[Continuous determination of blood flow in human skin by a heat conductivity measuring device]

Multilayer In Vitro Human Skin Tissue Platforms for Quantitative Burn Injury Investigation

This study presents a multilayer in vitro human skin platform to quantitatively relate predicted spatial time-temperature history with measured tissue injury response. This information is needed to elucidate high-temperature, short-duration burn injury kinetics and enables determination of relevant input parameters for computational models to facilitate treatment planning. Multilayer in vitro skin platforms were constructed using human dermal keratinocytes and fibroblasts embedded in collagen I hydrogels. After three seconds of contact with a 50-100 °C burn tip, ablation, cell death, apoptosis, and HSP70 expression were spatially measured using immunofluorescence confocal microscopy. Finite element modeling was performed using the measured thermal characteristics of skin platforms to determine the temperature distribution within platforms over time. The process coefficients for the Arrhenius thermal injury model describing tissue ablation and cell death were determined such that the predictions calculated from the time-temperature histories fit the experimental burn results. The activation energy for thermal collagen ablation and cell death was found to be significantly lower for short-duration, high-temperature burns than those found for long-duration, low-temperature burns. Analysis of results suggests that different injury mechanisms dominate at higher temperatures, necessitating burn research in the temperature ranges of interest and demonstrating the practicality of the proposed skin platform for this purpose.

In vitro burn model illustrating heat conduction patterns using compressed thermal papers

To date, heat conduction from heat sources to tissue has been estimated by complex mathematical modeling. In the present study, we developed an intuitive in vitro skin burn model that illustrates heat conduction patterns inside the skin. This was composed of tightly compressed thermal papers with compression frames. Heat flow through the model left a trace by changing the color of thermal papers. These were digitized and three-dimensionally reconstituted to reproduce the heat conduction patterns in the skin. For standardization, we validated K91HG-CE thermal paper using a printout test and bivariate correlation analysis. We measured the papers' physical properties and calculated the estimated depth of heat conduction using Fourier's equation. Through contact burns of 5, 10, 15, 20, and 30 seconds on porcine skin and our burn model using a heated brass comb, and comparing the burn wound and heat conduction trace, we validated our model. The heat conduction pattern correlation analysis (intraclass correlation coefficient: 0.846, p < 0.001) and the heat conduction depth correlation analysis (intraclass correlation coefficient: 0.93, p < 0.001) showed statistically significant high correlations between the porcine burn wound and our model. Our model showed good correlation with porcine skin burn injury and replicated its heat conduction patterns.

Optical assessment of skin blood content and oxygenation

The alteration of blood flow in the skin and subcutaneous tissue due to mechanical loading is of great importance in the prevention of decubitus ulcers. A technique is described for assessing changes in blood content optically. The results indicate that such changes occur after loading even though the deformation is maintained constant.

Optimization of a beam shaping bolus for superficial microwave hyperthermia waveguide applicators using a finite element method

Temperature inhomogeneity in hyperthermia treatments often limits the total thermal dose that can be delivered to the tumour region. To reduce such inhomogeneities, a prototype dynamically modifiable square array of saline-filled patches which attenuate microwave energy was developed for superficial treatments that use external microwave applicators. The array was situated inside the coupling water bolus that is often used with external applicators. The prototype has been previously tested clinically with promising results. A more complete theoretical analysis of the performance of this new bolus design and improvements to its design by modelling are presented here. The analysis was performed by performing five iterative simulations of the SAR pattern produced inside a tissue structure by a waveguide applicator with a water bolus containing the dynamic patch array attached. Between iterations the patch array configuration was modified in an attempt to improve the ability of the bolus to confine heating to an 'L'-shaped tumour region. These simulations were performed using the finite element method. The steady-state temperature profile was then computed using a finite element method based simulation of heat transfer that assumed a given applicator power level and water bolus temperature. Several iterations of these heat transfer simulations were performed with varying applicator power level and water bolus temperature to improve the confinement of heating to the target region. The analysis showed that the dynamic patch array should be capable of conforming heating to an 'L'-shaped target tumour region while limiting the heating to the surrounding normal tissue to an acceptable level.

