A multi-channel opto-electronic sensor to accurately monitor heart rate against motion artefact during exercise

A Guide to Measuring Heart and Respiratory Rates Based on Off-the-Shelf Photoplethysmographic Hardware and Open-Source Software

The remote monitoring of vital signs via wearable devices holds significant potential for alleviating the strain on hospital resources and elder-care facilities. Among the various techniques available, photoplethysmography stands out as particularly promising for assessing vital signs such as heart rate, respiratory rate, oxygen saturation, and blood pressure. Despite the efficacy of this method, many commercially available wearables, bearing Conformité Européenne marks and the approval of the Food and Drug Administration, are often integrated within proprietary, closed data ecosystems and are very expensive. In an effort to democratize access to affordable wearable devices, our research endeavored to develop an open-source photoplethysmographic sensor utilizing off-the-shelf hardware and open-source software components. The primary aim of this investigation was to ascertain whether the combination of off-the-shelf hardware components and open-source software yielded vital-sign measurements (specifically heart rate and respiratory rate) comparable to those obtained from more expensive, commercially endorsed medical devices. Conducted as a prospective, single-center study, the research involved the assessment of fifteen participants for three minutes in four distinct positions, supine, seated, standing, and walking in place. The sensor consisted of four PulseSensors measuring photoplethysmographic signals with green light in reflection mode. Subsequent signal processing utilized various open-source Python packages. The heart rate assessment involved the comparison of three distinct methodologies, while the respiratory rate analysis entailed the evaluation of fifteen different algorithmic combinations. For one-minute average heart rates' determination, the Neurokit process pipeline achieved the best results in a seated position with a Spearman's coefficient of 0.9 and a mean difference of 0.59 BPM. For the respiratory rate, the combined utilization of Neurokit and Charlton algorithms yielded the most favorable outcomes with a Spearman's coefficient of 0.82 and a mean difference of 1.90 BrPM. This research found that off-the-shelf components are able to produce comparable results for heart and respiratory rates to those of commercial and approved medical wearables.

Evaluation of Wrist-Worn Photoplethysmography Trackers with an Electrocardiogram in Patients with Ischemic Heart Disease: A Validation Study

PURPOSE

Photoplethysmography measurement of heart rate with wrist-worn trackers has been introduced in healthy individuals. However, additional consideration is necessary for patients with ischemic heart disease, and the available evidence is limited. The study aims to evaluate the validity and reliability of heart rate measures by a wrist-worn photoplethysmography (PPG) tracker compared to an electrocardiogram (ECG) during incremental treadmill exercise among patients with ischemic heart disease.

METHODS

Fifty-one participants performed the standard incremental treadmill exercise in a controlled laboratory setting with 12-lead ECG attached to the patient's body and wearing wrist-worn PPG trackers.

RESULTS

At each stage, the absolute percentage error of the PPG was within 10% of the standard acceptable range. Further analysis using a linear mixed model, which accounts for individual variations, revealed that PPG yielded the best performance at the baseline low-intensity exercise. As the stages progressed, heart rate validity decreased but was regained during recovery. The reliability was moderate to excellent.

CONCLUSIONS

Low-cost trackers AMAZFIT Cor and Bip validity and reliability were within acceptable ranges, especially during low-intensity exercise among patients with ischemic heart disease recovering from cardiac procedures. Though using the tracker as part of the diagnosis tool still requires more supporting studies, it can potentially be used as a self-monitoring tool with precautions.

Methodology for studying Relative Energy Deficiency in Sport (REDs): a narrative review by a subgroup of the International Olympic Committee (IOC) consensus on REDs

In the past decade, the study of relationships among nutrition, exercise and the effects on health and athletic performance, has substantially increased. The 2014 introduction of Relative Energy Deficiency in Sport (REDs) prompted sports scientists and clinicians to investigate these relationships in more populations and with more outcomes than had been previously pursued in mostly white, adolescent or young adult, female athletes. Much of the existing physiology and concepts, however, are either based on or extrapolated from limited studies, and the comparison of studies is hindered by the lack of standardised protocols. In this review, we have evaluated and outlined current best practice methodologies to study REDs in an attempt to guide future research.This includes an agreement on the definition of key terms, a summary of study designs with appropriate applications, descriptions of best practices for blood collection and assessment and a description of methods used to assess specific REDs sequelae, stratified as either Preferred, Used and Recommended or Potential Researchers can use the compiled information herein when planning studies to more consistently select the proper tools to investigate their domain of interest. Thus, the goal of this review is to standardise REDs research methods to strengthen future studies and improve REDs prevention, diagnosis and care.

