Modeling and interpretation of the bioelectrical impedance signal for the determination of the local arterial stiffness

Purpose: Stiffness of the large arteries (e.g., aorta) plays an important role in the pathogenesis of cardiovascular diseases. To date, the reference method for the determination of regional arterial stiffness is the measurement of the carotid-femoral pulse wave velocity (PWV) by tonometric techniques. However, this method suffers from several drawbacks and it remains limited in clinical routine.Methods: In the present study, the authors propose a new method based on the analysis of bioelectrical impedance (BI) signals for the determination of the local arterial stiffness. They show, from a theoretical model, a novel interpretation of the BI signals and they establish the relationship between the variations in the BI signal and the kinetic energy of the blood flow in large arteries. From this model, BI signals are simulated in the thigh and compared to experimental BI data. Finally, from the model, they propose a new index ( Ira ) related to the properties of the large artery for the determination of the local arterial stiffness. Results: The results show a good correlation between the simulated and the experimental BI signals. The same variations for both of them with different characteristics for rigid and elasticarteries can be observed. The measurement of the Ira index on 20 subjects at rest (mean age of 44 ± 16 yr ) for the determination of the local aortic stiffness presents a significant correlation with the PWV reference method ( R 2 = 0.77 ; P < 0.0001 with the Spearman correlation coefficient and Ira = 4.25 * PWV + 23.54 ). Conclusions: All the results suggest that the theoretical model and the new index could give a reliable estimate of local arterial stiffness

Time and Spatial Invariance of Impedance Signals in Limbs of Healthy Subjects by Time–Frequency Analysis

The bioelectric impedance technique is a non-invasive method that provides the analysis of blood volume changes in the arteries. This is made possible by an interpretation of the impedance signal variations. In this paper, time and spatial variations of such impedance signals are studied on recordings made on limbs of 15 healthy subjects at rest. For that purpose, the scalogram of each signal has been computed and quantitative measures based on energies were determined. The results show that the signals are statistically time invariant on three anatomical segments of the limbs: pelvis, thigh and calf. p Value varies between 0.20 and 0.52 for the absolute energies computed on scalograms of signals recorded at 5 min intervals. Moreover, the analysis made on the two legs of each subject shows that the signals are spatial invariant on the three anatomical segments. p Value varies between 0.0785 and 1.000 for the absolute energies computed on the scalograms of signals recorded simultaneously on the two legs. These conclusions will therefore help the clinicians in studying the temporal variations of physiological parameters on limbs with the impedance technique. Moreover, the results on the spatial invariance make possible the comparisons of these parameters with those given by other acquisition techniques

Time-resolved fluorescence intensity issued from a heterogeneous slab: Sensitivity characterization

Optical imaging using fluorescent contrast agents has become an interesting tool to differentiate diseased lesions from normal tissue. However, several sensitivity characterizations may strongly influence the time-dependent fluorescence measurements. Herein, we present a numerical model based on the finite element method that allows the simulation of time-resolved reflectance and transmittance signals from heterogeneous media mimicking breast tissues with an embedded fluorescent object (tumor). The influence, on the computed signals, of several tumor depths, as well as various fluorophore concentrations and several fluorescent markers targeting are analyzed. The results show the possibility of uncoupling location depth from the shape of the target. Therefore, the analysis of the time to reach half the maximum intensity is validated as a good localization scheme. Then, the transmitted data show that the maximal detected intensity at the bottom of the medium is very sensitive to the dye concentration but not to the tumor shape. Moreover, the strong competition between concentration determination and fluorophore distribution is presented. These results will lead to a better detection and localization of tumors

Power-law scaling behaviour of impedance signal time series of healthy subjects at rest

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Measurement of the local aortic stiffness by a non-invasive bioelectrical impedance technique

Aortic stiffness measurement is well recognized as an independent predictor of cardiovascular mortality and morbidity. Recently, a simple method has been proposed for the evaluation of the local aortic stiffness (AoStiff) using a non-invasive bioelectrical impedance (BI) technique. This approach relies on a novel interpretation of the arterial stiffness where AoStiff is computed from the measurement of two new BI variables: (1) the local aortic flow resistance (AoRes) exerted by the drag forces onto the flow; (2) the local aortic wall distensibility (AoDist). Herein, we propose to detail and compare these three indices with the reference pulse wave velocity (PWV) measurement and the direct assessment of the aortic drag forces (DF) and distensibility (DS) obtained by the magnetic resonance imaging technique. Our results show a significant correlation between AoStiff and PWV (r = 0.79; P < 0.0001; 120 patients at rest; mean age 44 ± 16 years), and also between AoRes and DF (r = 0.95; P = 0.0011) and between AoDist and DS (r = 0.93; P = 0.0022) on eight patients at rest (mean age 52 ± 19 years). These first results suggest that local aortic stiffness can be explored reliably by the BI technique

