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Biomedical subjects

P M Farr

Publications and source records attributed to P M Farr.

At least 19 recordsLinked to original sources
PubMed1992

The relationship between chronological age and the erythemal response to ultraviolet B radiation.

To investigate whether erythemal responses to ultraviolet radiation alter with age, we have reviewed the results of monochromator phototesting in adults and children, and have measured the dose-response curves for UVB erythema in a further 38 subjects. There was no significant difference between adults and children in minimal erythema dose (MED) at 300 nm; the median MED in 254 adults was 34 mJ/cm2 (range 14-80 mJ/cm2) and in 24 children aged less than 15 years was 30 mJ/cm2 (range 10-80 mJ/cm2). Objective measurements of UVB-induced erythema were performed in 15 subjects aged below 25 years and 23 subjects aged above 60 years. A dose-response curve for UVB erythema was constructed for each subject and the slope of the steepest part of each curve calculated by logit regression; the values in the young subjects were greater than in the older group (P less than 0.02). However, there was no difference between the two groups in either the visually assessed MED or the calculated UVB dose required to produce a constant degree of mild erythema.

Adult↗
PubMed1992

Neutrophilic alveolitis in Sweet's syndrome.

In a case of Sweet's syndrome (acute febrile neutrophilic dermatosis) neutrophilic alveolitis was found by lung biopsy. Pulmonary disease in this condition may be underrecognised yet, like the dermatological features, it responds rapidly to corticosteroids.

Aged↗
PubMed1992

A dose-response study of irritant reactions to sodium lauryl sulphate in patients with seborrhoeic dermatitis and atopic eczema.

The susceptibility of the skin of patients with seborrhoeic dermatitis to surfactant irritation was investigated and compared to that of a group of normal subjects and patients with a history of atopic eczema. Responses to six concentrations of sodium lauryl sulphate (SLS), applied to forearm skin, were assessed clinically and measured by laser Doppler flowmetry. Analysis of dose-response curves showed statistically significant increased susceptibility to SLS-induced irritation in patients with seborrhoeic dermatitis and atopic eczema compared with normal subjects. Increased susceptibility to chemical irritation may be important in the pathogenesis of seborrhoeic dermatitis.

Adolescent↗
PubMed1991

Sunscreen protection against UVB, UVA and blue light: an in vivo and in vitro comparison.

The photoprotection against UVB, UVA and blue light provided by a widely prescribed sunscreen (RoC 15+ A+B) was compared with two new products containing microfine titanium dioxide (Sun E45 lotion SPF 15 and Sun E45 cream SPF 25) [corrected]. Comparisons were made in vivo using photosensitive patients with either chronic actinic dermatitis or erythropoietic protoporphyria, and in vitro using a newly developed spectrophotometric assay. Good agreement was obtained between the in-vivo and in-vitro methods at each waveband. All products showed high protection against UVB radiation, but the products containing microfine titanium dioxide showed significantly higher protection against both UVA and blue light than RoC 15+ A+B. Products containing microfine titanium dioxide are likely to offer superior photoprotection in those patients who are abnormally sensitive to long wavelength ultraviolet radiation than products which are currently available on prescription.

Adult↗
PubMed1991

PUVA treatment of psoriasis in the United Kingdom.

Information concerning the operation of 134 PUVA units in 96 dermatology centres in the U.K. was collected by a postal questionnaire. The most common protocol was to give PUVA three times weekly in the treatment of psoriasis, and to choose the initial dose of UVA according to skin type. However, the initial UVA dose encompassed a range of five or more within each skin type.

Clinical Protocols↗
PubMed1991

The action spectrum between 320 and 400 nm for clearance of psoriasis by psoralen photochemotherapy.

We have compared the effectiveness of oral 8-methoxypsoralen photochemotherapy (PUVA) using ultraviolet fluorescent lamps with peak emission at either 325, 352 or 370 nm in the treatment of 24 patients with psoriasis. The forearms of each patient were treated three times weekly with two of the three lamps. The erythemal sensitivity of each patient was tested before the first treatment to ensure that equally erythemal doses of radiation were given from each of the lamps. A side-to-side comparison was used to assess response to treatment at weekly intervals for the 6 weeks of the trial. The lamp with peak emission at 325 nm was shown to be significantly superior to either of the other lamps in terms of response assessed at weekly intervals, and time to clearance of psoriasis. An action spectrum, constructed from the median doses required for clearance of psoriasis using each of the lamps, showed that the effectiveness of the radiation decreased exponentially with increasing wavelength throughout the UVA waveband, such that radiation at 320 nm was an order of magnitude more effective than at 360 nm. This suggests that lamps with peak emission around 325 nm will be more effective than those conventionally used in PUVA units with a peak emission at 352 nm. Lamps with peak emission around 325 nm are also highly effective in the treatment of psoriasis with phototherapy alone. Thus a single treatment unit containing these lamps could be used either for PUVA or ultraviolet phototherapy of psoriasis, avoiding duplication or irradiation equipment.

Adolescent↗
PubMed1991

The relationship between plasma psoralen concentration and psoralen-UVA erythema.

The plasma 8-methoxypsoralen (8-MOP) concentration was measured in 60 patients commencing psoralen photochemotherapy (PUVA). At the time of blood sampling each patient was phototested using a series of 10 exposures to UVA. The resulting erythema was measured objectively 72 h after irradiation and dose-response curves for psoralen-UVA erythema were constructed. Although the dose of 8-MOP was calculated according to body weight, patients receiving 30 mg of 8-MOP had a significantly lower mean plasma concentration than those receiving higher doses. There was no significant correlation between plasma 8-MOP concentration and minimal phototoxic dose, either estimated visually or calculated from the dose-response curves. However the slope of the dose-response curve showed significant correlation with plasma 8-MOP concentration. The variation between patients in the rate of increase of the erythemal response, but not the variation in threshold sensitivity, can be explained by difference in plasma psoralen concentration.

Adolescent↗
PubMed1991

Measurement of cutaneous inflammatory reactions using a scanning laser-Doppler velocimeter.

The performance of a new scanning laser-Doppler velocimeter (LDV), which can rapidly measure blood flux over a large area of skin without contact with the skin surface, was compared with that of a conventional laser-Doppler instrument. The vascular response was measured to a range of doses of UVB, and dilutions of contact allergens and sodium lauryl sulphate. The detection threshold of the scanning LDV was equal to, or lower than, that of the conventional instrument. For allergic contact hypersensitivity reactions (ACH), the coefficient of variation was significantly less using the scanning LDV. The scanning LDV allowed accurate measurement of the change in area that occurs with increasing intensity of inflammatory reaction. For ACH reactions the area of inflammation continued to increase at dilutions where blood flux had reached a plateau. The flare area was found to increase linearly with log dose of histamine with no change in blood flux.

Dermatitis↗
PubMed1990

Inhibition of photosensitivity in erythropoietic protoporphyria with terfenadine.

The effect of terfenadine on the response to irradiation with blue light was measured in seven patients with erythropoietic protoporphyria. Terfenadine caused significant inhibition of the immediate flare reaction, but did not alter the erythemal response localized to the irradiation sites. Treatment with beta-carotene had no effect on the flare and erythemal responses. However, the flare reaction was still inhibited by terfenadine during treatment with beta-carotene. These results show that histamine release is involved in the mechanism of porphyrin photosensitivity. H1 receptor antagonists may be of use in the treatment of patients with erythropoietic protoporphyria.

Adolescent↗