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Biomedical subjects

O T Tan

Publications and source records attributed to O T Tan.

At least 55 records · Page 3Linked to original sources
PubMed1987

The pulsed dye laser: its use at 577 nm wavelength.

The ability to increase laser-induced cutaneous blood vessel damage selectivity is dependent upon optimizing various intrinsic laser parameters. Varying the laser emission wavelength, pulse duration, and/or incident energy dosage allows the clinician potential improvement in the laser treatment of cutaneous small blood vessel processes such as port-wine hemangioma and telangiectasia. The pulsed dye laser at 577 nm and a pulse duration of 300 to 400 microseconds, incorporates desired laser parameters into its design. Clinical evaluation of the therapeutic outcome with this laser reveals favorable results while significantly minimizing potential adverse side effects.

Hemangioma↗
PubMed1987

Tunable pulsed dye laser for the treatment of benign cutaneous vascular ectasia.

A tunable pulsed dye laser emitting at 577 nm and 360 microseconds pulse width was used to treat benign cutaneous vascular ectasias other than port wine stain in 77 patients. Except for leg telangiectasias (34 patients), the overall response was excellent. Forty-two of forty-five patients with hemangiomas, spider nevi, angioma serpiginosum, venous lakes or facial telangiectasias showed excellent results after 1-4 consecutive treatments. Scarring was observed in none of the patients. These results confirm previous data on the use of the tunable dye laser in the treatment of port wine stain, and suggest that 577 nm wavelength and 360 microseconds pulse width allow the selective photothermolysis of vascular cutaneous ectasias with better clinical results than previously reported.

Adult↗
PubMed1987

Treatment of port-wine stains at 577 nm: clinical results.

A pulsed, dye laser at 577 nm was used to treat 65 patients with port-wine stains. Results clearly indicate that the laser parameters of dose, wavelength, and pulse duration contribute to the outcome of laser treatment of port-wine stains.

Adolescent↗
PubMed1987

[Selective photothermolysis: contribution to the treatment of flat angiomas (port wine stains) by laser].

Since 1962, lasers have been used in dermatology and have become the first choice in the treatment of superficial, vascular ectasia. Lasers are unique sources of light; they are coherent, monochromatic, collimated and intense. By careful selection of wavelength, pulse duration, and intensity, it is often possible to selectively confine a laser effect to a specific histologic structure in tissue, depending upon the tissue properties. The ideal treatment of Port Wine Stains (PWS) should irreversibly damage the ectatic vessels but minimize heating of the epidermis and superficial dermis. A theory, called selective photothermolysis, predicts the optimal combination of laser parameters of achieving this ideal treatment of PWS to be a wavelength of 577 nm, a pulse duration of 0.35-10 msec, and an energy per surface area of about 7-8 J/cm2. Laser wavelength: The wavelength of 577 nm is preferred because it: maximizes the selective absorption by hemoglobin, minimizes absorption by epidermal melanin, provides sufficient depth of penetration in the blood to coagulate 0.1 mm vessels allows penetration of light into dermis up to 1 mm. Laser pulse duration: A pulse-width in the range of 0.35-10 msec allows the temperature elevation to be uniform inside the vessel and to be confined to the vessel area. Shorter pulses superheat the red blood cells causing explosive boiling and hemorrhage. Longer pulses allow heat to diffuse away from vessels, requiring greater energies per pulse to achieve vessel damage. An increased energy per pulse increases the risk of excessive damage to surrounding tissue.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1986

Tunable dye laser (577 nm) treatment of port wine stains.

Despite steady improvement in the laser treatment of port wine stains (PWS), hypertrophic scarring remains a serious side-effect in approximately 10% of patients. The tunable dye laser (577 nm) has been shown to cause selective vascular destruction in normal and PWS skin. We have treated ten patients using a tunable dye laser (577 nm, 300 mu sec) resulting in clearing of the PWS without any evidence of hypertrophic scarring. Treatment requires no anesthesia or wound care, and there were no postoperative infections.

