Gregor Geršak

Non-contact heart rate and heart rate variability measurements: A review

Abstract The following paper investigates published work on non-contact human physiological parameter measurement, more precisely measurement of the human heart rate (HR) and consequently the heart rate variability (HRV), which is considered to be an important marker of autonomic nervous system activity proven to be predictive of the likelihood of future health related events. The ability to perform measurements of cardiac activity in a non-contact manner could prove to become an important alternative to the conventional methods in the clinical field as well as in the more commercially oriented fields. Some of the published work so far indicates that the measurement of cardiac activity in a non-contact manner is indeed possible and in some cases also very precise, however there are several limitations to the methods which need to be taken into account when performing the measurements. The following paper includes a short description of the two conventional methods, electrocardiogram (ECG) and photoplethysmography (PPG), and later on focuses on the novel methods of non-contact measuring of HR with capacitively coupled ECG, Doppler radar, optical vibrocardiography, thermal imaging, RGB camera and HR from speech. Our study represents a comparative review of these methods while emphasising their advantages and disadvantages.

Novel Methods for Noncontact Heart Rate Measurement: A Feasibility Study

The following paper investigates four novel methods for noncontact measurement of heart rate (HR) and consequently its derivate HR variability, an important marker of autonomic activity proven to be predictive of likelihood of future health related events. Feasibility study of basic principles is focused on measurements of signal-to-noise ratio with respect to the distance between the subject and HR sensor/apparatus. The discussed methods are divided into the following two groups: the methods measuring electromagnetic energy generated by the bioelectrical activity within the cardiac muscle (referred to as direct methods), and the methods measuring displacement of a part of the subjects body caused by the periodic physical contractions of the heart (referred to as indirect methods). The first group is represented by a measuring device which detects changes in surrounding electric field, whereas the second group consists of measuring devices that use the Doppler effect phenomena (microwave radar, ultrasound radar) and audio signal acquired by a condenser microphone. All measuring devices were assembled and put to test. The results indicate that noncontact measuring of HR is possible, especially for distances of less than 50 cm meeting essential requirements for HR diagnostic purposes.

A procedure for evaluation of non-invasive blood pressure simulators

Non-invasive blood pressure (NIBP) simulators are used in clinical environment for quick checks of blood pressure monitors as a part of technical maintenance and health-care quality assurance system. They are also included in various tests within the procedures for testing NIBP monitors. In practice simulators are often subject to mechanical and electromagnetic shocks which could effect their measuring function. Our objective was to design a procedure for testing the reliability and quality of simulators in order to ensure reliable testing of NIBP monitors. Procedure for evaluation of NIBP simulators, consisting of a static and dynamic test, is proposed. Static test consisted of procedures derived from common electro-mechanical manometer calibration, while dynamic test included testing of repeatability of simulator’s output. A commercial simulator was tested. Among others, the results indicated that evaluations of NIBP simulators should be performed regularly with a suitable time interval in order to track the metrological quality of the simulator in time. Acceptance criteria for a reliable simulator in both static and dynamic sense are proposed.

Evaluation of non-invasive blood pressure simulators

Non-invasive blood pressure (NIBP) simulators are electro-mechanical devices used for testing and evaluating oscillometric non-invasive blood pressure monitors. Simulators are used mainly in clinical environment to assist with routine and after-repair testing of NIBP monitors. In this paper we suggest basic procedures for evaluating a NIBP simulator; assessing its suitability and quality. Proposed evaluation procedure consists of a static calibration and a dynamic evaluation. In static calibration the simulator is calibrated as a common indicating barometer. In dynamic evaluation the output waveforms are investigated (repeatability of the output according to different static pressures and heart rates, repeatability of the output at a constant blood pressure magnitude). Proposed evaluation procedure represents a minimal set of tests to ensure the simulator can be used for testing NIBP monitors. A commercial simulator SmartArm (by Clinical Dynamics, USA) was evaluated according to it and the results are presented.

Influence of video content type on users’ virtual reality sickness perception and physiological response

Abstract Virtual Reality (VR) sickness (Cybersickness) is an affliction and a challenge, common to users of virtual environments. We therefore asked ourselves this research question: “Can video content type influence users’ VR sickness and physiological response?” We conducted a study with 26 participants, who watched two omnidirectional videos of different content types (neutral and action content) on five distinct video conditions: 2D TV screen, three generations of Oculus Rift VR HMDs (DK1, DK2 and CV1) and on the mobile Samsung GearVR HMD. The Simulator Sickness Questionnaire and the Subjective Units of Distress Scale in combination with the measurement of the physiological parameters (electrodermal activity and skin temperature, respiratory frequency and heart rate) were used to assess the VR sickness effects. The results show that video content type as well as users’ background preferences (preference to adrenaline sports) affected the users’ VR sickness perception. Considering various video conditions, significantly less VR sickness effects were reported with the TV condition than with any VR devices. The results of the subjective questionnaires were correlated with the objective physiological measurements, whereby skin conductance strongly correlated with the VR sickness effects. The effects were also more pronounced in cases of action video content type. Furthermore, we show there is a strong correlation when assessing the VR sickness effects using subjective questionnaire-based methods (the Simulator Sickness Questionnaire and the Subjective Units of Distress Scale) of various complexity, indicating the simple methods (only one question), can effectively be used as well.