Forebrain Deletion of αGDI in Adult Mice Worsens the Pre-Synaptic Deficit at Cortico-Lateral Amygdala Synaptic Connections

The GDI1 gene encodes αGDI, which retrieves inactive GDP-bound RAB from membranes to form a cytosolic pool awaiting vesicular release. Mutations in GDI1 are responsible for X-linked Intellectual Disability. Characterization of the Gdi1-null mice has revealed alterations in the total number and distribution of hippocampal and cortical synaptic vesicles, hippocampal short-term synaptic plasticity and specific short-term memory deficits in adult mice, which are possibly caused by alterations of different synaptic vesicle recycling pathways controlled by several RAB GTPases. However, interpretation of these studies is complicated by the complete ablation of Gdi1 in all cells in the brain throughout development. In this study, we generated conditionally gene-targeted mice in which the knockout of Gdi1 is restricted to the forebrain, hippocampus, cortex and amygdala and occurs only during postnatal development. Adult mutant mice reproduce the short-term memory deficit previously reported in Gdi1-null mice. Surprisingly, the delayed ablation of Gdi1 worsens the pre-synaptic phenotype at cortico-amygdala synaptic connections compared to Gdi1-null mice. These results suggest a pivotal role of αGDI via specific RAB GTPases acting specifically in forebrain regions at the pre-synaptic sites involved in memory formation

Effect of skin temperature on skin endothelial function assessment

PURPOSE: Microcirculatory dysfunction plays a key role in the development of sepsis during which core temperature is often disturbed. Skin microvascular assessment using laser techniques has been suggested to evaluate microvascular dysfunction during sepsis, but skin microcirculation is also a major effector of human thermoregulation. Therefore we aimed to study the effect of skin temperature on endothelial- and non-endothelial microvascular responses.METHODS: Fifteen healthy participants were studied at different randomized ambient temperatures leading to low (28.0+/-2.0 degrees C), intermediate (31.6+/-2.1 degrees C), and high (34.1+/-1.3 degrees C) skin temperatures. We measured skin blood flow using laser speckle contrast imaging on the forearm in response to vasodilator microvascular tests: acetylcholine (ACh) iontophoresis, sodium nitroprussiate (SNP) iontophoresis, and post-occlusive reactive hyperemia (PORH). The results are expressed as absolute (laser speckle perfusion units, LSPU) or normalized values (cutaneous vascular conductance, CVC in LSPU/mmHg and multiple of baseline). RESULTS: Maximal vasodilation induced by these tests is modified by skin temperature. A low skin temperature induced a significant lower vasodilation for all microvascular tests when results are expressed either in absolute values or in CVC. For example, ACh peak was 57.6+/-19.6 LSPU, 66.8+/-22.2 LSPU and 88.5+/-13.0 LSPU for low, intermediate and high skin temperature respectively (p<0.05). When results are expressed in multiple of baseline, statistical difference disappeared. CONCLUSIONS: These results suggest that skin temperature has to be well controlled when performing microvascular assessments in order to avoid any bias. The effect of skin temperature can be corrected by expressing the results in multiple of baseline

Relationship between aortic stiffness and a local pulsatile indice from the peripheral cutaneous microvasculature

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Guest Editorial Special Issue on Cardiovascular System Monitoring and Therapy: Innovative Technologies and Internet of Things

The papers in this special section focus on cardiovascular system monitoring and therapy. The number of devices for the measurement and interpretation of biological systems that describe performance of the cardiovascular system is growing. Among others, this is due to the improvement of circuit and system design that renders the devices wearable and easy to use. Moreover, internetworking enables these devices to exchange data. Their true impact on patient care is highly dependent on the quality and relevancy of the data acquired. The design of circuits and systems to answer the growing demand and the necessity to have portable and connected devices lead to a focus on designing ultra-low power apparatus, mixed-signal devices, using nanoscale electronics. Microelectronic issues are therefore at the heart of the demand. All this requires inter-disciplinary collaborations between scientists, engineers, medical researchers, and practitioners. The interconnection of these embedded devices, known as Internet of Things, is expected to usher in the medical field, among others to study the cardiovascular system of patients. Data processing and storage will also take place in the healthcare information technology. Furthermore, key issues such as data security and privacy will be determinants of the utility of these systems and impact in healthcare monitoring and management. This special issue aimed to provide a forum for both established experts and newinvestigators to share their developments, knowledge, and insights for the further design of circuits and systems aiming at being integrated in sensors to monitor or treat the cardiovascular system