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 ðSpO 2 Þ 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 SpO 2 s using a custom made finger blood oxygen saturation PPG=SpO 2 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 ðp < 0:05Þ 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 SpO 2 changes than the commercial pulse

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Abstract-Spectral analysis of Heart Rate Variability (HRV) is used for the assessment of cardiovascular autonomic control. In this study data driven adaptive technique Empirical Mode Decomposition (EMD) and the associated Hilbert spectrum has been used to evaluate the effect of local anesthesia on HRV parameters in a group of fourteen patients undergoing brachial plexus block (local anesthesia) using transarterial technique. The confidence limit for the stopping criteria was establish and the S value that gave the smallest squared deviation from the mean was considered optimal. 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 the standard deviation. The Intrinsic Mode Function (IMF) components were assigned to the Low Frequency (LF) and the High Frequency (HF) part of the signal by making use of the center frequency and the standard deviation spectral extension estimated from the marginal spectrum of the IMF components. The analysis procedure was validated with the help of a simulated signal which consisted of two components in the LF and the HF region of the HRV signal with varying amplitude and frequency. 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 amplitude 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 thirteen of the fourteen patients included in this study.

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This is the accepted version of the paper.This version of the publication may differ from the final published version. The acquired signals were analysed and oxygen saturations estimated from the frequency spectra in the cardiac and respiratory frequency ranges. Assuming that respiratory modulation affects blood volumes in veins to a greater extent than in arteries, the local venous oxygen saturation was estimated. Estimated venous oxygen saturation was found to be 3.1% (±4.2%) lower than the estimated arterial saturation. Permanent