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Development of a measurement procedure for the assessment of carotid blood pressure by means of Laser Doppler Vibrometry
Full text linkL'ipertensione è uno dei principali fattori di rischio per numerose patologie, quali infarto del miocardio, insufficienza cardiaca e renale, ictus, e rappresenta la principale causa di morte al Mondo.
Risulta, pertanto, fondamentale il monitoraggio della pressione arteriosa nell'ambito della prevenzione dell'insorgere di gravi patologie.
Lo scopo del presente lavoro è di validare una procedura di misura per la determinazione della pressione arteriosa carotidea mediante la tecnica della vibrometria Laser Doppler (LDV).
Essa è una tecnica di misura senza contatto ad elevata sensibilità, in grado di rilevare le vibrazioni della pelle legate all'attività cardiovascolare.
Nel presente lavoro, il segnale LDV è stato acquisito su 28 soggetti sani ed è stato calibrato per mezzo di un opportuno modello matematico esponenziale per ottenere la forma d'onda di pressione carotidea a partire dallo spostamento del vaso sanguigno.
I risultati ottenuti sono stati confrontati con due tecniche di riferimento, la sfigmomanometria e la tonometria arteriosa.
La pressione sistolica ottenuta dal segnale LDV calibrato ha mostrato una deviazione percentuale inferiore del 4% e del 8 % rispetto a quella ottenuta tramite cuffia sfigmomanometrica e tonometria rispettivamente. L'integrazione del segnale e l'applicazione di un modello di calibrazione sono state considerate quali significative fonti di incertezza, e si è stimata un'incertezza complessiva di circa il 15 % nella misura della pressione sistolica.
Dal segnale LDV sono stati determinati altri significativi parametri emodinamici quali il tempo di eiezione del ventricolo sinistro e la rigidità arteriosa.
In conclusione, la tecnica di misura proposta mostra buona correlazione con i metodi di misura di riferimento, benchè vadano prese in considerazione alcune criticità quali l'individuazione del punto di misura, la presenza di artefatti da movimento e di fenomeni di riflessione non legati all'impulso pressorio oggetto di studio.High blood pressure is a great risk factor for several physiological diseases, i.e. myocardial infarction, heart failure, stroke, renal failure.
Therefore, blood pressure measurement is a fundamental aspect of health monitoring.
The aim of the present work is to validate a measurement procedure for the assessment of carotid blood pressure by means of Laser Doppler Vibrometry (LDV).
LDV is a non-contact technique able to detect the skin vibrations due to the cardiovascular activity.
In this study, LDV signal was acquired from 28 healthy participants and it was calibrated by means of an exponential mathematical model in order to obtain the carotid pressure waveform from the displacement of the vessel.
The results have been compared with two standard techniques for the assessment of blood pressure, sphygmomanometric method and arterial applanation tonometry.
The systolic peak of the calibrated waveform from LDV showed an average percentage deviation inferior to 10 % from the one assessed by means of reference techniques.
The accuracy of the present measurement technique is discussed, considering the signal integration and the application of the calibration model as significant contributions to the total amount of uncertainty. An average percentage uncertainty of around 15 % has been obtained in the measure of carotid systolic pressure.
Moreover, other hemodynamic significant parameters, such as arterial stiffness and Left Ventricular Ejection Time, have been derived from LDV data, showing good correlation with the measures of the reference methods.