Validation of Wearable Digital Devices for Heart Rate Measurement During Exercise Test in Patients With Coronary Artery Disease

OBJECTIVE

To assess the accuracy of recently commercialized wearable devices in heart rate (HR) measurement during cardiopulmonary exercise test (CPX) under gradual increase in exercise intensity, while wearable devices with HR monitors are reported to be less accurate in different exercise intensities.

METHODS

CPX was performed for patients with coronary artery disease (CAD). Twelve lead electrocardiograph (ECG) was the gold standard and Apple watch 7 (AW7), Galaxy watch 4 (GW4) and Bio Patch Mobicare 200 (MC200) were applied for comparison. Paired absolute difference (PAD), mean absolute percentage error (MAPE) and intraclass correlation coefficient (ICC) were evaluated for each device.

RESULTS

Forty-four participants with CAD were included. All the devices showed MAPE under 2% and ICC above 0.9 in rest, exercise and recovery phases (MC200=0.999, GW4=0.997, AW7=0.998). When comparing exercise and recovery phase, PAD of MC200 and AW7 in recovery phase were significantly bigger than PAD of exercise phase (p<0.05). Although not significant, PAD of GW4 tended to be bigger in recovery phase, too. Also, when stratified by HR 20, ICC of all the devices were highest under HR of 100, and ICC decreased as HR increased. However, except for ICC of GW4 at HR above 160 (=0.867), all ICCs exceeded 0.9 indicating excellent accuracy.

CONCLUSION

The HR measurement of the devices validated in this study shows a high concordance with the ECG device, so CAD patients may benefit from the devices during high-intensity exercise under conditions where HR is measured reliably.

Evaluating the usability of a co-designed power assisted exercise graphical user interface for people with stroke

BACKGROUND

Digital advancement of power assisted exercise equipment will advance exercise prescription for people with stroke (PwS). This article reports on the remote usability evaluation of a co-designed graphical user interface (GUI) and denotes an example of how video-conference software can increase reach to participants in the testing of rehabilitation technologies. The aim of this study was to evaluate the usability of two sequential versions of the GUI.

METHODS

We adopted a mixed methods approach. Ten professional user (PU) (2M/8F) and 10 expert user (EU) participants (2M/8F) were recruited. Data collection included a usability observation, a 'think aloud' walk through, task completion, task duration and user satisfaction as indicated by the Post Study System Usability Questionnaire (PSSUQ). Identification of usability issues informed the design of version 2 which included an additional submenu. Descriptive analysis was conducted upon usability issues and number of occurrences detected on both versions of the GUI. Inferential analysis enabled comparison of task duration and PSSUQ data between the PU and EU groups.

RESULTS

Analysis of the 'think aloud' walkthrough data enabled identification of 22 usability issues on version 1 from a total of 100 usability occurrences. Task completion for all tasks was 100%. Eight usability issues were directly addressed in the development of version 2. Two recurrent and 24 new usability issues were detected in version 2 with a total of 86 usability occurrences. Paired two tailed T-tests on task duration data indicated a significant decrease amongst the EU group for task 1.1 on version 2 (P = 0.03). The mean PSSUQ scores for version 1 was 1.44 (EU group) and 1.63 (PU group) compared with 1.40 (EU group) and 1.41 (PU group) for version 2.

CONCLUSIONS

The usability evaluation enabled identification of usability issues on version 1 of the GUI which were effectively addressed on the iteration of version 2. Testing of version 2 identified usability issues within the new submenu. Application of multiple usability evaluation methods was effective in identifying and addressing usability issues in the GUI to improve the experience of PAE for PwS. The use of video-conference software to conduct synchronous, remote usability testing is an effective alternative to face to face testing methods.

Reduction in the Motion Artifacts in Noncontact ECG Measurements Using a Novel Designed Electrode Structure

A noncontact ECG is applicable to wearable bioelectricity acquisition because it can provide more comfort to the patient for long-term monitoring. However, the motion artifact is a significant source of noise in an ECG recording. Adaptive noise reduction is highly effective in suppressing motion artifact, usually through the use of external sensors, thus increasing the design complexity and cost. In this paper, a novel ECG electrode structure is designed to collect ECG data and reference data simultaneously. Combined with the adaptive filter, it effectively suppresses the motion artifact in the ECG acquisition. This method adds one more signal acquisition channel based on the single-channel ECG acquisition system to acquire the reference signal without introducing other sensors. Firstly, the design of the novel ECG electrode structure is introduced based on the principle of noise reduction. Secondly, a multichannel signal acquisition circuit system and ECG electrodes are implemented. Finally, experiments under normal walking conditions are carried out, and the performance is verified by the experiment results, which shows that the proposed design effectively suppresses motion artifacts and maintains the stability of the signal quality during the noncontact ECG acquisition. The signal-to-noise ratio of the ECG signal after noise reduction is 14 dB higher than that of the original ECG signal with the motion artifact.

