Dolorimeter

A dolorimeter is an instrument used to measure pain tolerance. Dolorimetry has been defined as "the measurement of pain sensitivity or pain intensity." There are several kinds of dolorimeter that have been developed. Dolorimeters apply steady pressure, heat, or electrical stimulation to some area, or move a joint or other body part and determine what level of heat or pressure or electric current or amount of movement produces a sensation of pain. Sometimes the pressure is applied using a blunt object, or by locally increasing the air pressure on some area of the body, and sometimes by pressing a sharp instrument against the body.

Palpometer
A dolorimeter known as the Sonic Palpometer was developed at the University of Victoria in British Columbia, Canada. Patents have been applied for worldwide. The Sonic Palpometer uses ultrasound and computer technology to automate the physician's technique of palpation to determine sensitivity of some part of the patient's body.

The related Pressure Controlled Palpometer (PCP) uses a pressure-sensitive piece of plastic film to determine how much pressure is being applied in palpation. This technique appears to be more reliable than unaided palpation.

Techniques using lasers
Svensson et al (1997) describe the use of a CO2 laser or a contact thermode to heat the skin and elicit a pain response.

A laser-based dolorimeter called a Dolorimeter Analgesia meter is marketed by IITC Life Sciences.

Techniques using heat lamps
Another pain measurement device uses heat from a 500 Watt lamp which is delivered to a small area of skin.

Other dolorimeters

 * Baseline Algorimeter from the Kom Kare Company.
 * Björnström's algesimeter measures sensitivity of the skin to pain.
 * Boas' algesimeter measures sensitivity over the epigastrium

Other terms for similar instruments include algesiometer, algesichronometer (which also takes time into consideration), analgesia meter, algometer, algonometer, prick-algesimeter, pressure-algometer.

Dolorimeters for animals
The Hot Plate analgesia meter measures response to mice and rats placed on a hot plate.

The Tail Flick analgesia meter measures the movement of the animal's tail in response to a painful sensation. An intense light beam is focused on the animal's tail, and then a timer begins. When the animal flicks its tail, the timer stops and the recorded time is a measure of the pain threshold.

A pressure analgesia meter uses a stepper motor to gradually increase pressure on the animal's paw.

History
In 1940, James D. Hardy, Harold G. Wolff and Helen Goodell of Cornell University introduced the first dolorimeter as a method for evaluating the effectiveness of analgesic medications. They did their work at New York Hospital. They focused the light of a 100 Watt projection lamp with a lens on an area of skin that had been blackened. They found that most people expressed a pain sensation when the skin temperature reached 113 °F (45 °C). They also found that after the skin temperature reached 152 °F (67 °C), the pain sensations did not intensify even if the heat was increased. They developed a pain scale, called the "Hardy-Wolff-Goodell" scale, with 10 gradations, or 10 levels. They assigned the name of "dols" to these levels. Unfortunately, other researchers were not able to reproduce the results of Hardy, Wolff and Goodell and the device and the approach was abandoned. Harvard Medical School Professor and Massachusetts General Hospital Anaesthetist Henry K. Beecher (1957) expressed skepticism about this method of measuring pain.

In 1945, Time Magazine reported that Cleveland's Dr. Lorand Julius Bela Gluzek had developed a dolorimeter that measured pain in grams. Dr. Gluzek claimed that his dolorimeter was 97% accurate.