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.     

Assessment of penetration of quantum dots through in vitro and in vivo human skin using the human skin equivalent model and the tape stripping method

Quantum dots (QDs) are rapidly emerging as an important class of nanoparticles (NPs) with potential applications in medicine. However, little is known about penetration of QDs through human skin. This study investigated skin penetration of QDs in both in vivo and in vitro human skin. Using the tape stripping method, this study demonstrates for the first time that QDs can actually penetrate through the stratum corneum (SC) of human skin. Transmission electron microscope (TEM) and energy diverse X-ray (EDX) analysis showed accumulation of QDs in the SC of a human skin equivalent model (HSEM) after dermal exposure to QDs. These findings suggest possible transdermal absorption of QDs after dermal exposure over a relatively long period of time.     

Effect of temperature on tether extraction, surface protrusion, and cortical tension of human neutrophils

Neutrophil rolling on endothelial cells, the initial stage of its migrational journey to a site of inflammation, is facilitated by tether extraction and surface protrusion. Both phenomena have been studied extensively at room temperature, which is considerably lower than human body temperature. It is known that temperature greatly affects cellular mechanical properties such as viscosity. Therefore, we carried out tether extraction, surface protrusion, and cortical tension experiments at 37 degrees C with the micropipette aspiration technique. The experimental temperature was elevated using a custom-designed microscope chamber for the micropipette aspiration technique. To evaluate the constant temperature assumption in our experiments, the temperature distribution in the whole chamber was computed with finite element simulation. Our simulation results showed that temperature variation around the location where our experiments were performed was less than 0.2 degrees C. For tether extraction at 37 degrees C, the threshold force required to pull a tether (40 pN) was not statistically different from the value at room temperature (51 pN), whereas the effective viscosity (0.75 pN.s/microm) decreased significantly from the value at room temperature (1.5 pN.s/microm). Surface protrusion, which was modeled as a linear deformation, had a slightly smaller spring constant at 37 degrees C (40 pN/microm) than it did at room temperature (56 pN/microm). However, the cortical tension at 37 degrees C (5.7+/-2.2 pN/microm) was substantially smaller than that at room temperature (23+/-8 pN/microm). These data clearly suggest that neutrophils roll differently at body temperature than they do at room temperature by having distinct mechanical responses to shear stress of blood flow.     

Direct visualization of lipid domains in human skin stratum corneum's lipid membranes: effect of pH and temperature

The main function of skin is to serve as a physical barrier between the body and the environment. This barrier capacity is in turn a function of the physical state and structural organization of the stratum corneum extracellular lipid matrix. This lipid matrix is essentially composed of very long chain saturated ceramides, cholesterol, and free fatty acids. Three unsolved key questions are i), whether the stratum corneum extracellular lipid matrix is constituted by a single gel phase or by coexisting crystalline (solid) domains; ii), whether a separate liquid crystalline phase is present; and iii), whether pH has a direct effect on the lipid matrix phase behavior. In this work the lateral structure of membranes composed of lipids extracted from human skin stratum corneum was studied in a broad temperature range (10 degrees C-90 degrees C) using different techniques such as differential scanning calorimetry, fluorescence spectroscopy, and two-photon excitation and laser scanning confocal fluorescence microscopy. Here we show that hydrated bilayers of human skin stratum corneum lipids express a giant sponge-like morphology with dimensions corresponding to the global three-dimensional morphology of the stratum corneum extracellular space. These structures can be directly visualized using the aforementioned fluorescence microscopy techniques. At skin physiological temperatures (28 degrees C-32 degrees C), the phase state of these hydrated bilayers correspond microscopically (radial resolution limit 300 nm) to a single gel phase at pH 7, coexistence of different gel phases between pH 5 and 6, and no fluid phase at any pH. This observation suggests that the local pH in the stratum corneum may control the physical properties of the extracellular lipid matrix by regulating membrane lateral structure and stability.     

Cyclic gas exchange in the giant burrowing cockroach, Macropanesthia rhinoceros: effect of oxygen tension and temperature

The giant burrowing cockroach, Macropanesthia rhinoceros, is endemic to north-eastern Australia and excavates a permanent burrow up to 1m deep into soil. Using flow-through respirometry, we investigated gas exchange and water loss at three different oxygen tensions (21%, 10% and 2% at 20 degrees C) and temperatures (10, 20 and 30 degrees C at 21% oxygen). M. rhinoceros employ cyclic gas exchange (CGE) making the species by far the largest insect known to engage in discontinuous ventilation. CGE featured rhythmic bursts of CO(2) dispersed among inter-burst periods of reduced output. CGE was most commonly observed at 20 degrees C and degraded at <10% oxygen. Mild hypoxia (10% oxygen) resulted in a lengthening of the burst period by approximately two-fold; this result is complementary to oxygen consumption data that suggests that the burst period is important in oxygen uptake. When exposed to severe hypoxia (2% oxygen), CGE was degraded to a more erratic continuous pattern. Also, during severe hypoxia, total water loss increased significantly, although CO(2) release was maintained at the same level as in 21% oxygen. During CGE, an increase in temperature from 10 to 20 degrees C caused both water loss and CO(2) output to double; from 20 to 30 degrees C, CO(2) output again doubled but water loss increased by only 31%.     

Predicting the effect of relative humidity on skin temperature and skin wettedness

The purpose of this research is to investigate the relative humidity effects on skin temperature and skin wettedness for different operative temperatures. For this aim, thermal interactions between human body and environment are simulated. In this simulation, Gagge 2-node model is used but includes some significant modifications. The simulation is to apply the Gagge 2-node model to individual segments rather than to whole body. Also, the results of the simulation are compared with present measurements, and available experimental data and simulated results in the literature in order to present reliability of the 16 segments-Gagge 2-node model. It is determined that the simulation results are in good agreement with measured results obtained from present experiments, and simulated results and experimental data in the literature.     

