A cool response-The influence of ambient temperature on capillary refill time.

OBJECTIVE: To describe the effect of low ambient temperature on skin temperature and capillary refill (CR) time in forehead, sternum and finger pulp. METHODS: An observational, nonrandomized experimental study on 15 healthy subjects (6 females) in a cold room (8°C). Outcome measures were skin temperature and quantified CR test after application of a standardized blanching pressure (9 N/cm2 ) using digital photographic polarization spectroscopy to generate CR times. RESULTS: The finger pulp showed marked temperature fall and prolonged CR times (>10 seconds). The CR registrations of the forehead and sternum were more comparable to curves observed in a control material at room temperature, and skin temperature falls were less marked. CR times were not prolonged in forehead measurements. At the sternum, some individuals showed CR times beyond guideline recommendations despite only a marginal reduction in skin temperature. CONCLUSIONS: Low ambient temperature is a strong independent factor for CR time at peripheral sites. Reservation about sternum as a site of measurement is warranted since cold provocation produced prolonged CR times in some individuals. We found that the forehead is the most thermostable of the 3 sites and thus the preferred site to avoid ambient temperature artifact in measuring CR time.

Reflectance spectroscopy: to shed new light on the capillary refill test.

To use Bioengineering methodology is used to achieve, at five anatomical sites, a detailed, quantitative assessment of the return of blood content to the blanched area, during the Capillary Refill (CR) test. An observational, non-randomized, experimental study on 23 healthy subjects (14 females) was performed in our climate controlled skin physiology laboratory. Our main outcome measures were based on the chronological assessment and quantification of red blood cell concentration (RBC) after the release of blanching pressure in the CR test, using Tissue Viability Imaging (TiVi), a digital photographic technique based on polarisation spectroscopy. TiVi enabled collection of detailed data on skin RBC concentration during the CR test. The results were shown as curves with skin blood concentration (TiVi-value) on the y-axis and the time on the x-axis. Quantitative CR responses showed site and temperature variability. We also suggest possible objective endpoint values from the capillary refill curve. Detailed data on skin RBC concentration during the CR test is easily obtained and allows objective determination of end points not possible to achieve by naked eye assessment. These findings have the potential to place the utility of the CR test in a clinical setting in a new light. Picture: Regular photograph and TiVi Image showing CR test and corresponding graph for the CR response.

Tissue viability imaging (TiVi) in the assessment of divergent beam UV-B provocation.

In routine clinical phototesting and in basic research, naked eye dermatological assessment is the "gold standard" for determining the patient's minimal erythemal dose (MED). In UV-B testing with a divergent, radially attenuating beam of characterised dosimetry, laser Doppler perfusion imaging has been previously used to give quantitative description of reactivity to doses above the MED in addition to a "single-dose" objective determination of the MED itself. In the present paper, the recently developed tissue viability imaging (TiVi) technology is presented for the first time as a reliable, easily applicable, high-resolution alternative to LDPI in the divergent beam testing concept. Data obtained after provocation with a range of doses was analysed in order to determine the reaction diameter, which can be related to the MED using field dosimetry. The dose-response features of exposure above the MED and the relationship between naked eye readings and the diameter were determined from the image data. TiVi data were obtained faster than LDPI data and at a higher spatial resolution of 100 µm instead of 1 mm. A tool was developed to centre over the erythema area of the acquired image. Response data could be plotted continuously against dose. Thresholding of processed images compared to naked eye "gold standard" readings showed that the normal skin value +4 standard deviations produced a good fit between both methods. A linear fitting method for the dose-response data provided a further method of determination of the reaction diameter (MED). Erythemal "volume under the surface (VUS)" for the reaction provided a new concept for visualising information. TiVi offers advantages over LDPI in the acquisition and analysis of data collected during divergent beam testing. An increased amount of data compared to traditional phototesting is easily and more objectively obtained which increases applicability in the clinical and research environment.

A new device for assessing changes in skin viscoelasticity using indentation and optical measurement.

