Temperature distribution in human skin and subdermal tissues

Temperature profiles have been computed in the skin and subdermal part of a human body for (i) various values of environmental temperature, rate of sweat evaporation and wind velocity, (ii) rate of blood mass flow, (iii) rate of metabolic heat generation and (iv) three different sets of thicknesses of skin layers. The mathematical equations have been considered for a one-dimensional steady-state case. The two important physical parameters, namely rate of blood mass flow and rate of metabolic heat generation, have been assigned position-dependent values. The latter is also taken as linearly dependent on the tissue temperature. Analytic solutions have been obtained for the three layers of the region. These forms of solution facilitate the study of parameter dependence.     

Explicit formula of finite difference method to estimate human peripheral tissue temperatures during exposure to severe cold stress

During cold exposure, peripheral tissues undergo vasoconstriction to minimize heat loss to preserve the maintenance of a normal core temperature. However, vasoconstricted tissues exposed to cold temperatures are susceptible to freezing and frostbite-related tissue damage. Therefore, it is imperative to establish a mathematical model for the estimation of tissue necrosis due to cold stress. To this end, an explicit formula of finite difference method has been used to obtain the solution of Pennes' bio-heat equation with appropriate boundary conditions to estimate the temperature profiles of dermal and subdermal layers when exposed to severe cold temperatures. The discrete values of nodal temperature were calculated at the interfaces of skin and subcutaneous tissues with respect to the atmospheric temperatures of 25 °C, 20 °C, 15 °C, 5 °C, −5 °C and −10 °C. The results obtained were used to identify the scenarios under which various degrees of frostbite occur on the surface of skin as well as the dermal and subdermal areas. The explicit formula of finite difference method proposed in this model provides more accurate predictions as compared to other numerical methods. This model of predicting tissue temperatures provides researchers with a more accurate prediction of peripheral tissue temperature and, hence, the susceptibility to frostbite during severe cold exposure.     

Contribution of Subcutaneous Connective Tissues to the Epithelialization and Cyst Formation by the Skin Transplanted Subcutaneously

Skins and hollow organs have been shown to form epithelialized cysts when transplanted into subcutaneous tissue of a recipient animal, expanding their surface areas. This system seems to offer a good potential for regenerating organs. We investigated the functional and structural contribution of epithelia and connective tissue compartments in this regeneration system with two experimental systems.Key Words: skin, epithelialization, transplantation, GFP, epidermis, cystDispase-separated epidermis often forms epithelialized cysts when combined with dermal connective tissue whereas dispase-separated epidermis alone does not form cysts or epithelialize, indicating the functional importance of the dermal connective tissue in the regeneration process.When GFP rats were used as donors for the skin, the donor-derived tissue was composed of whole epidermis and parts of the connective tissue cells and blood vessels under the newly epithelialized portion of the cyst wall. Small capillaries of granulation tissues were shown to be of recipient origin, but some large vessels were of donor origin. These results showed the significant functional and structural contribution of dermal connective tissue in the regeneration of the skin in subdermal transplant.     

Contribution of Subcutaneous Connective Tissues to the Epithelialization and Cyst Formation by the Skin Transplanted Subcutaneously

Skins and hollow organs have been shown to form epithelialized cysts when transplanted into subcutaneous tissue of a recipient animal, expanding their surface areas. This system seems to offer a good potential for regenerating organs. We investigated the functional and structural contribution of epithelia and connective tissue compartments in this regeneration system with two experimental systems.

Dispase-separated epidermis often forms epithelialized cysts when combined with dermal connective tissue whereas dispase-separated epidermis alone does not form cysts or epithelialize, indicating the functional importance of the dermal connective tissue in the regeneration process.

When GFP rats were used as donors for the skin, the donor-derived tissue was composed of whole epidermis and parts of the connective tissue cells and blood vessels under the newly epithelialized portion of the cyst wall. Small capillaries of granulation tissues were shown to be of recipient origin, but some large vessels were of donor origin. These results showed the significant functional and structural contribution of dermal connective tissue in the regeneration of the skin in subdermal transplant.     

