Use of thigh pressure cuffs to modulate simulated microgravity-induced changes in the skin measured with high-resolution B-scan ultrasound.

OBJECTIVE: The aim of the present study was to evaluate the fluid shift in a simulated microgravity experiment and to test the use of thigh cuffs to help alleviate the problem. METHODS: The change in skin thickness was assessed by a 20 MHz B-scan ultrasound device. This was performed on eight volunteers who underwent two successive 7-day periods of -6 degrees anti-orthostatic bed-rest, with or without the daytime use of thigh cuffs. The thigh cuffs were used to counteract the development of facial oedema. RESULTS: In the control group (without thigh cuffs), the results showed a steady increase in skin thickness of the combined dermis and hypodermis of the forehead and a reduction of the thickness of this tissue on the tibia. For the countermeasure group, although thigh cuffs were only employed during the daytime - being removed at night - their use reduced the amplitude and kinetics of the fluid shift, resulting in greater beneficial effects at the end of the day than early in the morning. CONCLUSION: These results of objective measurements of skin made using a non-invasive high frequency ultrasonography method confirm reports by cosmonauts of a reduction in facial oedema and a more 'comfortable' adaptation to microgravity by the use of thigh cuffs during space flight. This system is potentially promising for investigating fluid shifts in the skin and may prove useful in the evaluation of some oedematous skin diseases, as well as their therapy.

Skin ageing: changes of physical properties of human skin in vivo.

We have investigated in vivo the change with age of various parameters that describe the physical properties of skin. The parameters were derived from pressure/displacement curves obtained by applying reduced pressure to a small area of skin and measuring the resulting displacement by 20 MHz scan echography. By fitting the pressure/displacement curves to a theoretical model, the following skin parameters were obtained: E, Young's modulus or stiffness (in Pascals); sigma(0), the initial stress (in Pascals); and the unrestored energy ratio (UER), an index related to cutaneous non-elasticity. These parameters, which are used in mechanics to define the intrinsic physical characteristics of materials, were measured for the first time on volar forearm skin of 206 male and female subjects, aged between 6 months and 90 years. The results showed that skin thickness increases until maturity and decreases for women over 50-60 years old, Young's modulus E increases linearly with age, and ageing is divided into two phases for natural stress, sigma(0) and the non-elasticity index UER. Natural stress sigma(0) increases until maturity and then rapidly decreases. The non-elasticity index decreases until puberty and steadily increases after puberty. This new procedure provides a simple quantitative assessment of the physical properties of the skin, revealing that the skin becomes thinner, stiffer, less tense and elastic with ageing.

The DopFet system: a new ultrasonic Doppler system for monitoring and characterization of fetal movement.

To enable the investigation of fetal movement in a manner similar to fetal heart rate (FHR) monitoring we have developed an apparatus (the DopFet system) that consists of a pair of miniature sensors, a 2-MHz continuous-wave directional Doppler electronic module and a laptop personal computer. One of the sensors is aimed at the fetal limbs and the other at the thorax to detect heart and upper body movements. The signals are analyzed, presented in real-time and postprocessed by software developed by us. The postprocessing software computes a number of parameters (the DopFet parameters) describing fetal movement. These parameters can be divided into two categories: parameters that describe the quantity of fetal movement (i.e., number of movements) and parameters that describe qualitative aspects of fetal movement (i.e., average movement duration). Future studies using the DopFet system will be aimed at discovering which of these parameters or combination of parameters is the best indicator of fetal well-being. We present an example of a 0.5 h recording and the results of testing on 23 volunteer mothers. These results show good sensitivity of the system compared to real-time ultrasound (US). The system detects 96% of rolling movements, 100% of flexion movements and 97% of leg movements.

Effects of fetal and maternal breathing on the ultrasonic Doppler signal due to fetal heart movement.

Fetal heart rate (FHR) monitoring is widely used to evaluate fetal health and is based on the detection of movements of the fetal heart by Doppler ultrasound. Fetal health can also be evaluated by prolonged observation of body- and pseudo-respiratory movements using two-dimensional ultrasound. Fetal breathing movements are in particular considered to be an important indicator of fetal well being. Ultrasonic Doppler signals caused by movements of the fetal heart were analyzed in detail. The signals were acquired from five healthy fetuses. Minor changes in the insonification geometry gave rise to great variations in the aspects of successive heartbeats. The signals are shown to contain information on both maternal and fetal respiratory movements. This may facilitate the development of a simple method for fetal respiration monitoring coupled to standard FHR monitoring.

