Amateur Athlete iPhone apps
here
"Drinking simulator" is for entertainment (and educational) purposes only. It simulates the effect of a specified number of drinks and time on our level of blood alcohol concentration. An alarm sounds when this reaches the DUI limit (0.08 %).
The lag time between drinking and peak blood alcohol level can be surprisingly long. Also, the time required to "process" alcohol down to safe levels can be longer than expected. The accuracy of the simulation is best if you are a man weighing about 155 lb. If you smaller, then the simulation will under-predict the alcohol level in your blood and vice versa.
The model that the calculations are based on is explained on the "How it works" page. Basically, chemical engineering principles are used to model the flow of alcohol between five fluid-like compartments in our body and its "processing" in our liver.
"How it works" is organized in the following manner:
Important caveat: This app is for entertainment (and educational) purposes only.
The level of alcohol in our blood depends on the amount of alcohol we have consumed and the amount of time that has passed. In this "Drinking simulator",
simulates the consumption of one "standard" drink.
simulates the
passage of 5 minutes.
zeroes the number of drinks and time passed.
This app could be used by someone at a bar, party or a fishing trip to either predict how many drinks they can have over a given time frame and stay within their drinking limit or to know how much time needs to pass before their blood alcohol level reachs a safe value. The lag time between drinking and peak blood alcohol level can be surprisingly long. Also, the time required to "process" alcohol down to safe levels can be longer than expected. The accuracy of the simlation is best if you are a man weighing 155 lb. If you are smaller, than the simulation will under-predict the alcohol level in your blood and vice versa. This is because the size of the body compartments used in the simulation correspond to a 70 kg man. However, the predicted distribution of alcohol in different parts of the body is less sensitive to overall body size.
During the winter of 2008, I had the opportunity to teach a course in chemical engineering to the 4th year cadets at the Royal Military College of Canada in Kingston. The textbook we used was “Elements of Chemical Reaction Engineering”1. Given some teaching freedom and the fact that these student would probably never work in a normal chemical engineering job because of their military future, I chose examples to work through that I found interesting. The last assignment we did also formed the basis for the final exam and I called it “Human Ethanol Processing”. It was a model, in chemical engineering terms, of the flow and "processing" of alcohol in human body2. The students liked it.
The fluid-like parts of the body are divided into five compartments with interconnections between some of them. Each compartment was modelled as a well-mixed tank (a CSTR in chemical engineering terms). The stomach was considered to have a variable volume with one input (from the mouth) and one output (to the GI). Its volume was exactly the same as the volume of alcoholic beverage remaining in it. From the stomach, alcoholic fluid is squeezed into the gastrointestinal tract (GI) at a rate that depends on the volume of beverage in the stomach (and the alcohol concentration). The more beverage in the stomach, the faster it flows into the GI tract and surrounding tissues. There is a continuous flow of fluid through the liver--about 2/3 from the GI tract and 1/3 from the blood stream. It is in the liver where alcohol is metabolised enzymatically. However, fluids pass through the liver quickly compared to the rate that it gets broken down or metabolised. So, for each pass through, most alcohol remains untouched. The blood is considered part of the central compartment, which also includes other organs, including the brain and skin. There is a continuous bypass of some blood through the muscles and fat tissues, which are lumped into the fifth compartment. Below is a schematic showing how these five compartments are related to each other:
In the methods described by Fogler et. al. (see below), the liver was modelled as a plug-flow reactor rather than a well-stirred tank. However, I found that almost identical results were obtained, in this case, for either approach. It is because the residence time of ethanol in the liver is so short relative to its reaction rate that the concentration of ethanol is almost constant from one end to the other.
The first step in alcohol metabolism is oxidation to acetic acid (with acetaldehyde as the intermediate):
The rate of ethanol metabolism was modelled by the following rate expression:
where CE is the concentration of ethanol in the liver and Vmax,ALDH and KM, ALDH are constants related to the enzyme reaction.