Accuracy of the Apple Watch Series 6 and the Whoop Band 3.0 for assessing heart rate during resistance exercises

This study aimed to determine heart rate accuracy measured by wearable devices during resistance exercises at various intensities. Twenty-nine participants (16 female) aged 19-37 years participated in this cross-sectional study. Participants completed five resistance exercises; Barbell Back Squat, Barbell Deadlift, Dumbbell Curl to Overhead Press, Seated Cable Row, and Burpees. During the exercises, heart rate was concurrently measured using the Polar H10, the Apple Watch Series 6 and the Whoop 3.0. The Apple Watch had high agreement with the Polar H10 during Barbell Back Squats, Barbell Deadlift, and Seated Cable Rows (rho > 0.832) and moderate to low agreement during Dumbbell Curl to Overhead Press and Burpees (rho > 0.364). The Whoop Band 3.0 had high agreement with the Polar H10 during Barbell Back Squats (r > 0.697), moderate agreement during Barbell Deadlift and Dumbbell Curl to Overhead Press (rho > 0.564) and low agreement during Seated Cable Rows and Burpees (rho > 0.383). The results varied across exercises and intensities and indicated the most favourable outcomes for the Apple Watch. In conclusion, our data suggest that the Apple Watch Series 6 is suitable for measuring heart rate during exercise prescription or monitoring resistance exercise performance.

Semiconductor Multimaterial Optical Fibers for Biomedical Applications

Integrated sensors and transmitters of a wide variety of human physiological indicators have recently emerged in the form of multimaterial optical fibers. The methods utilized in the manufacture of optical fibers facilitate the use of a wide range of functional elements in microscale optical fibers with an extensive variety of structures. This article presents an overview and review of semiconductor multimaterial optical fibers, their fabrication and postprocessing techniques, different geometries, and integration in devices that can be further utilized in biomedical applications. Semiconductor optical fiber sensors and fiber lasers for body temperature regulation, in vivo detection, volatile organic compound detection, and medical surgery will be discussed.

A multidevice and multimodal dataset for human energy expenditure estimation using wearable devices

We present a multi-device and multi-modal dataset, called WEEE, collected from 17 participants while they were performing different physical activities. WEEE contains: (1) sensor data collected using seven wearable devices placed on four body locations (head, ear, chest, and wrist); (2) respiratory data collected with an indirect calorimeter serving as ground-truth information; (3) demographics and body composition data (e.g., fat percentage); (4) intensity level and type of physical activities, along with their corresponding metabolic equivalent of task (MET) values; and (5) answers to questionnaires about participants' physical activity level, diet, stress and sleep. Thanks to the diversity of sensors and body locations, we believe that the dataset will enable the development of novel human energy expenditure (EE) estimation techniques for a diverse set of application scenarios. EE refers to the amount of energy an individual uses to maintain body functions and as a result of physical activity. A reliable estimate of people's EE thus enables computing systems to make inferences about users' physical activity and help them promoting a healthier lifestyle.

Exercise training in paediatric congenital heart disease: fit for purpose?

Exercise and physical activity (PA) have been shown to be effective, safe and feasible in both healthy children and children with congenital heart disease (CHD). However, implementing exercise training as an intervention is still not routine in children with CHD despite considerable evidence of health benefits and well-being. Understanding how children with CHD can safely participate in exercise can boost participation in PA and subsequently reduce inactivity-related diseases. Home-based exercise intervention, with the use of personal wearable activity trackers, and high-intensity interval training have been beneficial in adults' cardiac rehabilitation programmes. However, these remain underutilised in paediatric care. Therefore, the aims of this narrative review were to synthesise prescribed exercise interventions in children with CHD, identify possible limitation to exercise training prescription and provide an overview on how to best integrate exercise intervention effectively for this population into daily practice.

