Biomedical Engineering Reference
In-Depth Information
and Kulkarni, 1963; Larsson, 1965). The range of methanol found in
blood of normal individuals (not occupational) exposed ranged from
0.32 to 2.61mg/l (Sedivec et al., 1981; Lee et al., 1992; Osterloh et al.,
1996; Batterman and Franzblau, 1997). The methanol comes from diet
and normal metabolism (the breakdown of protein methyl esters).
3.3.2 High Exposure
In the case of high exposure to methanol, the rate-limiting step in the
breakdown of methanol in humans is the conversion of formate to
carbon dioxide and water. The saturation of formic acid dehydrogenase
in humans leads to increase in formate and hydrogen ion in the blood.
This buildup results in acidosis and toxicity in humans associated with
over exposure to methanol. This response is not seen in rats because of
their abilities to clear formate more efficiently than humans (Kavet and
Nauss, 1990). The monkey metabolizes methanol much more like
humans than rats. When formate clearance in rats and monkeys has
been compared, the clearance of formate is 2-21/2 times faster in rats
than what is found in monkeys. The half-life in rats for formate
clearance is about 12 minutes versus 31 minutes in monkey (Kavet
and Nauss, 1990). A comparison of the lethal dose of methanol in
humans to other animals shows that the lethal dose in monkey is about
three times higher than humans and in the rat about nine times higher
than humans. This makes humans more sensitive to the lower dose of
methanol than rodents and monkeys. Most toxicity studies in rodents
are done at doses above the acute lethal dose in humans. In cases of
human fatalities due to methanol poisoning, the formic acid in the blood
is estimated to be about 640-1100mg/l (Wallage and Watterson, 2008).
3.3.3 Over Exposure
3.3.3.1 Symptoms
Methanol poisoning in humans starts with signs of
intoxication such as central nervous system (CNS) effects (depression,
headache, dizziness, nausea, and vomiting) followed by 12-24 hours or
more of little or no symptoms then visual disturbances (blurred vision,
indistinct vision, altered visual field, and eye pain followed by
