Oxygen toxicity Totally Explained

Everything about Oxygen Toxicity totally explained

Oxygen toxicity or oxygen toxicity syndrome (also known as the "Paul Bert effect" or the "Lorrain Smith effect") is severe hyperoxia caused by breathing oxygen at elevated partial pressures.
The high concentration of oxygen damages cells. The precise mechanism(s) of the damage caused by these reactive oxygen species are not known, but oxygen gas has a propensity to react with certain metals to form superoxide which may attack double bonds in many organic systems, including the unsaturated fatty acid residues in cells. High concentrations of oxygen are known to increase the formation of free-radicals which harm DNA and other structures (see nitric oxide, peroxynitrite, and trioxidane). Normally, the body has many defense systems against such damage (see glutathione, catalase, and superoxide dismutase) but at higher concentrations of free oxygen, these systems are eventually overwhelmed with time, and the rate of damage to cell membranes exceeds the capacity of systems which control or repair it. Cell damage and cell death then results.

Hyperoxia

Hyperoxia is excess oxygen in body tissues or higher than normal partial pressure of oxygen. Hyperoxia is caused by breathing gas at pressures greater than normal atmospheric pressure or by breathing oxygen-rich gases at normal atmospheric pressure for a prolonged period of time.

Types of oxygen toxicity

In humans, there are several types of oxygen toxicity In 1912, Bornstein developed cramps in his hands and legs while breathing oxygen at 2.8 ATA for 51 minutes. Behnke et. al. were the first to observe visual field contraction on dives between 1.0 and 4.0 ATA.During World War II, Donald and Yarbrough et. al. performed many studies on oxygen toxicity to support the initial use of closed circuit oxygen rebreathers. They discovered the effects of underwater immersion and exercise. In the decade following World War II, Lambertsen et. al. made further discoveries on the effects of oxygen at pressure as well as methods of prevention. In the years since, research on CNS toxicity has centered around methods of prevention and safe extension of tolerance.

Clinical Relevance

As CNS toxicity is caused by breathing oxygen at elevated ambient pressures, patients undergoing hyperbaric oxygen therapy are at risk of suffering hyperoxic seizures. Treatment of seizures during treatment consists of removing the patient from oxygen, thereby dropping the partial pressure of oxygen delivered. Many Nitrox-capable dive computers also calculate this "Oxygen Loading".
The aim is to avoid activating the alarm by reducing the ppO₂ of the breathing gas or the length of time breathing gas of higher ppO₂. As the ppO₂ depends on the fraction of oxygen in the breathing gas and the depth of the dive, the diver can obtain more time on the oxygen clock by diving at a shallower depth, by breathing a less oxygen-rich gas or by shortening the exposure to oxygen-rich gases.

Pulmonary oxygen toxicity

Experimentally, early symptoms of breathing 100% oxygen are breathing difficulty and substernal pain or discomfort. The lungs show inflammation and pulmonary edema. and model for prediction pulmonary oxygen toxicity based on pulmonary function are key documents in the development of operational oxygen procedures. In 1988, Hamilton et. al. wrote procedures for NOAA to establish oxygen exposure limits for habitat operations.

Clinical Relevance

The risk of bronchopulmonary dysplasia ("BPD") in infants, or adult respiratory distress syndrome in adults, begins to increase with exposure for over 16 hours to partial pressures of 0.5 bar or more. At sea-level, 0.5 bar is exceeded by gas mixtures having oxygen fractions greater than 50%. Lung oxygen toxicity damage-rates at sea-level pressure rise non-linearly between the 50% threshold of toxicity, and the rate of damage on 100% oxygen. For this reason, intensive care patients requiring more than 60% oxygen, and especially patients at fractions near 100% oxygen, are considered to be at especially high risk, since if the situation isn't corrected, the treatment may begin to cause lung damage which contributes to need for the high-oxygen mixture. Care must be used in distinguishing oxygen mole fraction from oxygen partial pressure. Partial pressures between 0.2 bar (normal at sea level) and 0.5 bar usually are considered non-toxic. BPD is reversible in the early stages during "break" periods on lower oxygen pressures, but it may eventually result in irreversible lung damage, if allowed to progress to severe damage. Usually several days of exposure without "oxygen breaks" are needed to cause severe lung damage.
Oxygen toxicity is a potential complication of mechanical ventilation with pure oxygen, where it's called the respiratory lung syndrome.
In the treatment of Decompression Sickness, divers are exposed to long periods of oxygen breathing under hyperbaric conditions. This exposure coupled with that from the dive that preceded the symptoms can be a significant cummulative oxygen exposure and pulmonary toxicity may occur. Hyperoxic myopia has occurred in closed circuit oxygen rebreather divers with prolonged exposures.

Hyperventilation

Oxygen toxicity isn't a major factor in hyperventilating, as some people believe. The problems caused by hyperventilating are due to decreased carbon dioxide within the blood. With or without hyperventilating, it's impossible to develop oxygen toxicity breathing air at typical surface atmospheric pressure.

Further Information

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