LOCALISED TEMPERATURE PERCEPTION

IN HEALTHY ADULTS

Jérôme Foussier

Medical Information Technology, RWTH Aachen, Pauwelsstr. 20, 52074 Aachen, Germany

Jennifer Caffarel, Jürgen Te Vrugt

Philips Technologie GmbH Forschungslaboratorien Aachen, Weißhausstr. 2, 52066 Aachen, Germany

Steffen Leonhardt

Medical Information Technology, RWTH Aachen, Pauwelsstr. 20, 52074 Aachen, Germany

Keywords: Local temperature perception, Peltier element, Temperature sensation rate.

Abstract: This paper presents a testing procedure for local temperature perception with a following evaluation of the

acquired information. Relative temperature changes had to be noticed by the subjects. To apply a

temperature effect a peltier element arrangement, permitting to cool down and heat up with one element, has

been utilized. First results show good correlation with a warmth sensation scale, although highly subjective

parameters have been interpreted. The error rate in detecting small temperature changes is higher than for

larger changes, except for very high changes, which caused temperature misperceptions.

1 BACKGROUND

In some therapies the effect of cooling and heating is

used to treat illnesses (e.g. cryotherapy in pain

management, taking cold showers after a sauna

session or in photo thermal therapy). Another

treatment shows that cooling down fresh burn

wounds to a certain temperature improves healing

and limits tissue damage (Venter, T., Karpelowsky,

J., Rode, H., 2000). The use of superficial heat

results in higher tendons and ligament flexibility,

muscle spasm reduction, pain alleviation, blood flow

elevation or even boosts the metabolism (Kaul M.

P.; Herring S. A., 1994).

In therapies the affected areas sometimes are

smaller so that an overall cooling or heating would

not make more sense than a local temperature

change. In general the human body is a bad

temperature measurement device and the

temperature sensation increases while stimulating

bigger areas

(Parsons, K. C., 2003). It is possible to

believe there is a change to hot temperatures even

when temperature is decreasing. This can be shown

by the “grill effect” (Craig, A. D., 2002) for

example, where two metal plates, one hotter than the

other, both over skin temperature, are placed close-

by, and the person perceives a hot sensation. The

first grill illusion was created by interlaced warm

and cold stimuli at 40°C and 20°C by Thunberg in

1896 (Defrin, R. et al., 2002). Reducing the area

reduces the complexity of the hardware and the

needed power. The stimulation would be more

precise.

Mostly, larger areas of the body are heated up or

cooled down, but what about cooling and heating

local spots and can even small temperature changes

(e.g. ±1°C) be detected on a small area of skin? If

not, how big should the temperature step should at

least be to notice a change and is there a difference

between hot to cold change or cold to hot? This

paper will describe a testing procedure to answer

those questions.

2 TECHNICAL DESCRIPTION

In general the designed system handles temperature

ranges from 17°C to 40°C in a controlled way,

199

Foussier J., Caffarel J., Te Vrugt J. and Leonhardt S..

LOCALISED TEMPERATURE PERCEPTION IN HEALTHY ADULTS.

DOI: 10.5220/0003154801990203

In Proceedings of the International Conference on Biomedical Electronics and Devices (BIODEVICES-2011), pages 199-203

ISBN: 978-989-8425-37-9

 2011 SCITEPRESS (Science and Technology Publications, Lda.)

regarding the safe temperature ranges applied to the

skin, where temperatures below 15°C become

“slightly painful” as described in a study to develop

a European safety standard for touching cold

surfaces (Malchaire, J., et al., 2002). An application

of more than 45°C, close to burn threshold, evokes

pain (Parsons, K. C., 2003).

2.1 Cooling and Heating Device

The cooling and heating device consists of a 2.5cm

high built up peltier element arrangement (Figure 1).

Both sides of the element are glued on 3x3cm large

aluminum plates, of course thermally isolated each

other. Similar arrangements can also be found in

other construction, e.g. for rating the performance of

a peltier element. The bottom “cold” side is applied

to the skin. On the “hot” side, a ribbed heat sink with

a top-mounted fan ensures the dissipation of heat,

which is provoked by the peltier element itself, due

to the general poor energy efficiency of about 50-

60%. By inverting the flow direction of the electrical

current, it is possible to switch the “hot” and the

“cold” side of the peltier element, hence allowing

cooling and heating of the skin with one single

element.

Figure 1: Schematic view of the assembly.

2.2 Temperature Controller

A microcontroller controls the temperature on the

skin side by permanently evaluating the embedded

and calibrated temperature sensor. Using peltier

elements with alternating voltages or currents means

a further loss in efficiency, because the heat transfer

direction is inverted during the negative peaks of the

signal. This is the reason why a microcontroller-

regulated DC controller has been built to prevent the

negative effect and to keep the temperature constant

at the desired value. It also allows temperature

change rates on the skin in the order of 1-3°C/s.

The temperature controller can be managed via a

personal computer and adequate software. With a

graphical user interface (GUI), the investigator is

able to set the output temperature either manually or

automatically with a predefined list. A graph

displays real-time measured temperature values to

be able to control the correct functioning of the

hardware. In addition, an automatic program can be

started, which switches between two fixed

temperatures for a defined duration.