Accuracy of heart rate measurements of three smartwatch models in dogs

This study was aimed to evaluate the accuracy of heart rate (HR) measurements using three smartwatch models designed for human use when applied to dogs. A group of 15 mixed breed dogs, ages ranging from 2 to 3 years, weighing between 20 and 30 kg were used. The Garmin Fenix 5X plus (GF5Xp), Samsung Gear S3 (SGS3), and Polygold A-6 (PDA6), were randomly placed on the tibia of dogs to collect the HR recordings every 5 minutes for 1 hour. A veterinary patient monitor (VPM) was used as the reference method. A Bland-Altman plot was applied to determine the difference between smartwatches. The receiver operating characteristic curves were developed analysis for sensitivity and specificity. The HR measured by VPM ranged from 65 to 200 bpm (mean, 149.3 ± 28.1 bpm; median, 154 bpm). Among the smartwatches, the lowest (44 bpm) HR was measured by PDA6, while the highest (201 bpm) was measured by SGS3. Among the smartwatches; GF5Xp and SGS3 had slopes equal to 1 and residual standard deviation closer to 0, in agreement with VPM. At the cut-off HR (160 bpm), SGS3 had the highest sensitivity (97.4%), whereas PDA6 had the lowest sensitivity (68.0%). The specificity of GF5Xp, SGS3, and PDA6 was 97.1%, 98.0%, and 98.0%, respectively. The SGS3 and GF5Xp can be ideal tools for veterinarians to monitor the HR of dogs without requiring an additional device.

Flexible Wearable Sensors for Cardiovascular Health Monitoring

Cardiovascular diseases account for the highest mortality globally, but recent advances in wearable technologies may potentially change how these illnesses are diagnosed and managed. In particular, continuous monitoring of cardiovascular vital signs for early intervention is highly desired. To this end, flexible wearable sensors that can be comfortably worn over long durations are gaining significant attention. In this review, advanced flexible wearable sensors for monitoring cardiovascular vital signals are outlined and discussed. Specifically, the functional materials, configurations, mechanisms, and recent advances of these flexible sensors for heart rate, blood pressure, blood oxygen saturation, and blood glucose monitoring are highlighted. Different mechanisms in bioelectric, mechano-electric, optoelectric, and ultrasonic wearable sensors are presented to monitor cardiovascular vital signs from different body locations. Present challenges, possible strategies, and future directions of these wearable sensors are also discussed. With rapid development, these flexible wearable sensors will potentially be applicable for both medical diagnosis and daily healthcare use in tackling cardiovascular diseases.

Accuracy and Reliability of Pulse O2 Saturation Measured by a Wrist-worn Oximeter

This study aims to evaluate the accuracy of the Garmin Forerunner 245 heart rate (HR) and pulse O₂ saturation (SpO₂) sensors compared with electrocardiogram and medical oximeter, from sea level to high altitude. Ten healthy subjects underwent five tests in normoxia and hypoxia (simulated altitudes from 3000 to 5500 m), consisting in a 5-min rest phase, followed by 5-min of mild exercise. Absolute error (±10 bpm for HR and ±3% for SpO₂, around criterion) and intraclass correlations (ICC) were calculated. Error rates for HR remained under 10%, except at 3000 m, and ICCs evidenced a good reliability between Garmin and criterion. Overall SpO₂ was higher than criterion (P<0.001) with a >50% error rate (>80% above 4800 m), and a poor reliability with criterion. The Garmin device displayed acceptable HR data at rest and exercise for all altitudes, but failed to provide trustworthy SpO₂ values, especially at high altitude, where a pronounced arterial O₂ desaturation could lead to acute mountain sickness in hypoxia-sensitive subjects, and its life-threatening complications; moreover, readings of overestimated SpO₂ values might induce trekkers into further hazardous behavior by pursuing an ascent while being already at risk. Therefore, its use to assess SpO₂ should be proscribed in altitude for acclimatization evaluation.

Validity of the Polar Vantage M watch when measuring heart rate at different exercise intensities

Background

The use of wrist worn wearable fitness trackers has been growing rapidly over the last decade. The growing popularity can be partly attributed to the improvements in technology, making activity trackers more affordable, comfortable and convenient for use in different fitness and environmental applications. Fitness trackers typically monitor activity level, track steps, distance, heart rate (HR), sleep, peripheral capillary oxygen saturation and more, as the technology continuously is advancing. In terms of measuring HR, photoplethysmography (PPG) is a relatively new technology utilised in wearables. PPG estimates HR through an optical technique that monitors changes in blood volume beneath the skin. With these new products becoming available it is important that the validity of these devices be evaluated. Therefore, the aim of this study was to assess the validity of the Polar Vantage M (PVM) watch to measure HR compared to medical grade ECG on a healthy population during a range of treadmill exercise intensities.

