Microgravity.
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Adaptation, Physiological↗
Biomedical subjects
F Patat
Publications and source records attributed to F Patat.
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.
Aerospace Medicine↗
Micro-emboli detection: an ultrasound Doppler signal processing viewpoint.
Several studies have been carried out in the last twenty years on the characterization and detection of cerebral artery emboli. From the detection point of view, the existing methods are largely based on the classical Fourier analysis of which the well known limitations provide poor accuracy. This paper first recalls existing methods based on Fourier, Wigner-Ville and wavelet approaches. It then presents new emboli detection methods based on parametric signal processing approaches. The basic idea of these parametric methods is to compare the Doppler embolic signal to its autoregressive model. The detection principle consists in constructing a decision information which contains the signature of the micro-embolus being sought. The detection is finally evaluated using receiver operating characteristic (ROC) curves. Comparison between the new methods and classical approaches is performed using a realistic embolic signal simulation. Furthermore, to validate our theoretical study, we tested our new algorithms using in vivo signals. This comparison shows the significant inaccuracy of existing methods to detect micro-emboli.
Algorithms↗
[Medical and psychological status of one-year-old premature babies without severe disability. Case-control prospective study].
BACKGROUND: This case-control prospective study was conducted to determine whether and how medical, psychological and affective development differs from premature to full-term newborns without severe disability. POPULATION AND METHODS: Newborns under or at 33 weeks gestation (W) were included from December 1992 to January 1994 and were matched with two controls. The same examiners evaluated each infant at the effective postnatal age of nine to ten months. RESULTS: Fifty premature babies (average gestational age [GA] = 30.7 W) were compared to 100 controls. The main problems were bronchopulmonary (P = 0.03) and sleep (P = 0.027) disorders. Motor disability was suspected in 9% of the cases and none control (P = 0.00003, OR = 3.44). By multivariate analysis, cases differed from the controls by infant-mother relation disturbances (OR = 13.3), motherhood anxiety (OR = 13.3), poor expressiveness (OR = 5.6), peripheral tonus anomalies (OR = 39.5) and sleep troubles (OR = 5.8). CONCLUSION: Premature newborns had risks for the child-mother relation but not for psychoaffective development disturbances.
Case-Control Studies↗
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.).
Adult↗
Effective density estimators based on the K distribution: interest of low and fractional order moments.
The K distribution is an efficient model to the nonRayleigh statistics of the envelope of backscattered signals in random media. This modeling leads to estimate a parameter of effective density by means of the calculation of statistical moments of the envelope signal. In this study, we propose a mathematical analysis of an effective density estimator previously used and based on superior order moments. In order to improve the effective density estimate, we propose several estimators based on low and fractional order moments. The performances of these estimators are evaluated both with simulated signals and in an experimental context with synthetic foams. Estimators based on low and fractional moments appear to be more robust than superior moment-based estimator and an improvement of the spatial resolution of the estimate can be obtained. Results also confirm the capability of the effective density parameter to characterize the spatial distribution of scattering structures.
Computer Simulation↗
[High resolution ultrasound imaging: value in treatment of basocellular carcinoma by cryosurgery].
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.
Adult↗
[Percutaneous absorption: topical and systemic treatments].
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Administration, Topical↗
Ultrasound: present and future.
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Contrast Media↗
Experimental and numerical models of acute intracranial hypertension and basilar artery blood flow velocity.
A numerical model based on Navier-Stokes equations was used in conjunction with an experimental model in rabbits to study the effects of acute intracranial hypertension on basilar artery blood flow velocity. The hypertension was induced by pressure transmission via an epidural pressure sensor inserted into a parietal intracranial opening. A critical value of half of the diastolic arterial pressure for the intracranial cerebral pressure was determined by both numerical and experimental models. At this intracranial cerebral pressure level, the total input resistance and total input compliance, determined by the numerical model, exhibited an increase of 27% and 10%, respectively, and the tissular compliance a decrease of 25% from their physiologic baseline values. When the intracranial cerebral pressure reaches the level of the diastolic arterial pressure, a zero diastolic flow is observed into the cerebral vascular system. This study validates the theoretical model, which could be used in assessing intracranial cerebral pressure noninvasively in humans when O2 pressure can be stabilized.