Galerkin's finite element-Laplace transform technique to transient heat migration in human skin and subcutaneous tissues

Galerkin's finite element-Laplace transform technique (GAFELTTE) has been used to study transient temperature distribution in human skin and subcutaneous tissues. This study incorporates heat conduction, heat carried by perfusion of blood in the capillary beds and metabolic heat generation in the tissues. Different values of various quantities have been considered in all three parts, namely epidermis, dermis and subcutaneous tissues, depending on physiological considerations. The GAFELTTE provides interface temperatures for a wide range of the values of skin surface temperatures. These values have been used to obtain temperature profiles in the region considered. Steady-state temperature distribution has been deduced from the solution obtained by GAFELTTE and has been compared with the results obtained by using different methods.     

Heat transfer analysis of skin during thermal therapy using thermal wave equation

Specifying exact geometry of vessel network and its effect on temperature distribution in living tissues is one of the most complicated problems of the bioheat field. In this paper, the effects of blood vessels on temperature distribution in a skin tissue subjected to various thermal therapy conditions are investigated. Present model consists of counter-current multilevel vessel network embedded in a three-dimensional triple-layered skin structure. Branching angles of vessels are calculated using the physiological principle of minimum work. Length and diameter ratios are specified using length doubling rule and Cube law, respectively. By solving continuity, momentum and energy equations for blood flow and Pennes and modified Pennes bioheat equations for the tissue, temperature distributions in the tissue are measured. Effects of considering modified Pennes bioheat equation are investigated, comprehensively. It is also observed that blood has an impressive role in temperature distribution of the tissue, especially at high temperatures. The effects of different parameters such as boundary conditions, relaxation time, thermal properties of skin, metabolism and pulse heat flux on temperature distribution are investigated. Tremendous effect of boundary condition type at the lower boundary is noted. It seems that neither insulation nor constant temperature at this boundary can completely describe the real physical phenomena. It is expected that real temperature at the lower levels is somewhat between two predicted values. The effect of temperature on the thermal properties of skin tissue is considered. It is shown that considering temperature dependent values for thermal conductivity is important in the temperature distribution estimation of skin tissue; however, the effect of temperature dependent values for specific heat capacity is negligible. It is seen that considering modified Pennes equation in processes with high heat flux during low times is significant.     

Temperature over tumors in hairless mice

The question of whether tumors are warmer or colder than surrounding tissue is considered in these experiments which use a highly suitable animal model, the hairless mouse. Temperatures of skin over induced growing subdermal tumors in these mice were monitored by AGA 680 Color Thermovision. The skin over the tumors does not cool over time but on the contrary becomes warmer. This is probably due to an increase in vascularization rather than increased metabolic rate.     

Concealed weapons: erectile claws in African frogs

Vertebrate claws are used in a variety of important behaviours and are typically composed of a keratinous sheath overlying the terminal phalanx of a digit. Keratinous claws, however, are rare in living amphibians; their microstructure and other features indicate that they probably originated independently from those in amniotes. Here we show that certain African frogs have a different type of claw, used in defence, that is unique in design among living vertebrates and lacks a keratinous covering. These frogs have sectorial terminal phalanges on their hind feet that become functional by cutting through the skin. In the resting state, the phalanx is subdermal and attached to a distal bony nodule, a neomorphic skeletal element, via collagen-rich connective tissue. When erected, the claw breaks free from the nodule and pierces the ventral skin. The nodule, suspended by a sheath attached to the terminal phalanx and supported by collagenous connections to the dermis, remains fixed in place. While superficially resembling the shape of claws in other tetrapods, these are the only vertebrate claws known to pierce their way to functionality.     

Effect of dermal tumours on temperature distribution in skin with variable blood flow

Several investigations have been made for the heat flow problems in skin and subdermal tissues under normal physiological and atmospheric conditions. This paper considers the existence of a malignant tumour in the underlying tissues of epidermis of a human body. The surrounding tissues are assumed to have normal physiological functions, namely self-controlled metabolic activity, variable blood flow and perspiration. For the malignant portion the metabolic activity is taken to be continuous and uncontrolled. The effect of this factor is studied on the temperature profiles of the skin.     