Methods

A total of 30 healthy participants (n = 17 males, n = 13 females) were recruited for this study. The validity of the PVM watch to measure HR was compared against the gold standard 5-lead ECG. The study was conducted on 2 separate testing days with 24–48 h between sessions. Participants completed the Bruce Treadmill Protocol, and HR was measured every 30 s. Validation of the PVM watch in comparison to the ECG was measured with an Intraclass Correlation Coefficient (ICC) and associated 95% confidence intervals (CI) and levels of agreement were identified with Bland–Altman plots with 90% limits of agreement. Linear regression analysis was performed to calculate the value of r² computing the variation of HR obtained by the PVM watch and ECG.

Results

In total, 30 participants completed the protocol, with data from 28 participants utilised for statistical analysis (16 males, 14 females, 26.10 ± 3.39 years, height 52.36 m ± 7.40 cm, mass 73.59 ± 11.90 kg). A strong and significant correlation was found between the PVM watch and ECG, demonstrating good criterion validity (p < 0.05, r² = 0.87). Good validity was seen for day 1 and day 2 for stage 0 (ICC = 0.83; 95% CI [0.63–0.92], ICC = 0.74; 95% CI [0.37–0.88]), stage 1 (ICC = 0.78; 95% CI [0.52–0.90], ICC = 0.88; 95% CI [0.74–0.95]), and stage 2 (ICC = 0.88; 95% CI [0.73–0.94], ICC = 0.80; 95% CI [0.40–0.92]). Poor validity was demonstrated on day 1 and day 2 for stages 3–5 (ICC < 0.50).

Conclusion

This study revealed that the PVM watch had a strong correlation with the ECG throughout the entire Bruce Protocol, however the level of agreement (LoA) becomes widely dispersed as exercise intensities increased. Due to the large LoA between the ECG and PVM watch, it is not advisable to use this device in clinical populations in which accurate HR measures are essential for patient safety; however, the watch maybe used in settings where less accurate HR is not critical to an individual’s safety while exercising.

A Textile Sleeve for Monitoring Oxygen Saturation Using Multichannel Optical Fibre Photoplethysmography

Textile-based systems are an attractive prospect for wearable technology as they can provide monitoring of key physiological parameters in a comfortable and unobtrusive form. A novel system based on multichannel optical fibre sensor probes integrated into a textile sleeve is described. The system measures the photoplethysmogram (PPG) at two wavelengths (660 and 830 nm), which is then used to calculate oxygen saturation (SpO₂). In order to achieve reliable measurement without adjusting the position of the garment, four plastic optical fibre (POF) probes are utilised to increase the likelihood that a high-quality PPG is obtained due to at least one of the probes being positioned over a blood vessel. Each probe transmits and receives light into the skin to measure the PPG and SpO₂. All POFs are integrated in a stretchable textile sleeve with a circumference of 15 cm to keep the sensor in contact with the subject’s wrist and to minimise motion artefacts. Tests on healthy volunteers show that the multichannel PPG sensor faithfully provides an SpO₂ reading in at least one of the four sensor channels in all cases with no need for adjusting the position of the sleeve. This could not be achieved using a single sensor alone. The multichannel sensor is used to monitor the SpO₂ of 10 participants with an average wrist circumference of 16.0 ± 0.6 cm. Comparing the developed sensor’s SpO₂ readings to a reference commercial oximeter (reflectance Masimo Radical-7) illustrates that the mean difference between the two sensors’ readings is −0.03%, the upper limit of agreement (LOA) is 0.52% and the lower LOA is −0.58%. This multichannel sensor has the potential to achieve reliable, unobtrusive and comfortable textile-based monitoring of both heart rate and SpO₂ during everyday life.

A Study on the Effect of Contact Pressure during Physical Activity on Photoplethysmographic Heart Rate Measurements

Heart rate (HR) as an important physiological indicator could properly describe global subject's physical status. Photoplethysmographic (PPG) sensors are catching on in field of wearable sensors, combining the advantages in costs, weight and size. Nevertheless, accuracy in HR readings is unreliable specifically during physical activity. Among several identified sources that affect PPG recording, contact pressure (CP) between the PPG sensor and skin greatly influences the signals.

METHODS

In this study, the accuracy of HR measurements of a PPG sensor at different CP was investigated when compared with a commercial ECG-based chest strap used as a test control, with the aim of determining the optimal CP to produce a reliable signal during physical activity. Seventeen subjects were enrolled for the study to perform a physical activity at three different rates repeated at three different contact pressures of the PPG-based wristband.

RESULTS

The results show that the CP of 54 mmHg provides the most accurate outcome with a Pearson correlation coefficient ranging from 0.81 to 0.95 and a mean average percentage error ranging from 3.8% to 2.4%, based on the physical activity rate.

