Fri, May 16, 2003 - Page 19 News List

Tech reviews

By David Momphard  /  STAFF REPORTER

Time was when having your temperature taken was a pain in the butt, or at least a mild discomfort. In the 1800s, German physician Carl Wunderlich made the original study of normal human body temperature by inserting a thermometer in the rectum of thousands of Europeans.

The result of his study was that a healthy human body should be some 37℃ at rest (Wunderlich was also among the first to describe fever as a symptom, not a disease by itself).

While rectal temperature is still considered the most accurate, scientists and physicians have since been looking for an easier means of taking a temperature without asking patients to drop their pants.

The process is now much easier than in Wunderlich's day, but not necessarily as accurate. Anyone living in SARS-affected Taipei knows that temperature readings can vary with each new building they enter.

There are two reasons for this: First, your body naturally changes temperature over the course of the day and, second, different thermometers will record different temperatures based on the type of technology involved.

The consensus among physicians today is the most accurate of these devices are the ones that are the newest to the market; temporal artery thermometers, so called because they gauge your temperature on the side of your forehead at the temple.

These devices were developed by the Exergen Corporation in the US and studies by both Boston Children's Hospital and Harvard Medical School have found that the company's device is more accurate than ear thermometry and more accurate than even rectal thermometers in responding to changes in fever.

The reason for this, doctors say, is that the temple sits on the carotid artery, the artery that carries blood directly from the aorta to the head and the only such artery positioned close enough to the skin's surface to provide the access needed to take an accurate measurement.

These devices all use an infrared beam which takes from several dozen to a thousand measurements per second. The best of them measure the temperature of both the tissue covering the artery and the ambient temperature, then calculate the average of the highest readings. This latter point is where lesser models fail; trying to quantify the skin temperature with the body's core temperature.

Exergen's TemporalScanner is considered among the best of its kind for its ability to tackle this equation, but currently isn't in wide use in Taiwan. Most local establishments that are screening patrons for fever are using less expensive models that often don't factor in the skin's relation to a room's ambient temperature and so do not provide as accurate a reading.

Other types also use infrared technology but aren't as accurate as the best of the temporal models.

Spot infrared thermometers often look like a science-fiction ray gun and work by directing a beam of light at the forehead or inner ear. The drawback to these models, other than their lack of accuracy, is the danger that comes with accidentally shining the infrared beam in the subject's eyes, which can cause temporary blindness and sometimes permanent damage.

The more popular variety that uses the same technology is the ear thermometer. While these aren't likely to make you go blind, they're not very likely to accurately take your temperature either.

Dozens of ear thermometers tested at the National Physics Laboratory in the UK showed that some models erred by up to 0.5℃.

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