Isobaric counterdiffusion
Encyclopedia
Isobaric Counterdiffusion, Inert Gas Counterdiffusion , or ICD is the term used to describe the physiologic effect when the diffusion
of different gases occurs in opposite directions while under a constant ambient pressure
.
, and Quinn in 1973 in subjects who breathed one inert gas mixture (nitrogen
or neon
) while being surrounded by another (helium
).
An example of this would be a patient breathing nitrous oxide
in an operating room (surrounded by air). Cuffs on the endotracheal tubes must be monitored as nitrous oxide will diffuse into the air filled space causing the volume to increase. In laparoscopic surgery
, nitrous oxide is avoided since the gas will diffuse into the abdominal or pelvic cavities causing an increase in internal pressure. In the case of a tympanoplasty
, the skin flap will not lay down as the nitrous oxide will be diffusing into the middle ear
.
An example of this would be breathing air in an heliox
environment. The helium in the heliox diffuses into the skin quickly, while the nitrogen diffuses more slowly from the capillaries to the skin and out of the body. The resulting effect generates supersaturation in certain sites of the superficial tissues and the formation of inert gas bubbles.
An example of this was shown in the literature by Harvey in 1977 as divers switched from a nitrogen mixture to a helium mixture they quickly developed itching followed by joint pain. Saturation divers
breathing hydreliox
switched to a heliox
mixture and developed symptoms of decompression sickness
during Hydra V. More recently, Doolette and Mitchell have described ICD as the basis for inner ear
decompression sickness and suggest "breathing-gas switches should be scheduled deep or shallow to avoid the period of maximum supersaturation resulting from decompression".
's more recent study of Inner Ear Decompression Sickness (IEDCS) now shows that the inner ear may not be well-modelled by common (e.g. Bühlmann) algorithms. Doolette and Mitchell propose that a switch from a helium-rich mix to a nitrogen-rich mix, as is common in technical diving when switching from trimix to nitrox on ascent, may cause a transient supersaturation of inert gas within the inner ear and result in IEDCS. A similar hypothesis to explain the incidence of IEDCS when switching from trimix to nitrox was proposed by Steve Burton, who considered the effect of the much greater solubility of nitrogen than helium in producing transient increases in total inert gas pressure, which could lead to DCS under isobaric conditions. Recompression with oxygen is effective for relief of symptoms resulting from ICD.
Diffusion
Molecular diffusion, often called simply diffusion, is the thermal motion of all particles at temperatures above absolute zero. The rate of this movement is a function of temperature, viscosity of the fluid and the size of the particles...
of different gases occurs in opposite directions while under a constant ambient pressure
Ambient pressure
The ambient pressure on an object is the pressure of the surrounding medium, such as a gas or liquid, which comes into contact with the object....
.
Background
Isobaric Counterdiffusion was first described by Graves, Idicula, LambertsenChristian J. Lambertsen
Christian James Lambertsen was an American environmental medicine and diving medicine specialist who was principally responsible for developing the United States Navy frogmen's rebreathers in the early 1940s for underwater warfare...
, and Quinn in 1973 in subjects who breathed one inert gas mixture (nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
or neon
Neon
Neon is the chemical element that has the symbol Ne and an atomic number of 10. Although a very common element in the universe, it is rare on Earth. A colorless, inert noble gas under standard conditions, neon gives a distinct reddish-orange glow when used in either low-voltage neon glow lamps or...
) while being surrounded by another (helium
Helium
Helium is the chemical element with atomic number 2 and an atomic weight of 4.002602, which is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table...
).
Clinical Relevance
In medicine, ICD is the diffusion of gases in different directions that can increase the pressure inside open air spaces of the body and surrounding equipment.An example of this would be a patient breathing nitrous oxide
Nitrous oxide
Nitrous oxide, commonly known as laughing gas or sweet air, is a chemical compound with the formula . It is an oxide of nitrogen. At room temperature, it is a colorless non-flammable gas, with a slightly sweet odor and taste. It is used in surgery and dentistry for its anesthetic and analgesic...
in an operating room (surrounded by air). Cuffs on the endotracheal tubes must be monitored as nitrous oxide will diffuse into the air filled space causing the volume to increase. In laparoscopic surgery
Laparoscopic surgery
Laparoscopic surgery, also called minimally invasive surgery , bandaid surgery, or keyhole surgery, is a modern surgical technique in which operations in the abdomen are performed through small incisions as opposed to the larger incisions needed in laparotomy.Keyhole surgery makes use of images...
