Customized optoelectronic in-ear sensor approaches for unobtrusive continuous monitoring of cardiorespiratory vital signs

Abstract

Customization of diagnostic and therapeutic pathways in medicine and personalization of medical devices are currently major trends in biomedical engineering together with miniaturization, digitalization and increasingly ambient and unobtrusive sensor strategies. This article presents a novel optoelectronic sensor: its concept is based on simple, easy-to-use classical photoplethysmography technology, but is attached to the ear. Via the ear channel or the inner tragus, the sensor detects diagnostically relevant parameters from peripheral arterial and venous blood volume movement (including heart rate, heart rate variability, respiratory activity, blood oxygen saturation and other subdermal blood phenomena). The diagnostic system consists of customizable i) sensor forms, ii) biodata mining, and iii) communication protocols sent to the medical control center. This article describes novel possibilities for cardiorespiratory monitoring with these sensors characterized by enhanced customization features. In contrast to established art sensor applications on fingers or toes, this optical in-ear sensor technology offers additional physiological and technological advantages by mining vital signs in the ear channel. Since the optical in-ear sensor is comfortable, noninvasive and unobtrusive, it is recommended not only for patients at high cardiovascular risk but also (potentially) for homecare application and the monitoring of physical activities, e.g. during high altitude climbing. Preliminary results demonstrate that vital signs can be assessed with sufficient robustness and accuracy and that, due to the customized sensor application, patient comfort is higher compared with the classical wearable (non-customized) sensors.

Comparison of Three Prototypes of PPG Sensors for Continual Real-Time Measurement in Weak Magnetic Field

“…for storage or next processing. On the other hand, there exist also specialized reflectance in-ear PPG sensors (placed in the auditory canal) which must be individually customized depending on the ear channel proportions [ 19 ]. These types of PPG sensors, mainly used in the systems for SpO 2 continual monitoring, are usually connected to the POXI device by an electric cord [ 20 ].…”

“…A de-trending operation [ 15 ] is important in the case of a raw PPG signal, but it is usually not applied on VPG and APG signals. In addition, the PPG signal generally contains a noise component and can be often partially disturbed or degraded [ 19 ]. Therefore, the sensed PPG signal must be filtered prior to its processing and determination of HR values.…”

Stress Level Detection and Evaluation from Phonation and PPG Signals Recorded in an Open-Air MRI Device

“…This physiological and mental stress can effectively be identified by the parameters derived from the photo-plethysmography (PPG) signal, as heart rate (HR), Oliva-Roztocil index (ORI) [5] pulse transit time [6], pulse wave velocity [7], blood oxygen saturation, cardiac output [8], and others. The amplitude of the picked-up PPG signal is usually not constant, and it can often be partially disturbed or degraded [9]. The stress is associated with the autonomic nervous system and it can be expressed by higher variability in interbeat intervals (IBI) assessed from the PPG wave as pulse rate variability (PRV) and from the electrocardiogram (ECG) as HR variability (HRV).…”

First-Step PPG Signal Analysis for Evaluation of Stress Induced during Scanning in the Open-Air MRI Device

“…In the present paper, we describe photoplethysmographic (PPG) measurement using an optical sensor for non-invasive pickup of vital functions of the vascular system from the skin [ 8 , 9 ] by detecting blood volume changes inside the tissue. Signal filtering and further processing yields a clean PPG waveform that is then used to determine an instantaneous heart rate and other specific parameters applicable in systems for medical assessment [ 10 , 11 , 12 ], and/or utilized for biometric authentication [ 13 ], among others. In addition, this type of a sensor enables measurement in the low magnetic field present in the scanning area of an MRI device.…”