Boudewijn Venema

Advances in Reflective Oxygen Saturation Monitoring With a Novel In-Ear Sensor System: Results of a Human Hypoxia Study

Pulse oximetry is a well-established, noninvasive photoplethysmographic method to monitor vital signs. It allows us to measure cardiovascular parameters, such as heart rate and arterial oxygen saturation, and is considered an essential monitoring tool in clinical routine. However, since many of the conventional systems work in transmission mode, they can only be applied to the thinner or peripheral parts of the body, such as a finger tip. This has the major disadvantage that, in case of shock-induced centralization and a resulting drop in perfusion, such systems cannot ensure valid measurements. Therefore, we developed a reflective in-ear sensor system that can be worn in the ear channel like a headphone. Because the sensor is integrated in an ear mold and positioned very close to the trunk, reliable measurement is expected even in case of centralization. An additional advantage is that the sensor is comfortable to wear and has considerable resistance to motion artifacts. In this paper, we report on hypoxia studies with ten healthy participants which were performed to analyze the system with regard to the detection of heart rate and arterial oxygen saturation. It was shown earlier that, due to the high signal quality, heart rate can easily be detected. Using the conventional calculation principle, based on Beer-Lamberts law combined with a single-point calibration method, we now demonstrate that the detection of arterial oxygen saturation in the human ear canal is possible using reflective saturation sensors.

Evaluating Innovative In-Ear Pulse Oximetry for Unobtrusive Cardiovascular and Pulmonary Monitoring During Sleep

Homecare is healthcare based on the principle “outpatient before inpatient,” with the aim of moving at least some care-delivery to the home. But reliable determination of vital signs at home requires new, smart sensors, which can be used by the patients themselves. We present a novel pulse oximetry sensor worn in the ear channel. It was previously shown that measurement of heart rate, arterial oxygen saturation and related respiratory information can be performed with reliable accuracy under laboratory conditions. The present study explores the clinical feasibility of the sensor system for cardiovascular monitoring during sleep, with the aim to diagnose sleep apnea. For this, human trials were performed in a sleep laboratory including patients with a clinical suspicion of sleep apnea. Besides a general analysis of the sensors signal quality during sleep, the evaluation focuses on heart rate dynamics and time-variant oxygen saturation. In addition, several methods to derive respiration rate from photoplethysmographic signals are examined and discussed. Results from the in-ear sensor are compared with standard polysomnography monitoring and demonstrate that this novel system allows long-term nocturnal measurement of heart rate, oxygen saturation and respiratory rate with sufficient accuracy.

Robustness, Specificity, and Reliability of an In-Ear Pulse Oximetric Sensor in Surgical Patients

For many years, pulse oximetry has been widely used in the clinical environment for a reliable monitoring of oxygen saturation (S_pO₂) and heart rate. But since common sensors are mainly placed to peripheral body parts as finger or earlobe, it is still highly susceptible to reduced peripheral perfusion, e.g., due to centralization. Therefore, a novel in-ear pulse oximetric sensor (placed against the tragus) was presented in a prior work which is deemed to be independent from perfusion fluctuations due to its proximity to the trunk. Having demonstrated the feasibility of in-ear S_pO₂ measurement with reliable specificity in a laboratory setting, we now report results from a study on in-ear S_pO₂ in a clinical setting. For this, trials were performed on 29 adult patients undergoing surgery. In-ear S_pO₂ data are compared with S_pO₂ data obtained by blood gas analysis, and with three reference pulse oximeters applied to the finger, ear lobe, and forehead. In addition, we derived an S_pO₂-independent perfusion index by means of the wavelengths used. The feasibility and robustness of in-ear S_pO₂ measurement is demonstrated under challenging clinical conditions. S_pO₂ shows good accordance with S_pO₂, a high level of comparability with the reference pulse oximeters, and was significantly improved by introducing a new algorithm for artifact reduction. The perfusion index also shows a good correlation with the reference data.