Acute Disease↗
High-resolution real-time ultrasonic scanner.
High spatial resolution is required for echographic exploration of the skin, microvessels or small laboratory animals. With the scanner described here, high resolution is obtained by means of a strongly focused, wide-band 17 MHz center frequency transducer (-6 dB bandwidth: 22 MHz). The movement of this transducer above the skin provides a 6 mm wide and 5 mm deep echographic cross-section with an image rate of 15 images/s. The resolution is about 0.08 mm in axial and 0.2 to 0.3 mm in lateral directions. The device was tested on phantoms in water and in vivo on normal and pathological skin in the Department of Dermatology. With the easy-to-handle probe, explorations were made on psoriasis, basocellular carcinoma, malignant melanoma and sarcoidosis.
Basal Cell Carcinoma↗
Hemodynamic and hormonal effects of prolonged anti-G suit inflation in humans.
This study examined the hemodynamic consequences of prolonged lower body positive-pressure application and their relationship to changes in the plasma concentration of the major vasoactive hormones. Six men [36 +/- 2 (SE) yr] underwent 30 min of sitting and then 3 h of 70 degrees head-up tilt. An antigravity suit was applied (60 Torr legs, 30 Torr abdomen) during the last 2 h of tilt. In a similar noninflation experiment, the endocrine responses were measured in the suited subjects tilted for 3 h. Two-dimensional echocardiography was used to calculate ventricular volume and cardiac output. Measurements were made 30 min before and 30 and 90 min after inflation. Immediately after inflation, mean arterial pressure increased by 7 +/- 2 Torr and heart rate decreased by 16 +/- 4 beats/min. Left ventricular end-diastolic volume and systolic volume increased significantly (P less than 0.05) at 30 and 90 min of inflation. Cardiac output increased after 30 min of inflation and returned to the preinflation level at 90 min. Plasma norepinephrine and plasma renin activity were maximally suppressed after 15 and 90 min of inflation, respectively (P less than 0.05). No such hormonal changes occurred during control. Plasma sodium, potassium, and osmolality remained unchanged during both experiments. Thus, prolonged application of lower body positive pressure induces 1) a transient increase in cardiac output and 2) a marked and sustained decrease in plasma norepinephrine and plasma renin activity, which reflect an inflation-induced decrease in sympathetic activity.
Adult↗
[The role of ultrasound technique in blood group typing].
The work presented here concerns the study and fabrication of a robot. This tool allows one to bring out the enormous potential represented by the interaction of ultrasounds with globular suspension. The traditional hemagglutination techniques employ the systematic use of a centrifuge and mechanical suspension. The advantage of these processes is the acceleration of reactions, however, the major inconvenience remains in the difficulty of automating these tests completely, especially when microplaques are used. Our study demonstrates that the force of the ultrasonic radiation created in an atmosphere of suspension is susceptible to replacing all mechanical movements. In a stationary ultrasonic field the erythrocytes in suspension assemble towards the pressure points. This phenomenon is characterized by a faster rate of sedimentation favoring agglutination as well. Under certain conditions the ultrasonic bundle produces small whirlwinds in the bowl. The result of this process is the homogenization of the suspension which permits the differentiation between the positive and negative reactions. With these observations in mind we developed a programmable robot prototype, the goal of which was to provide us with a means of greater investigation. The originality of this technique necessitated the realization of a high frequency ultrasound captor with large range and power. For supplying the necessary energy to the transducer we developed an electronic force based on the principle of commutation. The automation is controlled by a programmable microsequensor. This instrument will allow a standardization of a protocol primarily for tests of the group ABO. The results obtained are very encouraging; the next step is to further advance experimentation in more delicate tests.(ABSTRACT TRUNCATED AT 250 WORDS)
Blood Grouping and Crossmatching↗
Cardiovascular response to lower body negative pressure before, during, and after ten days head-down tilt bedrest.