On a differential basis, the molar balances for each of the five compartments are shown below:
Basically, the terms on the left hand side represent rates of ethanol entering a compartment and the terms on the right side represent rates of ethanol leaving. The balance around the liver also has a depletion term (r) due to metabolism.
The symbols need explaining. The compartment volumes (in liters) are those with a capital V and a subscript (S for stomach, G for GI tract, M for muscles, L for liver and C for central).
So the first balance around the stomach says that the rate of volume decrease depends on the current volume of stomach contents. The flow through rates for the liver and muscles are mu_L and mu_M (liters/min.).
For a standard 69.4 kg man, the volumes and volumetric rates are:
VC = 11.56 liters
VM = 25.76 liters,
VL = 1.11 liters,
VG = 2.4 liters,
mu_L = 1.25 liters/min, and
mu_M = 1.5 liters/min.
The kS term is a stomach emptying coefficient. It turns out to be a non-linear function of the amount of ethanol in the stomach. The kS coefficient was modelled as:
kS = kSmax/(1 + aD^2)
where
a = 1.22 mol-2,
kSmax = 0.05 min-1 and
D = dose, moles of ethanol in the stomach.
The values for ethanol metabolism were:
KM = 0.0004 mol/liter
KmaxALDH = 2.2 mmol/(min kg liver)
As a check on the program validity, the predicted results were the same as Fogler’s predicted results, which was also consistent with the experimental results shown in Fig. 2C in Ref. 2 (for ten 70 kg men).
The model sems to predict nicely the amount (as moles) of ethanol throughout the body as a function of time including metabolism in the liver. The model is quite good at predicting blood alcohol concentration (moles/liter) if you are a 70 kg man. However, what if you are not? For the same amount of ethanol, a larger compartment means the concentration is lower. This is because concentration is moles of ethanol per unit volume (liter) of compartment. So, if you have smaller compartments than the 70 kg man then the ethanol concetration will be higher for the same amount of ethanol. So, for the same number of drinks and time, the ethanol concentration in your blood will be higher than predicted with this model. The reverse is true if your body mass is greater than 70 kg. However, the time of the peak blood alcohol level will be the same regardless of your body mass.
A standard drink (beer, wine or spirits) corresponds to very closely the same amount of alcohol3 . A 12 oz. beer (~5% alcohol), a glass of wine (5 oz., ~12% ethanol), and a shot of hard liquor (~40% alcohol, 1.5 oz.) each have 0.6 oz. of pure ethanol.
Wikipedia has a nice explanation of the different ways that alcohol contration in the blood is expressed4. The unit of measure in the United States , Australia and Canada is percent BAC by volume. One percent BAC is equivavlent to 0.2174 mol/liter. The following table is from the Wikipedia site:
| BAC, % | Behaviour |
| 0.01-0.03 | average person appears normal |
| 0.03-0.59 | mild euphoria, sense of well-being, relaxtion, talkativeness, decreased inhibition |
| 0.06-0.10 | blunted feelings, disinhibition, extroversion, impaired sexual pleasures |
| 0.11-0.20 | over-expression, emotional swings, anger or sadness, boisterousness |
| 0.21-0.29 | stupor, loss of understanding, impaired sensations |
| 0.30-0.39 | severe depression, unconsciousness, death possible |
| >0.40 | unconsciousness, death |
The level for a drunk driving charge in the United States and Canada is a BAC percent greater than 0.08%.
1Elements of Chemical Reaction Engineering, 4th Edition, H. Scott Fogler and Nihat M. Gurmen, Prentice Hall, 2008.
2David M. Umulis, Nihat M. Gurmen, Prashant Singh, H. Scott Fogler, “A physiologically based model for ethanol and acetaldehyde metabolism in human being, Alcohol, 35, p. 3-12, 2005.
3http://pubs.niaaa.nih.gov/publications/
Practitioner/pocketguide/
pocket_guide2.htm.
4http://en.wikipedia.org/wiki/Blood_
alcohol_content.