, nitrous oxide is avoided since the gas will diffuse into the abdominal or pelvic cavities causing an increase in internal pressure. In the case of a tympanoplasty
Tympanoplasty
Tympanoplasty is the surgical operation performed for the reconstruction of the eardrum and/or the small bones of the middle ear .-Classification:...
, the skin flap will not lay down as the nitrous oxide will be diffusing into the middle ear
Middle ear
The middle ear is the portion of the ear internal to the eardrum, and external to the oval window of the cochlea. The mammalian middle ear contains three ossicles, which couple vibration of the eardrum into waves in the fluid and membranes of the inner ear. The hollow space of the middle ear has...
.
Diving Relevance
In diving, ICD is the diffusion of gases in different directions that can produce the formation of bubbles without decompression, without changes in the environmental pressure. Two forms of this phenomenon have been described by Lambertsen:Superficial ICD
Superficial ICD occurs when the inert gas breathed by the diver diffuses more slowly into the body than the inert gas surrounding the body.An example of this would be breathing air in an 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...
environment. The helium in the heliox diffuses into the skin quickly, while the nitrogen diffuses more slowly from the capillaries to the skin and out of the body. The resulting effect generates supersaturation in certain sites of the superficial tissues and the formation of inert gas bubbles.
Deep Tissue ICD
Deep Tissue ICD occurs when different inert gases are breathed by the diver in sequence. The rapidly diffusing gas is transported into the tissue faster than the slower diffusing gas is transported out of the tissue.An example of this was shown in the literature by Harvey in 1977 as divers switched from a nitrogen mixture to a helium mixture they quickly developed itching followed by joint pain. Saturation divers
Saturation diving
Saturation diving is a diving technique that allows divers to reduce the risk of decompression sickness when they work at great depth for long periods of time....
breathing hydreliox
Hydreliox
Hydreliox is an exotic breathing gas mixture of helium, oxygen and hydrogen.It is used primarily for research and scientific deep diving, usually below . Below this depth, extended breathing of heliox gas mixtures may cause high pressure nervous syndrome . Two gas mixtures exist that attempt to...
switched to a 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...
mixture and developed symptoms of decompression sickness
Decompression sickness
Decompression sickness describes a condition arising from dissolved gases coming out of solution into bubbles inside the body on depressurization...
during Hydra V. More recently, Doolette and Mitchell have described ICD as the basis for inner ear
Inner ear
The inner ear is the innermost part of the vertebrate ear. In mammals, it consists of the bony labyrinth, a hollow cavity in the temporal bone of the skull with a system of passages comprising two main functional parts:...
decompression sickness and suggest "breathing-gas switches should be scheduled deep or shallow to avoid the period of maximum supersaturation resulting from decompression".
ICD Prevention
Lambertsen made suggestions to help avoid ICD while diving. If the diver is surrounded by or saturated with nitrogen, they should not breathe helium rich gases. Lambertson also proposed that gas switches that involve going from helium rich mixtures to nitrogen rich mixtures would be acceptable, but changes from nitrogen to helium should include recompression. However Doolette and MitchellSimon Mitchell
Simon Mitchell is a New Zealand physician specializing in occupational medicine, hyperbaric medicine and anesthesiology. Trained in medicine, Dr Mitchell was awarded a PhD for his work on neuroprotection from embolic brain injury. Mitchell has also published more than 45 research and review...
's more recent study of Inner Ear Decompression Sickness (IEDCS) now shows that the inner ear may not be well-modelled by common (e.g. Bühlmann) algorithms. Doolette and Mitchell propose that a switch from a helium-rich mix to a nitrogen-rich mix, as is common in technical diving when switching from trimix to nitrox on ascent, may cause a transient supersaturation of inert gas within the inner ear and result in IEDCS. A similar hypothesis to explain the incidence of IEDCS when switching from trimix to nitrox was proposed by Steve Burton, who considered the effect of the much greater solubility of nitrogen than helium in producing transient increases in total inert gas pressure, which could lead to DCS under isobaric conditions. Recompression with oxygen is effective for relief of symptoms resulting from ICD.