403 research outputs found
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Heart Rate Variability (HRV) and cardiovascular dynamic changes during local anesthesia
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Perfusion Changes at the Forehead Measured by Photoplethysmography during a Head-Down Tilt Protocol
Photoplethysmography (PPG) signals from the forehead can be used in pulse oximetry as they are less affected by vasoconstriction compared to fingers. However, the increase in venous blood caused by the positioning of the patient can deteriorate the signals and cause erroneous estimations of the arterial oxygen saturation. To date, there is no method to measure this venous presence under the PPG sensor. This study investigates the feasibility of using PPG signals from the forehead in an effort to estimate relative changes in haemoglobin concentrations that could reveal these posture-induced changes. Two identical reflectance PPG sensors were placed on two different positions on the forehead (above the eyebrow and on top of a large vein) in 16 healthy volunteers during a head-down tilt protocol. Relative changes in oxygenated (∆HbO2), reduced (∆HHb) and total (∆tHb) haemoglobin were estimated from the PPG signals and the trends were compared with reference Near Infrared Spectroscopy (NIRS) measurements. Also, the signals from the two PPG sensors were analysed in order to reveal any difference due to the positioning of the sensor. ∆HbO2, ∆HHb and ∆tHb estimated from the forehead PPGs trended well with the same parameters from the reference NIRS. However, placing the sensor over a large vasculature reduces trending against NIRS, introduces biases as well as increases the variability of the changes in ∆HHb. Forehead PPG signals can be used to measure perfusion changes to reveal venous pooling induced by the positioning of the subject. Placing the sensor above the eyebrow and away from large vasculature avoids biases and large variability in the measurements
Modeling X-chromosome inactivation and reactivation during human development
Stem-cell-based embryo models generate much excitement as they offer a window into an early phase of human development that has remained largely inaccessible to scientific investigation. An important epigenetic phenomenon during early embryogenesis is the epigenetic silencing of one of the two X chromosomes in female embryos, which ensures an equal output of X-linked gene expression between the sexes. X-chromosome inactivation (XCI) is thought to be established within the first three weeks of human development, although the inactive X-chromosome is reactivated in primordial germ cells (PGCs) that migrate to the embryonic gonads. Here, we summarize our current understanding of X-chromosome dynamics during human development and comment on the potential of recently established stem-cell-based models to reveal the underlying mechanisms
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Investigation of photoplethysmmographic signals and arterial blood oxygen saturation values (SpO(2)) during blood pressure cuff-induced hypoperfusion
Photoplethysmography is a non-invasive electro-optical technique widely used in the study and monitoring of the pulsations associated with changes in blood volume in a peripheral vascular bed. Photoplethysmography is used in the estimation of arterial oxygen saturation (SpO2) by pulse oximetry. A reflectance finger photoplethysmographic (PPG) probe and a multiplexed data acquisition system operating simultaneously at two wavelengths and incorporating an external lead II electrocardiogram (ECG) reference channel, and a commercial finger pulse oximeter has been developed. The aim of this study is to investigate the morphology and amplitude of PPG signals and its effect on pulse oximetry during blood pressure cuff-induced hypoperfusion. PPG signals and SpO2s and standard ECG traces were obtained from 14 healthy volunteers and displayed on a personal computer. Measurable PPG signals at both infrared and red wavelengths were obtained from all induced pressures prior to full brachial occlusion. There are statistically significant differences between the ac PPGs in the low pressures (0 to 80 mmHg) than those in the upper pressures (90 to 150 mmHg) at both wavelengths. Both pulse oximeters showed gradual decrease of saturations during induced hypoperfusion which demonstrate the direct relation between blood volumes (PPG amplitudes), arterial vessel stenosis and blood oxygen saturation. The custom made pulse oximeter was found to be more sensitive to SpO2 changes than the commercial pulse oximeter especially at high occluding pressures
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Estimation of instantaneous venous blood saturation using the Photoplethysmograph (PPG) waveform
Non-invasive estimation of regional venous saturation (SxvO2) using a conventional pulse oximeter could provide a means of obtaining clinically relevant information. This study was carried out in order to investigate the hypothesis that SxvO2 could be estimated by utilising the modulations created by positive pressure ventilation in the photoplethysmograph (PPG) signals. The modulations caused by the mechanical ventilator were extracted from oesophageal PPG signals obtained from 12 patients undergoing cardiothoracic surgery. The signals analysed in this work were acquired in a previous study. For the purpose of this analysis the raw PPG signal was considered to have three major components, ac PPG signal (cardiac related component), a static component or dc PPG signal (created mostly by the absorption of light by surrounding tissue) and the ventilator modulation component. These components were then used to estimate instantaneous arterial blood oxygen saturation (SpO2) and SxvO2 by utilising time-frequency analysis technique of smoothed-pseudo Wigner–Ville distribution (SPWVD). The results showed that there was no significant difference in the traditionally-derived (time-domain) arterial saturation and the instantaneous arterial saturation. However, the instantaneous venous saturation was found to be significantly lower than the estimated time-domain and instantaneous arterial saturation (P=<0.001, n=12)
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Pilot investigation of photoplethysmographic signals and blood oxygen saturation values during blood pressure cuff-induced hypoperfusion
Photoplethysmography (PPG) is a non-invasive electro-optical technique widely used in the monitoring of the pulsations associated with changes in blood volume in a peripheral vascular bed. The technique is based on the absorption properties of vascular tissue when it is transilluminated by light. Photoplethysmography is also used in the estimation of arterial blood oxygen saturation (SpO2) by pulse oximetry where the technique relies on the presence of adequate peripheral arterial pulsations. The aim of this study was to investigate (14 healthy volunteers) the effect of pressure cuff-induced hypoperfusion on PPG signals and SpO2s using a custom made finger blood oxygen saturation PPG/SpO2 sensor and a commercial finger pulse oximeter. PPG signals with high signal-to-noise ratios were obtained from all induced pressures prior to full brachial occlusion. An Analysis of Variance (ANOVA) on ranks showed that there are statistically significant differences (p<0.05) between the PPGs in the low pressures (0–80 mmHg) than those in the upper pressures (90–150 mmHg). Both pulse oximeters showed gradual decrease of saturations during induced hypoperfusion which demonstrate the direct relation between blood volumes (PPG amplitudes), arterial vessel stenosis and blood oxygen saturation. The custom made pulse oximeter was found to be more sensitive to SpO2 changes than the commercial pulse oximeter especially at high occluding pressures
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Empirical mode decomposition analysis of HRV data from patients undergoing local anaesthesia (brachial plexus block)
Spectral analysis of heart rate variability (HRV) is used for the assessment of cardiovascular autonomic control. In this study, a data-driven adaptive technique called empirical mode decomposition (EMD) and the associated Hilbert spectrum has been used to evaluate the effect of local anaesthesia on HRV parameters in a group of 14 patients undergoing axillary brachial plexus block. The normalized amplitude Hilbert spectrum was used to calculate the error index associated with the instantaneous frequency. The amplitude and the frequency values were corrected in the region where the error was higher than twice standard deviation. The intrinsic mode function (IMF) components were assigned to the LF and the HF part of the signal by making use of the centre frequency and the standard deviation spectral extension estimated from the marginal spectrum of the IMF components. The optimal range of the stopping criterion was found to be between 4 and 9 for the HRV data. The statistical analysis showed that the LF/HF ratio decreased within an hour of the application of the brachial plexus block compared to the values at the start of the procedure. These changes were observed in 13 of the 14 patients included in this study
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