Characterisation of gravity-induced facial skin oedema using biophysical measurement techniques.

BACKGROUND/AIMS: In humans, the microgravity environment can be expected to induce swelling of facial tissues and shrinking of the tissues in the lower limbs, together with a loss in body weight. To evaluate fluid shifts in skin, the head-down bed-rest model was used. The aim of the present study was to evaluate the appearance of facial oedema in subjects undergoing anti-orthostatic bed-rest at an angle of -10 degrees. METHODS: The forehead of each of four subjects was measured before and after 1, 10 and 24 h in this head-down tilt position. At these time points, interstitial fluid migration and facial oedema were assessed using a high resolution B-scan ultrasound and a device for measuring the skin's mechanical properties. RESULTS: The results obtained showed a progressive increase in dermal thickness and initial stress, and a reduction in stiffness and elasticity of the skin during the study period. CONCLUSIONS: This preliminary study has demonstrated the feasibility of the method in measuring fluid displacement and retention in the skin. Furthermore, it highlights the influence of fluids on the mechanical behaviour of the skin. These techniques could be used for studying the redistribution of liquid masses during periods spent in space.

In vivo model of the mechanical properties of the human skin under suction.

BACKGROUND/AIMS: A new method for the in vivo characterization of the mechanical properties of skin has been developed. This comprises a suction chamber and an ultrasound device to measure both the vertical displacement of the skin's surface, and the skin's thickness. METHODS: A mathematical model of the mechanical behaviour of a taught elastic membrane is used to obtain a set of parameters intrinsic to the skin, such as Young's modulus (E) and the initial stress (sigma0), which reflect the stiffness and the natural tension of the skin, respectively. We also calculated an index of non-elasticity of the skin (unrestored energy ratio, UER), which takes into account the volume of tissue mobilized. It determines a ratio between the energy input to the skin and the energy it dissipates. These parameters were evaluated from the volar forearm of 10 normal male volunteers. RESULTS: The results were: 129+/-88 kPa for E, 13.5+/-5 kPa for sigma0, and 0.42+/-0.04 for UER; with reproducibilities of 9.5%, 12.4% and 6.4%, respectively. CONCLUSIONS: This new suction device was found useful for the study of the behaviour of the skin, and the device may be used for the evaluation of certain skin diseases and their therapy.

Sex- and site-dependent variations in the thickness and mechanical properties of human skin in vivo.

A new method for the in vivo characterization of the physical properties of skin is presented. This comprises an ultrasound device to measure the vertical displacement of the surface of the skin, as well as its thickness and that of the hypodermis under suction. In combination with this, a mathematical model is used to calculate the following skin parameters: Young's modulus, the initial stress and an index of non-elasticity. These parameters were evaluated from the volar forearm and the forehead of 30 male and 30 females, of similar ages (28 +/- 6-years-old). The sensitivity of the testing procedure, allowing the characterization of the mechanical parameters of the skin, easily differentiated these two sites, and in some cases, differences between women and men were demonstrated. The main results showed for both sexes that the thickness (P = 0.0001), Young's modulus (P = 0.0001), and the index of non-elasticity (P = 0.0001) were greater for the forehead than for the ventral forearm, but that the initial stress was lower (P = 0.0001). The results show that the skin is thicker, stiffer and less tense and elastic on the forehead than on the ventral forearm, suggesting structural differences between these two sites (collagen fibre network, elastic fibres, epidermis, stratum corneum, microvascularization, actinic damage, presence of sebaceous glands, etc.). It is hoped that this device will be useful for the evaluation of certain skin disorders (scleroderma, Ehlers-Danlos syndrome, cutis laxa, oedema, etc.) and their therapy, as well as being a useful tool in skin ageing and cosmetic product assessment.

High frequency (20 MHz) ultrasonic devices: advantages and applications.

