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      Theory and Developments in an Unobtrusive Cardiovascular System Representation: Ballistocardiography

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          Due to recent technological improvements, namely in the field of piezoelectric sensors, ballistocardiography – an almost forgotten physiological measurement – is now being object of a renewed scientific interest.

          Transcending the initial purposes of its development, ballistocardiography has revealed itself to be a useful informative signal about the cardiovascular system status, since it is a non-intrusive technique which is able to assess the body’s vibrations due to its cardiac, and respiratory physiological signatures.

          Apart from representing the outcome of the electrical stimulus to the myocardium – which may be obtained by electrocardiography – the ballistocardiograph has additional advantages, as it can be embedded in objects of common use, such as a bed or a chair. Moreover, it enables measurements without the presence of medical staff, factor which avoids the stress caused by medical examinations and reduces the patient’s involuntary psychophysiological responses.

          Given these attributes, and the crescent number of systems developed in recent years, it is therefore pertinent to revise all the information available on the ballistocardiogram’s physiological interpretation, its typical waveform information, its features and distortions, as well as the state of the art in device implementations.

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          Which parameters of beat-to-beat blood pressure and variability best predict early outcome after acute ischemic stroke?

          In hypertensive populations, increasing blood pressure (BP) levels and BP variability (BPV) are associated with a greater incidence of target organ damage. After stroke, elevated 24-hour BP levels predict a poor outcome, although it is uncertain whether shorter-length BP recordings assessing mean BP levels and BPV have a similar predictive role. The objectives of this study were to compare the different measures of beat-to-beat BP and BPV on outcome after acute ischemic stroke and assess whether these parameters were affected by stroke subtype. Ninety-two consecutive admissions with a CT-confirmed diagnosis of acute ischemic stroke were recruited, of whom 54 had cortical infarction, 29 subcortical, and 9 posterior circulation infarction. Casual and two 5-minute recordings of beat-to-beat BP (Finapres, Ohmeda) were made under standardized conditions within 72 hours of ictus, with mean BP levels taken as the average of this 10-minute recording and BPV as the standard deviation. Outcome was assessed at 30 days as dead/dependent or independent (Rankin
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            A comparative study of different artefact removal algorithms for EEG signals acquired during functional MRI.

            In electroencephalographic (EEG) measurements performed during functional Magnetic Resonance Imaging (fMRI), imaging and cardiac artefacts strongly contaminate the EEG signal. Several algorithms have been proposed to suppress these artefacts and most of them have shown important improvements with respect to uncorrected signals. However, the relative performances of these algorithms have not been properly assessed. In particular, it is not known to what extent such algorithms deteriorate the EEG signal of interest. In this study, we propose to cross-validate different methods proposed for artefact correction, using a forward model to generate EEG and MR-related artefacts. The methods are assessed under various experimental conditions (described in terms of EEG sampling rate, artefacts amplitude, frequency band of interest, etc.). Using experimental data, we also tested the performance of the correction methods for alpha rhythm imaging and for epileptic spike reconstruction. Results show that most of the methods allow the observation of the modulation of alpha rhythms and the identification of spikes, despite subtle differences between algorithms. They also show that over-filtering the data may degrade the EEG. Our results indicate that the optimal artefact removal technique should be chosen according to whether one is interested in fast (>10 Hz) vs. slow (<10 Hz) oscillations or in evoked vs. ongoing activity.
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              Assessment of a wrist-worn device in the detection of obstructive sleep apnea.

              To assess the accuracy of a wrist-worn device (Watch_PAT100) to diagnose obstructive sleep apnea (OSA). Thirty adult subjects with and without suspected OSA simultaneously had a standard in-laboratory polysomnogram (PSG) and wore the Watch_PAT100 during a full-night recording. PSG sleep and respiratory events were scored according to standard criteria. Watch_PAT data were analyzed with an automated computerized algorithm which calculated the frequency of respiratory events per hour of actigraphy measured sleep using a combination of peripheral arterial tonometry (PAT) signal attenuation, desaturation on pulse oximetry, and changes in heart rate. This yielded a PAT apnea hypopnea index (AHI). Mean age was 47.0+/-14.8 years, mean body mass index 31.0+/-7.6 kg/m(2), mean PSG AHI 23+/-23.9 events per hour, and mean PAT AHI 23+/-15.9 events per hour. There was a significant correlation between PAT AHI and AHI by PSG (r=0.87, P<0.001). To assess sensitivity and specificity of Watch_PAT, we constructed receiver operator characteristic curves using a variety of AHI threshold values (10, 15, 20, and 30 events per hour). Optimal combinations of sensitivity and specificity for the various thresholds were 82.6/71.4, 93.3/73.3, 90.9/84.2, and 83.3/91.7, respectively. The Watch_PAT is a device that can detect OSA with reasonable accuracy. Thus, the Watch_PAT may be a useful method to diagnose OSA.

                Author and article information

                Open Biomed Eng J
                The Open Biomedical Engineering Journal
                Bentham Open
                10 October 2010
                : 4
                : 201-216
                Instituto de Telecomunicações, Instituto Superior Técnico, Torre Norte piso 10, Av. Rovisco Pais 1, 1049-001, Lisboa, Portugal
                Author notes
                [* ]Address correspondence to this author at the Instituto de Telecomunicações, Instituto Superior Técnico, Torre Norte piso 10, Av. Rovisco Pais 1, 1049-001, Lisboa, Portugal; Tel: +351 21 841 84 54; Fax: +351 21 841 84 72; E-mail: eduardo.pinheiro@ 123456lx.it.pt
                © Pinheiro et al.; Licensee Bentham Open.

                This is an open access article licensed under the terms of the Creative Commons Attribution Non-Commercial License ( http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted, non-commercial use, distribution and reproduction in any medium, provided the work is properly cited.



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