Quantification of error between the heartbeat intervals measured form photoplethysmogram and electrocardiogram by synchronisation

Abstract

Currently, heartbeat intervals required for the analysis of heart rate variability (HRV) are derived from electrocardiogram (ECG). Many investigators have explored the possibility of using photoplethysmography (PPG), for the analysis of HRV. However, all these studies are based on statistical approach and have used the correlation coefficient for the comparison of HRV data obtained using ECG and PPG, which is inappropriate as the causal relationship between the R-peaks in ECG and the systolic peaks in PPG is well known in physiology. In this study, the heart beat intervals measured from PPG, are compared, beat by beat, with the corresponding beat intervals of same cardiac cycle obtained from the synchronously recorded ECG and the differences between them are taken as errors. These errors are verified to exactly match with the variations in the pulse transit times (PTTs), beat by beat. The error in the measurement of heartbeat intervals using PPG is quantified by obtaining the root mean square of the errors associated with each beat interval for a subject. The rms error, which is found to vary between 0.17 and 1.81% across the study group of 42 subjects, can be treated as insignificant, considering the nonstationary character of physiological signals. The errors are compared and interpreted with the variations in PTT. In view of these findings, PPG can be considered as a low cost, safe and more convenient alternative to ECG, as a wearable sensor outside hospital environment, for the analysis of HRV, without compromising on accuracy.     

Heartbeat counting is unrelated to heartbeat detection: A comparison of methods to quantify interoception

Recent research has identified individual differences in interoceptive sensitivity as a key source of variation in action, cognition, and emotion. This research has relied heavily on a single method for assessing interoceptive sensitivity: the accuracy of counting heartbeats while at rest. The validity of this method was assessed here by comparing the heartbeat counting (HBC) performance of 48 individuals with their heartbeat detection (HBD) performance. The HBC task required participants to report the numbers of heartbeats counted during brief signaled periods and indexed cardioceptive accuracy by the difference between the numbers of reported and actual heartbeats. In the HBD task, participants indicated the temporal location of heartbeat sensations relative to the onset of ventricular contraction. On each trial, they judged whether heartbeat sensations were or were not simultaneous with brief tones presented at one of six fixed delays following R waves of the ECG. In this method, cardioceptive accuracy or precision was indexed by variability in the temporal locations, relative to the R wave, of tones judged to be simultaneous with heartbeat sensations. Although intratask correlations indicated that each method yielded reliable scores, intertask correlations showed that HBC scores were unrelated to HBD scores. These results, which indicate that heartbeat detection and heartbeat counting are distinct processes, raise important questions about the assessment of interoceptive sensitivity and the involvement of this attribute in the psychological processes that have been associated with it on the basis of their correlations with HBC performance.     

Noninvasive heart rate monitoring system for avian embryos based on the ballistocardiogram

A noninvasive heart rate (HR) monitoring system for avian embryos has been developed based on the ballistocardiogram (BCG). The BCG was detected using a phonograph cartridge as a record of the velocity of the minute ballistic movements of the eggshell, which are generated by recoil and impact of heart contraction and blood ejection. The autocorrelation coefficients (ACCs) of the detected signal were computed to confirm whether the detected signal contained ballistic movement. An envelope of ACC was calculated by the monitoring system to measure the intervals between peaks and/or highly correlated parts in the ACC, and then the system obtained HR by measuring these intervals. To demonstrate the valid range of the detecting method, the BCGs of chickens and Japanese quail embryos of different ages were measured. The result of the experiment shows that the BCGs of chickens and quail embryos are detected fully after about two-thirds of the incubation period has passed. The monitoring system will enable us to perform long-term HR measurement for developing avian embryos up to hatching.     

Covert respiration measures for the detection of concealed information

A mock-theft experiment was designed to assess the efficiency of two covert respiration measures in detection of concealed information. The covert measures were further compared with three standard measures typically used for the detection of concealed knowledge (electrodermal, respiration and finger pulse measures). Results revealed that the covert respiration measures produced good discrimination between "guilty" (participants possessing concealed knowledge) and "innocent" participants. One of the covert measures produced detection efficiency that was similar to that of the standard respiration and finger pulse measures, but less than the electrodermal measure.     

Experiential Virtual Scenarios With Real-Time Monitoring (Interreality) for the Management of Psychological Stress: A Block Randomized Controlled Trial

Background

The recent convergence between technology and medicine is offering innovative methods and tools for behavioral health care. Among these, an emerging approach is the use of virtual reality (VR) within exposure-based protocols for anxiety disorders, and in particular posttraumatic stress disorder. However, no systematically tested VR protocols are available for the management of psychological stress.

Objective

Our goal was to evaluate the efficacy of a new technological paradigm, Interreality, for the management and prevention of psychological stress. The main feature of Interreality is a twofold link between the virtual and the real world achieved through experiential virtual scenarios (fully controlled by the therapist, used to learn coping skills and improve self-efficacy) with real-time monitoring and support (identifying critical situations and assessing clinical change) using advanced technologies (virtual worlds, wearable biosensors, and smartphones).

Methods

The study was designed as a block randomized controlled trial involving 121 participants recruited from two different worker populations—teachers and nurses—that are highly exposed to psychological stress. Participants were a sample of teachers recruited in Milan (Block 1: n=61) and a sample of nurses recruited in Messina, Italy (Block 2: n=60). Participants within each block were randomly assigned to the (1) Experimental Group (EG): n=40; B1=20, B2=20, which received a 5-week treatment based on the Interreality paradigm; (2) Control Group (CG): n=42; B1=22, B2=20, which received a 5-week traditional stress management training based on cognitive behavioral therapy (CBT); and (3) the Wait-List group (WL): n=39, B1=19, B2=20, which was reassessed and compared with the two other groups 5 weeks after the initial evaluation.

