Search PubMed⌕ Search

Biomedical subjects

H A Green

Publications and source records attributed to H A Green.

12 recordsLinked to original sources
PubMed2006

How affected is oxygen metabolism in DWI lesions?: A combined acute stroke PET-MR study.

OBJECTIVE: To use back-to-back diffusion-weighted imaging (DWI) and PET to obtain quantitative measures of the cerebral metabolic rate of oxygen (CMRO(2)) within DWI lesions, and to assess the perfusion-metabolism coupling status by measuring the cerebral blood flow and the oxygen extraction fraction within DWI lesions. METHODS: Six prospectively recruited acute carotid-territory stroke patients completed the imaging protocol, which was commenced 7 to 21 hours from onset and combined DWI derived from state-of-the-art diffusion tensor imaging sequencing using a 3-T magnet and fully quantitative (15)O-PET. The PET variables were obtained in individual DWI lesions in each patient. RESULTS: Across patients, the CMRO(2) was reduced in the DWI lesion relative to mirror (mean reduction 39.5%; p = 0.028). Examining individual DWI lesions, however, revealed considerable variability in the extent of this CMRO(2) reduction. The flow-metabolism coupling pattern underlying the DWI lesion was also variable, including ongoing ischemia, mild oligemia, and partial or complete reperfusion. DISCUSSION: Diffusion-weighted imaging (DWI) lesions generally reflect substantial disruption of energy metabolism. However, the degree of metabolic disruption is variable, indicating DWI lesions may not always represent irreversibly damaged tissue. Finally, because DWI lesions can persist despite reperfusion, assessment of perfusion is necessary for interpretation of DWI changes in acute stroke.

Aged↗
PubMed1997

Parentage, reproductive skew and queen turnover in a multiple-queen ant analysed with microsatellites.

We investigated the fine genetic structure of colonies of the ant, Leptothorax acervorum, to examine how queens share parentage (skew) in a social insect with multiple queens (polygyny). Overall, 494 individuals from eight polygynous field colonies were typed at up to seven microsatellite loci each. The first main finding was that surprisingly many sexual progeny (60% of young queens and 49% of young males) were not the offspring of the extant queens within their colonies. This implies that a high turnover (brief reproductive lifespan) of queens within colonies could be an important feature of polygyny. The second main result was that in most colonies relatedness among sexual progeny fell significantly below that expected among full siblings, proving that these progeny were produced by more than one singly-mated queen, but that skew in two colonies where the data permitted its calculation was moderate to high. However, relative to a German population, the study population is characterized by low queen-queen relatedness and low skew in female production, which is in line with the predictions of skew theory.

Animals↗
PubMed1993

Skin graft take and healing following 193-nm excimer, continuous-wave carbon dioxide (CO2), pulsed CO2, or pulsed holmium: YAG laser ablation of the graft bed.

BACKGROUND: Ablative lasers have been used for cutaneous surgery for greater than two decades since they can remove skin and skin lesions bloodlessly and efficiently. Because full-thickness skin wounds created after thermal laser ablation may require skin grafting in order to heal, we have examined the effect of the residual laser-induced thermal damage in the wound bed on subsequent skin graft take and healing. In a pig model, four different pulsed and continuous-wave lasers with varying wavelengths and radiant energy exposures were used to create uniform fascial graft bed thermal damage of approximately 25, 160, 470, and 1100 microns. Meshed split-thickness skin graft take and healing on the thermally damaged fascial graft beds were examined on a gross and microscopic level on days 3 and 7, and then weekly up to 42 days. RESULTS: Laser-induced thermal damage on the graft bed measuring greater than 160 +/- 60 microns in depth significantly decreased skin graft take. Other deleterious effects included delayed graft revascularization, increased inflammatory cell infiltrate at the graft-wound bed interface, and accelerated formation of hypertrophied fibrous tissue within the graft bed and underlying muscle. CONCLUSIONS: Ablative lasers developed for cutaneous surgery should create less than 160 +/- 60 microns of residual thermal damage to permit optimal skin graft take and healing. Pulsed carbon dioxide and 193-nm excimer lasers may be valuable instruments for the removal of full-thickness skin, skin lesions, and necrotic tissue, since they create wound beds with minimal thermal damage permitting graft take comparable to that achieved with standard surgical techniques.