OBJECTIVE: This paper investigates the problems, advantages and potential applications of 20 MHz ultrasonic devices. METHOD: Aqueous gel and a thin appropriate membrane to enclose the front tip were used with 20 MHz probes without obvious decrease in resolution and sensitivity compared to the results obtained without a membrane and this considerably facilitates their routine use. RESULTS: Many applications with linear scanning were evaluated in dermatology, ophthalmology (investigations of the anterior chamber of the eye, checking of corneal grafts), stomatology (detection and evaluation of periodontal disease) and in the field of measurement of very low velocities in small vessels by means of a duplex probe comprising two 20 MHz transducers: an imaging transducer and an inclined blood flow measurement transducer. Velocity profiles (velocities less than 0.50 mm/s) were measured in 100-300 microm diameter vessels using a cross-correlation method. CONCLUSION: The use of 20 MHz frequency limits resolution but we have shown that this frequency allows the development of easy to handle probes.

In vivo high-frequency ultrasonic characterization of human dermis.

The aim of this study is in vivo skin tissue characterization of young and old human cutaneous tissues by estimating the slope of the attenuation coefficient. The method used is the centroid algorithm with a second-order autoregressive model to perform the spectral analysis. Backscattered signals are acquired with a 40-MHz transducer fixed on a three-dimensional robot. Diffraction phenomena are eliminated via an axial translation of the transducer that allows the acquisition of the signal in the focal zone. The slope of the attenuation coefficient is estimated on phantoms of known attenuation, in order to validate the method. Preliminary measurements of the slope of the attenuation coefficient are subsequently performed in the echographic mode on abdominal human skin samples in vitro at 40 MHz. After assessing the reproducibility of the measurement of the attenuation coefficient slope in human dermis at 40-MHz in vivo, this is carried out on the volar face of the forearm of 150 healthy subjects aged 14-85 yr. The values measured range from 0.7 to 3.6 dB/cm.MHz. The main result of this study is the decrease with advancing age of the attenuation coefficient slope, which may reflect structural modifications of human dermis with age.

High-frequency estimation of the ultrasonic attenuation coefficient slope obtained in human skin: simulation and in vivo results.

In vivo ultrasonic characterization of the skin was performed at 40 MHz by estimating the slope of the attenuation coefficient in the human dermis. The centroid algorithm was first tested on simulated backscattered RF lines with a second-order autoregressive model to carry out the spectral analysis. A relative error of less than 8.5% and a relative precision of less than 6% were predicted for a 2-mm tissue thickness and for temporal window sizes ranging from 0.25 to 0.45 micros. In vivo measurements performed on 138 healthy volunteers yielded values of the attenuation coefficient slope ranging from 0.8 to 3.6 dB/cm MHz. A decrease was observed with advancing age, but no significant difference appeared between men and women. The results from this study suggest that this acoustic parameter shows the effect of the ageing process on normal skin tissue in vivo.

Distance of foetal movement measured using the analytical signal derived from non-directional Doppler sound.

Foetal heart rate (FHR) monitoring using the Doppler shift resulting from the movements of the foetal heart is a standard examination in most obstetrical wards. Other movements also give rise to a low frequency Doppler shift. These signals are incompletely understood. Their characteristics may offer a way for diagnostic exploitation through complementing or replacing time consuming ultrasound observation of foetal movements. It is shown that a wealth of information is contained in these signals which can easily be extracted on line by a standard PC computer using straightforward methods of signal processing. In its amplitude an ultrasonic Doppler signal contains information concerning the size of the reflector in movement and speed as frequency. The displacement of the reflector can also be derived from the phase evolution of a complex Doppler signal. Examples of signals generated by various types of foetal activity are shown and analyzed.

[High resolution ultrasound imaging: value in treatment of basocellular carcinoma by cryosurgery]. / Imagerie ultrasonore haute résolution: utilité pour le traitement des carcinomes basocellulaires par cryochirurgie.