A new approach using the Pierce two-node model for different body parts

This paper presents a new approach, in applying the Pierce two-node model, to predict local skin temperatures of individual body parts with good accuracy. In this study, local skin temperature measurements at 24 sites on the bodies of 11 human subjects were carried out in a controlled environment under three different indoor conditions (i.e. neutral, warm and cold). The neutral condition measurements were used to adjust the local skin set-points in the model for each body part. Additional modifications to the calculation algorithm were introduced corresponding to different body parts. The local core set-points were then calculated, using a line search method, as the input values that allow the model to predict the skin temperatures with maximum deviation of ±0.1°C for the neutral condition. The model predictability was verified for the other two indoor conditions, and the results show that the modified model predicts local skin temperatures with average deviation of ±0.3°C.     

SD大鼠皮肤组织病理学观察

目的观察不同日龄SD大鼠皮肤组织学结构。方法10％甲醛固定,行石蜡切片,HE染色。结果新生大鼠皮肤较薄,透明层缺乏,皮脂腺发育良好。6月龄时表皮、真皮和皮下组织明显增厚,毛囊增粗,生长旺盛,毛囊深入皮下脂肪层。24月龄时,大鼠皮脂腺及汗腺萎缩,表皮变薄,真皮成纤维细胞、血管数量减少,弹力纤维变细。结论不同日龄SD大鼠皮肤组织学结构有差异。     

Early excision and skin grafting of selected burns of the face and neck

Since 1979, 16 patients with facial and neck burns have been treated with excision and skin grafting within the first 4 days of injury. The injuries were tangentially excised and immediately covered with split-thickness skin grafts. Detailed consecutive results are presented. The patients can be divided into three groups. Group 1 consisted of small subdermal or circumscribed deep dermal burns of the face (n = 8). Healing was quick. Some patients developed signs of overgrafting. As a late result, unevenness and discoloration were seen. Group 2 consisted of mixed deep dermal and subdermal burns of the face and neck (n = 5). Usually, minor areas had to be regrafted. Some patients developed hypertrophic scars at border areas. In the completely excised and grafted area, the skin was smooth, pliable, and discolored. Group 3 consisted mostly of subdermal burns of the face and neck (n = 3). The surgical trauma was significant. Small areas had to be regrafted. Ectropion and microstomia developed. It is concluded that in selected cases of deep dermal and subdermal burns, early excision and skin grafting will result in faster healing and less scarring than expectant treatment.     

The treatment of alkaline burns of the skin by neutralization

Literature reports dating as far back as 1927 have lured clinicians into the belief that alkaline skin burns are best treated by water dilution and that neutralization attempts should be avoided. Although this belief has never been substantiated, neutralization of an alkaline burn of the skin with acid was thought to increase tissue damage secondary to the exothermic nature of acid-base reactions. The authors proposed that topical treatment of alkaline burns with a weak acid such as 5% acetic acid (i.e., household vinegar) would result in rapid tissue neutralization and reduction of injury in comparison to water irrigation alone. In a rat skin burn model, animals were exposed to an alkaline injury when filter paper (2 cm in diameter) saturated with 2N sodium hydroxide was placed over the volar aspect of the animal for a period of 1 minute. Treatment was initiated 1 minute after injury and included either neutralization with a 5% acetic acid solution (n = 8) or irrigation (n = 8) with water. Skin temperature and pH were monitored using subdermal needle probes until the pH of the skin returned to physiologic values. Punch-biopsy specimens were obtained from the wound edges 24 hours after injury to assess burn depth and leukocyte infiltration, and biopsies were repeated 10 days later to assess wound healing. The authors proposed that neutralization of an alkaline substance with household vinegar (i.e., 5% acetic acid solution) would result in rapid neutralization and thus reduce extent of tissue injury. Animals treated with acetic acid demonstrated a more rapid return to physiologic pH (14.69 +/- 4.06 minutes versus 31.62 +/- 2.83 minutes; p < 0.001), increased depth of dermal retention (0.412 +/- 0.136 mm versus 0.214 +/- 0.044 mm; p = 0.015), decreased leukocyte infiltrate (31.0 +/- 5.1 cells/high-power field versus 51.8 +/- 6.8 cells/high-power field; p < 0.001), and improved epithelial regeneration (4.0 +/- 0.6 cell layers versus 1.7 +/- 0.5 cell layers; p < 0.001) when compared with animals treated with water irrigation. No difference was detected in peak pH (10.35 +/- 0.28 pH versus 10.36 +/- 0.25 pH; p = 0.47) nor in rise of skin temperature (maximum temperature, 32.8 degrees C versus 32.9 degrees C; p = 0.33) between acetic acid-neutralized and water-irrigated burn wounds. The observed benefits of treating alkaline burns with 5% acetic acid in the rat model are significant and require clinical testing.     

