Skin temperature of UV-induced erythema correlated to laser Doppler flowmetry and skin reflectance measured redness

Background/aims: The sensitivity of human skin to UV radiation is investigated by visual grading of the resulting erythema reactions 24 h after exposure to a series of increasing UV doses. Visual erythema assessment is, however, subjective and depends on pigmentation and redness of the adjacent un-irradiated skin and can be aided by skin reflectance spectroscopy and laser Doppler blood flow measurements. Erythema is accompanied by a raised skin temperature, and this reaction might be utilised as a simple objective measurement of UV sensitivity. Methods: Sixteen patients with cutaneous malignant melanoma, 16 patients with basal cell carcinoma, and 36 healthy people were phototested with simulated sunlight on previously UV un-exposed buttock skin. The resulting erythema reactions were graded visually 20-24 h post-exposure and measured by skin reflectance spectroscopy and laser Doppler flowmetry, and the surface skin temperature was determined in the erythema reactions and in adjacent un-irradiated skin by a contact thermometer. Results: Skin surface temperature in UV-induced erythema reactions was dose dependent, was statistically identical in skin cancer patients and in healthy people, and was age independent. The average temperature increase in barely perceptible erythema was 0.7°C (SD=1.1°C), and in bright red erythema it was 3.5°C (SD=2.0°C). Skin surface temperature increases were correlated to measurements by skin reflectance spectroscopy and by laser Doppler flowmetry. Conclusions: Skin surface temperature changes can be used as a simple objective measurement of UV sensitivity in healthy people and in skin cancer patients and may be particularly useful in heavily pigmented people where visual assessment of erythema is difficult or impossible.     

Skin temperature and phototest evaluation

The degree of erythema following UV irradiation is known to depend upon skin temperature at the time of UV exposure. We investigated whether changes in skin temperature at the time of erythema assessment influenced the level of erythema. Twenty-two healthy people (mean age 26 years) were irradiated with solar simulated radiation on previously UV un-exposed buttock skin. The erythematous reactions were evaluated 20–24 h after irradiation by visual scoring and by measurements of skin reflectance and laser Doppler flowmetry. The readings were done at the baseline level at 21°C room temperature where skin temperature was 30.0±1.7°C and subsequently after skin warming to 37.2±2.5°C and after cooling to 22.8±2.6°C. After skin warming, a clinically evaluated erythema grade [0, (+), +, + +, +++] was scored higher for at least one reaction in 10 of 22 individuals (45%). In the same proportion of subjects, changes to lower erythema grades were detected upon cooling. Skin warming caused an increase in laser Doppler blood flux, but skin cooling did not have a significant effect on cutaneous perfusion. Skin redness measured by skin reflectance was relatively stable during the cooling phase, but a significant increase in skin redness was noted for 0 reaction upon skin warming. For + + and + + + reactions a small but significant decrease in reflectance was noted. Our results indicate that alterations in skin temperature, especially a temperature increase, modulates the degree of UV-induced erythema moderately. The temperature-dependent changes as an assessment of the (+) reaction are of practical significance, since this reaction is used for the assessment of cutaneous photosensitivity.     

Alterations of skin microcirculatory rhythmic oscillations in different positions of the lower extremity.

Microcirculatory vasomotion is considered to be an important mechanism promoting and facilitating the transfer of blood cells through skin capillaries. Since skin vulnerability of the leg is closely associated with gravitational factors and skin micro-circulation, we investigated by a laser Doppler apparatus influence of postural changes on skin blood flow oscillations in lower limbs of healthy volunteers. Our data show a marked decrease in microcirculatory oscillation amplitudes at a frequency 7.6 (+/- 0.6) min-1 after lowering the leg. This could be reversed by the application of compressive bandage. Our study points toward a potentially important mechanism of microcirculatory impairment during orthostasis.     

Electronic UV dosimeters

Background/aims: The pathogenic role of ultraviolet (UV) in the development of skin cancer, skin ageing and immunosuppression makes it important to monitor human exposure to UV radiation. In a previous study we constructed UVB and UVC dosimeters based on a thermoluminescent phenomenon induced by UV in CaF₂:Dy and CaF₂ crystals. However, these dosimeters were insensitive to UVA radiation and readout was time-consuming. In the present study we aimed to develop an electronic dosimeter suitable for UVA, UVB and UVC. The principle of this dosimeter is a measure of accumulated electric current induced by UV on a photodetector.
Methods: Electric current induced by UV on a photodetector was accumulated in a Plessey's E-cell coulometer. A special reading device was constructed to quantify total charge of the coulometer. Sensitivity for UVA, UVB and UVC was achieved by the use of appropriate filters in front of the photodetector.
Results: The sensitivity of the electronic dosimeter increased with increasing wavelength of UV radiation; therefore, in UVB and UVC dosimeters the use of amplifiers was necessary. A linear response to UVA, UVB and UVC was achieved.
Conclusion: Dosimeters with a linear response to increasing doses of UVA, UVB and UVC have been constructed for personal monitoring of UV exposure.     

Epidermal thickness,skin pigmentation and constitutive photosensitivity

The important factors for UV sensitivity in humans are considered to be the skin pigmentation and the epidermal thickness. In this study on 73 Caucasians (age 20–85 years), we investigated in UV unexposed buttock skin the relationship between the UV sensitivity and constitutive skin pigmentation and thickness of the stratum corneum and the cellular part of the epidermis, in 34 normal people and in 39 skin cancer patients (20 patients with cutaneous malignant melanoma and 19 patients with basal cell carcinoma of the skin). Skin pigmentation was measured by skin reflectance spectroscopy, and UV sensitivity by phototest with a solar simulator. Thicknesses of the stratum corneum and the cellular part of the epidermis were determined by light microscopic evaluation of skin biopsies from the phototest areas. We found that epidermal thickness was independent of skin type and was not correlated to constitutive skin pigmentation. Thickness of the stratum corneum was statistically not different in normal persons and in skin cancer patients (P=0.4l) and was independent of gender (P=0.61) and age (P=0.56), while thickness of the cellular epidermis decreased with age (P<0.01). Stratum corneum thickness was found to be of minor importance for the constitutive UV sensitivity (accounting for on average 11% of the total photoprotection), which was mainly determined by the constitutive skin pigmentation (goodness-of-fit for correlation r=0.83). A theoretical model for the relationship of UV dose to induction of clinical erythema grade and skin pigmentation and thickness of the stratum corneum was developed. Objective measurements of skin pigmentation in UV unexposed skin by skin reflectance spectroscopy in Caucasians, normal people and people with cutaneous malignant melanoma and basal cell carcinoma of the skin predicts the constitutive UV sensitivity with a high degree of precision.     

Ultrasound in dermatology. Part I. High frequency ultrasound

This paper addresses the basic terminology of modern ultrasound equipment for the examination of the skin, the technical limitations of currently available equipment and the normal skin structure. Different applications for dermatosonography are discussed, and the paper summarises current knowledge about common sources of variation in the ultrasound image of the skin, such as skin tumours and selected skin diseases.