OBJECTIVE: We conducted a prospective evaluation of the contribution of high-resolution ultrasound imaging prior to cryosurgery for basocellular carcinoma and in search for recurrence. PATIENTS AND METHODS: All patients seen between 1992 and 1994 at the skin tumor clinic and treated by cryosurgery were included. Ultrasound imaging using 20 MHz prototype was performed prior to cryosurgery and 2 months later. RESULTS: Among 101 patients treated, 112 basocellular carcinomas were treated by cryosurgery. Ultrasound imaging provided good visualization of the tumor limits in all cases. The ultrasound aspect was anechogenic, often with rare areas of highly dense echoes. The tumor limits described by ultrasound imaging were larger than the clinical limits in 32% of the cases. In 8 of the 16 cases of recurrent tumors, the ultrasound examination revealed the recurrence first. In the other 8 cases, clinical manifestations were confirmed by ultrasonography. In our series, recurrence of basocellular carcinoma was statistically more frequent when the depth of the tumor was 3 mm (ultrasonographic measurement) or when the lateral limits established by ultrasound assessment were greater than the clinical evaluation. DISCUSSION: These findings demonstrate that high-resolution ultrasound imaging of basocellular carcinomas prior to cryosurgery: 1) visualizes tumor limits allowing adapted cryosurgery, 2) identifies factors with predictive value for recurrence, 3) can identify recurrences early. Ultrasound imaging of the skin is a useful non-invasive technique for pre- and post-therapeutic assessment of skin tumors and could be a particularly useful tool for "blind" cryosurgery destruction of skin tumors.

Feto-maternal circulation: mathematical model and comparison with Doppler measurements.

OBJECTIVES: Clinicians are more and more frequently studying fetal blood flow velocity curves recorded by Doppler ultrasound in vital organs such as the placenta and fetal brain to evaluate fetal well-being. We have therefore developed a mathematical model of the utero-placental and fetal circulations which could be used for teaching and for a better understanding of regulatory mechanisms. METHODS: The model is based on two basic elements-an arterial segment and a bifurcation-and we have reproduced the major arteries of the feto-maternal circulation combining these basic elements. The mathematical model of the system is based on the Navier-Stokes equations. The peripheral areas such as the brain, kidneys and placenta are modeled by a simple Windkessel model and the model computes instantaneous flow and pressure at any point in the fetal arterial tree and the uterine arteries. RESULTS: We have compared the computed instantaneous flow curves and pressure with in vivo data and our results agree with the findings in physiological situations and in gravidic hypertension. CONCLUSIONS: Our model provides new interesting insights into fetal hemodynamics such as a better understanding of the mismatch impedance phenomena and is a promising model for the study of blood redistribution mechanisms in hypoxic situations.

An in vivo method for measuring the mechanical properties of the skin using ultrasound.

In this study, we report a new and original device called the "echorheometer," comprising a suction system with an ultrasound scanner (A-mode, TM-mode and B-mode) that enables the simultaneous visualization and measurement of the deformation of skin structures in vivo. With the scanner described here, high resolution is obtained using a strongly focused, wide-band 20-MHz center frequency transducer, with an axial resolution of 0.07 mm. This device can determine, noninvasively, not only those skin structures that are involved in the deformation, but also their morphological variation and their extent of involvement with the degree of stress applied. Using this device, the behavior of the dermis and subcutaneous fat, while under suction, was investigated on the volar forearm of 10 volunteers. The results showed that the resistance to the applied vertical stress is essentially due to the dermis rather than the subcutaneous fat, and that there is a certain amount of infiltration of fluid into the tissues under suction. In addition, it was shown that the dermal response to an applied suction is initially due to its own natural tension and that, with increasing deformation, the intrinsic dermal elasticity has a greater contribution to the resistance of stress. With this information, we hope to develop a mechanical model to define appropriate mechanical parameters for skin. This will allow the evaluation of changes in the dermis and also enable therapeutic intervention to be assessed. Furthermore, it could also be applied to studies of skin ageing and the assessment of cosmetic product efficacy (emolliency, hydratation, etc.).

Fetal heart modelling based on a pressure-volume relationship.

Study of the cardiovascular system of the human fetus is based on non-invasive measurement methods such as Doppler echography systems. The circulation conditions in fetal vessels are usually evaluated by resistance indices, giving limited physiological information on distal territories such as the placenta or the brain. To enhance the understanding of human fetal haemodynamics, a numerical model of the fetal heart has been developed, using the hydraulic-electric analogy. The model is based on a mechanical hypothesis of parallel functioning of the right and left ventricles, considered to have analogue elastance properties. Their behaviour is equivalent to that of a single ventricle ejecting an equivalent blood volume of 7 ml in the aorta. The characterisation of the equivalent ventricle is based on the determination of a set of four parameters (Emax, Vo, kv and Po) representing the maximum ventricle contractility, a reference volume, and volume and pressure constants, respectively. The model proposed is validated by studying the effects of preload and afterload variations on the fetal heart work, and by comparing the numerical results with literature and measured data. The model constitutes the first step towards a global model of the cardiovascular system of the human fetus.

