Liquid respiration is a form of respiration where normal air respiratory organisms absorb oxygen-rich fluids (such as perfluorocarbon), rather than inhaling the air.
It requires certain physical properties such as gas solubility, density, viscosity, vapor pressure, and fat solubility which in part, but not all, perfluorochemicals (perfluorocarbons) have. Thus, it is important to choose an appropriate PFC for a particular biomedical application, such as fluid vents, drug delivery or blood substitutes. The physical properties of PFC fluids vary substantially; However, one common trait is its high solubility for respiratory gas. In fact, this fluid carries more oxygen and carbon dioxide than blood.
In theory, liquid breathing can be helpful in treating 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 vents, standard application mode has not been set.
Video Liquid breathing
Approach
Since liquid breathing is still a very experimental technique, there are several approaches proposed.
Total liquid vents
Although total liquid velocity (TLV) with fully fluid filled lungs can be useful, a tubular system containing a complex liquid required is a disadvantage compared to gas vents - the system must incorporate membrane, heating, and pump oxygenators to provide to, and remove from aliquots tidal pulmonary volume of perfluorocarbon (PFC) is conditioned. One study group led by Thomas H. Shaffer argues that with the use of microprocessors and new technologies, it is possible to maintain better control of respiratory variables such as residual liquid functional capacity and tidal volume over TLV compared to gas vents. Consequently, total ventilation of the liquid requires a special liquid ventilator similar to a medical ventilator except that it uses inhalable liquids. Many prototypes are used for animal experiments, but experts recommend the continued development of the liquid ventilator against clinical applications. Preclinical precipitated liquid ventilators (Inolivent) are currently being developed jointly in Canada and France. The main application of this liquid ventilator is the ultra-rapid induction of therapeutic hypothermia after cardiac arrest. It has been shown to be more protective than the slow cooling method after an experimental heart attack.
Partial liquid vents
In contrast, partial fluid ventilation (PLV) is a technique in which PFC is implanted into the lungs to a volume close to functional residual capacity (about 40% of total lung capacity). Conventional mechanical ventilation produces a tidal volume above the breath. This mode of liquid ventilation seems more technologically feasible than total fluid vents, as PLV can use technology currently available in many neonatal intensive care units (NICUs) worldwide.
The effects of PLV on oxygenation, carbon dioxide removal and pulmonary mechanics have been investigated in several studies in animals using various models of lung injury. PLV clinical applications have been reported in patients with acute respiratory distress syndrome (ARDS), meconium aspiration syndrome, congenital diaphragm hernia and neonatal respiratory distress syndrome (RDS). To properly and effectively perform the PLV, it is important to
- the patient dose appropriately for a specific lung volume (10-15 ml/kg) to recruit alveolar volume
- redose the lungs with PFC fluid (1-2 ml/kg/hr) to fight the evaporation of PFC from the lung.
If PFC fluid is not maintained in the lungs, the PLV can not effectively protect the lung from the biophysical forces associated with the gas ventilator.
New application mode for PFC has been developed.
Partial fluid ventilation (PLV) involves filling the lungs with fluid. This liquid is perfluorocarbon, also called Liquivent or Perflubron. This liquid has several unique properties. It has a very low surface tension, similar to surfactant, a substance produced in the lungs to prevent alveoli from collapsing and sticking together during respiration. It also has a high density, oxygen easily diffuses through it, and may have some anti-inflammatory properties. In the PLV, the lungs are filled with fluid, the patient is then ventilated with a conventional ventilator using a protective lung ventilation strategy. This is called partial fluid ventilation. The hope is that the fluid will help transport oxygen to the lung part that is inundated and filled with debris, helping to throw away the debris and open more alveoli that improve lung function. The study of PLV involves comparison with a ventilator strategy designed to minimize lung damage.
steam PFC
Evaporation of perfluorohexane with two calibrated anesthetic vaporizers for perfluorohexane has been shown to increase gas exchange in oleic acid induced lung injury in sheep.
