Thermal Biofeedback

James Wright
Humboldt State University

Thermal biofeedback provides feedback on changing skin 
temperature. Skin temperature is a significant characteristic 
because it is linked to sympathetic nervous system arousal which 
affects vasoconstriction and vasodilation and therefore blood 
flow. Sympathetic nervous system arousal leads to increased 
vasoconstriction, reducing the blood volume and cooling the skin.
Thermal biofeedback is measured by heating a temperature 
sensitive probe called a "thermistor", made of small pieces of 
heat-sensitive electrical material encased in electrically 
insulated material, taped or strapped to the skin. A thermistor 
only makes thermal contact with the skin, not electrical contact, 
and will only accept heat from the skin, maintaining the same 
temperature as the skin to which it is attached, with a slight 
delay. The probe works by reducing electrical resistance when it 
increases in temperature and increasing electrical resistance when 
it cools. Ohm's Law (V=IR) specifies that under constant voltage, 
increasing the resistance (R) will decrease the current (I) and 
lowering the resistance increase the current. Therefore, as the 
thermistor cools, its resistance to electrical current increases 
and less current will flow through the thermistor. As the 
thermistor warms, its inherent resistance is lowered and more 
current flows through it. In this way, information about 
temperature is sent electrically.
While no particular site is superior for the attachment of 
the thermistors, two principles must be taken into account: 1) 
surfaces with fewer sweat glands are preferred since sweating can 
lead to artifacts caused by evaporative cooling and 2) the 
attachment site should not be artificially warmed by other parts 
of the body or objects. Other artifacts occur due to temperature 
changes not resulting from vasoconstriction or vasodilation, such 
as cool or warm room temperature, breeze, probe contact, 
"blanketing", and chill. A cool room may, for the same degree of 
vasoconstriction, lower skin temperature simply because cool air 
absorbs more heat than warm air. The effect of a cool room may 
also absorb more heat from the probe in a likewise fashion. A 
breeze exaggerates the cooling effect since moving air absorbs 
more heat from the skin than still air and moving air evaporates 
sweat more quickly than still air. The temperature of the room 
will set the approximate low temperature limit for the body, since 
a body cannot cool more than the air surrounding it. This is not 
an issue except in un-air conditioned rooms in a hot climate. 
Additionally, differences in temperature effect the circuits of 
the biofeedback device by slightly increasing or decreasing 
resistance in the device. If the probe lifts from the skin, lower 
readings are likely. Furthermore, covering the probe with a hand, 
clothing or other object, called "blanketing", will give higher 
readings. Someone entering from a cold outside environment will 
likely have cold skin, especially extremities, and care must be 
taken to allow them back to temperature before beginning a thermal 
biofeedback session.     
Natural warming occurs with the stopping of activity and 
especially with rest. Natural warming also takes place after 
ingestion of caffeine, nicotine, and other chemicals. Body 
position can also affect sympathetic nervous system arousal and 
peripheral blood flow.
Another important factor in thermal biofeedback is 
restricting the use of caffeine and nicotine since both are proven 
strong peripheral vasoconstrictors. Interestingly, psychological 
studies have shown that caffeine and nicotine are most commonly 
used by high-anxious people.
Thermal biofeedback has found application in the improvement 
of circulation, relaxation of breathing, migraine headaches, 
Raynaurd's disease, hypertension, diabetes, and Irritable Bowel 
Syndrome. 
Thermal biofeedback has been shown to be quite effective for 
migraine and mixed headaches (symptoms resemble both migraine and 
tension headaches). A meta-study of 25 clinical studies of 
propranolol, the leading migraine medication, and 35 relaxation 
and thermal biofeedback studies could reveal no consistent 
advantage for either treatment.
Pediatric headaches have been found to respond more 
effectively to relaxation and biofeedback. In a study by Blanchard 
(1992) he found that thermal biofeedback "has consistently led to 
significant improvement and to 67% or better of the samples being 
clinically improved." He also states "headache reductions noted at 
the end of treatment have been maintained at follow-up of up to 1 
year." Blanchard concludes from his study "TBF (thermal 
biofeedback) may be the treatment of choice for pediatric 
migraine." Other studies have shown marked improvement for over 
80% of subjects.
Conclusions about the effectiveness of thermal biofeedback 
for menstrual-related migraines are not yet clear. There is at 
present weak support. 
More than twenty years has passed since the discovery of the 
association between reduced migraine headaches and hand warming. A 
threshold for migraine reduction seems to be 96?F. In another 
study by Blanchard (Blanchard, et al., 1983) found that 63% of 
subjects who achieved hand warming  above this threshold were 
successful in migraine pain reduction.
Raynaud's disease symptoms involve spasm of the arterioles 
and small arteries in the digits of the hands and feet and tri-
phasic skin color changes. Occasionally, symptoms effect the nose 
and tongue, yet rarely involve the thumb. Spasm duration may be 
from minutes to hours. Cold exposure is the usual stimulus for 
spasms, but emotional and other psychological events may trigger 
them. Vasospastic attacks may be lessened significantly with 
peripheral vasoconstriction. The study by Friedman (Friedman, 
1987) employed a cold stimulus as a challenge with thermal 
biofeedback. There was 66.8% reduction in symptoms in the thermal 
feedback group, as opposed to a 32.6% reduction without thermal 
biofeedback, and a 92.5% reduction in symptoms for the group 
employing the cold stimulus challenge and thermal biofeedback. 
These results were maintained for 3 years following treatment.     
Thermal biofeedback can be used as a breathing feedback 
system to enhance relaxed breathing by attaching the thermistor to 
the scalp apex. Normal levels of CO2 increases cerebral blood 
flow. It has been asserted that this gives an index of blood flow 
in the brain.
Patients trained with thermal biofeedback were observed to 
reduce their blood pressure. Additionally, supine and standing 
norepinephrine levels decreased with biofeedback trained reduction 
in blood pressure. In another study incorporating thermal 
biofeedback with blood pressure monitoring, EMG, and breath rate, 
58% of patients were able to eliminate medication and an 
additional 35% of patients reduced hypertension medication by 
half. A third study by McGrady (1994) had 49% of thermal 
biofeedback patients lowering mean arterial pressure by at least 
5mm Hg. Significant decreases in measures of anxiety and plasma 
aldosterone also were observed.
The rationale for the use of thermal biofeedback is that 
increased sympathetic nervous system activity commonly observed 
during stress constricts the blood vessels in the skin. The 
decreased blood flow results in lower temperatures. In contrast, 
decreased sympathetic activation results in less vasoconstriction. 
Therefore, as patients warm their hands they are decreasing 
neurally mediated vasoconstriction. However, Friedman (1991) has 
shown that increases in temperarture mediated by thermal 
biofeedback by non-hypertensives depends on non neural factors 
whose identities have yet to be determined.
Thermal biofeedback may be useful in maintaining circulation 
in the hands and feet, although data on this application is 
incomplete. A study by Bailey, (Bailey, et al., 1990), reported a 
patient with little temperature sensation was still able to 
increase hand and finger temperature via thermal biofeedback. 
A study by Guthrie (1983) treated diabetes mellitus type I 
patients with a combination of thermal biofeedback and EMG (more 
common for diabetes). Four of seven patients achieved a decrease 
in units of insulin required to maintain glucose levels. 
Thermal biofeedback has also been used in the treatment of 
Irritable Bowel Syndrome, with mixed results, to help reduce 
autonomic arousal and disregulation. While early results showed 
promise, larger samples of patients showed clinical improvement 
similar to that of placebo. However, those that underwent 
biofeedback and relaxation training had treatment gains that 
lasted up to four years, which could not be said of the placebo 
group.
Thermal biofeedback has shown a proven track record for 
attenuating symptoms in a variety of disorders and further 
applications are continually being examined and evaluated. 

