<p class="first" id="d1182253e65">The straight chain aliphatic hydrocarbons ethane
and pentane have been advocated as
noninvasive markers of free-radical induced lipid peroxidation in humans. In in vitro
studies, the evolution of ethane and pentane as end products of n-3 and n-6 polyunsaturated
fatty acids, respectively, correlates very well with other markers of lipid peroxidation
and even seems to be the most sensitive test available. In laboratory animals the
use of both hydrocarbons as in vivo markers of lipid peroxidation has been validated
extensively. Although there are other possible sources of hydrocarbons in the body,
such as protein oxidation and colonic bacterial metabolism, these apparently are of
limited importance and do not interfere with the interpretation of the hydrocarbon
breath test. The production of hydrocarbons relative to that of other end products
of lipid peroxidation depends on variables that are difficult to control, such as
the local availability of iron(II) ions and dioxygen. In addition, hydrocarbons are
metabolized in the body, which especially influences the excretion of pentane. Because
of the extremely low concentrations of ethane and pentane in human breath, which often
are not significantly higher than those in ambient air, the hydrocarbon breath test
requires a flawless technique regarding such factors as: (1) the preparation of the
subject with hydrocarbon-free air to wash out ambient air hydrocarbons from the lungs,
(2) the avoidance of ambient air contamination of the breath sample by using appropriate
materials for sampling and storing, and (3) the procedures used to concentrate and
filter the samples prior to gas chromatographic determination. For the gas chromatographic
separation of hydrocarbons, open tubular capillary columns are preferred because of
their high resolution capacity. Only in those settings where expired hydrocarbon levels
are substantially higher than ambient air levels might washout prove to be unnecessary,
at least in adults. Although many investigators have concentrated on one marker, it
seems preferable to measure both ethane and pentane concurrently. The results of the
hydrocarbon breath test are not influenced by prior food consumption, but both vitamin
E and beta-carotene supplementation decrease hydrocarbon excretion. Nevertheless,
the long-term use of a diet high in polyunsaturated fatty acids, such as in parenteral
nutrition regimens, may result in increased hydrocarbon exhalation. Hydrocarbon excretion
slightly increases with increasing age. Short-term increases follow physical and intellectual
stress and exposure to hyperbaric dioxygen.(ABSTRACT TRUNCATED AT 400 WORDS)
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