Search PubMed⌕ Search

Biomedical subjects

R M Dwyer

Publications and source records attributed to R M Dwyer.

At least 37 records · Page 2Linked to original sources
PubMed1986

Comparison of laser-welded and sutured arteriotomies.

We compared the histologic features, tensile strength, and collagen synthesis of laser-welded and sutured arteriotomies. Four bilateral canine femoral or carotid arteries, 2 cm long, were studied at one through four weeks postoperatively, with one vessel (control) closed with interrupted 6-0 polypropylene sutures and the contralateral vessel (experimental) welded with an argon laser (0.5 W [1417 J/cm2], four-minute exposure per 1-cm length of incision). Histologic examination revealed that laser-welded arteriotomies had less inflammatory reaction, more normal collagen and elastin reorientation, and similar endothelial continuity when compared with the control, sutured wounds. The tensile strength of the one- and two-week laser-welded specimens was less than that of sutured wounds and became approximately equal to sutured repairs at three and four weeks. There were no significant differences in the rate of collagen synthesis. There was no evidence of abnormal healing in the laser-welded specimens, suggesting that argon laser welding may be an alternative to suture repair of arteriotomies.

Animals↗
PubMed1986

Biological effects of laser welding on vascular healing.

The feasibility of welding thin-walled microvessels by laser has been established. This report summarizes our experience using laser welding to repair thick-walled, high-pressure, 4 to 8-mm canine arteries using CO2, Nd:YAG, and argon lasers. The CO2 laser did not produce seals that could withstand arterial pressure. Nd:YAG laser welds were initially successful, but the majority failed within 20 to 40 minutes. The argon laser uniformly sealed 2-cm-length arteriotomies that healed rapidly within 4 to 6 weeks and had less foreign body response compared to sutured controls. Laser welding may represent an alternative for repair of small- and large-diameter vessels with several advantages compared to conventional suture techniques.

Animals↗
PubMed1986

Skin closure by Nd:YAG laser welding.

Skin incisions 6 mm in length were made on the backs of hairless mice. Control wounds were closed with interrupted 5-0 Prolene sutures, and experimental wounds were approximated and closed by laser welding using a Nd:YAG laser. The wounds were examined daily, and specimens were excised at weekly intervals for histopathologic study, transmission electron microscopy, tensile strength determination, and type I collagen-specific messenger ribonucleic acid measurements. The laser-welded wounds demonstrated rapid healing. Histologic study showed a functional scar tissue at day 7 and a minimal residue of the original wound at day 14. Tensile strength of the control and experimental wounds was similar at all time points. The levels of collagen-specific messenger ribonucleic acid were significantly higher in the sutured group in comparison with the laser group or with normal control skin. This study suggests that laser welding might have advantages over suturing, since the former is sterile and nontactile, does not require introduction of foreign material into the wound, and provides subjectively improved cosmetic results.

Animals↗
PubMed1985

Differential effects of Nd-YAG laser on collagen and elastin production by chick embryo aortae in vitro. Relevance to laser angioplasty for removal of atherosclerotic plaques.

Aortae from 17-day old chick embryos were subjected to irradiation with a Nd:YAG laser at energy densities varying from 1.2 - 4.7 X 10(3) J/cm2. The aortae were pulse-labeled in vitro with [3H]proline or [14C]valine, and the synthesis of collagenous polypeptides and soluble elastin was examined by SDS-polyacrylamide gel electrophoresis, followed by fluorography and quantitative scanning densitometry. Irradiation of the aortae with Nd:YAG laser resulted in inhibition of the synthesis of the extracellular matrix proteins. The production of collagen was inhibited to a considerably larger degree than the production of elastin. Thus, the biosynthetic pathway for collagen production appears to be more susceptible to laser inhibition than the corresponding pathway for elastin production. These observations may have relevance to laser angioplasty which has been proposed to be applicable for removal of atherosclerotic plaques in human vessels. Specifically, the results suggest that inhibition of the extracellular matrix production may result in weakening of the vessel wall with subsequent aneurysm formation and rupture.

Animals↗
PubMed1985

Computer analysis of laser dosimetry data: a method of accurate energy density delivery.

In the past, utilization of the laser in medicine has been limited by the lack of accurate quantification of the energies delivered to the tissue. Data obtained in the course of this investigation have demonstrated the relationships which exist between the energy delivered to the tissue and the optical system composed of the fiber and focusing lens. A continuous-wave multimode Nd:YAG laser (1,064 nm) was used in these experiments. Utilizing the beam scan technique previously described, we recorded over 100 beam profiles at various distances from the handpiece (fiber optic and lens). Computer analysis of our data established the mathematical correlation between the surface area of the irradiated spot and the distance of the handpiece to the target, thus allowing us to predict the surface area of the irradiated spot to any desired distance. By duplicating our methods with his particular optical system, the clinician or any laser user has the capacity to determine the energy delivered to the tissue (J/cm2) by knowing the power of the laser (watts), the time of exposure (seconds), and the distance of the handpiece to the treatment site (centimeters).

