It is often repeated that the human body is approximately 60-70% water. According to H.H. Mitchell, Journal of Biological Chemistry 158, the brain and heart are composed of 73% water, and the lungs are about 83% water. The skin contains 64% water, muscles and kidneys are 79%, and even the bones are watery: 31%. Ethanol has a great affinity for water. The two substances are completely miscible i.e. they fully dissolve in each other, in any ratio, to make a single homogeneous liquid. Based on this, the instant a person introduces ethanol in the mouth, even before swallowing, the ethanol begins to mix with any water present, not just in the saliva, but in the gums and other mouth tissue. Upon swallowing, the ethanol quickly moves into the digestive system lining and the blood. Once ethanol gets in the blood, it is carried to all body tissue, including the brain and the lungs.
Accurate Precise Reliable
Water in the Body
Pathway to the Brain
The number one job of the heart is to get blood (and now ethanol) to the lungs to pick up Oxygen, and to the brain to provide vital sustenance. Especially on an empty stomach, many people will notice that it does not take long after drinking an alcoholic beverage to feel it. This means ethanol has arrived at the brain. Having more than approximately one drink an hour exceeds the ability of the liver to break the ethanol down and adds to the ethanol concentration in the brain.
The amount of ethanol in the brain determines the amount of what is essentially anesthesia. The amount of ethanol in the blood directly determines the amount of ethanol in the brain. By measuring the ethanol concentration in the blood at any given moment, the amount of brain dysfunction can be known at that same moment. Because of the nature of the lungs, measuring the ethanol concentration in the breath is also a real time method of measuring the amount of brain dysfunction.
The Lungs
The airways of the lungs are like the roots of a tree, starting with the windpipe and branching into ever smaller pathways into every corner of the lungs. At the ends of the smallest pathways there are several million air sacs hanging like grapes on vines. Capillaries carrying blood to and from the air sacs smother the alveolar surface like a sheet. Separated by a membrane a couple of cells thick, the surface area between breath in the alveoli and blood in the capillaries is on the order of 100 square yards or about the size of a tennis court.
Blood / Breath Exchange
It is through this interface that Oxygen, carbon dioxide, and ethanol molecules are able to freely interchange between a gaseous form and being dissolved in the blood. Within the lungs, in a virtual instant, ethanol vapor reaches an equilibrium concentration with the dissolved ethanol concentration in the blood. Hopefully it now becomes clear why we can measure the concentration of ethanol in breath from the deep lung, and in turn know the concentration of ethanol in the blood. If we know the concentration of ethanol in the blood of the lungs, we know that same concentration is in the blood of the brain, and in turn can predict the amount of brain dysfunction.
Alcohol Breath Testing
Because of human physiology i.e. the affinity of ethanol for the human body along with the interlinked proximity of blood, breath, heart, lungs, and brain, measuring that ethanol concentration in the body and tying it to the amount of brain dysfunction becomes uniquely straightforward.
In summary, imagine if you will, that you’ve had a few drinks, are feeling relaxed, and your ethanol-carrying blood is pumping around between heart, lungs and brain. While that is going on, you suddenly take in a deep breath of fresh air into your lungs, maybe the amount to fill a gallon milk jug. That gallon of breath is sucked into the deep lung as if it were thinly spread across a continuous sheet of blood the size of a tennis court. In an instant your breath is filled with ethanol molecules in proportion to how many are dissolved in your blood. As you breathe out, and that air from deep in your lungs exits your mouth, think whether it is reasonable that someone could accurately measure a sample of that breath for ethanol concentration and make a sound decision whether you should be driving or operating heavy equipment.
