How to Understand Non-Invasive Breath Analyzers

6106
Advertisement

Breath Analyzers are used to descry and quantify the alcohol content in the subject’s breath non-invasively. These are invented by Robert Frank Borkenstein. These devices generate an estimated Blood Alcohol Concentration (BAC) in some acceptable units. Although the observed air/breath has small amount of alcohol concentration, though the results are relatively true to the actual values.

Evaporation of alcohol from the circulating blood to the lungs air is the basis of Breath Analyzer devices. After absorption of alcohol by the digestive organs, it enters the blood stream and travels through the body. During the breathing process, the oxygen from the lungs air enters into the blood and carbon-dioxide from the blood stream evaporates into the breath. When a person is drunk, in addition to carbon-dioxide, a modest quantity of alcohol also gets released into the breath through gaseous exchange process. As per The Henry’s law, the quantity of alcohol available in the person’s breath depends on its concentration in the blood stream. In equilibrium, the ratio of concentration of alcohol in blood (Blood Alcohol Concentration-BAC) to that in breath (Breath Alcohol Concentration-BrAC) is 2300:1 and it is almost constant. Statutory BAC limits are reported in concentration units of mg/100 ml, mg/g, g/l or mg/ml and the corresponding BrAC limits are reported as mg/l, g/l and g/100 ml, depending on the country.

Figure 1. Gaseous exchange (a) Normal person; (b) Drunken person
Figure 1. Gaseous exchange (a) Normal person; (b) Drunken person

To get a reliable BAC measurement, the sampled breath must be nearest to the blood vessel. Figure 1 shows the gaseous exchange profile of a normal person and a drunken person. In lungs there present a small deep capillaries viz. alveoli which are closest to the blood vessels by a thin membrane. Carbon-dioxide from the blood vessels along with alcohol content is exhaled through the alveoli.

Breath alcohol concentration measures how intoxicated a person is at a given time. The results can fluctuate even within the course of a day. The more alcohol a person consumes, the higher his BAC should be. If he stops consuming alcohol, his BAC may still continue to rise because some of the alcohol consumed earlier may not have been absorbed into the bloodstream at the time of the initial testing. Eventually, if consumption is discontinued, the level of alcohol in the blood should begin to drop, resulting in a lower BAC.

Advertisement

The ongoing demand to create a device for Breath Analysis which should be portable, accurate, simple to operate & calibrate, provide data safety and integrable with modern smartphones prompted STMicroelectroincs to develop “Breath Analyzer” using embedded technology. The design is compact and easy to calibrate at user level using NFC link. The high quality solenoid air-pump along with Fuel-Cell sensor makes these devices veracious.

Solenoid Air Pump
Solenoid air pump is used to collect the sample, then throwing it on-to the sensor wafer (Fuel-Cell). The sensor is then activated for a predefined interval; say 200 mS. The collected sample is then blown-out through solenoid air-pump to reset the sensor wafer so that the new sample could be collected. This way, the procedure is triparted – Sampling; Holding and Reset. The solenoid air-pump area is directly proportional to the sample volume. The typical values of solenoid diameter and sample volume are given in the Table-1 below:

Screen Shot 2016-04-04 at 18.08.29
Table-1: Solenoid air-pump diameter vs. sample volume

Advertisement


1 COMMENT

SHARE YOUR THOUGHTS & COMMENTS

Please enter your comment!
Please enter your name here