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Carbon monoxide (CO) is a toxic gas.

Carbon monoxide (CO) is a toxic gas and it is very difficult for people to detect because it is colorless, odorless, tasteless and initially non-irritating. A product of incomplete combustion of organic matter due to insufficient oxygen, carbon monoxide is often produced in domestic or industrial settings by motor vehicles that run on gasoline, diesel, methane, or other carbon-based fuels. Exposure at 100 ppm or greater can be dangerous to human health .The main manifestations of CO poisoning develop in the organ systems most dependent on oxygen use, the CNS and the heart. The initial symptoms of acute CO poisoning include headache,nausea, malaise, and fatigue. The resultant effects of CO toxicity are impaired oxygen delivery and utilization at the cellular level. Under normal conditions, CO levels in the plasma are approximately 0mmHg because it has a higher diffusion coefficient and the body easily gets rid of it. When CO is not ventilated out it binds to hemoglobin to produce a compound known as carboxyhemoglobin (HbCO). It binds hemoglobin 230-270 times more avidly than oxygen, such that small concentrations can result in significant levels of HbCO. Hemoglobin is a tetramer with four oxygen binding sites. The binding of carbon monoxide at one of these sites increases the oxygen affinity of the remaining three sites.This causes the hemoglobin molecule to retain oxygen that would otherwise be delivered to the tissue causing hypoxic tissue injury. CO also binds to other molecules such as myoglobin and mitochondrial cytochrome oxidase. CO has a high affinity for myoglobin, about 60 times greater than that of oxygen. Carbon monoxide bound to myoglobin may impair its ability to utilize oxygen. This causes reduced cardiac out put and hypotension, which may result in brain ischemia. CO binding to cytochrome oxidase interferes with aerobic metabolism and ATP synthesis. Cells respond by switching to anaerobic metabolism, causing anoxia, lactic acidosis, and eventual cell death. The rate of dissociation between CO and cytochrome oxidase is slow, causing a relatively prolonged impairment of oxidative metabolism.

Carbon monoxide is neurotoxic and toxic to the cardiovascular system. The effects of carbon monoxide on the body systems are not immediately obvious due to its odourless, colourless and non irritating properties hence the damage is done in most cases before it is detected.