Permeation of inert gases through human skin: modeling the effect of skin blood flow

We present an analytic method for determining the effects of skin perfusion--vasculature and flow rates--on the flux of inert gases through human skin. We systematically specify the underlying blood flow and examine the resulting fluxes of several gases, allowing for the appropriate tissue resistances. For physiological flows, the stratum corneum has an effect equivalent to a series resistance. Helium flux at low total flow depends primarily on subdermal perfusion, but at higher flow, middermal and subpapillary effects become important. The fluxes of less permeable gases, such as argon and xenon, depend on middermal and subpapillary flow at lower total flows. From any single measurement of gas flux, it is difficult to establish an unambiguous value for the underlying blood flow, but the simultaneous measurement of different gases narrows the range of plausible conditions.     

Tissue impedance and temperature measurements in relation to necrosis in experimental cryosurgery

Tissue temperature and impedance were measured in dog skin during freezing in situ. The previously frozen skin was removed by punch biopsies 3 days later to permit microscopic evaluation of the extent of necrosis. The histologic observations were related to the temperature and impedance measurements in an effort to determine the usefulness of the monitoring techniques in clinical cryosurgery. Tissue temperature and impedance have a definite relationship in tissue freezing, but the range of temperatures about any impedance values causes some concern. The tissue biopsies showed that an impedance value of at least 10 Mohms is not always associated with tissue death. In these experiments, there was the usual range of temperatures in relation to tissue death, but tissue temperatures of -30 degrees C and colder were always associated with complete necrosis. It is concluded that tissue temperatures are the more accurate and useful monitoring technique to supplement clinical judgment. However, impedance techniques may also be used to monitor therapy, especially if used primarily to monitor depth of therapy, and if controlled by clinical judgment wary of the inaccuracy of the technique.     

Subglandular breast reduction: the evolution of a minimal scar approach to breast reduction

The authors describe a new modification of the breast reduction procedure. By means of an inframammary incision, the breast is mobilized from the chest wall, and a "doughnut" annulus of breast tissue is removed from the undersurface of the gland. No skin is excised. The nipple-areola complex is left attached to a central core of breast tissue that receives its blood supply from the subdermal plexus of vessels. When the resulting defect is closed within the breast by strategically placed sutures, the base of the gland is narrowed, the breast is projected forward, and the circumareolar and vertical scars of other techniques are eliminated. The authors report their results in a series of 37 patients.     

Actual temperature during and thermal response after whole-body cryotherapy in cryo-cabin

Whole-body cryotherapy (WBC) involves exposing minimally dressed participants to very cold air (injecting liquid nitrogen with temperature −195 °C), either in a specially designed chamber (cryo-chamber) or cabin (cryo-cabin), for a short period of time. The aim of this study was to examine the actual temperature of the air in the cryo-cabin at different locations throughout the cabin by using human subjects and a manikin. Additionally, we monitored skin temperature before and for 60 min after the cryo-cabin session. Twelve subjects completed one 3 min cryo-cabin session. Temperature next to the skin was assessed during the session, while the skin temperature was monitored before, 3 min after and every 10 min for 60 min after completing the session. There was a statistically significant interaction (time×position) for temperature among the different body parts during the WBC, and for skin temperature among different body parts after the cryo-cabin session. Statistically significant time effects during and following cryo-cabin session were present for all body parts. We showed that actual temperature in the cryo-cabin is substantially different from the one reported by the manufacturer. Thermal response after cryo-cabin session is similar to response observed after cryo-chamber cold exposure reported in previously published studies. This could be of great practical value as cryo-cabins are less expensive and easier to use compared to cryo-chambers.     