Adolescent↗
PubMed1986

Effect of cutaneous hypoxia upon erythema and pigment responses to UVA, UVB, and PUVA (8-MOP + UVA) in human skin.

The effect of oxygen deprivation upon UVA-, UVB-, and PUVA-induced pigment and erythema responses in normal human skin was examined. Before exposure, varying degrees of hypoxia in the skin of the forearm were achieved by inflating a sphygmomanometer cuff applied to the upper arm. After the transcutaneously measured pO2 had stabilized, sites on the inner forearm were exposed to UVA, UVB, or 8-MOP + UVA radiation, to determine dose thresholds for the induction of erythema and pigmentation at different cuff pressures. Inflation of the cuff to greater than systolic pressure completely inhibited immediate and delayed pigment responses (IPD, DT) to UVA doses greater than 10 times the normal pigmentation threshold dose. UVA-induced delayed erythema responses were partially inhibited by cuff inflation: 2.7 times the minimal erythema dose of UVA was necessary to cause an erythema response when exposure occurred during vascular occlusion. In contrast, erythema and pigment responses to UVB and PUVA were unaltered by cuff pressures exceeding systolic pressure during exposure. Inhibition of UVA-induced erythema and pigment responses by vascular occlusion were reversed by the transcutaneous diffusion of 100% O2. These findings indicate that the cutaneous responses to UVA and UVB occur by separate pathways differing with respect to O2 dependence. Our findings agree with those of other studies which indicate that PUVA-induced phototoxicity and melanogenesis are not O2-dependent.

Administration, Topical↗
PubMed1986

Effect of dye laser pulse duration on selective cutaneous vascular injury.

The pulsed dye laser at 577 nm, a wavelength well absorbed by oxyhemoglobin, causes highly selective thermal injury to cutaneous blood vessels. Confinement of thermal damage to microvessels is, in theory, related to the laser exposure time (pulsewidth) on selective vascular injury. This study investigates the effect of 577 nm dye laser pulsewidth on selective vascular injury. Nine Caucasian, normal volunteers received 577 nm dye laser exposures at pulsewidths of 1.5-350 microseconds to their skin. Clinical purpura threshold exposure doses were determined in each volunteer, and biopsies of threshold and suprathreshold doses were examined in each volunteer. The laser exposure dose required to produce purpura increased as pulsewidth increased in all 9 subjects (p less than 0.001). This finding corresponds to laser pulsewidths equal to or exceeding the thermal relaxation times for dermal blood vessels. Histologically, vessel damage was selectively, but qualitatively, different for short vs long pulsewidths. Pulsewidths shorter than 20 microseconds caused vessel wall fragmentation and hemorrhage, whereas longer pulsewidths caused no significant hemorrhage. The purpura noted clinically appears to be due to a coagulum of intralumenal denatured erythrocytes. At 24 h, there was marked vessel wall necrosis at all pulsewidths. The short pulsewidths may cause erythrocyte vaporization, rapid thermal expansion, and mechanical vessel rupture with hemorrhage. Long pulsewidths appear to cause thermal denaturation with less mechanical vessel damage. The selective, nonhemorrhagic, vascular necrosis caused by the long-pulsewidth dye laser may lead to a more desirable clinical outcome in the therapy of blood vessel disease processes.

Capillary Permeability↗
PubMed1986

Histologic responses of port-wine stains treated by argon, carbon dioxide, and tunable dye lasers. A preliminary report.

Although the blue-green argon laser light has been used successfully to treat port-wine stains (PWSs) for many years, it produces substantial epidermal damage. We have previously shown in normal human skin that pulsed yellow tunable dye lasers (577-nm wavelength) can cause highly selective damage to cutaneous microvessels with minimal injury to the overlying epidermis. Pulsed tunable dye lasers also produce selective vascular injury in the abnormal vessels of PWSs, with clinically apparent lightening of the lesions. Both epidermal injury and fibrosis are less severe with this laser treatment than with argon and carbon dioxide laser treatments. Clinical and histologic responses of PWSs treated by argon, CO2, and pulsed yellow dye lasers were compared and followed up for one month in three patients. Although larger and longer-term clinical trials are necessary to fully evaluate this new treatment modality, it appears that pulsed yellow laser radiation offers a more selective, less traumatic, and probably superior form of treatment for PWSs.