Animals↗
PubMed1993

Aging, sun damage, and sunscreens.

Intrinsic aging deleteriously changes the structure and function of human skin. Acute and chronic sun exposure may accelerate the aging processes in skin. Patients should avoid sun during the peak hours of sunshine, wear protective clothing, and use sunscreens while outdoors. Acceptable medical and surgical treatments may be offered to patients who manifest the cutaneous consequences of aging and sun exposure.

Aged↗
PubMed1992

Middermal wound healing. A comparison between dermatomal excision and pulsed carbon dioxide laser ablation.

BACKGROUND: Continuous-wave carbon dioxide lasers are not widely used for the surgical removal of most skin lesions because it is difficult to control laser ablation and the extensive laser-induced thermal damage slows healing. Pulsed lasers provide means to reduce thermal damage produced during laser ablation and permit precise control of tissue removed during ablation. Using a swine model, we compared on a gross and microscopic level the healing of middermal wounds of similar depth and area created by a dermatome and a focused pulsed CO2 laser. RESULTS: Pulsed CO2 laser ablation removed skin precisely and bloodlessly with 85 +/- 15 microns (mean +/- SD) of residual thermal damage covering the surface of the wound. Compared with the dermatome, tissue reepithelialization was delayed in the laser wounds at day 3. By day 7, epithelial coverage of the laser-created wounds was not significantly different from the dermatome-created wounds. No significant difference in the appearance of the two wounds was noted at 42 days. CONCLUSIONS: We conclude that the focused pulsed CO2 laser is capable of precisely and bloodlessly ablating skin with conservation of residual subjacent adnexal elements, minimal early interference with epibolic epithelial outgrowth, and no pathologic effects on the wound healing process. Pulsed CO2 lasers may be a valuable instrument for the conservative ablation of skin and skin lesions.

Animals↗
PubMed1992

Burn depth estimation using indocyanine green fluorescence.

Expedient primary excision of deep dermal and full-thickness burn wounds with subsequent skin grafting is the standard of care in most burn institutions, but differentiating full-thickness from partial-thickness burns is often difficult. Because accurate early assessment of burn depth may improve care, a variety of technical methods have attempted to measure burn depth but these methods have had limited success. We describe a new technique to determine burn depth that uses infrared (840- to 850-nm) fluorescence emission from intravenously administered indocyanine green following excitation with infrared (780 nm) and UV light (369 nm). Full-thickness and partial-thickness burns in hairless rat skin were distinguished based on the infrared-induced and UV-induced fluorescence intensity ratios relative to normal, unburned skin immediately after the burn and on post-burn days 1 through 3 and 7. Dual-wavelength excitation of indocyanine green infrared fluorescence can delineate full-thickness from partial-thickness burns at an early date, allowing prognosis, surgical planning, and early primary excision and grafting.

Animals↗
PubMed1991

DNA damage induced by 193-nm radiation in mammalian cells.

The contribution of DNA damage to the effects of 193-nm excimer laser radiation on mammalian cells in culture was studied in order to evaluate the mutagenic potential of this UV wavelength in vivo. Two approaches were taken: measurement of pyrimidine dimer-specific endonuclease-sensitive sites/megabase and comparison of the 193-nm radiation-induced cytotoxicity in normal versus DNA repair-deficient cells. The formation of pyrimidine dimer-specific endonuclease-sensitive sites/megabase was inversely related to the thickness of the cytoplasm overlying the nuclei of normal human fibroblasts (NHF) and Chinese hamster ovary cells. The results of these measurements and a calculation of the absorption coefficient of cytoplasm indicate that each 1 micron of cytoplasm attenuates the incident radiation by greater than 90% and, therefore, the nuclear DNA in tissue will be highly protected from 193-nm radiation by overlying cytoplasm. The reduction in colony-forming ability induced by 254-nm, 193-nm, and X-ray radiation was measured in NHF, xeroderma pigmentosum (group A) cells, and ataxia telangiectasia cells. Xeroderma pigmentosum (group A) cells were 16.5 times more sensitive to 254-nm radiation but only 3.5 times more sensitive to 193-nm radiation than NHF cells, indicating that cyclobutylpyrimidine dimers were not the major lethal lesion formed at 193 nm. AT cells were 3.4 times more sensitive to X-rays than NHF cells, but these cell types were almost equally sensitive to 193-nm radiation, indicating that 193 nm did not induce the same type of lethal lesions as X-rays.