A feasibility study evaluating innovative in-ear pulse oximetry for unobtrusive cardiovascular homecare monitoring during sleep

In this paper, we present a novel pulseoximetric sensor which can be worn in the ear channel. In previous work, we could demonstrate that measurement of heart rate (HR), arterial oxygen saturation (SpO2) and respiratory related information can be performed with reliable accuracy. Since these results were obtained under laboratory conditions, we now studied the feasibility of a clinical appliance of the sensor system for cardiovascular monitoring during sleep which may allow diagnosis of sleep apnea in future. Therefore, we performed human trials in a sleep laboratory with patients with a clinical suspicion of sleep apnea. The evaluation focus on heart rate and oxygen saturation. Results was compared with standard polysomnography (PSG) measurements and demonstrate that nocturnal long-term measurement of oxygen saturation and heart rate is possible with sufficient accuracy.

Active and Passive Optical Imaging Modality for Unobtrusive Cardiorespiratory Monitoring and Facial Expression Assessment

Because of their obvious advantages, active and passive optoelectronic sensor concepts are being investigated by biomedical research groups worldwide, particularly their camera-based variants. Such methods work noninvasively and contactless, and they provide spatially resolved parameter detection. We present 2 techniques: the active photoplethysmography imaging (PPGI) method for detecting dermal blood perfusion dynamics and the passive infrared thermography imaging (IRTI) method for detecting skin temperature distribution. PPGI is an enhancement of classical pulse oximetry. Approved algorithms from pulse oximetry for the detection of heart rate, heart rate variability, blood pressure-dependent pulse wave velocity, pulse waveform-related stress/pain indicators, respiration rate, respiratory variability, and vasomotional activity can easily be adapted to PPGI. Although the IRTI method primarily records temperature distribution of the observed object, information on respiration rate and respiratory variability can also be derived by analyzing temperature change over time, for example, in the nasal region, or through respiratory movement. Combined with current research areas and novel biomedical engineering applications (eg, telemedicine, tele-emergency, and telemedical diagnostics), PPGI and IRTI may offer new data for diagnostic purposes, including assessment of peripheral arterial and venous oxygen saturation (as well as their differences). Moreover, facial expressions and stress and/or pain-related variables can be derived, for example, during anesthesia, in the recovery room/intensive care unit and during daily activities. The main advantages of both monitoring methods are unobtrusive data acquisition and the possibility to assess vital variables for different body regions. These methods supplement each other to enable long-term monitoring of physiological effects and of effects with special local characteristics. They also offer diagnostic advantages for intensive care patients and for high-risk patients in a homecare/outdoor setting. Selected applications have been validated at our laboratory using optical PPGI and IRTI techniques in a stand-alone or hybrid configuration. Additional research and validation is required before these preliminary results can be introduced for clinical applications.

Photoplethysmography-based in-ear sensor system for identification of increased stress arousal in everyday life

In this work, we present an in-ear system for physiological and psychological stress detection based on photoplethysmography, acceleration, and temperature measurements. The complete system is used to extract vital signs from healthy subjects, who are exposed to psychologically demanding tasks. The newly developed sensor system is integrated into our IPANEMA body sensor network and, thus, can be used in combination with several sensor modalities. The capability of the stress level estimation is validated in an human stress experiment. To obtain information on the current stress level, several well-known indicators are utilized like the heart rate variability, surgical stress index or the Oliva and Roztocil index.

In-Ear SpO2 Monitoring with a Novel Optoelectronic Sensor for Long-Term Conditions

In this paper, a system which provides a reflective photoplethysmographic (PPG) measurement with an optoelectronic sensor is presented. To analyze the performance of the system concerning S p O 2 measurement, we performed human hypoxia studies. Since individual S p O 2 values correlate particularly well with the arterial blood oxygen saturation S a O 2, which are obtained by arterial blood gas analysis (BGA), a S p O 2 measurement in the human ear seems to be possible. Global calibration turned out to be challenging due to a parallel shift between calibration curves. Therefore, an initial single-pointcalibration at normal oxygen saturation is proposed. However, with an experimental setup it could be demonstrated that hydrostatic blood pressure has more influence on reflective pulse oximetry than expected and could be the main reason for the initial bias in S p O 2 measurements with small reflective pulse oximetry sensors.