Does hormonal skin aging exist? A study of the influence of different hormone therapy regimens on the skin of postmenopausal women using non-invasive measurement techniques.

BACKGROUND AND DESIGN: The skin properties of 98 postmenopausal women with hormone replacement therapy (oestradiol gel or patches) or without hormone replacement therapy were studied using non-invasive techniques: skin thickness with skin echography, skin hydration with a dryness score and measurement of capacitance, skin surface lipids with a Sebumeter and microtopography with image analysis of cutaneous replicas. RESULTS: In this open study we demonstrated an increase in skin thickness and sebum in the treated group in comparison to the untreated group (7-15% according to area for skin thickness, 35% for sebum). Hydration and microtopography were not different in the two groups. CONCLUSIONS: Postmenopausal women who were receiving hormonal substitution have a greater thickness and casual level than untreated women. We therefore suggest that hormonal aging exists and that cutaneous atrophy can be prevented with hormone replacement therapy.

[Quantification and monitoring of vascular resistance in the lower limbs by the Doppler method (animal model)]. / Quantification et monitorage des résistances vasculaires du membre inférieur. Par méthode doppler (modèle animal).

The object of this study was to define and validate a non-invasive method of evaluation and monitoring of vascular resistances in the leg. Blood flow velocity was measured by Doppler ultrasound in an animal model (ewe) with similar blood flow characteristics in the lower limb as man and allowing access to the required invasive measurements for validation of the method (pressure and flow). Vascular resistances distal to the measuring point (femoral, for example) were assessed using the resistance index R = D/S, S being the peak systolic deflection and D that of diastolic reflux of the Doppler spectral analysis of flow in the femoral artery. The values and variations of this resistance index were compared with the vascular resistances calculated from measurements of pressure and flow at the point of Doppler sampling and expressed in mmHg/ml/min. Femoral flow was measured by Doppler ultrasound (Doppler-echo), and mean pressure by an arterial catheter introduced into the abdominal aorta. Compression of the lower limb veins induced a venous return resulting in a reduction of cardiac output and femoral flow. During compression, femoral flow decreased by an average of 29% (p < 0.001) although mean pressure and heart rate did not change significantly. The femoral resistance index (Rf) increased by an average of 37.5% (p < 0.01) and vascular resistances increased by 45.9% (p < 0.01). Injection of 1 mg adrenaline induced peripheral vasoconstriction with an increase in blood pressure and a decrease in heart rate and femoral flow.(ABSTRACT TRUNCATED AT 250 WORDS)

Vascular resistance quantification in high flow resistance areas using the Doppler method.

The objective of the present study is to define and validate on an animal model (ewe) a new Doppler parameter for the assessment and monitoring of the vascular resistances in high resistance to flow areas (lower limbs, placenta with vascular disease). The high resistance index (HRI) was derived from the transmission line theory and defined as: HRI = D/S with S the amplitude of the systolic peak and D that of the diastolic reverse flow. Validation of the HRI was performed on adult ewes. Distal lower limb vascular resistances were evaluated from the Doppler femoral waveform (HRI) and compared with the classic vascular resistances (Rv), calculated from pressure and flow (mmHg/mL/min). The femoral flow variations were measured by duplex (echo-Doppler) method and the mean pressure through an arterial catheter inserted into the abdominal aorta. Two tests were used in this study: (1) A calibrated venous compression of the lower limbs extremity: The femoral flow dropped by 29%, the pressure and heart rate did not change, the HRI increased by 37% (p < 0.01), and the vascular resistance (Rv) by 46% (p < 0.01). (2) The intravenous injection of 1 mg adrenaline: The arterial pressure increased by 70% (p < 0.001), the heart rate and femoral flow dropped by 50% (p < 0.001), and 35% (p < 0.001), the HRI increased by 70% (p < 0.01) and the vascular resistances (Rv) by 140% (p < 0.01). During the two tests, the HRI changed in proportion with the "classic" vascular resistances.(ABSTRACT TRUNCATED AT 250 WORDS)