A parametric study of thermal therapy of skin tissue

A thermal therapy for cancer in skin tissue is numerically investigated using three bioheat conduction models, namely Pennes, thermal wave and dual-phase lag models. A laser is applied at the surface of the skin for cancer ablation, and the temperature and thermal damage distributions are predicted using the three bioheat models and two different modeling approaches of the laser effect. The first one is a prescribed surface heat flux, in which the tissue is assumed to be highly absorbent, while the second approach is a volumetric heat source, which is reasonable if the scattering and absorption skin effects are of similar magnitude. The finite volume method is applied to solve the governing bioheat equation. A parametric study is carried out to ascertain the effects of the thermophysical properties of the cancer on the thermal damage. The temperature distributions predicted by the three models exhibit significant differences, even though the temperature distributions are similar when the laser is turned off. The type of bioheat model has more influence on the predicted thermal damage than the type of modeling approach used for the laser. The phase lags of heat flux and temperature gradient have an important influence on the results, as well as the thermal conductivity of the cancer. In contrast, the uncertainty in the specific heat and blood perfusion rate has a minor influence on the thermal damage.     

Efficacy and mechanism of adenovirus-mediated VEGF-165 gene therapy for augmentation of skin flap viability

Skin ischemic necrosis due to vasospasm and/or insufficient vascularity is the most common complication in the distal portion of the skin flap in reconstructive surgery. This project was designed to test our hypothesis that preoperative subdermal injection of adenoviral vectors encoding genes for vascular endothelial growth factor-165 (Ad.VEGF-165) or endothelial nitric oxide (NO) synthase (Ad.eNOS) effectively augments skin viability in skin flap surgery and that the mechanism of Ad.VEGF-165 gene therapy involves an increase in synthesis/release of the angiogenic and vasodilator factor NO. PBS (0.5 ml) or PBS containing Ad.VEGF-165, Ad.eNOS, or adenovirus (Ad.Null) was injected subdermally into the distal half of a mapped rat dorsal skin flap (4 x 10 cm) 7 days preoperatively, and skin flap viability was assessed 7 days postoperatively. Local subdermal gene therapy with 2 x 10(7)-2 x 10(10) plaque-forming units of VEGF-165 increased skin flap viability compared with PBS- or Ad.Null-injected control (P < 0.05). Subdermal Ad.VEGF-165 and Ad.eNOS gene therapies were equally effective in increasing skin flap viability at 5 x 10(8) plaque-forming units. Subdermal Ad.VEGF-165 therapy was associated with upregulation of eNOS protein expression, Ca2+ -dependent NOS activity, synthesis/release of NO, and increase in capillary density and blood flow in the distal portion of the skin flap. Injection of the NOS inhibitor Nomega-nitro-L-arginine (15 mg/kg im), but not the cyclooxygenase inhibitor indomethacin (5 mg/kg im), 45 min preoperatively completely abolished the increase in skin flap blood flow and viability induced by Ad.VEGF-165 injected subdermally into the mapped skin flap 7 days preoperatively. We have demonstrated for the first time that 1) Ad.VEGF-165 and Ad.eNOS mapped skin flap injected subdermally into the mapped skin flap 7 days preoperatively are equally effective in augmenting viability in the rat dorsal skin flap compared with control, 2) the mechanism of subdermal Ad.VEGF-165 gene therapy in augmenting skin flap viability involves an increase in NO synthesis/release downstream of upregulation of eNOS protein expression and Ca2+ -dependent NOS activity, and 3) the vasodilating effect of NO may predominantly mediate subdermal Ad.VEGF gene therapy in augmenting skin flap blood flow and viability.     

Measurement of torso skin temperature under clothing

The influence of clothing on skin temperature distributions of the torso was investigated during and after cold exposure. Volunteers were cooled for one hour at 5 degrees C while wearing clothing designed to have insulation which was intended to be relatively uniformly distributed. Three different thicknesses of clothing were used. Following thermistor measurements of skin temperatures during the cold exposures, clothing was quickly removed from the upper parts of the body to enable thermographic investigations of the temperature distributions of the front of the bare torso. The evolution of temperature distributions were then studied at different ambient temperatures (5 degrees C and 20 degrees C) as a function of the thickness of the insulation which had previously been worn. The patterns of the temperature distributions, and the range and standard deviation of torso temperatures were all found to be relatively constant in spite of the different thicknesses of clothing worn or in the time-variant mean torso temperatures which resulted. The front torso sites normally used for the determination of mean skin temperatures were found to be on portions of the torso which were cooler than the surrounding regions. It was concluded that a site midway between the umbilicus and a nipple yields a more accurate estimate of mean torso temperature in the conditions of the present study.