CONCLUSION

Authors found that changes in the CP have greater effects on PPG-HR signal quality than those deriving from the intensity of the physical activity and specifically, the individual best CP for each subject provided reliable HR measurements even for a high intensity of physical exercise with a Bland-Altman plot within ±11 bpm. Although future studies on a larger cohort of subjects are still needed, this study could contribute a profitable indication to enhance accuracy of PPG-based wearable devices.

Measurement latency significantly contributes to reduced heart rate measurement accuracy in wearable devices

The purpose of this study was to determine the extent to which measurement latency has significance for the accuracy of heart rate (HR) measured by wearable devices during physical activities. Thirty participants (15 female) aged 18-50 years (mean 24.8, 6.3 SD years) with weight ranging from 53-87 kg (mean 70.5, 9.4 SD kg) participated in this cross-sectional study. Participants completed three submaximal exercise conditions; cycling, treadmill walking/running and rapid arm movements. During the exercises, HR was concurrently measured using the Polar H10 (PL), the Apple Watch 2 (AW) and the Garmin Forerunner 235 (GF). Measurement latency significantly affected the discrepancy in HR measures and measurement latency accounted for 15% (GF) and 2% (AW) of the explained discrepancy in HR between the criterion measure PL and the GF and AW. However, the findings also showed that the magnitude of HR measurement latency differed notably among the two wearable devices and measurement latency was greatly influenced not only by type but also by the intensity of exercise. These findings contribute to our understanding of wearable device HR measures discrepancy and this knowledge may be of assistance when electing to use wearable devices to monitor physical exertion in different contexts.

Is Continuous Heart Rate Monitoring of Livestock a Dream or Is It Realistic? A Review

For all homoeothermic living organisms, heart rate (HR) is a core variable to control the metabolic energy production in the body, which is crucial to realize essential bodily functions. Consequently, HR monitoring is becoming increasingly important in research of farm animals, not only for production efficiency, but also for animal welfare. Real-time HR monitoring for humans has become feasible though there are still shortcomings for continuously accurate measuring. This paper is an effort to estimate whether it is realistic to get a continuous HR sensor for livestock that can be used for long term monitoring. The review provides the reported techniques to monitor HR of living organisms by emphasizing their principles, advantages, and drawbacks. Various properties and capabilities of these techniques are compared to check the potential to transfer the mostly adequate sensor technology of humans to livestock in term of application. Based upon this review, we conclude that the photoplethysmographic (PPG) technique seems feasible for implementation in livestock. Therefore, we present the contributions to overcome challenges to evolve to better solutions. Our study indicates that it is realistic today to develop a PPG sensor able to be integrated into an ear tag for mid-sized and larger farm animals for continuously and accurately monitoring their HRs.

Optical Fibre Sensor for Simultaneous Measurement of Capillary Refill Time and Contact Pressure

The widely applied capillary refill time (CRT) measurement is currently performed by manually applying pressure and using a stopwatch to record the time taken for the skin to recover its normal colour after a blanching pressure is applied. This method is highly subjective and observer-dependent. This paper presents a new, integrated optical sensor probe, combining monitoring of the capillary refilling process with the blanching pressure applied. The sensor consists of an optical fibre-based reflectance photoplethysmography (PPG) sensor to measure the reflected light signal, as well as a fibre Bragg grating (FBG) to measure the applied blanching pressure and to indicate the time when pressure is released. This sensor was applied to calculate the CRT (1.38 ± 0.66 s) of 10 healthy adult volunteers with (55.2 ± 21.8 kPa) blanching pressures. The form of the capillary refilling data was investigated by fitting using an exponential regression model (R² > 0.96). The integrated probe has the potential to improve the reliability of CRT measurements by standardising the optimum duration and magnitude of the pressure.

Accuracy of wearable heart rate monitors in cardiac rehabilitation

Background

To assess the accuracy of four wearable heart rate (HR) monitors in patients with established cardiovascular disease enrolled in phase II or III cardiac rehabilitation (CR).

Methods

Eighty adult patients enrolled in phase II or III CR were monitored during a CR session that included exercise on a treadmill and/or stationary cycle. Participants underwent HR monitoring with standard ECG limb leads, an electrocardiographic (ECG) chest strap monitor (Polar H7), and two randomly assigned wrist-worn HR monitors (Apple Watch, Fitbit Blaze, Garmin Forerunner 235, TomTom Spark Cardio), one on each wrist. HR was recorded at rest and at 3, 5, and 7 minutes of steady-state exercise on the treadmill and stationary cycle.

