SAQMG2

Microtopography is the detailed study of surface features on a microscopic level.

Epidermal grooves are the creases visible on the surface of skin that form geometric patterns on a microscopic level. Epidermal ridges are the ridges apparent at only some sites and are due to the organised arrangement of the dermal papillae, giving rise to the characteristic fingerprints.

The primary determining factors of the mechanical properties of skin are the fibrous networks of collagen and elastin fibres and the interstitial fluid of the dermis. For the keratinous skin of the soles of the feet and palms of the hand, the thick, keratinous outer layer of the epidermis is also important.

The problem of tearing of a specimen being tensile tested in vitro may be minimised by ensuring that the specimen is clamped evenly so that stress concentrations are not produced and by using adhesive.

There are three phases in a typical tensile stress-strain curve produced in vitro.

Residual strain is the offset of the loading curve to the unloading curve. It gradually reduces to around zero over about six cycles.

Artefacts produced by the initial handling of a skin specimen may be reduced by preconditioning the specimen by subjecting it to several loading cycles until the residual strain is effectively reduced to zero.

If the body position during a tensile test in vivo is not standardised the initial skin tension will vary, so that the duration of the phase I of the stress-strain curve will vary according to the amount of pretension.

Langer lines are evidence of the anisotropic nature and the pretension of skin.

The extensibility of skin varies from site to site according to the functional requirements of the skin.

Three parameters that may be determined from an indentation test are: depth of indentation, initial recovery, and the recovery after a fixed period.

The two parameters may be controlled during an indentation test are applied load and depth of indentation.

The environment of the specimen must be controlled during creep and stress relaxation tests performed in vitro, to prevent the specimen drying out.

The time that an object can be held with a temperature above 43ºC is inversely related to its temperature.

The improvement of the signal could be caused by the reduction in the resistance of the stratum corneum as the subject started to sweat and may indicate that the skin was not adequately prepared. This could be eliminated by adequately preparing the site or by using needle electrodes. The artefact in phase with the subject's walking cycle is probably due to the changes in skin resistance as the subject moves, stretching the skin under the electrodes, and changing the position of the skin relative to the underlying tissues. This could be reduced by placing the electrodes where the skin movement is minimal and by using needle electrodes.

Bony prominences, such as the sacrum and trochanter, are particularly vulnerable to pressure sores.

By using the pressure-time tolerance curve in Figure 14, state whether or not the following pressure applications are safe or unsafe: (i) pressure of 10 kPa for 3 hours - safe (it is below the curve) (ii) pressure of 10 kPa for 8 hours - unsafe (it is above the curve) (iii) pressure of 60 kPa for 1 hour - unsafe (it is above the curve).

A non-blanchable erythemia response indicates that there is severe damage to the skin with leakage of blood into the skin tissue.

The procedures used in Hagisawa's study mimicked the technique used clinically to detect tissue distress.

The skin thickness generally decreases by 20% with age.

The age-related changes observed in indentation test parameters are: slower to reach total indentation, slower to recovery from indentation, and reduction in total indentation.