Animals↗
PubMed1990

Pulsed carbon dioxide laser ablation of burned skin: in vitro and in vivo analysis.

Pulsed lasers produce efficient and precise tissue ablation with limited residual thermal damage. In this study, the efficiency of pulsed CO2 laser ablation of burned and normal swine skin was studied in vitro with a mass loss technique. The heats of ablation for normal and burned skin were 2,706 and 2,416 J/cm3 of tissue ablated, respectively. The mean threshold radiant exposures for ablating normal skin and eschar were 2.6 J/cm2 and 3.0 J/cm2, respectively. Radiant exposures greater than 19 J/cm2 produced a plasma, which decreased the efficiency of laser ablation. Thus the radiant exposures for efficient ablation range from 4 to 19 J/cm2, and within this radiant exposure range 20-40 microns of tissue are ablated per pulse. We also examined, on a gross and histopathologic basis, in vivo burn eschar excision with a pulsed CO2 laser. The laser allowed bloodless excisions of full thickness burns on the backs of male hairless rats. The zone of thermal damage was approximately 85 microns over the subjacent fascia. The pulsed CO2 laser can ablate burn eschar efficiently, precisely, and bloodlessly and may prove valuable for the excision of burned and necrotic tissue.

Animals↗
PubMed1987

Orbital metastasis from a carcinoid tumor. Computed tomography, magnetic resonance imaging, and electron microscopic findings.

An otherwise asymptomatic 63-year-old woman with a history of a carcinoid tumor of the ileum and a cutaneous melanoma of the shoulder developed unilateral proptosis. Orbital ultrasonography, computed tomography, and magnetic resonance imaging revealed a large, well-circumscribed orbital mass involving the superior rectus muscle. The surgically excised tumor was studied by light microscopy, histochemistry, and transmission electron microscopy. These studies confirmed the diagnosis of carcinoid tumor. The clinical and pathologic features of this rare type of orbital metastasis are discussed.

Carcinoid Tumor↗
PubMed1987

Unscheduled DNA synthesis in human skin after in vitro ultraviolet-excimer laser ablation.

DNA damage repaired by the excision repair system and measured as unscheduled DNA synthesis (UDS) was assessed in freshly excised human skin after 193 and 248 nm ultraviolet (UV)-excimer laser ablative incisions. Laser irradiation at 248 nm induced DNA damage throughout a zone of cells surrounding the ablated and heat-damaged area. In contrast, with 193 nm irradiation UDS was not detected in cells adjacent to the ablated area, even though DNA strongly absorbs this wavelength. Our results suggest that the lack of UDS after 193 nm irradiation is due to: "shielding" of DNA by the cellular interstitium, membrane, and cytoplasm, DNA damage that is not repaired by excision repair, or thermal effects that either temporarily or permanently inhibit the excision repair processes.

Adult↗
PubMed1982

Utilization of an established rat hepatoma cell lime for mutation studies.

A selected strain of rat hepatoma cells was evaluated for its utility in the assay of mutation. We demonstrate that these cells have practical and theoretical advantages over most other mammalian cells utilized for the mutation assay at the HGPRT locus. Characteristics of the H4IIE cell line which enhance the ability of the HGPRT assay to detect mutation include: intrinsic metabolic capabilities; small cell size, and lack of mobility; colony-forming efficiency of 85-95%; a background mutation level between 0.9 and 3 mutants per 10(5) viable cells; and the ability to proliferate in medium containing 5% fetal bovine serum and 5% horse serum. The optimal expression period for the maximum frequency of mutants was investigated using UVC as the mutagenic agent, and found to plateau after 8-10 days. The metabolic capacity of this cell line was demonstrated using 2-aminoanthracene and cyclophosphamide, two types of mutagens requiring biotransformation for activity. We conclude that the use of the H4/HGPRT system could prove valuable in the mutagenic screening of suspect environmental agents.

Animals↗