BACKGROUND/AIMS: Skin is a viscoelastic material, comprised of fluidic and fibrous components. Changes in viscoelasticity can arise due to a number of conditions including dehydration, swelling (associated with injury or disease), impaired heart function, rehydration therapy, ageing, scarring, sun exposure and genetic conditions affecting connective tissue. Quantification of changes in skin viscoelasticity due to these processes is of great clinical interest in the fields of therapy monitoring, wound healing and disease screening. However, devices currently available to measure aspects of the mechanical properties of skin have limitations in ease-of-use, accessibility, and depth of measurement. This paper describes a new technique to follow changes in the viscoelasticity of the skin, using a novel approach to an indentation manoeuvre. The device is portable, low-cost and easy to use while at the same time providing rich information on the mechanical response of the skin. METHODS: The method proposed optically tracks the skin's recovery from an initial strain, made with a novel linear indentor, using diffuse side-lighting and a CCD video camera. Upon indentation, the skin's elastin fibres are stretched and fluid is displaced from the compressed region. When the indentor is removed, the rate of recovery of the skin from this imprint is therefore principally dependent on its hydration and elasticity. Using the blue colour plane of the image and polarisation filtering, it is possible to examine the surface topography only, and track the decay of the imprint over time. RESULTS: The decrease in size of the imprint over time (decay curve) recorded by the device is shown to agree with the theoretical predictions of an appropriate viscoelastic model of skin mechanical behaviour. The contributors to the response measured using the indentation device are fully characterised and evaluated using separate measurement techniques including high-frequency ultrasound, polarisation spectroscopy and optical coherence tomography. CONCLUSION: The device developed is capable of tracking the viscoelastic response of skin to minimal indentation. The high precision achieved using low-cost materials means that the device could be a viable alternative to current technologies.

Tissue viability (TiVi) imaging: temporal effects of local occlusion studies in the volar forearm.

Tissue Viability (TiVi) imaging is a promising new technology for the assessment of microcirculation in the upper human dermis. Although the technique is easily implemented and develops large amounts of observational data, its role in the clinical workplace awaits the development of standardised protocols required for routine clinical practice. The present study investigates the use of TiVi technology in a human, in vivo, localized, skin blood flow occlusion protocol. In this feasibility study, the response of the cutaneous microcirculation after provocation on the volar surface of the forearm was evaluated using a high temporal-low spatial resolution TiVi camera. 19 healthy subjects - 10 female and 9 male - were studied after a localized pressure was applied for 5 different time periods ranging from 5 to 25 seconds. Areas corresponding to 100 x 100 pixels (2.89 cm(2)) were monitored for 60 seconds prior to, during and after each occlusion period. Our results demonstrated the removal of blood from the local area and a hyperaemic response supporting the suitability of TiVi imaging for the generation of detailed provocation response data of relevance for the physiological function of the skin microcirculation in health and disease.

Cutaneous bioengineering instrumentation standardization: the Tissue Viability Imager.

BACKGROUND: Tissue Viability Imaging (TiVi) is a new bioengineering technology intended for remote two-dimensional mapping of skin red blood cell concentration (RBC(conc)). Before use in the laboratory, work-site and dermatology clinic, critical performance parameters of this emerging technology require careful evaluation. OBJECTIVE: To assess short- and long-term stability, image uniformity, distance and image size dependence, ambient light and curvature influence in a production batch of Tissue Viability Imagers. METHODS: Four Tissue Viability Imagers from the same production batch were evaluated at two laboratories (one industrial and one dermatological) with respect to critical parameter performance. RESULTS: The average systematic drift in sensitivity over time was 0.27% and <1.02% for all four units tested. Difference in sensitivity between units was limited to 4.1% and was due to offset rather than gain deviation. Spatial variation in image uniformity was below 3.08% and 1.93% in the corners and centre of an individual image, respectively. This spatial variation could be further reduced to 0.25% and 0.13%, respectively by image normalization. Ambient light from a 40 W bulb or a 11 W fluorescent light source at a distance of 50-60 cm above the object, reduced the recorded values by about 10%, while the camera to object distance and image size had no detectable influence on sensitivity. Curved objects, such as human forearm, demonstrated an edge effect limited to below 10%. CONCLUSION: The critical TiVi performance parameters evaluated proved stable in relation to expected variations in skin RBC(conc) over time. Calibration by way of a two-point method may reduce differences in sensitivity between instruments to further facilitate inter-laboratory comparison of results.

Tissue viability imaging: mapping skin erythema.