References

Schwartz 1995 Biofeedback: A Practioner'S Guide. The Guilford 
Press. New York, New York

Blanchard, E.B. 1992 Psychological treatment of benign headache 
disorders. Journal of Consulting and Clinical Psycology, 60(4), 
537-551

Blanchard, E.B., Andrasik, F., Neff, D.F., Arena, J.G., Ahles 
T.A., Jurish, S.E., Pallmeyer, T.P., Saunders, N.L., Teders, S.J., 
Barron, K.D., and Rodickok, L.D. 1983 Psychophysiological 
responses as predictors of response to behavioral treatment of 
chronic headache. Behavior Therapy, 14(3), 357-374

Freedman, R.R 1987 Long-term effectiveness of behavioral 
treatments for Raynaurd's disease. Behavior Therapy, 18, 387-399

McGrady, A.V. 1994 Effects of group relaxation training and 
thermal biofeedback on blood pressure and related 
psycophysiological variables in essential hypertension. 
Biofeedback and Self-Regulation, 19(1), 51-66

Freedman, R.R. 1991 Physiological mechanisms of temperature 
biofeedback. Biofeedback and Self-Regulation, 16, 95-115

Guthrie, D., Moeller, T., and Guthrie R. 1983 Biofeedback and its 
application to the stabilization and control of diabetes mellitus. 
American Journal of Clinical Biofeedback 6(2), 82-87

Copyright © 2003, Dr. John M. Morgan, All rights reserved - This page last edited April 23, 2003
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