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How is it that a breathalyzer can measure [br]the alcohol content in someone’s blood,

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hours after they had their last drink, [br]based on their breath alone?

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Exhaled breath contains trace amounts [br]of hundreds, even thousands,

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of volatile organic compounds:

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small molecules lightweight enough [br]to travel easily as gases.

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One of these is ethanol, [br]which we consume in alcoholic drinks.

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It travels through the bloodstream [br]to tiny air sacs in the lungs,

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passing into exhaled air [br]at a concentration 2,000 times lower,

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on average, than in the blood.

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When someone breathes [br]into a breathalyzer,

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the ethanol in their breath [br]passes into a reaction chamber.

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There, it’s converted to another molecule,[br]called acetic acid,

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in a special type of reactor that produces[br]an electric current during the reaction.

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The strength of the current [br]indicates the amount of ethanol

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in the sample of air, [br]and by extension in the blood.

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In addition to the volatile [br]organic compounds like ethanol

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we consume in food and drink,

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the biochemical processes of our cells [br]produce many others.

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And when something disrupts [br]those processes, like a disease,

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the collection of volatile [br]organic compounds in the breath

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may change, too.

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So could we detect disease [br]by analyzing a person’s breath,

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without using more invasive [br]diagnostic tools

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like biopsies, blood draws, and radiation?

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In theory, yes,

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but testing for disease is a lot more [br]complicated than testing for alcohol.

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To identify diseases,

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researchers need to look at a set [br]of tens of compounds in the breath.

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A given disease may cause [br]some of these compounds

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to increase or decrease in concentration, [br]while others may not change—

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the profile is likely to be different [br]for every disease,

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and could even vary for different stages [br]of the same disease.

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For example, cancers are among [br]the most researched candidates

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for diagnosis through breath analysis.

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One of the biochemical changes [br]many tumors cause

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is a large increase [br]in an energy-generating process

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called glycolysis.

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Known as the Warburg Effect,

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this increase in glycolysis results [br]in an increase of metabolites like lactate

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which in turn can affect a whole cascade [br]of metabolic processes

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and ultimately result [br]in altered breath composition,

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possibly including an increased [br]concentration of volatile compounds

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such as dimethyl sulfide.

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But the Warburg Effect is just one [br]potential indicator of cancerous activity,

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and doesn’t reveal anything [br]about the particular type of cancer.

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Many more indicators are needed [br]to make a diagnosis.

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To find these subtle differences,

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researchers compare the breath [br]of healthy people

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with the breath of people [br]who suffer from a particular disease

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using profiles based on hundreds [br]of breath samples.

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This complex analysis [br]requires a fundamentally different,

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more versatile type of sensor [br]from the alcohol breathalyzer.

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There are a few being developed.

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Some discriminate [br]between individual compounds

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by observing how the compounds move [br]through a set of electric fields.

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Others use an array of resistors [br]made of different materials

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that each change their resistance [br]when exposed to a certain mix

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of volatile organic compounds.

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There are other challenges too.

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These substances are present [br]at incredibly low concentrations—

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typically just parts per billion,

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much lower than ethanol concentrations [br]in the breath.

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Compounds’ levels may be affected [br]by factors other than disease,

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including age, gender, nutrition, [br]and lifestyle.

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Finally, there’s the issue

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of distinguishing which compounds [br]in the sample

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were produced in the patient’s body

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and which were inhaled [br]from the environment

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shortly before the test.

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Because of these challenges, [br]breath analysis isn’t quite ready yet.

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But preliminary clinical trials [br]on lung, colon,

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and other cancers [br]have had encouraging results.

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One day, catching cancer early [br]might be as easy as breathing in and out.