BACKGROUND: Tissue Viability Imaging (TiVi) is an emerging bioengineering technology intended for two-dimensional mapping of skin erythema and blanching. Before TiVi can be effectively used in studies of diseased or damaged skin, the variability in normal skin red blood cell concentration (RBC(conc)) requires evaluation. OBJECTIVE: To demonstrate how TiVi maps spatial and temporal variations in normal skin RBC(conc) at the dorsal side of the hand at rest and during post-occlusive hyperemia. METHODS: Short-term and day-to-day variations in skin RBC(conc) were quantified at the dorsal side of the hand in four healthy volunteers at rest. In a separate study, the increase in skin RBC(conc) was recorded during post-occlusive hyperemia. RESULTS: A lower skin RBC(conc) (179-184 TiVi units) was observed at the back of the hand and base of the thumb compared with areas adjacent to the nailfoldfold region of the fingers (190-213 TiVi units). The short-term variation (within 70 s) was <2% in all areas of the dorsal side of the hand, while day-to-day variations were in the range 5-7% in the back of the hand and up to 10% in areas adjacent to the nailfold region. In the post-occlusive hyperemia phase, up to a 60% increase in skin RBC(conc) was observed in the early part of the reactive hyperemia phase. This increase in skin RBC(conc) successively decreased but remained about 18% above the pre-occlusion level after 30 min. CONCLUSION: Establishment of healthy skin RBC(conc) reference values is important for the design of versatile test procedures for assessment of skin damage caused by vibration tools, chemical exposure or peripheral vascular disease.

Comparison of tissue viability imaging and colorimetry: skin blanching.

BACKGROUND: Operator-independent assessment of skin blanching is important in the development and evaluation of topically applied steroids. Spectroscopic instruments based on hand-held probes, however, include elements of operator dependence such as difference in applied pressure and probe misalignment, while laser Doppler-based methods are better suited for demonstration of skin vasodilatation than for vasoconstriction. OBJECTIVE: To demonstrate the potential of the emerging technology of Tissue Viability Imaging (TiVi) in the objective and operator-independent assessment of skin blanching. METHODS: The WheelsBridge TiVi600 Tissue Viability Imager was used for quantification of human skin blanching with the Minolta chromameter CR 200 as an independent colorimeter reference method. Desoximetasone gel 0.05% was applied topically on the volar side of the forearm under occlusion for 6 h in four healthy adults. In a separate study, the induction of blanching in the occlusion phase was mapped using a transparent occlusion cover. RESULTS: The relative uncertainty in the blanching estimate produced by the Tissue Viability Imager was about 5% and similar to that of the chromameter operated by a single user and taking the a(*) parameter as a measure of blanching. Estimation of skin blanching could also be performed in the presence of a transient paradoxical erythema, using the integrated TiVi software. The successive induction of skin blanching during the occlusion phase could readily be mapped by the Tissue Viability Imager. CONCLUSION: TiVi seems to be suitable for operator-independent and remote mapping of human skin blanching, eliminating the main disadvantages of methods based on hand-held probes.

Sub-epidermal imaging using polarized light spectroscopy for assessment of skin microcirculation.

BACKGROUND/AIMS: Many clinical conditions that affect the microcirculation of the skin are still diagnosed and followed up by observational methods alone in spite of the fact that non-invasive, more user-independent and objective methods are available today. Limited portability, high cost, lack of robustness and non-specificity of findings are among the factors that have hampered the implementation of these methods in a clinical setting. The aim of this study is to present and evaluate a new, portable and easy-to-use imaging technology for investigation of the red blood cell (RBC) concentration in the skin microvasculature based on the method of polarization light spectroscopy using modified standard digital camera technology. METHODS: The use of orthogonal linear polarization filters over both the flash source and the detector array removes the polarization-retaining light reflected from the epidermal layer. Only the depolarized light backscattered from the papillary dermal matrix reaches the detector array. By separating the RGB color planes of an image acquired in this manner and applying a dedicated image processing algorithm, spectroscopic information about the chromophores in the dermal tissue can be attained. If the algorithm is based on a differential principle in which the normalized differences between the individual values of the red and green color plane are calculated, tissue components with similar spectral signature in both planes are suppressed, while components with different spectral signatures such as RBCs are enhanced. RESULTS: In vitro fluid models compare well with theory and computer simulations in describing a linear relationship between the imager output signal termed the tissue viability index (TiVi(index)) and RBC concentration in the physiological range of 0-4% RBC fraction of tissue volume (cc=0.997, n=20). The influence of oxygen saturation on the calculated RBC concentration is limited to within -3.9% for values within the physiological range (70-100% oxygen saturation). Monte Carlo simulations provide information about the sampling depth (about 0.5 mm on the average) of the imaging system. In vivo system evaluation based on iontophoresis of acetylcholine displays a heterogeneous pattern of vasodilatation appearing inside the electrode area after about 10 min. Topical application of methyl nicotinate and clobetasol propionate further demonstrates the capacity to document the extent and intensity of both an increase (erythema) and a decrease (blanching) in the skin RBC concentration without movement artifact and with compensation for irregularity in pigmentation. CONCLUSIONS: Polarization light spectroscopy imaging for assessment of RBC concentration in the skin microvasculature is a robust and accessible technique for the clinical setting. Additionally, the technique has pre-clinical research applications for investigation of the spatial and temporal aspects of skin erythema and blanching as well as a potential role in drug development, skin care product development and skin toxicological assessment.