3 TEMPERATURE

PERCEPTION TEST

For the test the cooling and heating device was

attached to the forearm (see Figure 2).

Figure 2: Peltier element with fixing cuff applied to the

forearm.

This location is easily accessible, the fat layer is

not very thick and the thin skin is sensitive. In

addition possible hairiness of the person does not

affect the application.

Table 1: Overview of all subjects (values are in the format:

mean (standard deviation)).

Overall Female Male

Number 11 4 7

Over 30 yrs. 6 2 4

Under 30 yrs. 5 2 3

Age 36.8 (10.4) 33.75 (10.1) 38.6 (10.5)

neutral

[°C] 33.1 (2.1) 32.3 (0.5) 33.6 (2.6)

Table 1 gives an overview of all the subjects who

attended the test, where T

neutral

gives the individual

perception of the neutral sensed temperature of the

applied element. As not only the temperature but

also the kind of applied material and the contact

pressure play a role in temperature perception, the

neutral temperature is not necessarily equal to the

real skin temperature of the person. This is due to

BIODEVICES 2011 - International Conference on Biomedical Electronics and Devices

200

different contact coefficients and different resulting

contact temperatures t

(Lutz, P., 2002).

2211

tbtb

⋅

(1)

where b

and b

are the contact coefficients in

125.0 −−

°CmWs , t

and t

the contact temperatures

of the two materials in °C. Example values for

wood, steel and skin contact coefficients are

wood

≈ 400, b

steel

≈ 14000 and b

skin

≈ 1000. At room

temperature (22°C) the contact temperatures

between skin (34°C) and steel/wood are respectively

23°C and 31.5°C. This shows that wood feels

warmer than steel at equal object temperatures. To

feel the aluminum plate as neutral it consequently

has to be heated up and kept at a constant

temperature. It is important that the person has to get

used to the whole element, before the test can be

started to avoid any bias sensation. Afterwards the

test can be initiated:

The whole test procedure consists of five

different subtests:

1. Determining the neutral sensed temperature

neutral

of the peltier element

2. Varying the temperature slightly (max. ±Δ3°C)

around T

neutral

randomly

3. Varying the temperature in bigger random steps

(max. –Δ22°C and +Δ6°C to T

neutral

)

4. Cycling in time steps of 20s between two fixed

temperatures (e.g. 18°C ↔ 33°C)

5. Same as 2.

In case of an extreme discomfort, the subjects

were instructed how to remove the element from the

fixation rapidly and by themselves. The subjects

were asked to describe every change they noticed

and to rate their perception (e.g. spatial, temperature

and comfort), without knowing the actual

temperature value. The investigators wrote down

every remark during the test while the computer

displayed and recorded the temperature

measurement values. None of the persons sensed an

extreme discomfort with the applied temperatures.

Each subtest started and ended with the neutral

temperature to avoid any accommodation or greater

loss in sensitivity. The total duration of the test was

approximately 30 minutes for each person.

4 RESULTS AND DISCUSSION

Mainly there are two possibilities to interpret the

obtained information. The first one would be to

determine the difference between two temperature

set points, the second the difference between the

neutral temperature of the person and the set point.

For a start the focus was set on the first possibility,

by gathering all the occurrences of temperature steps

from the test (410 in total). To obtain a

representative graphical evaluation, five temperature

steps have been merged into one group and

normalised to the total number of occurrences in this

group.

Figure 3 shows the result of all persons. “■ 0”

means that the person did not detect a change or was

unsure, “■ ==” denotes a correct (e.g. sensation of

warming for an increase in temperature) and “■ !=”

an incorrect sensed temperature change.

Distinguishing between female/male persons or

under/over 30 years old persons did not produce

significant differences in results. The absolute sums

of the occurrences in the seven ranges are as

follows: [75, 26, 51, 119, 42, 31, 66]. Greater

temperature steps are better distinguishable (>70%)

than smaller steps and uncertainties or incorrect

answers are almost insignificant. The overall

average percentage of incorrect answers is less than

15%.

Grouped temperatures (normalised, m/f)

0,00

0,10

0,20

0,30

0,40

0,50

0,60

0,70

0,80

0,90

1,00

<-12°C -12…-8°C -7…-3°C -2…2°C 3…7°C 8…12°C >12°C

Temperature steps

Occurrences

Figure 3: Overall evaluation of perceived temperature

steps (normalised for male and female).

The above described test procedure allows

interpreting the average temperature sensation over

the whole testing time. As subtest 2 and subtest 5

use equal temperature steps (see chapter 3), one just

performed at the beginning, the other at the end of

the whole test, it is possible to give a trend on how

the sensitivity altered, especially for small changes

around the neutral temperature (±Δ3°C). The results

for this are given in Table 2, which gives a separate

LOCALISED TEMPERATURE PERCEPTION IN HEALTHY ADULTS

201

view on all, male and female persons, over and

under 30 years old persons. It is clear, that sensing

performance decreases. The subjects found it harder

to detect the small temperature steps after having

performed the two subtests with bigger temperature

steps before. If they had guessed for the temperature

changes, statistically the “==” and the “!=” data

would have changed similarly. In fact only the “==”

degraded significantly and the persons either tended

to say nothing or were confused by the sensation

(reconstructed on the basis of the acquisition

protocol) which leads in higher values for the “0”.