Computers↗
PubMed1984

Nonthermal effects of ND:YAG laser on biological functions of human skin fibroblasts in culture.

Previous studies have indicated that laser can selectively affect the biological functions of cells. In the present study, the role of a thermal component in laser-induced alterations in the biology of human skin fibroblasts was examined. Cells were cultured on 96-well tissue culture plates, subjected to treatment with the Nd:YAG laser (wavelength 1,064 nm), and the temperature of the medium was monitored by a microprobe connected to a telethermometer . For comparison, parallel cultures were heated to the same temperatures by tungsten-halogen lamp. The cell cultures were analyzed for collagen synthesis by incubating the cultures with [3H]proline, and the collagen production was assayed by the synthesis of nondialyzable [3H]hydroxyproline. The rate of DNA replication was also determined by measuring the uptake of [3H]thymidine. A marked decrease of collagen production and thymidine incorporation was noted in the cultures subjected to Nd:YAG laser. No such decreases were noted in cultures heated to the corresponding temperatures by tungsten-halogen lamp. The results thus indicate that the biochemical alteration caused by the Nd:YAG laser in human fibroblast functions cannot be explained on the basis of thermal effects.

Collagen↗
PubMed1984

Laser treatment of keloids: a clinical trial and an in vitro study with Nd:YAG laser.

Biochemical studies utilizing keloid fibroblast cultures revealed that Nd:YAG laser selectively suppressed collagen production by these cells. Based on these in vitro observations, eight patients with keloids were treated with Nd:YAG laser in a nondestructive manner. Results, with a 3-year follow-up, indicated flattening and softening of the lesions. Thus, the results suggest that Nd:YAG laser is an effective treatment modality for keloids, and its mechanism may involve bioinhibition of fibroblast functions.

Adult↗
PubMed1984

Control of connective tissue metabolism by lasers: recent developments and future prospects.

Various laser modalities are currently in extensive use in dermatology and plastic surgery, particularly for treatment of vascular and pigmented lesions. A relatively new area of laser utilization involves the possible biologic effects of the lasers. In this overview, we are summarizing our recent studies, which indicate that lasers at specific wavelengths and energy densities modulate the connective tissue metabolism by skin fibroblasts both in vitro and in vivo. Specifically, the neodymium-yttrium-aluminum-garnet (Nd: YAG) laser was shown to selectively suppress collagen production both in fibroblast cultures and in normal skin in vivo, thus suggesting that this laser modality may be useful for the treatment of fibrotic conditions such as keloids and hypertrophic scars. Furthermore, two low-energy lasers, helium-neon (He-Ne) and gallium-arsenide (Ga-As), were shown to stimulate collagen production in human skin fibroblast cultures, suggesting that these lasers could be used for enhancement of wound healing processes. These experimental approaches illustrate the future possibilities for applying lasers for the modulation of various biologic functions of cells in tissues and attest to the potential role of lasers in the treatment of cutaneous disorders.

Animals↗
PubMed1983

The qualitative effects of laser irradiation on human arteriosclerotic disease.

To determine the effects of laser irradiation upon human coronary atherosclerotic disease, coronary plaques were extracted from fresh human cadaver hearts. Seventy-four diseased artery samples were sectioned either transversely or longitudinally and subjected to laser treatment from argon-ion and carbon dioxide sources. The laser beam affected vaporization and patency in fibrous, lipoid, and calcified plaques as observed histologically. Calcified blockage showed greater extent of charred remnants following controlled thermal injury than did fibrous or lipoid obstructions. The area and depth of penetration varied directly with intensity and duration of photoirradiation and inversely with the density of the atherosclerotic tissue. This study supports further research work on the use of lasers to effect relief of atherosclerotic obstructions.

Coronary Disease↗
PubMed1983

Wound healing: biological effects of Nd:YAG laser on collagen metabolism in pig skin in comparison to thermal burn.

Pig skin was treated with the Nd:YAG laser at 1,060 nm or electrocautery, at energy densities of 649 +/- 20 J/cm2 and 612 J/cm2, respectively. Biopsies of treated areas and of normal skin were performed at 7, 14, and 60 days after treatment and processed for histology, electron microscopy and biochemical assays. Wound healing, as shown histologically, was similar in both treated groups. Depth of injury appeared to reach reticular dermis at day 7 in each treated group. However, thermal burn was more destructive of regular collagen, whereas the laser appeared to damage deep dermal blood vessels without destroying surrounding connective tissue. Biochemical assays revealed increased collagen production and increased collagenolytic activity 7 days after laser injury. However, by day 60, there was a reduction in total collagen content in laser treated skin below that of normal skin, which correlated with decreased collagen synthesis and unchanged collagenolytic activity. In burn specimens there was an initial decrease in total collagen content which reverted to normal by day 60. Active collagen degradation occurred at all 3 time points, but a marked increase in synthetic activity occurred as the burn scar was laid down. Laser treatment resulted in reduction of the amount of collagen below that in burn scarred or normal skin, suggesting that classical scar formation may be inhibited. These results indicate that the Nd:YAG laser may be useful for the treatment of keloids and hypertrophic scars.