Results

Across all exercise conditions, the chest strap monitor (Polar H7) had the best agreement with ECG (r_c=0.99) followed by the Apple Watch (r_c=0.80), Fitbit Blaze (r_c=0.78), TomTom Spark (r_c=0.76) and Garmin Forerunner (r_c=0.52). There was variability in accuracy under different exercise conditions. On the treadmill, only the Fitbit Blaze performed well (r_c=0.76), while on the stationary cycle, Apple Watch (r_c=0.89) and TomTom Spark (r_c=0.85) were most accurate.

Conclusions

In cardiac patients, the accuracy of wearable, optically based HR monitors varies, and none of those tested was as accurate as an electrode-containing chest monitor. This observation has implications for in-home CR, as electrode-containing chest monitors should be used when accurate HR measurement is imperative.

Adaptive Noise Reduction Algorithm to Improve R Peak Detection in ECG Measured by Capacitive ECG Sensors

Electrocardiograms (ECGs) can be conveniently obtained using capacitive ECG sensors. However, motion noise in measured ECGs can degrade R peak detection. To reduce noise, properties of reference signal and ECG measured by the sensors are analyzed and a new method of active noise cancellation (ANC) is proposed in this study. In the proposed algorithm, the original ECG signal at QRS interval is regarded as impulsive noise because the adaptive filter updates its weight as if impulsive noise is added. As the proposed algorithm does not affect impulsive noise, the original signal is not reduced during ANC. Therefore, the proposed algorithm can conserve the power of the original signal within the QRS interval and reduce only the power of noise at other intervals. The proposed algorithm was verified through comparisons with recent research using data from both indoor and outdoor experiments. The proposed algorithm will benefit a noise reduction of noisy biomedical signal measured from sensors.

Variable Accuracy of Wearable Heart Rate Monitors during Aerobic Exercise

PURPOSE

Athletes and members of the public increasingly rely on wearable HR monitors to guide physical activity and training. The accuracy of newer, optically based monitors is unconfirmed. We sought to assess the accuracy of five optically based HR monitors during various types of aerobic exercise.

METHODS

Fifty healthy adult volunteers (mean ± SD age = 38 ± 12 yr, 54% female) completed exercise protocols on a treadmill, a stationary bicycle, and an elliptical trainer (±arm movement). Each participant underwent HR monitoring with an electrocardiogaphic chest strap monitor (Polar H7), forearm monitor (Scosche Rhythm+), and two randomly assigned wrist-worn HR monitors (Apple Watch, Fitbit Blaze, Garmin Forerunner 235, and TomTom Spark Cardio), one on each wrist. For each exercise type, HR was recorded at rest, light, moderate, and vigorous intensity. Agreement between HR measurements was assessed using Lin's concordance correlation coefficient (rc).

RESULTS

Across all exercise conditions, the chest strap monitor (Polar H7) had the best agreement with ECG (rc = 0.996) followed by the Apple Watch (rc = 0.92), the TomTom Spark (rc = 0.83), and the Garmin Forerunner (rc = 0.81). Scosche Rhythm+ and Fitbit Blaze were less accurate (rc = 0.75 and rc = 0.67, respectively). On treadmill, all devices performed well (rc = 0.88-0.93) except the Fitbit Blaze (rc = 0.76). While bicycling, only the Garmin, Apple Watch, and Scosche Rhythm+ had acceptable agreement (rc > 0.80). On the elliptical trainer without arm levers, only the Apple Watch was accurate (rc = 0.94). None of the devices was accurate during elliptical trainer use with arm levers (all rc < 0.80).

CONCLUSION

The accuracy of wearable, optically based HR monitors varies with exercise type and is greatest on the treadmill and lowest on elliptical trainer. Electrode-containing chest monitors should be used when accurate HR measurement is imperative.

The usefulness and actual use of wearable devices among the elderly population

BACKGROUND AND OBJECTIVE

Elderly populations are more prone to diseases and need continuous monitoring of parameters to ensure good health. Wearable devices (WDs) can be helpful in the early detection and management of medical conditions. However, less is known about the use of currently available WDs among elderly populations. The objectives of this study were to determine the usefulness and actual use of wearable devices among the elderly population.

METHODS

Our methodology was based on a systematic review and a survey questionnaire. In the systematic review, search was conducted in four databases PubMed, MDPI, Sage, and Scopus with search terms "wearable device" and "elderly", "wearable sensor" and "elderly". The inclusion criteria were the studies which described health-related wearable devices, its use as the outcome, conducted on a minimum of ten participants and published in the last five years. The survey was conducted on the MOOCs (Massive Open Online Course) platform. The questionnaire was related to the use of technology, intention to use, security and privacy concerns, and willingness to pay.

