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Biomedical subjects

J J McCann

Publications and source records attributed to J J McCann.

At least 19 recordsLinked to original sources
PubMed1992

Rules for colour constancy.

Colours of objects tend to be constant regardless of the colour of the illuminant, therefore, regardless of the quanta catch of the retinal cones. Various mechanisms for this including context recognition, adaptation of retinal sensitivities and independent processing by receptor types have been proposed. These present experiments test the hypothesis that colours are determined by the normalized relationship between all colours in the field of view. In this hypothesis, colours are constant in classical experiments simply because changes of the illuminant do not disrupt the relationship between quanta catches across the field of view. The experiments consist of making sets of colour displays; each with the same relative quanta catches, but different absolute reflectances. 'Colour tautomi' arrays of five colour patches were printed using controlled amounts of yellow, magenta, cyan and black toners. The experiment began with a control 'colour tautomi' array of reflectances with measured relative quanta catches. New arrays of colours were then chosen that increased (or decreased) the reflectances, and quanta catches, a constant amount for the entire array. These changes were done independently for each receptor type. When these 'colour tautomi' are viewed in the room, each array has a different set of colours. When viewed in a restricted field of view, all arrays appear the same. In a further experiment new areas such as white are added to the display. Colour constancy is a field phenomenon controlled by the relative quanta catches in the field of view. Absolute colour constancy is controlled by the relative quanta catches in the field of view and the absolute quantum catches of the receptors.

Color Perception↗
PubMed1990

The redistribution of collagen in expanded pig skin.

Silicone tissue expanders were inserted subcutaneously in the buttocks of nine young pigs and gradually inflated to maximum capacity over 5 weeks. On the control side the expanders were left uninflated. Island buttock flaps were then raised, the expanders removed and the flaps spread into the same sites for 10 days. The tissue was harvested. Area measurements and full thickness skin biopsies were taken 10 days after flap inset in order to study the changes in collagen composition and isotypes in the skin layers. Ten days after inset of the flap the expanded skin had a mean 47% increase in surface area, was 9% thinner (from surface to implant), mostly due to thinning of the subcutaneous zone, but was not significantly different in water content, relative to the control skin. The expanded skin had a significant 9.3% increase (p less than 0.01, t test) in collagen content of the dermis. The relative proportions of Types I and III were not significantly changed by skin expansion in either the dermal/epidermal or subcutaneous/capsular zones. It is speculated that tensile factors during expansion stimulate the biosynthetic activity and/or mitotic activity of fibroblasts in the dermis to produce this gain in collagen in the expanded compared with unexpanded tissue.

Animals↗
PubMed1989

Epithelioma cuniculatum plantare.

The clinical and histological findings and treatment of three patients with this well differentiated squamous cell carcinoma of the foot are presented.

Aged↗
PubMed1989

Coumarin and 7-hydroxycoumarin treatment of canine obstructive lymphoedema.

1. Canine obstructive lymphoedema was created in one hind leg of 30 dogs by irradiation of the groin and surgical removal of surviving lymph glands and lymphatics. The opposite leg served as a control. Once the oedema had stabilized, groups of 10 dogs were treated orally with 12.5 mg day-1 kg-1 for 8 months with either one of the benzopyrones coumarin (2H-1-benzopyran-2-one) and 7-hydroxycoumarin (7-hydroxy-2H-1-benzopyran-2-one), or placebo. 2. The two benzopyrones significantly (P less than 0.01) but gradually reduced the oedema by 20-30% over 8 months, as judged by circumferential measurements of the oedematous and control limbs. There was no change with the placebo. 3. In the oedematous fluids (lymph and interstitial fluid), benzopyrone treatment reduced the protein content and increased acid and neutral proteinase activity compared with the control limbs, while the levels of the proteinase inhibitor alpha 2-macroglobulin remained unchanged. Furthermore, these active drugs reduced the excess water content, thickness and hydroxyproline content of skin biopsies from oedematous limbs compared with those from control limbs. No changes were observed for the placebo group. 4. These biochemical changes suggest that benzopyrones can reduce the excess proteinaceous fluid in lymphoedema by increasing the levels of proteinase activity relative to the number of proteinase inhibitors. As a secondary event the amount of fibrosis in the skin is also reduced, presumably by an increase in collagenase activity from the mononuclear phagocytes. 5. These results support the hypothesis that benzopyrones activate the production of proteinases by mononuclear phagocytes.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Changes in area and thickness of expanded and unexpanded axial pattern skin flaps in pigs.