Skin microcirculation in healthy subjects and patients with arteriosclerosis

The concept to use the human skin microcirculation as a pharmacological in-vivo test system is old; however, methods developed in the 50s have been abandoned because of side effects and/or use of radioactive substances. We describe a newly developed minimally invasive method that allows in-vivo pharmacology in the human skin microcirculation injecting very low doses of a substance of drug without any systemic effects. The double injection technique (DIT) bears the potential to predict the effects of a drug and/or the vascular reactivity or dysfunction of other less accessible areas of the circulation (e.g. the myocardium). The DIT has been applied for studies in healthy volunteers and patients with atherosclerosis; the focus of interest was endothelial (dys-)function and the effect of exogenous vasoactive drugs. Using endothelin antagonists, we investigated the role of endogenous endothelin under physiological conditions and in atherosclerosis. The NO-synthase inhibitor L-NMMA has been applied to study the L-arginine-NO-pathway and the role of endothelial adrenoceptors. Ongoing studies with the DIT comparing coronary and skin microcirculation may help to develop minimally invasive methods to predict the effects of drugs and vascular function in the heart.

Noninvasive, quantitative determination of muscle blood flow in man by a combination of venous-occlusion plethysmography and computed tomography

Because of the lack of non-invasive methods for measuring muscle blood flow, quantitative investigations of blood flow in the skeletal muscle of hypertensive subjects are rare. We therefore developed a new method for the determination of muscle blood flow noninvasively and quantitatively by a combination of computed tomography and venous occlusion plethysmography (strain-gauge method). At two sites on one forearm (p = site of the largest diameter, d = 1 cm proximal to the epicondyle lat.) the volumes of tissues [Vt = total volume, VM = muscle volume, VSk = bone volume, VR = residual volume = Vt - (VM + VSk)] were determined by computed tomograms and total forearm blood flow (Fp and Fd, respectively in ml/100 ml tissue x min) measured by strain-gauge plethysmography. After correcting for the bone volume at the different sites, Fp and Fd were transformed into the absolute influx rates of blood volume (Qp and Qd). From Qp and Qd and the different tissue volumes, the muscle blood flow (FM in ml/100 ml muscle x min) could be calculated: (formula; see text) Results thus derived were compared with data from the literature Cooper et al. (17). At rest there was neither a significant difference in Fp (own results: 3.62 +/- 1.67, Cooper: 3.25 +/- 1.42 ml/100 ml tissue x min, means +/- S.D.) nor in FM (4.08 +/- 2.07 and 3.66 +/- 1.57 ml/100 ml muscle x min, respectively), however, Fp and FM were significantly different (p less than 0.05). In the mean, FM was 13% greater than Fp, range: -40 to +38% (Cooper 15%, range: -17 to +43%). The individual difference could not be predicted by any of the parameters. Testing the procedure by means of a pharmacological agent (clonidine) with known effects on muscle blood flow (no change) and skin blood flow (decrease) revealed the correct reproduction of this hemodynamic pattern with our method. The usual identification of total with muscle blood flow would have led to false conclusions.

An instrument for measuring endometrial blood flow in the uterus, using two thermistor probes

An instrument was developed for continuous measurement of thermal conductance reflecting blood flow locally in the endometrium. The probe consists of two small thermistors, one sensing the tissue temperature, and the other working at 5 degrees C elevated temperature, sensing the heat loss caused by thermal conduction mainly due to the blood flow. The power needed to keep this temperature difference was recorded as a measure of flow. When the instrument was tested in model experiments, for measurement of flows at temperatures of 35 to 40 degrees C, stable recordings with high sensitivity were obtained and no influence of the surrounding temperature was observed. Recordings were also made in vivo in non-pregnant women by applying the instrument to the endometrium of the uterine fundus. Intrauterine pressure was recorded simultaneously. The blood flow recordings were stable over long periods in spite of changes in body temperature, but with fluctuations of up to 0.1 mW concomitant with uterine contractions. Pulse-syncronous variations in flow were recorded, indicating a high sensitivity and a short time constant of the instrument. The blood flow effects of vasoactive substances, i.e. vasopressin and a vasopressin antagonist, could readily be distinguished. It is concluded that this instrument can be used for semi-quantitative recordings of blood flow in cavities of the body, for example the uterus, which can be reached by small probes and that changes of body temperature do not effect the measurements.