Adult↗
PubMed1985

Transcutaneous oxygen tension as an index of maturity in hypertrophic scars treated by compression.

Sixteen patients undergoing compression treatment for scar hypertrophy were included in a study to evaluate physical indices of scar maturity. The results show that while thermographic measurements of scar temperature were not clinically valuable, rising levels of transcutaneous oxygen tension in treated scars correlated well with a reduction in scar thickness assessed both clinically and by ultrasound. It is postulated that low levels of tcpO2 in immature scars result from low oxygen diffusibility through scar tissue rather than from rapid metabolic consumption of oxygen by scar tissue.

Adolescent↗
PubMed1985

Ultrastructural changes in human skin after exposure to a pulsed laser.

Selective vascular injury following irradiation using a pulsed laser source at 577 nm was examined using ultrastructural methods in the skin of 3 fair-skinned healthy human volunteers. This vascular-specific damage was confined to the papillary dermis. Red blood cells were altered in several ways. As well as an increase in the electron density, configurational distortion modified the normal biconcave forms to ameboid structures. The most interesting finding was the appearance within these altered cells of well-defined circular/oval electron-lucent areas of 800 A diameter, possibly representing a heat-fixed record of steam formation within the red blood cell. In addition, considerable degenerative changes were evident in endothelial cells and pericytes, while mast cells, neutrophils, histiocytes, and fibroblasts as well as collagen bundles immediately surrounding most laser-damaged blood vessels appeared normal.

Adult↗
PubMed1985

Effect of skin temperature on selective vascular injury caused by pulsed laser irradiation.

The effect of skin temperature on vascular-specific injury caused by pulsed laser irradiation was examined. Ten healthy human volunteers were exposed to 1.5 microsecond pulses from a dye laser tuned to 577 nm. Compared to normothermic conditions (33 degrees C skin temperature) significantly more laser energy (p less than 0.01) was required to produce grossly visible purpura when the skin was cooled to 20 degrees C or heated to 40 degrees C. Histologically, laser-induced damage was confined to blood vessels at all three skin temperatures studied. At purpura threshold dose, there was intravascular agglutination without extravasation of red blood cells at 20 degrees C whereas at 33 degrees and 40 degrees C there was extravasation of red blood cells.

Adolescent↗
PubMed1984

The effect of epidermal pigmentation on selective vascular effects of pulsed laser.

The effect of epidermal pigmentation on the threshold exposure dose for inducing purpura with a tunable dye laser at 577 nm, 1.5 microseconds pulse duration, was studied in 21 human volunteers with varied genetically determined amounts of melanin. More laser energy was required to produce purpura as constitutive skin pigmentation increased. Histology showed that, in lighter skin, the laser threshold dose produced the most specific vascular injury with no disruption of surrounding structures. In more pigmented skin, damage occurred in the epidermal basal layer and very few changes were seen in blood vessels below.

Adolescent↗
PubMed1980

Blood flow changes with naftidrofuryl in systemic sclerosis and Raynaud's phenomenon.

Blood flow was measured in patients with Raynaud's phenomenon, systemic sclerosis and in normal controls by venous occusion plethysmography on the forearm and calf, and changes in blood flow in the finger were followed by calorimetry. Intravenous naftidrofuryl oxalate (praxilene) improved blood flow to the skin of the finger as measured calorimetrically in seven of sixteen patients with Raynaud's phenomenon and systemic sclerosis. The drug markedly reduced blood flow in the finger in all ten normal control subjects. However, naftidrofuryl increased blood flow as measured by venous occlusion plethysmography in the leg both of normal subjects and of those with Raynaud's phenomenon. In addition to these findings, no significant change in blood flow in response to the drug was observed in the forearm. The reasons for these regional differences are discussed and considered to be due to redistributuion of blood flow as a result of differences in pharmacological receptor activity in different parts of the body and possible also due to effects of central control.

Adult↗