Design and Clinical Evaluation of a Non-Contact Heart Rate Variability Measuring Device

The object of the proposed paper is to design and analyze the performance of a non-contact heart rate variability (HRV) measuring device based on ultrasound transducers. The rationale behind non-contact HRV measurement is the goal of obtaining a means of long term monitoring of a patient’s heart performance. Due to its complexity as a non-contact measuring device, influential physical quantities, error source and other perturbations were thoroughly investigated. For medical purposes it is of utmost importance to define the target uncertainty of a measuring method from the side of physicians, while it is the role of scientists to realistically evaluate all uncertainty contributions. Within this paper we present a novelty method of non-contact HRV measurement based on ultrasound transducers operating at two frequencies simultaneously. We report laboratory results and clinical evaluations are given for healthy subjects as well as patients with known heart conditions. Furthermore, laboratory tests were conducted on subjects during a relaxation period, and after 1 min physical activity

Sensewear Body Monitor in Psychophysiological Measurements

Recently, in different scientific areas there is an increasing interest in multiparameter monitoring devices capable of measuring physiological parameters. In this paper Sensewear PRO3 multiparameter body monitor (SW) is described and evaluated. The main goal of the research was to find out whether SW, primarily intended for energy expenditure measurements, has adequate resolution and time response to be used also in psychophysiological experiments. SW was evaluated in static, laboratory conditions and in real-life dynamic experiments. The results indicate that the measuring accuracy of the device is sufficient. The excellent ergonomy of the housing, time-stamp button and large dry electrodes make SW very suitable for long term measurements with low intrusiveness. The main disadvantage for the use in psychophysiological measurements is low skin conductance sensitivity and long time-constants of temperature measurements.

Absolute and Relative User Perception of Classification Accuracy in an Affective Video Game

Classification algorithms are used in affective computing to classify the state of the user and adapt the computer’s behaviour, but it is unclear how classification accuracy influences the overall user experience. We present a study in which classification accuracy is artificially pre-defined and used to adapt to the difficulty of a video game. Eighty subjects played the game and were told that difficulty would be adapted according to the measured brain activity. They played the game twice, with different classification accuracies, and then reported different aspects of their overall game experience using questionnaires. Classification accuracy was correlated with both in-game fun (r = 0.46) and satisfaction with the difficulty adaptation (r = 0.56). Most subjects could perceive a difference between two classification accuracies that differed by 16.7%. We tentatively posit that, for affective video games, an acceptable classification accuracy is 70–80%. Furthermore, studies that attempt to improve affect classification accuracy should aim for a practically meaningful improvement of 10%.

Measuring the Effect of Classification Accuracy on User Experience in a Physiological Game

Physiological games use classification algorithms to extract information about the player from physiological measurements and adapt game difficulty accordingly. However, little is known about how the classification accuracy affects the overall user experience and how to measure this effect. Following up on a previous study, we artificially predefined classification accuracy in a game of Snake where difficulty increases or decreases after each round. The game was played in a laboratory setting by 110 participants at different classification accuracies. The participants reported their satisfaction with the difficulty adaptation algorithm as well as their in-game fun, with 85 participants using electronic questionnaires and 25 using paper questionnaires. We observed that the classification accuracy must be at least 80% for the physiological game to be accepted by users and that there are notable differences between different methods of measuring the effect of classification accuracy. The results also show that laboratory settings are more effective than online settings, and paper questionnaires exhibit higher correlations between classification accuracy and user experience than electronic questionnaires. Implications for the design and evaluation of physiological games are presented.

Magnetic Balance for Teaching Metrology Concepts in Electrical Engineering

In this paper a successful and inexpensive laboratory exercise is presented for explaining basic metrology concepts (reference value, standard, measuring error, traceability of measurement, measuring uncertainty) to undergraduate students of electrical engineering. For a better understanding, a common mass measurement was used. Mass of weights was measured by using a modified audio speaker as a weight balance, working on the principle of electromagnetic levitation. Speaker-balance measuring range was 10 g to 1000 g, with relative uncertainty of 3%. Students could learn about problems of the definition of the kilogram, about mass measurements and balances, repeatability of measurements, uncertainty budget calculations, and common measuring uncertainty contributions.