Skin blood flow changes in anaesthetized humans: comparison between skin thermal clearance and finger pulse amplitude measurement

The effect of general anaesthesia on skin blood flow in the left hand, measured by a new non-invasive probe using the thermal clearance method was examined. A mercury silastic gauge was placed around the third left finger and the plethysmographic wave amplitude was recorded to measure changes in finger pulse amplitude. Heart rate (HR), mean arterial blood pressure (MABP) and skin temperature were also recorded. General anaesthesia was induced by droperidol and phenoperidine injection and propanidid infusion in eight female patients. Skin thermal clearance, plethysmographic wave amplitude, HR, MABP and skin temperature were 0.40 +/- 0.02 w X m-1 degree C-1, 9 +/- 1 mm, 98 +/- 5 beats X min-1, 12.50 +/- 0.93 kPa and 33.3 +/- 3.4 degrees C respectively. The minimal value of MABP was 9.58 +/- 1.06 kPa, whereas skin thermal clearance, plethysmographic wave amplitude, HR and skin temperature increased to 0.45 +/- 0.02 w X m-1 degree C-1, 29 +/- 3 mm, 110 +/- 4 beats X min-1 and 34.4 +/- 0.4 degrees C. Changes in skin thermal clearance correlated well with plethysmographic wave amplitude. Statistically significant changes in these two parameters occurred before significant change in HR, MABP or skin temperature. The results show that the new non-invasive probe using the thermal clearance method appears to be a useful device for measuring cutaneous microcirculation in anaesthetized humans, and responds more quickly than change in skin temperature, which is a delayed effect of skin blood flow change. Our results also show that the intensity of cutaneous vasodilatation induced by general anaesthesia did not relate to the vascular tone before anaesthesia.

Estimation of postmortem interval from rectal temperature by use of computer (III)--thermal conductivity of the skin

The postmortem rectal temperature fall is the most reliable objective finding for estimation of the postmortem interval within one or two days. However, the thermal properties of human corpses are little known when applying the heat transmission theory to the temperature fall of a human corpse, which is assumed theoretically to be an infinite cylinder. Therefore, the thermal conductivity of excised human skin was measured by the transient hot-wire method. The values in 12 specimens averaged 0.30 Kcal/m.h.°C. The theoretical error due to the experimental conditions such as the size of specimen or heating probe was within about five per cent, and the deviation of three measurements for each material was slight. Accordingly, the deviation of thermal conductivity in 12 materials was considered to be due to the individual disparity in age, sex and postmortem changes.

A contribution to the topography of temperature regulation in man

By means of climatic chamber studies the steady-state curves of body temperature and effector mechanisms of temperature regulation in man are determined for different areas of the body. Under cold conditions local temperature differences are considerable, whereas under warm conditions, the distribution of body heat is much more uniform. Evaporative heat loss, directly measured, and skin blood flow, recorded by the fluvographic method, show considerable local differences under the influence of environmental temperature. This should be the consequence of a "distributed parameter control strategy", which may be adapted to special requirements, such as exercise or partial thermal stress of the body. The experimental results form the basis for a mathematical model of human temperature regulation, and for further experimental studies which are devoted to clarifying the strategy of regulation with local distributed parameters.

Thermal recovery of the skin after cooling

A theoretical model of the skin is used to study the thermal recovery of the skin temperature after cooling. The analytical solution of the partial differential equation describing this model shows that recovery curves can be approximated by a two-exponential curve or even by a mono-exponential curve when the data from the first two minutes are omitted. With this model, it is possible to study the influence of the blood flow and the thermal conductivity lambda of the skin on the steady-state temperature and the decay constants mun. New experiments will be carried out to verify the relation between mu1, mu2 and the blood flow but now correcting for the influence of lambda, as predicted by the model.

Measurement of the thermal properties of human skin. A review

The effective use of techniques to detect and interpret surface and subsurface temperature patterns depends upon the thermal and electromagnetic properties of the tissues under examination. A review is made of the existent data concerned with the thermal characteristics of skin. The thermal conductivity, k, and thermal inertia, kpc, as measured as a function of local temperature are presented. The radiation properties of the skin are presented as a function of wavelength. It is concluded that the information currently available about the thermal properties and their normal variation with body site, skin color, and age is quite limited.