Striking points are the values for female persons in

the “!=” section, where the wrong perception of

temperatures increased instead of falling compared

to the other subjects. This could be explained by the

strong decrease in the “==” and the relative low

increase in the “0” section compared to the male

subjects. The incertitude for sensing a small

temperature change in this test is therefore higher for

female than for male persons.

Table 2: Comparison between the same subtests 2 and 5.

Subtest 2 Subtest 5 Difference

All 44.7% 37.8% -6.9%

Female 45.2% 35.5% -9.7%

Male 44.4% 39.2% -5.2%

> 30 years 37% 31.1% -5.9%

< 30 years 53.8% 45.9% -7.9%

All 14.1% 13.4% -0.7%

Female 9.7% 12.9% 3.2%

Male 16.7% 13.7% -3%

> 30 years 15.2% 13.3% -1.9%

< 30 years 12.8% 13.5% 0.7%

All 41.2% 48.8% 7.6%

Female 45.2% 51.6% 6.4%

Male 38.9% 47.1% 8.2%

> 30 years 47.8% 55.6% 7.8%

< 30 years 33.3% 40.5% 7.2%

Based on two existing scales of warmth

sensation, the Bedford comfort scale and the

ASHRAE sensation scale (Parsons, K. C., 2003), it

is possible to classify words like “cool”, “warm” and

“neutral” according to Table 3

(Parsons, K. C.,

2003).

Both combined with the delivered comments (a

total count of 341) of the tested persons, noted in the

acquisition protocol, and related to their neutral

perceived temperature, it is possible, even though

not always evident, to generate an intensity map of

the sensation (Figure 4). This is a potential

alternative to interpret the obtained data. In the

graph the temperature difference to the neutral

Table 3: Scales of warmth sensation.

Scale Bedford comfort scale

ASHRAE sensation

scale

7 Much too warm Hot

6 Warm Warm

5 Comfortably warm Slightly warm

4 Comfortable Neutral

3 Comfortably cool Slightly cool

2 Too cool Cool

1 Much too cool Cold

temperature is ranged from -22°C to +7°C on the

abscissa, where 0°C represents the neutral

temperature. The intensities of three temperatures

have been summed up, followed by a normalisation

to 1. The warmth scale is applied to the ordinate,

ranging from 1=cold to 7=hot.

Except for some outliers, especially around -

20°C, caused by a misperception of a big

temperature step (can be seen for “■ !=” in

Figure 3), the linear trend (dotted line) is clearly

noticeable and encourages the use of the sensation

scale as indicator, even if it could seem that the use

of words should deliver very vague information. It is

amazing that persons around the neutral temperature

(±Δ3°C) mostly say that it is comfortable, but cannot

notice small changes reliably (see Table 2).

Figure 4: Temperature sensation map, using a combination

of the Bedford comfort and the ASHRAE sensation scales.

In further work the post-analysis of the test by

another person should be replaced by a scale, where

the persons can enter themselves their perception in

the range of 1-7 (cold-hot). Integrated into a separate

input mask, such as a touch sensitive display, the

data acquisition could be automated as far as

possible thus reducing interpretation errors and the

amount of outliers which would give an even clearer

trend in the temperature sensation intensity map.

Also the effect of placebo could be investigated by

showing the persons “wrong” temperature values

and therefore subconsciously influencing their

temperature perception.

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The placement of the element shows one big

disadvantage: the exposure of the arm to the ambient

temperature could lead to a centralization of the

whole body resulting in colder extremities and a

possible lower temperature sensation. Answer to this

issue could be to cover the skin around the element

with a piece of cloth.

To conclude the discussion the results show that

small temperature changes (±Δ2°C in Figure 3) on a

small surface cannot be sensed reliably. For

reliabilities greater than 60% a temperature step of at

least ±Δ8°C is needed. A major difference between a

hot to cold and a cold to hot change could not be

definitively found in this testing, thus needing more

investigation on this open question.

ACKNOWLEDGEMENTS

Research was supervised by Prof. Dr.-Ing. Dr. med.

S. Leonhardt, RWTH Aachen University in Aachen

and has been supported by Dr. J. Caffarel and Dr. J.

te Vrugt of the Philips Research Aachen.

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and Sportsmedicine.

Parsons, K. C., 2003. Human thermal environments: the

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Craig, A. D., 2002. How do you feel? Interoception: the

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Defrin, R. et al., 2002. Sensory determinants of thermal

pain. In Brain

Malchaire, J., et al., 2002. Temperature Limit Values for

Gripping Cold Surfaces, In The Annals of

Occupational Hygiene.

Lutz, P., 2002. Lehrbuch der Bauphysik, Vieweg+Teubner

Verlag, 5th edition

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