The haemodynamic response to lower body negative pressure (LBNP) was studied in 6 test subjects before (baseline), during, and after (recovery) ten days of 6 degrees head-down bedrest. The LBNP protocol consisted of a 35 min control period, application of a staircase differential pressure profile (15 min at -15 mmHg; 5 min at -30 mmHg; 15 min at -40 mmHg), and a 10 min post-stress observation period. Cardiac output was measured by a foreign gas rebreathing technique. Finger plethysmographic arterial blood pressure (BP), ECG, and heart rate (HR), lower limb crossectional area, and the electrical impedance of three body segments were recorded continuously. As expected, HDT caused a decrease in plasma volume and total body fluid volume. Resting CO at the end of HDT was 16% below the baseline level and similar to CO in the upright position before HDT. Stroke volume (SV) was also reduced, but there were no significant changes in control HR or BP. Absolute changes in CO and SV during LBNP were similar at baseline and during HDT, but the relative changes were larger during HDT. HR and vasoconstriction responses were enhanced, but presyncope occurred in two subjects. Reduced cardiac filling with decreased stroke volume at rest is the apparent primary cause of the altered LBNP response during HDT.
Adult↗
Effect on the cardiac function of repeated LBNP during a 1-month head down tilt.
Cardiovascular assessment by ultrasound methods was performed during two long duration (1 month) Head Down Tilt (HDT) on 6 healthy volunteers. On a first 1 month HDT session, 3 of the 6 subjects (A, B, C) had daily several lower body negative pressure tests (LBNP), whereas the 3 subjects remaining (D, E, F) rested without LBNP. On a second 1 month HDT session subjects D, E, and F had daily LBNP tests and the A, B and C subjects did not. The cardiac function was assessed by Echocardiography, (B mode, TM mode). On all the "6 non LBNP" subjects the left ventricule diastolic volume (LVDV), the stroke volume (SV) and the cardiac output (CO) increase (+10%, -15%) after HDT then decrease and remain inferior (-5%, -5%) or equal to the basal value during the HDT. Immediately after the end of the HDT the heart rate (HR) increase (+10%, +30%) whereas the cardiac parameters decrease weakly (-5%, -10%) and normalize after 3 days of recovery. On the "6 LBNP" subjects the LVDV, SV and CO increase (+10%, 15%) after 1 h HDT as in the previous group then decrease but remain superior (+5%, +15%) or equal to the basal value. After the HDT session, the HR is markedly increased (+20%, +40%) the LVDV and SV decrease (-15%, -20%) whereas the CO increases or decreases depending on the amplitude of the HR variations. These parameters do not completely normalize after 3 day's recovery. Repeated LBNP sessions have a significant effect on the cardiovascular function as it maintains all cardiac parameters above the basal value. The LBNP manoeuvre can be considered as an efficient countermeasure to prevent cardiac disadaptation induced by HDT position and probably microgravity.
Adult↗
Influence of the measurement location on the resistance index in the umbilical arteries: a hemodynamic approach.
A computer model was used to study the primary factors generating the reduction in resistance index, (S-D)/S, values observed by ultrasonic Doppler measurements in the umbilical artery, from the fetal insertion to the placental insertion (S represents the amplitude of the systolic peak and D the amplitude of the diastolic peak). This hemodynamic approach shows that the placental resistance is the primary factor, the viscosity and the cord length playing secondary roles. Clinically, the position of the measurement along the cord is an important factor. To increase the sensitivity of the index, the Doppler measurement must be performed near the fetal insertion, whereas a measurement near the placental insertion will make the Doppler examination more specific.
Blood Flow Velocity↗
Cardiovascular disturbances induced by a 25 days spaceflight and a one month head down tilt.
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Adult↗
Hemodynamic, plasma renin activity and norepinephrine changes induced by anti-G suit inflation in man.
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Adult↗