A wearable 12-lead ECG T-shirt with textile electrodes for unobtrusive long-term monitoring – Evaluation of an ongoing clinical trial

The recording of a long-term ECG is an important diagnostic method in the field of cardiology, e.g. in order to investigate occasional arrhythmia. Standard Holter ECGs using adhesive electrodes may cause skin irritations to the patients and can also detach. In order to increase patient comfort and ease of handling, we developed a wearable 12-lead ECG T-shirt with dry textile electrode patches connected to a recording device by active circuitry. In this paper, we present the application and evaluation of our T-shirt in a clinical study, during which we obtained 422 hours of data from five subjects. We investigated the temporal coverage of our ECG T-shirt by identifying ECG signal segments with artefacts and those unaffected by artefacts using a three-stage artefact detection algorithm. Average coverage for individual leads ranged from 20.9% to 56.3%. After temporal fusion of all leads, coverage increased to up to 81.9%.

Remote vital parameter monitoring in neonatology – robust, unobtrusive heart rate detection in a realistic clinical scenario

Abstract Vital parameter monitoring of term and preterm infants during incubator care with self-adhesive electrodes or sensors directly positioned on the skin [e.g. photoplethysmography (PPG) for oxygen saturation or electrocardiography (ECG)] is an essential part of daily routine care in neonatal intensive care units. For various reasons, this kind of monitoring contains a lot of stress for the infants. Therefore, there is a need to measure vital parameters (for instance respiration, temperature, pulse, oxygen saturation) without mechanical or conductive contact. As a non-contact method of monitoring, we present an adapted version of camera-based photoplethysmography imaging (PPGI) according to neonatal requirements. Similar to classic PPG, the PPGI camera detects small temporal changes in the term and preterm infant’s skin brightness due to the cardiovascular rhythm of dermal blood perfusion. We involved 10 preterm infants in a feasibility study [five males and five females; mean gestational age: 26 weeks (24–28 weeks); mean biological age: 35 days (8–41 days); mean weight at the time of investigation: 960 g (670–1290 g)]. The PPGI camera was placed directly above the incubators with the infant inside illuminated by an infrared light emitting diode (LED) array (850 nm). From each preterm infant, 5-min video sequences were recorded and analyzed post hoc. As the measurement scenario was kept as realistic as possible, the infants were not constrained in their movements in front of the camera. Movement intensities were assigned into five classes (1: no visible motion to 5: heavy struggling). PPGI was found to be significantly sensitive to movement artifacts. However, for movement classes 1–4, changes in blood perfusion according to the heart rate (HR) were recovered successfully (Pearson correlation: r=0.9759; r=0.765 if class 5 is included). The study was approved by the Ethics Committee of the Universal Hospital of the RWTH Aachen University, Aachen, Germany (EK 254/13).

Accelerometer-assisted PPG Measurement During Physical Exercise Using the LAVIMO Sensor System

A method is presented for long-term monitoring of vital signs tested during physical exercise. The system is based on reflective photoplethysmography (PPG), whose main component is a micro-optoelectronic sensor. The sensor is sealed within a biocompatible otoplastic housing so that it can be placed in the external auditory canal. The electronic device has a Bluetooth connection which enables to record/visualize the PPG signal on a personal computer or SmartPhone. This technology was tested indoors with a subject running on a treadmill at different speeds. The PPG signal was recorded together with an ECG used as a reference, and with an accelerometer to monitor and record motor activity. Theaccelerometer data were later used to reduce motion artifacts in the PPG signal. The results show that the system has potential to monitor cardiac activity at moderate speed (up to 4 km/h), but with increasing speed (i.e. running) the motion artifacts dominate the PPG. Therefore, additional studies on signal processing are needed to actively reduce motion artifacts, including the accelerometer data.