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Thermography and thermoregulation of the face
© Rustemeyer et al; licensee BioMed Central Ltd. 2007
Received: 21 February 2006
Accepted: 15 March 2007
Published: 15 March 2007
Although clinical diagnosis of thermoregulation is gaining in importance there is no consistent evidence on the value of thermography of the facial region. In particular there are no reference values established with standardised methods.
Skin temperatures were measured in the facial area at 32 fixed measuring sites in 26 health subjects (7–72 years) with the aid of a contact thermograph (Eidatherm). A total of 6 measurements were performed separately for the two sides of the face at intervals of equal lengths (4 hours) over a period of 24 hours. Thermoregulation was triggered by application of a cold stimulus in the region of the ipsilateral ear lobe.
Comparison of the sides revealed significant asymmetry of face temperature. The left side of the face showed a temperature that was on the average 0.1°C lower than on the right. No increase in temperature was found following application of the cold stimulus. However, a significant circadian rhythm with mean temperature differences of 0.7°C was observed.
The results obtained should be seen as an initial basis for compiling an exact thermoprofile of the surface temperature of the facial region that takes into account the circadian rhythm, thus closing gaps in studies on physiological changes in the temperature of the skin of the face.
Within the framework of careful differential diagnosis of a wide range of different syndromes thermography has become increasingly important over the last few years since the introduction of the clinical diagnosis of thermoregulation by Schwamm1. Since it is simple and painless to perform and thus well accepted by patients, and its results are also well reproducible, thermography has become established an integral component of complex diagnostic schemata, especially in the diagnosis of pain and monitoring of the course of peripheral disorders of the cardiovascular circulation [2, 3]. The diagnosis of thermoregulation is used on the one hand to determine the pattern of skin temperature in selected areas of the body during minimal stress to the regulation system [4, 5], and on the other to record thermoregulation in these areas following the application of a defined cold stimulus [6, 7], laser irradiation  or even acupuncture .
previous diseases of the mouth, jaw or in the field of facial surgery
acute inflammations of the upper respiratory tract
facial cold injury or facial sunburn during the last 12 weeks
dental treatment during the last 4 weeks
pharmacotherapy with vasoactive substances or hormonal treatment including contraceptive pills
cosmetics in the face and neck area
use of nicotine or alcohol on the day of measurement
sports activities up to 2 hours before the measurement
Conduct of the study
While the circadian rhythm of the core body temperature is now probably one of the best investigated functions of the human body , to date there is no clear evidential basis on the circadian rhythm of the skin surface temperature in the facial region. Whereas muscular activity and ingestion of food were long considered to be decisive factors in the circadian fluctuations , these hypotheses have been disproved by various studies [25, 26]. In his classification of temperature differences in the trunk and extremities before and after stimuli triggering thermoregulation, Rost  defined differences of 0.1–0.2 C as static temperature and 0.3–0.5 C as reduced temperature following thermoregulation. However, this was also not confirmed by further studies in the facial region. More recent results indicate that the extent of thermoregulation is far smaller, the differences ranging between 0.1 and 0.2 C [21, 22].
In the present study particular consideration was given to the dependency of the surface temperatures and thermoregulation responses on the circadian rhythm. No clearly significant thermoregulation response to application of the cold stimulus was verified at any measuring time. The small changes in temperature detected in individual branches of the trigeminus nerve remained the same at all times of day, and thus the conduct of thermographic determinations at between 8 a.m. and 12 a.m. as recommended by Rost  failed to produce significant results. However, in healthy subjects increases in temperature of 0.1°C following application of a cold stimulus are only detectable in isolated cases, as demonstrated by Krischek-Bremerich and Bremerich . Thus the significance of the small differences in temperature still classified by the above authors as thermoregulation should be reconsidered.
While some authors  still assume lateral symmetry of corresponding measuring sites, others [27–29] report temperature asymmetries of between 0.1°C and 0.3°C in the facial region which follow a regular pattern. This is consistent with our own observations, showing that left facial side temperatures are in a mean 0.1°C consistently lower than on the right side with no significance on subjects' ages. Irrespective of lateral asymmetry, in our subjects the skin surface temperature in the facial region showed a significant circadian rhythm under standardised conditions. The mean temperature difference of 0.7°C was only slightly below the 1°C mean fluctuation in the core temperature reported by Brück  and that of 1.2°C to 1.5°C found by Hensel . The times at which the minimum and maximum temperatures were determined are also within the range demonstrated for the reference temperature, with a minimum in the early morning hours and a maximum in the evening.
The results of this study in healthy subjects should prompt a reconsideration of the significance of thermographic diagnosis in the facial region. The next goal should be to establish an exact thermoprofile of the skin surface temperature in the facial region that takes into account the circadian rhythms, thus filling in the gap with regard to the body surface temperature left by studies on physiological changes in body temperature to date.
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