Animals↗
PubMed1983

Effects of the Nd:YAG laser on DNA synthesis and collagen production in human skin fibroblast cultures.

Human skin fibroblasts were subjected to treatment with a Neodymium:YAG laser at 1060 nm with varying levels of energy determined by a reproducible method of dosimetry. DNA synthesis in the cells was measured by the incorporation of [3H]thymidine, and collagen production was monitored by the synthesis of nondialyzable [3H]hydroxyproline after incubation of cells with [3H]proline. Using energy levels equal to 1.7 X 10(3) J/cm2, a significant reduction in DNA synthesis was noted, while the cells remained viable as tested by the trypan blue exclusion test. With energy levels higher or equal to 2.3 X 10(3) J/cm2, the suppression of DNA synthesis was accompanied by cell nonviability. The collagen production, when measured immediately following the treatment with 1.7 X 10(3) J/cm2, was markedly reduced, and similar effects were observed with higher energy levels. However, when the cells were tested for collagen production at 20 hours following laser treatment, there was a significant decrease in collagen production at energy levels as low as 1.1 X 10(3) J/cm2, a dose that did not affect DNA synthesis or cell viability. Thus, the results indicate that the Nd:YAG laser can selectively suppress collagen production without affecting cell proliferation. These observations suggest that laser treatment could potentially be used to reduce collagen deposition in conditions such as keloids and hypertrophic scars.

Cells, Cultured↗
PubMed1982

A new method of dosimetry-a study of comparative laser-induced tissue damage.

The use of lasers in medicine and surgery has increased slowly-its effectiveness based on trial-and-error clinical experience. Very little comprehensive data has been published that scientifically presents dosage, energy, absorption, and comparisons between types of lasers. Our laboratory has developed a method for taking the guesswork out of laser dosage using scientific data to optimize therapy and give reproducible responses. Experiments were conducted using an argon laser, a neodymium: YAG laser, and a broad-band infrared light source. This preliminary study uses a beam scan technique, which for the first time permits accurate measurement of the laser intensity incident on tissue. Therefore, this protocol allows the standardization of dosage measurements with good experimental reproducibility in biological models. By using this accurate method of measuring the intensity delivered to pigskin, we are able to reproduce for the first time similar histological damage with the different energy sources.

Animals↗
PubMed1982

Nd: YAG laser therapy of rectosigmoid bleeding due to radiation injury.

The Nd:YAG laser was used to treat a patient bleeding from the rectosigmoid as a result of radiation injury related to therapy for cervical carcinoma. Successful laser therapy was performed after a diverting colostomy failed to control persistent bleeding. Further surgical procedures were not required. Characteristics of Nd:YAG laser as compared with those of the carbon dioxide and argon lasers are considered.

Carcinoma, Squamous Cell↗
PubMed1980

Cecal diverticulitis in young patients.

Of the patients with cecal diverticulitis, 24 to 50% are below the age of 30, and such cases are usually misdiagnosed preoperatively as appendicitis. Two young patients with cecal diverticulitis were diagnosed preoperatively by barium enemas. The barium enemas correctly identified the extent of the disease. Treatment was tailored to the clinical and roentgenographic findings with both patients requiring elective colon resections.

Adult↗
PubMed1978

Colon polyps, sebaceous cysts, gastric polyps, and malignant brain tumor in a family.

A unique family with a distinct syndrome of adenomatous colonic polyps and sebaceous cysts without osseous or soft tissue abnormalities is presented. One member had benign gastric polyps limited to the upper half of the stomach and another had a medulloblastoma of the cerebellum. A histologic feature in the colon of the propositus was the presence of atypical epithelium in flat mucosa as well as in the colonic polyps.

Adolescent↗
PubMed1976

Endoscopic argon-ion laser phototherapy of bleeding gastric lesions.

An argon-ion laser, coupled to a flexible fiberoptic endoscope, was used to photocoagulate experimentally produced bleeding gastric ulcers in dogs. Argon-ion laser phototherapy rapidly and effectively achieved hemostasis in all bleeding ulcers. Bleeding arteries up to 2 mm in diameter were photocoagulated. Intact normal gastric mucosa was exposed to laser energy for varying periods of time to determine if transmural photothermal injury occurred. Exposure for greater than 15 seconds at 1.0 w of throughput power caused microscopical evidence of transmural injury. Healed, laser-treated ulcers could not be differentiated from nontreated control ulcers or normal stomach one month after injury. The Beer law and the heattransfer factors relating to soft tissues are discussed. The coupled argon-ion laser-endoscope may be a safe tool to treat self-limited superficial bleeding gastric lesions.

Animals↗