RESULTS

The review identified 4915 articles, of which, 31 studies eventually met the inclusion criteria. All studies reported positive impacts after assessing devices, despite certain drawbacks. The majority of the samples were males. The survey revealed responses from 233 individuals out of the 1100 participants of the course. The survey results were categorized into two age groups: 54.3% were elderly (>65 years) and 45.49% were non-elderly (≤65 years). Very few elderly people were currently using WD. More than 60% of elderly people were interested in the future use of wearable devices, and preferred future use to improve physical and mental activities. A majority of the respondents were female.

CONCLUSIONS

This study suggests awareness should be created among elderly populations regarding the use of WDs for the early detection and prevention of complications and emergencies. Elderly populations are more prone to benefits from using WDs. The review concluded that devices should be tested on elderly groups as well, considering sex equality, and on both healthy and sick participants for better insights. The survey determined the elderly as frequent users of technology, but lack of knowledge of WD and demonstrated female interest in the use of WD. In future research on WDs, it is suggested that clinical studies be conducted for longer durations, and standard protocols such as age and sex equality should be considered. Requirements from both users and physicians should be acknowledged for better cognizance of WDs.

Wrinkled 2D Materials: A Versatile Platform for Low-Threshold Stretchable Random Lasers

A stretchable, flexible, and bendable random laser system capable of lasing in a wide range of spectrum will have many potential applications in next- generation technologies, such as visible-spectrum communication, superbright solid-state lighting, biomedical studies, fluorescence, etc. However, producing an appropriate cavity for such a wide spectral range remains a challenge owing to the rigidity of the resonator for the generation of coherent loops. 2D materials with wrinkled structures exhibit superior advantages of high stretchability and a suitable matrix for photon trapping in between the hill and valley geometries compared to their flat counterparts. Here, the intriguing functionalities of wrinkled reduced graphene oxide, single-layer graphene, and few-layer hexagonal boron nitride, respectively, are utilized to design highly stretchable and wearable random laser devices with ultralow threshold. Using methyl-ammonium lead bromide perovskite nanocrystals (PNC) to illustrate the working principle, the lasing threshold is found to be ≈10 µJ cm^-2 , about two times less than the lowest value ever reported. In addition to PNC, it is demonstrated that the output lasing wavelength can be tuned using different active materials such as semiconductor quantum dots. Thus, this study is very useful for the future development of high-performance wearable optoelectronic devices.

A Pulse Rate Detection Method for Mouse Application Based on Multi-PPG Sensors

Heart rate is an important physiological parameter for healthcare. Among measurement methods, photoplethysmography (PPG) is an easy and convenient method for pulse rate detection. However, as the PPG signal faces the challenge of motion artifacts and is constrained by the position chosen, the purpose of this paper is to implement a comfortable and easy-to-use multi-PPG sensor module combined with a stable and accurate real-time pulse rate detection method on a computer mouse. A weighted average method for multi-PPG sensors is used to adjust the weight of each signal channel in order to raise the accuracy and stability of the detected signal, therefore reducing the disturbance of noise under the environment of moving effectively and efficiently. According to the experiment results, the proposed method can increase the usability and probability of PPG signal detection on palms.

Reduction of Motion Artifacts and Improvement of R Peak Detecting Accuracy Using Adjacent Non-Intrusive ECG Sensors

Non-intrusive electrocardiogram (ECG) monitoring has many advantages: easy to measure and apply in daily life. However, motion noise in the measured signal is the major problem of non-intrusive measurement. This paper proposes a method to reduce the noise and to detect the R peaks of ECG in a stable manner in a sitting arrangement using non-intrusive sensors. The method utilizes two capacitive ECG sensors (cECGs) to measure ECG, and another two cECGs located adjacent to the sensors for ECG are added to obtain the information on motion. Then, active noise cancellation technique and the motion information are used to reduce motion noise. To verify the proposed method, ECG was measured indoors and during driving, and the accuracy of the detected R peaks was compared. After applying the method, the sum of sensitivity and positive predictivity increased 8.39% on average and 26.26% maximally in the data. Based on the results, it was confirmed that the motion noise was reduced and that more reliable R peak positions could be obtained by the proposed method. The robustness of the new ECG measurement method will elicit benefits to various health care systems that require noninvasive heart rate or heart rate variability measurements.