Nikolai Blanik

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.

Hybrid optical imaging technology for long-term remote monitoring of skin perfusion and temperature behavior

Abstract. Photoplethysmography imaging (PPGI) and infrared thermography imaging (IRTI) are contactless camera-based measurement methods for monitoring a wide range of basic vital parameters. In particular, PPGI enhances the classical contact-based photoplethysmography. Approved evaluation algorithms of the well-established PPG method can easily be adapted for detection of heart rate, heart rate variability, respiration rate (RR), respiratory variability (RV), and vasomotional activity with PPGI. The IRTI method primarily records temperature distribution of the observed object, but information on RR and RV can also be derived from IRTI by analyzing the development of temperature distribution in the nasal region. The main advantages of both monitoring methods are unobtrusive data acquisition and the possibility of assessing spatial assignment between vital parameters and body region. Hence, these methods enable long-term monitoring or the monitoring of effects with special local characteristics. Because the two systems supplement each, a combined hybrid application is proposed and its feasibility discussed.

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.

Non-contact monitoring techniques - Principles and applications

This work gives an overview about some non-contact methods for monitoring of physiological activity. In particular, the focus is on ballistocardiography, capacitive ECG, Infrared Thermography, Magnetic Impedance Monitroing and Photoplethymographic Imaging. The principles behind the methods are described and an inside into possible medical applications is offered.

Contact-free monitoring of circulation and perfusion dynamics based on the analysis of thermal imagery

Acute circulatory disorders are commonly associated with systemic inflammatory response (SIRS) and sepsis. During sepsis, microcirculatory perfusion is compromised leading to tissue hypoperfusion and potentially to multiple organ dysfunction. In the present study, acute lung injury (ALI), one of the major causes leading to SIRS and sepsis, was experimentally induced in six female pigs. To investigate the progress of body temperature distribution, measurements with a long-wave infrared camera were carried out. Temperature centralization was evidenced during ALI owing to impairments of peripheral perfusion. In addition, statistical analysis demonstrated strong correlations between (a) standard deviation of the skin temperature distribution (SD) and shock index (SI) (p<0.0005), (b) SD and mean arterial pressure (MAP) (p<0.0005), (c) ΔT/Δx and SI (p<0.0005), as well as between (d) ΔT/Δx and MAP (p<0.0005). For clarification purposes, ΔT/Δx is a parameter implemented to quantify the spatial temperature gradient. This pioneering study created promising results. It demonstrated the capacity of infrared thermography as well as of the indexes, SD and ΔT/Δx, to detect impairments in both circulation and tissue perfusion.

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.

Frequency-selective quantification of skin perfusion behavior during allergic testing using photoplethysmography imaging

Diagnosis of allergic immediate-type reactions is dependent on the visual assessment of the attending physician. With our novel non-obtrusive, camera-based photoplethysmography imaging (PPGI) setup, perfusion in the allergic testing area can be quantified and results displayed with spatial resolution in functional mappings. Thereby, each PPGI camera pixel can be assumed to be a classical (skin-based) reflective mode PPG sensor. An algorithm for post-processing of collected PPGI video sequences was developed to transfer black-and-white PPGI images into virtual 3D perfusion maps. For the first time, frequency selected perfusion quantification was assessed. For the presented evaluation, PPGI data from our clinical study were used [1]. For this purpose, different concentrations of histamine dilutions were administered to 27 healthy volunteers. Our results show clear trends in an increase in heartbeat synchronous perfusion rhythms and, simultaneously, a decrease of lower frequency vasomotor rhythms in these areas. These results, published for the first time, allow new insight into the distribution of skin perfusion dynamics and demonstrate the intuitive clinical usability of the proposed system.

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).