocarbon to quickly lower the body temperature of victims of cardiac arrest
Cardiac arrest
Cardiac arrest, is the cessation of normal circulation of the blood due to failure of the heart to contract effectively...
and other brain trauma to allow the brain to better recover.
The technology came to be called gas/liquid ventilation (GLV), and was shown able to achieve a cooling rate of 0.5° C
Celsius
Celsius is a scale and unit of measurement for temperature. It is named after the Swedish astronomer Anders Celsius , who developed a similar temperature scale two years before his death...
per minute in large animals. It has not yet been tried in humans.
Most recently, hypothermic brain protection has been associated with rapid brain cooling. In this regard, a new therapeutic approach is the use of intranasal perfluorochemical spray for preferential brain cooling. The nasopharyngeal (NP) approach is unique for brain cooling due to anatomic proximity to the cerebral circulation and arteries. Based on preclinical studies in adult sheep, it was shown that independent of region, brain cooling was faster during NP-perfluorochemical versus conventional whole body cooling with cooling blankets. To date, there have been four human studies including a completed randomized intra-arrest study (200 patients). Results clearly demonstrated that prehospital intra-arrest transnasal cooling is safe, feasible and is associated with an improvement in cooling time.
Space travel
Liquid immersion provides a way to reduce the physical stress of G forceG force
The g-force associated with an object is its acceleration relative to free-fall.It may also refer to:* G-Force , a 2009 film by Disney** G-Force , a 2009 video game based on the film...
s. Forces applied to fluids are distributed as omnidirectional pressures. Because liquids cannot be practically compressed, they do not change density under high acceleration such as performed in aerial maneuvers or space travel. A person immersed in liquid of the same density as tissue
Biological tissue
Tissue is a cellular organizational level intermediate between cells and a complete organism. A tissue is an ensemble of cells, not necessarily identical, but from the same origin, that together carry out a specific function. These are called tissues because of their identical functioning...
has acceleration forces distributed around the body, rather than applied at a single point such as a seat or harness straps. This principle is used in a new type of G-suit
G-suit
A G-suit, or the more accurately named anti-G suit, is worn by aviators and astronauts who are subject to high levels of acceleration force . It is designed to prevent a black-out and G-LOC caused by the blood pooling in the lower part of the body when under acceleration, thus depriving the...
called the Libelle G-suit, which allows aircraft pilots to remain conscious and functioning at more than 10 G acceleration by surrounding them with water in a rigid suit.
Acceleration protection by liquid immersion is limited by the differential density of body tissues and immersion fluid, limiting the utility of this method to about 15 to 20 G.
Extending acceleration protection beyond 20 G requires filling the lungs with fluid of density similar to water. An astronaut totally immersed in liquid, with liquid inside all body cavities, will feel little effect from extreme G forces because the forces on a liquid are distributed equally, and in all directions simultaneously. However effects will be felt because of density differences between different body tissues, so an upper acceleration limit still exists.
Liquid breathing for acceleration protection may never be practical because of the difficulty of finding a suitable breathing medium of similar density to water that is compatible with lung tissue. Perfluorocarbon fluids are twice as dense as water, hence unsuitable for this application. On the other hand, although perfluorochemicals are denser than water, lung tissue floats within the PFC filled lungs, and if the lungs are not over-filled, there is no compromise in pulmonary or systemic blood flow. Therefore, if the astronaut is immersed in liquid and their lungs are filled with liquid PFC, they should not experience adverse effects, in spite of the almost twofold density difference. Based on interviews with adult patients that experienced partial liquid ventilation, when they became conscious they were unaware that 20-30 ml/kg of PFC was in their lungs during recovery.
Examples in fiction
- Joe HaldemanJoe HaldemanJoe William Haldeman is an American science fiction author.-Life :Haldeman was born June 9, 1943 in Oklahoma City, Oklahoma. His family traveled and he lived in Puerto Rico, New Orleans, Washington, D.C., Bethesda, Maryland and Anchorage, Alaska as a child. Haldeman married Mary Gay Potter, known...