Volumetric flow mapping for microvascular networks by bimodality imaging with light microscope and Laser Doppler imager.

A method was developed to produce a composite image of microvascular networks with grayscales proportional to volumetric flows. Velocities in arterioles and venules were assessed with a high-resolution laser Doppler imager (LDI). The vascular structures were quantified from the micrograph with a computerized vessel detection algorithm. After registering the detected vascular network with the LDI scan, volumetric flows were calculated along the centerlines of the vessels. In vivo data were obtained from the hamster cheek pouch in 6 studies. Flow continuity of the flow map was evaluated by comparing the main flow (Q) with the sum of branch flows (Qs), averaging over the respective vessel segments incident to each bifurcation. The method was reproducible across the 6 studies with the correlation coefficient (r) between Qs and Q ranging from 0.913 to 0.986. In all, over 20,000 flow estimates from 360 vessel segments (24-160 microm in diameter) at 166 bifurcations were analyzed. With flow normalized between 0 and 1, the linear regression yielded: Qs = 1.03 Q + 0.006; r = 0.952, n = 166, P < 0.0005. The bimodality imaging method exploits a large amount of velocity and diameter data, and therefore should be useful for studying heterogeneous flows in the microvasculature.

A protocol for iontophoresis of acetylcholine and sodium nitroprusside that minimises nonspecific vasodilatory effects.

Iontophoresis of vasoactive substances is a promising tool for studying pharmacological aspects of the (patho)physiology of the microvasculature. However, nonspecific microvascular responses are a common problem in most protocols used. We studied the effect of current density (mA/cm2), charge density (mC/cm2), drug concentration (mass %) and vehicle concentration (M) on the nonspecific vasodilatation during iontophoresis of sodium chloride, acetylcholine (ACh) and sodium nitroprusside (SNP). We found that nonspecific vasodilatation depended on current density and charge density in both anodal and cathodal iontophoresis. The responses to ACh and SNP were dependent on current density, charge density and drug concentration. We found that by limiting current density (<0.01 mA/cm2) and charge density (<7.8 mC/cm2) and with adjusted concentrations for drugs and vehicles, it is possible to prevent nonspecific effects during iontophoresis of ACh and SNP, while maximum drug effects (plateaus in the dose-response curves) are still obtained. These new findings are important for future iontophoresis studies in which vasoactive drugs are used to assess microvascular function because the presented approach has advantages compared to older techniques, which mainly have attempted to suppress or compensate for the nonspecific responses during iontophoresis by the use of local anaesthetics or the measurement of drug-minus-vehicle responses, both of which present well-known experimental shortcomings.

Photon pathlength determination based on spatially resolved diffuse reflectance.

A method for the prediction of the average photon pathlength in turbid media has been developed. The method is based on spatially resolved diffuse reflectance with discrete source detector distances up to 2 mm. Light reflectance was simulated using a Monte Carlo technique with a one-layer model utilizing a wide range of optical properties, relevant to human skin. At a source detector separation of 2 mm, the pathlength can vary sixfold due to differences in optical properties. By applying various preprocessing and prediction techniques, the pathlength can be predicted with a root-mean-square error of approximately 5%. Estimation of the photon pathlength can be used, e.g., to remove the influence of optical properties on laser Doppler flowmetry perfusion readings, which are almost linearly related to the average photon pathlength.