Janko Drnovšek

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.

Infrared ear thermometers?parameters influencing their reading and accuracy

Infrared ear thermometers (IRETs) are extensively used for measuring the temperature of a human body. For accurate measurements with IRETs they have to be calibrated regularly with an appropriate and traceable calibration system. Such systems are neither widely available nor are there many competent (accredited) laboratories which can provide traceability for IRETs. This paper describes some important influential parameters in the calibration and use of IRETs, which were observed during the extensive research on IRETs and have not been reported in the literature yet. IRET readings, and consequently also their most important metrological characteristics, accuracy and uncertainty of measurement, depend on these influential parameters. According to our findings, we would like to warn users of medical radiation thermometers, not only IRETs but also forehead thermometers and infrared temperature scanning systems, that they should be extremely careful in selection, maintenance and use of medical radiation thermometers. Measurement accuracy, as it is required by several technical standards, is hard to achieve with the majority of currently available medical radiation thermometers.

Methods of reducing the uncertainty of the self-heating correction of a standard platinum resistance thermometer in temperature measurements of the highest accuracy

Self-heating of resistance thermometers is a well-known phenomenon, which occurs when the measuring current additionally heats up the sensing element. In the paper, the self-heating of standard platinum resistance thermometers (SPRTs) is studied with special emphasis on the investigation and evaluation of factors which contribute to the uncertainty of the self-heating correction. The basic two-current method for self-heating correction is analysed and additional correction methods are proposed, based on the optimal selection of currents and the use of more than two different currents. Using the advanced methods we can decrease the uncertainty of the self-heating correction from 0.04 to 0.01 mK. This decrease may not be significant in routine SPRT calibrations, but it can present an improvement in measurements of the highest accuracy, such as intercomparisons.

System for the determination of the size-of-source effect of radiation thermometers with the direct reading of temperature

The paper describes a system for the determination of the size-of-source effect (SSE) of radiation thermometers with the direct reading of temperature, which form the majority of commercial radiation thermometers. Optics in every radiation thermometer (RT) gathers radiation from a larger area than is defined by the nominal target size. Thus, a measured temperature is more or less dependent on available target area. Every radiation thermometer suffers from the SSE. We developed a system, based on a water-cooled holder, for measuring the SSE by a direct method. The system could be placed in front of any blackbody. Manufacturing of such a system was relatively easy and could be important for users of commercial radiation thermometers because the majority of those thermometers have direct reading of temperature. We measured the SSE characteristics by the direct method for a radiation thermometer with a linearized signal and direct reading of temperature. The results of the SSE were analysed for the direct method without correction of the background radiation and with correction of the background radiation. Knowledge about the SSE characteristic of a radiation thermometer is one of the key elements for correct temperature measurement.

Time series prediction with neural networks: a case study of two examples

A new approach to optimal presentation of a real world problem to a neural network that predicts chaotic time series is presented in the following paper. The proposed approach takes advantage of two measures of deterministic chaos in time series-the correlation exponent and the mutual information function. Its successfulness is most promising and is demonstrated on two time series.<<ETX>>

Measurement uncertainty, traceability and evaluation of test results in testing laboratories

The objective of this paper is to elaborate new elements related to metrological analysis in the field of testing, such as measurement uncertainty and traceability. Until now the international standard ISO 45001 did not explicitly require the uncertainty specifications in the area of testing to such an extent as the newly implemented standard ISO/IEC 17025. Therefore several additional steps should be performed in specifying the measurement and testing results, especially concerning performance of testing and other conformity assessment activities. The paper is focused on uncertainty analysis of a test procedure of the electrical safety of household appliances according to the European standard EN 60335-1. The traceability of measurements is presented. The example is chosen as a useful case study, as well as a very illustrative example, where many dilemmas could be highlighted. This particular case is relatively straightforward to evaluate due to the relative ease of traceability of electrical and thermal quantities. It is important that the measurement result and its uncertainty are correctly evaluated and on that basis the right conclusion of conformity or nonconformity with specifications is made. Therefore, knowledge and awareness of all facts about calibration, testing requirements and traceability are essential.

A learning algorithm for self-calibration of a voltage calibrator

An algorithm either to extend the calibration period or to reduce the measurement uncertainty of a DC voltage reference module is presented. This module is used either as a transfer, independent, or working standard, or as a reference module incorporated into a larger measuring system. The basic idea is that the deviation history of measured voltage differences of reference elements of a group reference module during the calibration period can be used as a learning period for a neural network. This neural network, when created, can numerically correct particular reference elements later in the working period. Results were obtained by simulation and evaluated on the basis of empirical data and simulated input functions. Hardware solutions to model this algorithm are discussed. >

Automated system for measuring temperature profiles inside ITS-90 fixed-point cells

The defining fixed points of the International Temperature Scale of 1990 (ITS-90) are temperature reference points for temperature calibration. The measured temperature inside the fixed-point cell depends on thermometer immersion, since measurements are made below the surface of the fixed-point material and the additional effect of the hydrostatic pressure has to be taken into account. Also, the heat flux along the thermometer stem can affect the measured temperature. The paper presents a system that enables accurate and reproducible immersion profile measurements for evaluation of measurement sensitivity and adequacy of thermometer immersion. It makes immersion profile measurements possible, where a great number of repetitions and long measurement periods are required, and reduces the workload on the user for performing such measurements. The system is flexible and portable and was developed for application to existing equipment in the laboratory. Results of immersion profile measurements in a triple point of water fixed-point cell are presented.

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.