Most PFCs with high vapor pressure are suitable for evaporation.
Aerosol-PFC
With perfluorooctane aerosol, significant increases in oxygenation and pulmonary mechanics are shown in adult sheep with oleic acid induced lung injury.
In piglets lacking surfactant, continuous improvement of gas exchange and pulmonary mechanics is demonstrated with Aerosol-PFC. Aerosol aids is very important for the effectiveness of PFC aerosolization, since PF5080 aerosolization (FC77 less purified) has been shown to be ineffective using different aerosol devices in surfactant-inactivated rabbits. Partial fluid ventilation and Aerosol-PFC reduce pulmonary inflammatory responses.
Maps Liquid breathing
Proposals using
Diving
The gas pressure increases with depth, rising 1 bar (14.5 psi (100 kPa)) every 10 meters to over 1,000 bar at the bottom of the Mariana Trench. Diving becomes more dangerous as depth increases, and diving in presents many dangers. All surface-breathing animals are subject to decompression diseases, including free-diving water and human mammals (see taravana ). Inhaling deeply can cause nitrogen narcosis and oxygen toxicity. Holding your breath as you ride after deep breathing can cause air embolism, exploding lungs, and collapsed lungs.
Special respiratory gas mixtures such as trimix or heliox improve the risk of decompression disease but do not eliminate it. Heliox further eliminates the risk of nitrogen narcosis but introduces the risk of helium tremor under about 500 feet (150 m). The atmospheric clothing keeps the body and breath pressure in 1 bar, eliminating most of the dangers of descending, ascending, and breathing in the depths. However, rigid clothing is large, clumsy, and very expensive.
Liquid breathing offers a third option, promising available mobility with flexible wetsuits and reducing the risk of stiff clothing. With fluid in the lungs, pressure inside the diver's lungs can accommodate changes in water pressure around it without the partial pressure of gas pressure required when the lungs are filled with gas. Liquid breathing will not result in saturation of body tissues with high pressure nitrogen or helium that occurs with non-fluid use, thereby reducing or eliminating the need for slow decompression.
A significant problem, however, arises from the high viscosity of the fluid and the corresponding reduction in its ability to remove CO 2 . All use of respiratory fluid for diving should involve total liquid venting (see above). The total liquid vent, however, has the difficulty of transferring enough fluid to bring CO 2 , since no matter how large the total pressure is, the amount of partial CO 2 gas pressure is available to dissolve the CO 2 into the respiratory fluid can not be more than the pressure where CO 2 is present in the blood (about 40 mm from mercury (Torr)).
At this pressure, most fluorocarbon fluids require about 70 mL/kg minute volume of fluid vents (about 5 L/min for adults 70 kg) to remove enough CO 2 for normal resting metabolism. It is a very much fluid to move, mainly because the liquid is thicker and denser than gas, (eg water about 850 times the density of the air). Any increase in diver metabolic activity also increases the production of CO 2 and respiratory rates, which are already at realistic flow rate limits in liquid respiration. It seems unlikely that someone will move 10 liters/minute of fluorocarbon fluid without the aid of a mechanical ventilator, so "breathing freely" may not be possible. However, it has been suggested that the liquid breathing system can be combined with a CO 2 scrubber connected to the diver's blood supply; US patents have been filed for such methods.
Medical care
The most promising area for the use of liquid ventilation is in the field of pediatric medicine. The first medical use of respiratory fluids was the treatment of premature infants and adults with acute respiratory distress syndrome (ARDS) in the 1990s. Respiratory fluid is used in clinical trials after development by Alliance Pharmaceuticals from perfluorooctyl bromide fluorochemicals, or perflubrons for the short term. Current positive pressure ventilation methods can contribute to the development of lung disease in premenstrual neonates, leading to diseases such as bronchopulmonary dysplasia. The liquid vents remove many of the high pressure gradients that are responsible for this damage. Furthermore, perfluorocarbons have been shown to reduce pulmonary inflammation, improve ventilation-perfusion mismatch and provide new routes for pulmonary administration.