In conclusion, the proposed measurement technique, for the assessment of carotid blood pressure, shows good agreement with the reference techniques. Overall, some critical issues must be considered, such as the correct localization of the measurement point, the presence of movement artifacts and reflection phenomena not related to the pressure pulse in the investigated vessel
A novel approach for features extraction in physiological signals
No full textThe authors have investigated a novel processing technique, which allows to measure possibly relevant features in the ECG (Electrocardiogram) signal according to the
morphology of its waveform. The aim of this work is to prove its efficacy in the assessment of the subject’s Heart Rate (HR) and to broaden its use to signals coming from different biomedical sensors (based on optical, acoustical and mechanical principles) for the computation of HR. The analysis technique proposed for the identification of the main feature (R-peak) in ECG signal provides results that are comparable to those obtained with traditional approaches. The approach has also been applied to other signals related to blood flow, such as PCG (Phonocardiography), PPG (Photoplethysmography) and VCG (Vibrocardiography), where standard algorithms (i.e. Pan & Tompkins) could not be widely applied. HR results from a measurement campaign on 8 healthy subjects have shown, respect to ECG, a deviation (calculated as 2 ) of ±3.3 bpm, ±2.3 bpm and ±1.5 bpm for PCG, PPG and VCG. Future work will involve the extraction of additional features from the previous signals, with the aim of a deeper characterization of them to better describe the subject’s health status
Census Transform Based Optical Flow for Motion Detection during Different Sinusoidal Brightness Variations
No full textThis work is a first approach of the implementation of a specific Optical Flow algorithm for motion detection in cases where the brightness variation is represented by a sine wave, whose characteristics vary across the different image sectors. The final goal would be the implementation of such an algorithm in thermal films recording a component undergoing a sinusoidal load. Mapping the motion field all over the thermal video time history, and deriving it in order to obtain a strain map, would enable both the simultaneous measurement of stress (by performing Thermoelastic Stress Analysis) and strain by a unique video, and the possibility of stress calibration, thus linking the digital levels in output to real stress values. In this scenario, the authors present the implementation of Census Transform based Optical Flow on a simulated video, where the brightness variation is modeled like the superimposition of sine waves equal for all pixels and different Gaussian spatial distributions frame after frame. The latter is used for creating different sine patterns for each image sector
Non-contact assessment of muscle contraction: Laser Doppler Myography
No full textElectromyography (EMG) is the gold-standard technique used for the evaluation of muscle activity and contraction. The EMG signal supports analysis of a number of important parameters including amplitude and duration, engagement of motor units, and functional characteristics associated with factors such a force production and fatigue. Recently, a novel measurement method (Laser Doppler Myography, LDM) for the non-contact assessment of muscle activity has been proposed to measure the vibro-mechanical behavior of the muscles that conventionally is referred to as the mechanomyogram (MMG). The fact that contracting skeletal muscles produce vibrations and sounds has been known for more than three centuries. The aim of this study is to report on the LDM technique and to evaluate its capacity to measure without contact some characteristics properties of skeletal muscle contractions. This is accomplished with the very high vibration sensitivity inherent in the Laser Doppler Vibrometry method (in comparison to commonly used devices such as microphones, piezo electric pressure sensors, and accelerometers). Data measured by LDM are compared with signals measured using standard surface EMG (sEMG) which requires the use of skin electrodes. sEMG and LDM signals are simultaneously acquired and processed. The LDM and sEMG signals are compared with respect to the critical features of muscle activation timing, signal amplitude and force production. LDM appears to be a reliable and promising technique that allows measurement without the need for contact with the patient skin. LDM has additional potential advantages in terms of sensor properties, insofar as there are no significant issues relating to bandwidth or sensor resonance, and no mass loading is applied to the skin
LDV arterial pulse signal: Evidence for local generation in the carotid
No full textThe external blood pressure pulse, recorded on a non-contact basis using the method of laser Doppler vibrometry (LDV), has been shown to be a rich source of information regarding cardiac and vascular dynamics. Considerable attention has been directed specifically to the pulse from the neck, overlying the carotid artery, which is of special interest because the carotid pulse is highly similar to the central aortic pressure pulse. The findings presented here are consistent with an interpretation of the signal at the neck as originating in the carotid artery. A detailed mapping study involving a 35 point matrix over the right neck disclosed a focal zone of maximal signal amplitude, with a course consistent with the tract of the underlying carotid. Appreciable individual differences in the 22 examinees were disclosed, particularly at lower sites. In addition to confirming a local source for the LDV carotid pulse, the data highlight the importance of accurate targeting considerations
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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