The spatial correlation of fluctuations of the blood flow in forearm skin

The oxygen tension at the skin surface, with the atmospheric oxygen supply excluded, may be measured polarographically on the human forearm. Under suitable environmental conditions, spontaneous fluctuations in skin surface oxygen tension can be recorded and these are the result of fluctuating blood flow in the superficial skin vessels. An array of separate cathodes in a single polarographic electrode assembly has been used to measure the fluctuations in blood flow which are occurring simultaneously at seven different points in the skin. Spectral analysis of a long recording of such fluctuations shows that most of the power is concentrated at the lower frequencies but does not reveal any clearly defined dominant frequency. It is clear, however, from inspection of the fluctuation patterns, that recurring bursts of activity occur with quite well-defined periodicities in the range of 30s to 5 min. There is a stronger correlation between the fluctuations occurring at points on the skin surface less than 1 mm apart than between points further apart, although there are clearly some components which are common to points separated by up to 5 mm which was the largest separation of cathodes used in these experiments. These observations are supported by the value of cross correlation coefficients between the channels. These results suggest that the observed fluctuations are the result of at least two factors. The first one is common to all the channels but the effect of this may be overridden by a second and more local one controlling the blood flow.

[The value of the thermocouple in the measurement of the gastric mucosal blood-flow. The influence of the occlusion of the celiac artery and prostaglandin E1 on the gastric mucosal blood flow. An experimental study in animals (author's transl)]

The study has been carried out to ensure the positive evidence of the measurement of the gastric mucosal blood-flow with the aid of the thermocouple (heat-clearance technique). The experiments have shown that the suction pressure of 600 mm mercury column which was used to fix the Thermocouple to the mucosa was indispensable in order to assess the blood-flow in the entire depth of the mucosa. Changes in the mucosal blood-flow are measuured at the same rate in all quadrants of the gastric corpus. The measuring of the blood-flow of a well circumscribed area of the mucosa is therefore representative for the entire corpus. Vasopressin led to a significant reduction of the gastric mucosal blood-flow measured with heat-clearance as well aminopyrine-clearance. There was a linear correlation between the results of both methods. Vasopressin selectively reduces the blood-flow of the gastric mucosa but not of the submucosa, the muscular layer and the serosa. Therefore it seems to be probable that changes in mucosal blood-flow selectively can be measured with the aid of the thermocouple. After previous stimulation with pentagastrin neither mucosal blood-flow nor acid secretion of the stomach were influenced by the occlusion of the celiac artery by 25 %. The occlusion of the celiac artery by 50 % reduced significantly the pentagastrin-stimulated gastric mucosal blood-flow whereas the acid secretion was not influenced. Prostaglandin E1 at a dose rate of 2 mug/kg-h increased significantly arterial and mucosal blood-flow as well as acid secretion of the stomach. In comparison PGE1 administered at a dose rate of 4 mug/kg-h reduced significantly gastric mucosal blood-flow and gastric secretion. PGE1 at a dose rate of 8 mug/kg-h did not produce any significant changes in blood-flow and secretion. The results suggested that the changes of gastric secretion observed with PGE1 were the consequence of primary changes in the gastric mucosal blood-flow.

PERIPHERAL VASCULAR EFFECTS OF MIXTURES OF ISOPRENALINE AND NORADRENALINE IN MAN

Mixtures of isoprenaline (0.05 mug/min) and noradrenaline (0.05, 0.1 and 0.25 mug/min) were infused into the brachial artery of subjects. The response, an initial transient increase in forearm blood flow followed by a decrease to or below the resting level, resembled the response to an intra-arterial infusion of adrenaline (0.05 to 0.5 mug/min). A five-fold increase in the dose of both drugs in the mixture resulted in a response which was matched by that to a five-fold increase in the dose of adrenaline. The intra-arterial infusions of mixtures and of adrenaline both reduced the thermal conductivity of the skin of the forearm. This result suggests that blood vessels in skeletal muscle responded qualitatively in the same manner to these infusions. Mixtures of isoprenaline (2 mug/min) and noradrenaline (10 mug/min) were infused intravenously into the subjects. The response was an initial transient increase followed by a smaller but sustained increase in the flow of blood to the forearm, and a fall in the flow of blood to the hand. These responses resembled those to the intravenous infusion of adrenaline (10 mug/min). We conclude that the action of adrenaline in the human arm can be explained on the basis of the response of two types of catechol amine receptor.