In order to explore drug delivery techniques that would be useful for partial and total fluid ventilation, more recent studies have focused on delivering PFC drugs using nanocrystal suspension. The first image is a computer model of PFC fluid (perflubron) in combination with gentamicin molecule.
The second picture shows the experimental results comparing plasma and gentamicin levels after intratracheal (IT) and intravenous (IV) doses of 5 mg/kg in newborn sheep during gas ventilation. Note that plasma dose IV levels greatly exceed IT dose levels over a 4-hour study period; whereas, the level of gentamicin lung tissue when delivered with intratracheal suspension (IT), uniformly exceeds the intravenous (IV) delivery approach after 4 h. Thus, the IT approach enables the delivery of more effective drugs to the target organ while maintaining a safer level systemically. Both images represent an in-vivo time course for 4 hours. A number of studies have now shown the effectiveness of PFC fluids as delivery vehicles to the lungs.
Clinical trials with premature infants, children and adults are performed. Because the safety of the procedure and its effectiveness is evident from the early stages, the US Food and Drug Administration (FDA) provides the product "fast track" status (ie an accelerated product review designed to bring it publicly as safely as possible) because of the potential savings of life. Clinical trials show that the use of perflubrons with ordinary ventilators improves results as much as using high-frequency oscillating ventilation (HFOV). But since perflubrons are no better than HFOV, the FDA does not approve perflubrons, and the Alliance is no longer pursuing partial fluid ventilation applications. Whether perflubrons will improve results when used with HFOV or have less long-term consequences than HFOV remains an open question.
In 1996, Mike Darwin and Steven B. Harris proposed using cold-liquid vents with perfluorocarbons to lower the body's temperature of heart attacks and other brain traumas quickly to better recover brain. The technology is called gas/fluid ventilation (GLV), and is proven to achieve a cooling rate of 0.5 Ã, Â ° C per minute in large animals. It has not been tried in humans.
Recently, hypothermic brain protection has been associated with rapid brain cooling. In this case, a new therapeutic approach is the use of intranasal perfluorochemical sprays for preferential brain cooling. The nasopharyngeal approach (NP) is unique to brain cooling due to the proximity of anatomy to the cerebral and arterial circulation. Based on preclinical studies on adult sheep, it was shown that independent of the region, brain cooling was faster during NP-perfluorochemical compared to conventional whole-body cooling with cooling blankets. To date, there have been four studies in humans including a random intra-arrest study completed (200 patients). The results clearly show that intra-hospital intra-premenstrual transnasal cooling is safe, feasible and associated with an increase in cooling time.
Space travel
Soaking fluids provides a way to reduce the physical pressure of G power. The force used for the fluid is distributed as omnidirectional pressure. Since liquids can not be practically compacted, they do not alter the density under high acceleration as done in air maneuvers or space travel. A person immersed in a liquid of equal density with a tissue has an accelerating force distributed around the body, rather than applied to a point such as a seat cord or a safety rope. This principle is used in a new type of G-suit called Libelle G-suit, which allows the pilot to remain conscious and function at acceleration of over 10 G by circling it with water in a rigid suit.
The acceleration protection by fluid immersion is limited by the differential density of body tissue and immersion fluid, limiting the usefulness of this method to about 15 to 20 G. Extending the acceleration protection beyond 20 G requires filling the lungs with a water-like density liquid. An astronaut completely immersed in a liquid, with fluid in all body cavities, will feel the slightest effect of extreme force G because the force in the fluid is distributed evenly, and in all directions simultaneously. But the effect will be felt because of differences in density between different body tissues, so the upper acceleration limit still exists.
Source of the article : Wikipedia
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