's 1975 Novel The Forever WarThe Forever WarThe Forever War is a science fiction novel by American author Joe Haldeman, telling the contemplative story of soldiers fighting an interstellar war between humanity and the enigmatic Tauran species...
describes liquid immersion and breathing in great detail as a key technology to allow space travel and combat with acceleration up to 25 G. - In The Lost Symbol by Dan BrownDan BrownDan Brown is an American author of thriller fiction, best known for the 2003 bestselling novel, The Da Vinci Code. Brown's novels, which are treasure hunts set in a 24-hour time period, feature the recurring themes of cryptography, keys, symbols, codes, and conspiracy theories...
, Robert Langdon (the protagonist) is completely submerged in breathable liquid mixed with hallucination agents and sedatives as a torture technique by Mal'akh (the antagonist). He goes through a near death experienceNear death experienceA near-death experience refers to a broad range of personal experiences associated with impending death, encompassing multiple possible sensations including detachment from the body; feelings of levitation; extreme fear; total serenity, security, or warmth; the experience of absolute dissolution;...
when he inhales the liquid and blacks out, losing control over his body, but is soon revived. - The James CameronJames CameronJames Francis Cameron is a Canadian-American film director, film producer, screenwriter, editor, environmentalist and inventor...
film The AbyssThe AbyssThe Abyss is a 1989 science fiction film written and directed by James Cameron. It stars Ed Harris, Mary Elizabeth Mastrantonio, and Michael Biehn. The original musical score was composed by Alan Silvestri...
features a character using liquid breathing to dive thousands of feet without compressing. The Abyss also features a scene with a rat submerged in and breathing fluorocarbon liquid, filmed in real life. - In the animeAnimeis the Japanese abbreviated pronunciation of "animation". The definition sometimes changes depending on the context. In English-speaking countries, the term most commonly refers to Japanese animated cartoons....
Neon Genesis EvangelionNeon Genesis Evangelion, commonly referred to as Evangelion, is a commercially and critically successful Japanese anime series that began airing in October 1995. The series was highly influential, and launched the Neon Genesis Evangelion franchise. It garnered several major animation awards...
, the cockpits of the titular MechaMechaA mech , is a science fiction term for a large walking bipedal tank or robot, including ones on treads and animal shapes.-Characteristics:...
are filled with a fictional oxygenated liquid called LCL which helps to dampen impacts on the pilot in battle and helps him to better psychically-synchronize with his biomechanical vehicle. - The aliens in the Gerry AndersonGerry AndersonGerry Anderson MBE is a British publisher, producer, director and writer, famous for his futuristic television programmes, particularly those involving specially modified marionettes, a process called "Supermarionation"....
UFO series use liquid-breathing spacesuits. - Hal ClementHal ClementHarry Clement Stubbs better known by the pen name Hal Clement, was an American science fiction writer and a leader of the hard science fiction subgenre.-Biography:...
's 1973 novel Ocean on Top portrays a small underwater civilization living in a 'bubble' of oxygenated fluid denser than seawater. - In an episode of the Adult SwimAdult SwimAdult Swim is an adult-oriented Cable network that shares channel space with Cartoon Network from 9:00 pm until 6:00 am ET/PT in the United States, and broadcasts in countries such as Australia and New Zealand...
cartoon series MetalocalypseMetalocalypseMetalocalypse is an American animated television series, created by Brendon Small and Tommy Blacha, which premiered on August 6, 2006 on Adult Swim...
, the other members of the band submerge guitarist Toki in a "liquid oxygen isolation chamber" while recording an album in the Mariana TrenchMariana TrenchThe Mariana Trench or Marianas Trench is the deepest part of the world's oceans. It is located in the western Pacific Ocean, to the east of the Mariana Islands. The trench is about long but has a mean width of only...
. - In an episode of the SyFySyfySyfy , formerly known as the Sci-Fi Channel and SCI FI, is an American cable television channel featuring science fiction, supernatural, fantasy, reality, paranormal, wrestling, and horror programming. Launched on September 24, 1992, it is part of the entertainment conglomerate NBCUniversal, a...
Channel show EurekaEureka (TV series)Eureka is an American science fiction television series that premiered on Syfy on July 18, 2006. Since then four seasons have aired, and a fifth is currently being filmed. The second half of season 4 began on SyFy on July 11, 2011 and ended on September 19, 2011...