The pig buttock flap model was used firstly, to compare changes in expanded axial skin flap area with control flaps prior to flap elevation and 3 or 4 months post-flap inset and, secondly, to compare the thickness of expanded and control flaps at elevation and for 3 to 6 months post-flap inset. Following 5 weeks' expansion and prior to elevation, the expanded tissue had gained a significant 63.3% mean increase in area compared with the control tissue (p less than 0.01). Immediately post elevation and inset, the expanded flaps were still significantly larger than the control flaps by a mean 29.8% (p less than 0.01) but had lost 56% of the original area gained. Little change in area occurred in the 3 months post-flap inset as the expanded flaps were still a mean 23.4% larger than the control (p less than 0.01). Dermal and cellular non-keratinised epidermal layers thickened markedly in expanded skin compared to control skin. Following elevation and inset of the flaps, both dermis and epidermis thickened in expanded and control flaps.

Animals↗
PubMed1988

Comparative viability of expanded and unexpanded axial pattern skin flaps in pigs.

A comparison of viable areas of axial pattern flaps post inset was made between expanded and non-expanded pig buttock island flaps. The deep circumflex iliac artery and vein supply approximately the proximal 14 x 10 cm area of this flap. Larger flaps were raised on expanded and control sides of eight pigs to determine if expansion increased the area of survival. In six of eight pigs whose initial tissue expansion did not create more than approximately a 50% increase in skin area, the expanded flaps had a statistically significant increase in viable skin area (proportionally) 10 days post inset than their control flaps (p less than 0.05). Two other pigs did not conform to this pattern. Their initial tissue expansion was greater than 50%, and the resulting area of flap viability was proportionally less in expanded flaps than the control flaps.

Animals↗
PubMed1988

Long term home care for the elderly: perceptions of nurses, physicians, and primary caregivers.

A qualitative research study was conducted to gain an understanding of the perceptions of nurses, physicians, and elderly caregivers regarding the experience of long term home care. The sample included 2 discharge planning nurses, 4 home health nurses, 4 geriatric physicians, and 12 nonprofessional spouse caregivers older than age 60. Analysis of the data revealed three distinct major topic areas: making decisions about home care, the nature of long term home care, and caregivers' concerns and needs. In general, most spouses want to provide home care for their partners but are often discouraged from doing so by their children and/or by health professionals. Caregivers receive little preparation for their roles, and most have little or no contact with the formal health care system.

Aged↗
PubMed1988

The fillet foot for endweight-bearing cover of below knee amputations.

Four patients with five severely traumatized lower legs but preserved feet were treated with fillet flaps from the foot to cover an elective, below knee amputation stump. The posterior tibial neurovascular bundle nourished and innervated this flap. While the posterior tibial artery and vein may be cut and re-anastomosed to prevent kinking and occlusion, the posterior tibial nerve should always be kept in continuity to maintain the quality of sensation to this flap. Four flaps survived and one necrosed secondary to venous insufficiency. Due to its innervation and the unique qualities of heel skin, the flap is very durable and has endweight-bearing capabilities. This has permitted the fitting of an endweight-bearing, total contact, fully extended, below knee prosthesis that appears to offer significant improvement in ease of use and normality of gait pattern over standard patellar tendon-bearing prostheses.

Adult↗
PubMed1987

The free radial forearm flap with and without bone for closure of large palatal fistulae.

Three cases of palatal fistulae closed by microvascular transfer of radial forearm flaps are presented. Vascularised bone was included in one flap and all operations were free of complications. Facial scarring is minimal and the secondary deformity in the arm has not been significant. It is suggested that this procedure presents fewer difficulties than other techniques for treating the large palatal fistula and may prevent the collapse of the alveolar arch which follows the scarring associated with closure by local tissue.

Adolescent↗
PubMed1987

Protein metabolism and fibrosis in experimental canine obstructive lymphedema.

