Biomedical subjects

Brian L Diffey

Publications and source records attributed to Brian L Diffey.

6 recordsLinked to original sources

PubMed2004

Towards optimal regimens for the UVB phototherapy of psoriasis: a mathematical model.

A mathematical model is described that predicts the response of psoriasis to a treatment course of UVB irradiation. The basis of the model is that UVB acts by a direct effect on keratinocytes and that cell cycle arrest is the major mode of action in the phototherapeutic response in psoriasis. Although it is unlikely that UVB causes resolution of psoriatic plaques through a single mechanism, the current model has been based on epidermal cell cycle arrest and entry into the terminal differentiation compartment because this is likely to be a significant rate-limiting factor in determining response to treatment. The model has been validated against results obtained from published clinical studies on narrowband (TL-01) UVB phototherapy for psoriasis. The principal outcomes of the model are that for a given erythemal response, the number of exposures required for clearance is almost independent of the frequency with which patients attend for treatment and that the higher the exposure dose per treatment, the more rapidly will clearance result. The model has been used to suggest optimal regimens for the treatment of outpatients and inpatients.

Cell Division↗

PubMed2003

Sun protection factor determination in vivo using a single exposure on sunscreen-protected skin.

BACKGROUND: Determining sunscreen sun protection factors (SPFs) in a cohort of volunteers, particularly on products designed to provide high levels of protection, can be time-consuming. The conventional approach is to administer to each subject a series of exposures (normally between five and seven) on their sunscreen-protected skin. METHOD: A method, based on Gaussian statistics, is proposed that requires just a single exposure on the sunscreen-protected skin in volunteers to arrive at a reliable estimate of the mean SPF of a test product. RESULTS/CONCLUSION: The method is shown to yield an estimate of a product's mean SPF that is comparable, or better, in accuracy to estimates obtained by conventional multi-exposure testing.

Cohort Studies↗

PubMed2002

Sources and measurement of ultraviolet radiation.

Ultraviolet (UV) radiation is part of the electromagnetic spectrum. The biological effects of UV radiation vary enormously with wavelength and for this reason the UV spectrum is further subdivided into three regions: UVA, UVB, and UVC. Quantities of UV radiation are expressed using radiometric terminology. A particularly important term in clinical photobiology is the standard erythema dose (SED), which is a measure of the erythemal effectiveness of a UV exposure. UV radiation is produced either by heating a body to an incandescent temperature, as is the case with solar UV, or by passing an electric current through a gas, usually vaporized mercury. The latter process is the mechanism whereby UV radiation is produced artificially. Both the quality (spectrum) and quantity (intensity) of terrestrial UV radiation vary with factors including the elevation of the sun above the horizon and absorption and scattering by molecules in the atmosphere, notably ozone, and by clouds. For many experimental studies in photobiology it is simply not practicable to use natural sunlight and so artificial sources of UV radiation designed to simulate the UV component of sunlight are employed; these are based on either optically filtered xenon arc lamps or fluorescent lamps. The complete way to characterize an UV source is by spectroradiometry, although for most practical purposes a detector optically filtered to respond to a limited portion of the UV spectrum normally suffices.

Calibration↗

PubMed2002

What is light?

Explore the source record for details and available documents.

Humans↗

PubMed2002

Is daily use of sunscreens of benefit in the U.K.?

BACKGROUND: There is an increasingly widespread belief that year-round use of topical agents containing ultraviolet (UV)-absorbing ingredients is an important factor in reducing the chronic degenerative cutaneous changes associated with sun exposure. OBJECTIVES: To evaluate the benefit of using sunscreens during different periods of the year for people living in the U.K. METHODS: An analysis was made of typical solar UV exposure at different times of the year in relation to different topical sunscreen practices. RESULTS: It was shown that using sun protection products during the six summer months (April-September) can reduce the lifetime (70 years) UV exposure of a person by an equivalent of almost 40 years unprotected exposure. However, virtually no benefit is gained from using UV protective products from October to March in the U.K. CONCLUSIONS; As their use is not without cost and the risk of adverse effects, topical products containing UV filters are best avoided during October to March in the U.K.

Adolescent↗

PubMed2002

The effect of UV absorbing sunscreens on the reflectance and the consequent protection of skin.

The in vivo reflectance spectra of Caucasian skin, coated with preparations containing sunscreen vehicle, vehicle with olive oil and vehicle with the UVB and UVA absorbers 2-ethylhexyl-4-methoxycinnamate and 4-t-butyl-4'-methoxydibenzoylmethane were determined. All preparations reduced the reflectance of skin throughout the UVA spectral range (320 to 400 nm), with the sunscreen preparations containing the UVB and UVB plus UVA absorbers reducing the reflectance more than the sunscreen vehicle alone. This phenomenon, which facilitates the penetration of UV radiation to the lower epidermis and dermal layers of skin and therefore lessens sunscreen efficacy, is attributed to optical coupling mediated by refractive index matching of the sunscreen to the upper epidermis. The greater reduction in skin diffuse reflectance caused by sunscreens containing methoxycinnamate is associated with this compound's high refractive index. Also, by determining the excitation spectra of the autofluorescence originating from the dermal layer of skin, the transmission spectra of the various components of sunscreen on skin were established, and these were in good general agreement with previously published spectra.

Benzoates↗