Relation between pain and temperature reception of human skin

On healthy volunteers we studied the effect of local cooling (14–16°C) and heating (40–42°C) of the skin of various zones of the leg to pain sensitivity, for evaluating which we used the method of recording the flexor reflex (FR) and electromyography of the anterior tibial muscle. It was established that changes in the FR depend not on the modality of thermo stimulation but on localization of the place of its application: on stimulating the skin above the tested flexor, the FR is facilitated, and on thermostimulation above the antagonist or contralateral agonist, the FR of the anterial tibial muscle is mainly inhibited. It was assumed that loss of the temperature modality is due to convergence of temperature and pain information on spinal interneurons of the "bimodal type" unidirectionally changing impulse activity under the effect of both temperature modalities. The different character of reaction of the FR to thermostimulation of different leg zones is examined from the position of control of afferent information by the spinal generator of locomotion.Institute of Physiology, Kazakhstan Academy of Sciences, Alma-Ata. Translated from Neirofiziologiya, Vol. 24, No. 5, pp. 604–611, September–October, 1992.     

Secretion of beta-hexosaminidase by cultured human skin fibroblasts. Kinetics, effect of temperature, cell density, serum concentration and pH.

The temporal relation between the fusion of mononucleated myoblasts into multinucleated fibres and the quantitative changes in the activity of creatine kinase isoenzymes was determined in rat skeletal muscle cell cultures. The effect of actinomycin D on the isoenzyme transition was investigated. The activity of creatine kinase in cultures prior to the onset of cell fusion is predominantly of the BB type. During the phase of cell fusion, there is a manyfold increase in creatine kinase activity. This is due to the appearance or great increase in the activity of the MM isoenzyme. During this period, increase in the BB isoenzyme activity is very small. Inhibition of RNA synthesis by actinomycin D shortly before the onset of cell fusion did not prevent cell fusion and isoenzyme transition during the first 6 h following application of the drug.     

Ozone,ultraviolet flux and temperature of the paleoatmosphere

Of all tropospheric species, ozone (O₃) comes closest to being naturally present at toxic levels. In addition, O₃ controls the ultraviolet flux reaching the Earth's surface and affects the temperature of the surface and atmosphere. For these reasons, O₃ was an important species of the paleoatmosphere. Surface and atmospheric levels of paleoatmospheric O₃ were calculated using a detailed photochemical model, including the chemistry of the oxygen, nitrogen, and hydrogen species and the effects of vertical transport. Surface and tropospheric O₃, as well as the total O₃ column, were found to maximize for an atmospheric oxygen level of 10^–1 present atmospheric level (PAL). Coupled photochemical/radiative-convective calculations indicate that the radiative effects of O₃ corresponding to an oxygen level of 10^–1 PAL resulted in a globally-averaged surface temperature increase of 4.5 K.Proceedings of the Fourth College Park Colloquium on Chemical Evolution:Limits of Life, University of Maryland, College Park, 18–20 October 1978.     

The effects of clothing thermal resistance and operative temperature on human skin temperature

Skin temperature is an essential physiological parameter of thermal comfort. The purpose of this research was to reveal the effects of clothing thermal resistance and operative temperature on local skin temperature (LST) and mean skin temperature (MST). The LSTs (at 32 sites) in stable condition were measured for different clothing thermal resistances 1.39, 0.5 and 0.1 clo. To study the effect of environmental temperature on LST and MST, the LSTs were also measured for operative temperatures 23, 26 and 33 °C. The experimental data showed that the effect of clothing thermal resistance on the foot was greater compared to the other human parts, and the effect of operative temperature on many parts of the human body was great, such as foot, hand, trunk, and arm. The MSTs measured on the conditions that air speed was under 0.1 m/s, RH was about 30–70%, and metabolic rate was about 1 met, were collected from previous studies. On the basis of these experimental data, a MST prediction equation with the operative temperature and clothing thermal resistance as independent variables, was obtained by multiple linear regression. This equation was a good alternative and provided convenience to predict the MST in different operative temperatures and clothing thermal resistances.     

Responses of human skin temperature and thermal sensation to step change of air temperature

1. 1. The purpose of this paper is to clarify the non-linearity of the human physiological and psychological responses to step change of air temperature by impulse response analysis using Discrete Fourier Transformation.

2. 2. Experiments were conducted to investigate the effect of thermal transients on human responses.

3. 3. Experimental conditions were as follows: lowering air temperature from 30 to 20°C and raising air temperature from 20 to 30°C.

4. 4. The responses of local skin temperature on lowering air temperature from 30 to 20°C are not necessarily opposite to the responses found on raising air temperature from 20 to 30°C.

5. 5. From impulse response analysis using Discrete Fourier Transformation, skin temperature responses to the opposite air temperature change do not necessarily coincide with each other whenever the same temperature stimulus is occurred.

Prediction of temperature profiles in the human skin and subcutaneous tissues

Exact mathematical solutions in terms of confluent hypergeometric and Airy's functions are obtained to study the steady state temperature distributions in human skin and subcutaneous tissues (SST). It is assumed that the skin is exposed to an air environment and heat transfer from the skin occurs by convection, radiation and evaporation. A mathematical model of the SST, accounting for heat conduction, perfusion of the capillary beds and metabolic heat productions of the dermis and subcutaneous tissues, has been solved to obtain interface temperatures for a wide range of environmental temperatures, rates of evaporation of sweat, wind speeds and relative humidities. The solutions provide inter-relationships between interface temperatures, thermal conductivities, metabolic heat production, blood perfusion, thicknesses of various layers of SST and ambient temperature.