, Sheriff Jack Carter is submerged in a tank of "oxygen rich plasmaPlasma (physics)In physics and chemistry, plasma is a state of matter similar to gas in which a certain portion of the particles are ionized. Heating a gas may ionize its molecules or atoms , thus turning it into a plasma, which contains charged particles: positive ions and negative electrons or ions...
" to be cured of the effects of a scientific accident. - In the movies Mission to MarsMission to MarsMission to Mars is a 2000 science fiction film directed by Brian De Palma from an original screenplay written by Jim Thomas, John Thomas, and Graham Yost. The film's story details a fictional portrayal of a manned Mars exploration mission gone awry in the year 2020...
and Event HorizonEvent horizonIn general relativity, an event horizon is a boundary in spacetime beyond which events cannot affect an outside observer. In layman's terms it is defined as "the point of no return" i.e. the point at which the gravitational pull becomes so great as to make escape impossible. The most common case...
, a character is depicted as being immersed in apparent breathable fluid before a high-acceleration launch. - In season 1, episode 13 of Seven Days chrononaut Frank Parker is seen breathing a hyper-oxygenated perfluorocarbon liquid that is pumped through a sealed full body suit that he is wearing. This suit and liquid combination allow him to board a Russian submarine through open ocean at a depth of almost 1000 feet. Upon boarding the submarine he removes his helmet, expels the liquid from his lungs and is able to breathe air again.
- Ben BovaBen BovaBenjamin William Bova is an American science-fiction author and editor. He is the recipient of six Hugo Awards for Best Professional Editor for his work at Analog Science Fiction in the 1970's.-Personal life:...
's novel JupiterJupiter (novel)Jupiter is a science fiction novel by American writer Ben Bova. This novel is part of the Grand Tour series of novels. It was first published in 2000.- Plot synopsis :...
features a craft in which the crew are suspended in a breathable liquid that allows them to survive in the high pressure environment of JupiterJupiterJupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with mass one-thousandth that of the Sun but is two and a half times the mass of all the other planets in our Solar System combined. Jupiter is classified as a gas giant along with Saturn,...
's atmosphere. - In the book Mechanicum from the Horus Heresy series of novels in the Warhammer 40,000 setting, physically crippled Titan pilots are encased in nutrient fluid tanks to allow them to continue operating beyond the limits normally imposed by the body.
- In the classic PC Turn-Based StrategyTurn-based strategyA turn-based strategy game is a strategy game where players take turns when playing...
game X-COM: Terror from the DeepX-COM: Terror from the DeepX-COM: Terror from the Deep is a strategy video game released in 1995 for the PC. It is the sequel to UFO: Enemy Unknown, and the second part of the X-COM series.-Gameplay:...
, "Aquanauts" fighting deep ocean conditions breathe a dense oxygen-carrying fluid. - In the Star Trek: The Next GenerationStar Trek: The Next GenerationStar Trek: The Next Generation is an American science fiction television series created by Gene Roddenberry as part of the Star Trek franchise. Roddenberry, Rick Berman, and Michael Piller served as executive producers at different times throughout the production...
novel "The Children of HamlinThe Children of HamlinThe Children of Hamlin is a science fiction novel set in the Star Trek expanded universe. The book is by Carmen Carter, and takes place in the The Next Generation era.-Synopsis:...
" the crew of the Enterprise-D encounter an alien race whose ships contain a breathable liquid environment.
See also
- Mechanical ventilationMechanical ventilationIn medicine, mechanical ventilation is a method to mechanically assist or replace spontaneous breathing. This may involve a machine called a ventilator or the breathing may be assisted by a physician, respiratory therapist or other suitable person compressing a bag or set of bellows...
- Breathing gasBreathing gasBreathing gas is a mixture of gaseous chemical elements and compounds used for respiration.Air is the most common and only natural breathing gas...
- Artificial gills (human)Artificial gills (human)Artificial gills are a device to let a human take in oxygen from surrounding water. This technology does not exist yet or is in early stage of being developed.-Methods:Several potential methods exist for the development of artificial gills...
- Liquid ventilatorLiquid ventilatorA liquid ventilator is similar to a medical ventilator except that it should be able to ensure reliable total liquid ventilation with a breatheable liquid...
External links
- Here, Breathe This Liquid from Discover Magazine
- Miracle Girl from Readers Digest