Mr. Jorge Herranz Olazábal Profile

Jorge Herranz Olazábal

at imec NL

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Proceedings Article | 27 March 2024 Presentation + Paper

Wearable, compact photo- and speckle plethysmography device for continuous non-invasive vital signs monitoring

Lena Schnitzler, Jorge Herranz Olazabal, Ilde Lorato, Marc Verhoeven, Evelien Hermeling, Jesse Kling

Proceedings Volume 12850, 128500C (2024) https://doi.org/10.1117/12.3001630

KEYWORDS: Signal to noise ratio, Cameras, Skin, Vital signs, Prototyping, Speckle, Semiconductor lasers, Reflection, Laser safety, Tissue optics

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Continuous real-time monitoring of hemodynamic variables has become very relevant in modern medicine not only in clinical settings, but also for consumer wearables. Wearable technologies allow for vital sign monitoring (VSM) and help to promptly react in urgent situations. Photoplethysmography (PPG), an optical method based on absorption changes, is a well-known technique for non-invasive monitoring of cardiovascular biomarkers. However, PPG quality can be significantly compromised by skin melanin content, low perfusion, and ambient light changes. Unreliability under these conditions could potentially lead to severe consequences if threatening events remain undetected. Speckle Plethysmography (SPG) is based on the measurement of speckle variations and shows a robust signal quality independent of skin melanin content and ambient light, which indicates that SPG is a more reliable technology for continuous VSM. We present a compact, wearable device for simultaneous PPG and SPG VSM. The system consists of a laser diode illuminating the tissue, and a camera that captures the reflected light, forming a speckle pattern. Additionally, an acquisition platform (portable computer) is used to send the information wirelessly to a computer. The system allows for software-controlled tuning of parameters to optimize signal quality. SPG and PPG are calculated from the images, visualized in real-time and recorded to analyze cardiovascular biomarkers such as heart rate, heart rate variability and others. This compact wearable device is the first step towards full SPG/PPG sensor integration to enable robust, low-cost, wearable, non-invasive VSM.

Proceedings Article | 12 March 2024 Presentation + Paper

Towards continuous blood pressure monitoring using speckle plethysmography

Ilde Lorato, Jorge Herranz Olazabal, Jesse Kling, Evelien Hermeling

Proceedings Volume 12838, 128380A (2024) https://doi.org/10.1117/12.3001627

KEYWORDS: Correlation coefficients, Electrocardiography, Signal detection, Signal processing, Blood pressure, Speckle, Cameras, Pulse signals, Video

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Speckle Plethysmography (SPG) is recently gaining interest as an addition to Photoplethysmography (PPG), due to higher Signal-to-Noise Ratio and the reduced sensitivity to both ambient light changes and variation in skin melanin content. SPG can be obtained by analyzing the spatial changes in the speckle pattern generated by a coherent light source over time. Continuous Blood Pressure (BP) monitoring is a particularly relevant topic in the biomedical domain as elevated BP is a major risk factor for cardiovascular diseases. Noninvasive methodologies are being researched as an alternative to cuff-based methods, which are considered uncomfortable and cumbersome. Typical approaches are Pulse Arrival Time (PAT), using Electrocardiogram (ECG) signals and PPG, or Pulse Waveform Analysis (PWA), by analyzing PPG’s morphological features. These approaches, however, still lack accuracy and require personalized BP models. SPG could offer better performance for this type of application. Therefore, in this work, ten subjects were monitored using a contact SPG system synchronized with simultaneous reference recordings of ECG, PPG, and BP signals. PAT and PWA features were calculated from SPG and ECG. The same features were calculated from PPG, which were used for benchmarking purposes. Linear regression analysis was performed between the extracted features and the reference BP. In addition, the inter-subject variability in the feature BP-slope and the correlation coefficients were analyzed. The results show a high correlation between the SPG features and BP. Furthermore, the SPG features resulted in a reduced inter-subject variability compared to the PPG-derived features, possibly indicating that SPG could be used for a generalized BP model.

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