Obstructive lymphedema is a pathologic condition resulting in the accumulation and stagnation of serum proteins in the lymphatics and interstitial spaces. In a canine model of obstructive lymphedema, one limb was rendered lymphedematous, and various biochemical parameters were determined in this and an unaffected control limb. Both lymph and interstitial fluid had significantly decreased acid proteinase activity (comprising mostly cathepsin D-like enzymes) and neutral proteinase activity (comprising metallo, sulfhydryl, and serine proteinases, and collagenase). Possible reasons for these decreases could be: (1) saturation of macrophages and their surrounding environment with whole or partially digested proteins, or (2) elevation in the levels of circulating inhibitors like alpha 2-macroglobulin. The lymphedematous skin was significantly thicker than control skin and had elevated levels of collagen. However, unlike some fibrotic conditions, the relative proportions of types I, III, and V collagen, as determined by pepsin solubilization and neutral salt fractionation of the collagen fibrils, were similar to those found in normal skin. It is speculated that a decrease in the breakdown of collagen by collagenase and a continuing synthesis of collagen by fibroblasts led to an imbalance in favor of collagen deposition in the skin.

Animals↗
PubMed1987

Some further characteristics of expanded tissue.

It has been shown that during expansion there is a component of migration of surrounding tissue that probably contributes to the available tissue in local reconstructive procedures. Although there is a 63 per cent increase through expansion of a given flap with a particular expander, this results in only a 30 per cent increase after elevation and inset. This increase is basically maintained for a 3- or 4-month period. The 56 per cent decrease in area probably results from contraction of the extensible skin. The 30 per cent that remains probably results from a combination of stretch evidenced by reorientation, along with an increase in the cellular and extracellular components of expanded tissue. Therefore, there are components of both loan and dividend in tissue expansion. This further understanding should be helpful in the planning of tissue expansion. (Editors' note: Although there may be some element of "loan" initially, from peripheral regions, no thinning of the periphery has been observed. To the contrary, the periphery appears normal. It is likely that transient thinning of the periphery causes increased mitotic activity, and that this area is also made to produce a "dividend" ultimately. Unless permanent thinning can be documented, the "dividend hypothesis" remains valid.

Animals↗
PubMed1977

Variegated color sensations from rod-cone interactions: flicker-fusion experiments.

Multicolored images were produced by the combination of two different color-separation images, one illuminated with 656 nm light and the other illuminated with 500 nm light. Flicker-fusion frequency measurements were used to identify the conditions in which the 500 nm light was below cone threshold. Under those conditions the multicolored images were shown to be generated by rod and long-wave cone interactions.

Color Perception↗
PubMed1976

Shifting linear growth during infancy: illustration of genetic factors in growth from fetal life through infancy.

A percentile linear growth chart, from the third to ninety-seven percentiles, was derived from longitudinal data on 90 normal full-term infants of middle class suburban families, and the individual growth curves of each infant was contrasted to the growth chart for the entire group. Individual shifting in growth rate was noted in two thirds of the infants. To better determine the timing and nature of these shifts in linear growth, a search was made for otherwise normal full-term infants who were at or below the tenth percentile for length at birth and who moved up to the fiftieth percentile or better by age 2 years and those who were at or above the ninetieth percentile at birth and moved down to the fiftieth percentile or less by 2 years of age. Those shifting upward had accelerated linear growth soon after birth; they achieved a new "channel" at a mean age of 11.5 months. Those shifting downward did not decelerate until after the first three to six months; they achieved a new channel by the mean age of 13 months. These findings plus the correlation coefficients relating parental size to the length of the infant at birth, one year, and two years of age are compatible with the following statements: Birth length relates predominantly to maternal size whereas by 2 years of age the length correlates best to mean parental height, reflecting the genetic growth factors of both parents. Those infants "catching-up" after birth usually do so in early infancy, whereas those "lagging-down" tend to do so in midinfancy.

Birth Weight↗
PubMed1975

Visibility of low-spatial-frequency sine-wave targets: Dependence on number of cycles.

The number of cycles in a low-frequency sinusoidal display is a crucial variable in determining the visibility of the display. In particular, the threshold contrast is essentially independent of spatial frequency for these displays. We have extended the above experiments, using more cycles and a variety of targets and observer tasks. The results confirm previous findings; they also show that the type of target or task has little influence. For low-frequency sinusoids that contain up to about 3 cycles, the threshold contrast is determined by the number of cycles. For high-number-of-cycles targets with spatial frequencies above 6-10 cycles per degree, visibility is predominantly dependent on the spatial frequency. The results suggest that the low-frequency decrease in reported MTF's is due to the decrease of the number of cycles used in determining them.

Fourier Analysis↗