Results

Although both treatments were able to significantly reduce perceived stress better than WL, only EG participants reported a significant reduction (EG=12% vs CG=0.5%) in chronic “trait” anxiety. A similar pattern was found for coping skills: both treatments were able to significantly increase most coping skills, but only EG participants reported a significant increase (EG=14% vs CG=0.3%) in the Emotional Support skill.

Conclusions

Our findings provide initial evidence that the Interreality protocol yields better outcomes than the traditionally accepted gold standard for psychological stress treatment: CBT. Consequently, these findings constitute a sound foundation and rationale for the importance of continuing future research in technology-enhanced protocols for psychological stress management.

Trial Registration

ClinicalTrials.gov: {"type":"clinical-trial","attrs":{"text":"NCT01683617","term_id":"NCT01683617"}}NCT01683617; http://clinicaltrials.gov/show/{"type":"clinical-trial","attrs":{"text":"NCT01683617","term_id":"NCT01683617"}}NCT01683617 (Archived by WebCite at http://www.webcitation.org/6QnziHv3h).     

Compact long-term recorder for the transabdominal foetal and maternal electrocardiogram

Foetal heart rate (FHR) monitoring is a proven means of assessing foetal health during the antenatal period. Currently, the only widely available instrumentation for producing these data is based on Doppler ultrasound, a technology that is unsuitable for long-term use. For nearly a century, it has been known that the foetal electrocardiogram (FECG) can be detected using electrodes placed on the maternal abdomen. Although these signals suggest an alternative means of FHR derivation, their use has been limited owing to problems of poor signal-to-noise ratio. However, the eminent suitability of the transabdominal FECG for long-term FHR monitoring has suggested that perseverance with the technique would be worthwhile. The paper describes the design, construction and use of a compact, long-term recorder of three channels of 24 h antenatal transabdominal data. Preliminary use of the recorder in around 400 short recording sessions demonstrates that FHR records of equivalent quality to those from Doppler ultrasound-based instruments can be extracted from such data. The success of FHR derivation is, on average, around 65% of the recording period from around 20 weeks gestation (although this figure is reduced from around 28–32 weeks, and the success rates exhibit a wide range when individual subjects are considered). These results demonstrate that the technique offers, not only a means of acquiring long-term FHR data that are problematic to obtain by other means, but also a more patient-friendly alternative to the Doppler ultrasound technique.     

Simple,noninvasive system for measuring the heart rate of avian embryos and hatchlings by means of a piezoelectric film

Using a flexible piezoelectric film, the authors developed a simple system to determine noninvasively the heart rate of chicken embryos and hatchlings. The film was piezoelectric polyvinylidene fluoride (PVDF), which is sensitive enough to detect cardiogenic ballistic movements of the egg (ballistocardiogram (BCG)) and precordial movements of the hatchling attributable to cardiac contractions (apexcardiogram (ACG)). The BCG could be detected, during the second half of incubation, by placing the egg on the PVDF film on a soft substrate. The detected signal was found to be a measure of movement velocity. The ACG could be measured when the hatchling's chest wall made contact with the PVDF film installed in a box in which the hatchling was confined. The heart rate was counted from the lag time of autocorrelation calculated for a certain time segment (e.g. 2s) of the BCG and ACG recordings.     

Applicability of adaptive noise cancellation to fetal heart rate detection using photoplethysmography

In this paper, an approach based on adaptive noise cancellation (ANC) is evaluated for extraction of the fetal heart rate using photoplethysmographic signals from the maternal abdomen. A simple optical model is proposed in which the maternal and fetal blood pulsations result in emulated signals where the lower SNR limit (fetal to maternal) is -25dB. It is shown that a recursive least-squares algorithm is capable of extracting the peaks of the fetal PPG from these signals, for typical values of maternal and fetal tissues.     

HRV信号关联维计算中参数选取的研究

健康和有疾病的心率变异性（HRV）参数有明显差异,计算关联维是识别这种差异的一种重要手段。用传统的G—P算法计算关联维时,嵌入维数m、延迟时间τ、及序列长度N等参数的选取会对最终计算结果有很大影响。本文从理论和实验方面论述了如何选取这些参数以获得正确的结果,并且将其应用于正常组和心率不齐疾病组进行对照,结果显示关联维可以有效地表征由于疾病对于心脏节律造成的影响。     

Comparison of correlation and modulus difference processing algorithms for the determination of foetal heart rate from ultrasonic Doppler signals

Microprocessor-based correlation processing is now widely used for the estimation of foetal heart rate from ultrasonic Doppler signals. The paper describes a technique having a, similar performance, to correlation but which will run three times faster on a microprocessor without an onboard hardware multiplier. This speed improvement results from replacing each multiplication operation of the correlation algorithm with a subtraction and a modulus operation. The algorithm, is thus referred to as the modulus difference algorithm. Typical waveforms are presented illustrating the responses of the two processors to continuous wave Doppler foetal heart signals for both wide (50 Hz) and narrow (4 Hz) preprocessor bandwidths. A quantitative comparison is given of the performance of the two methods in estimating the period of a synthetic signal with additive white Gaussian noise. This simulation represents the wideband preprocessor case. A theoretical derivation of the outputs for the narrowband preprocessor case is given, and actual outputs are shown for comparison. A tutorial approach is adopted throughout the paper.     

随行监护系统在运动状态下的心肺生理参数测量准确性研究

本文研究随行(穿戴式)生理参数监测系统在不同运动强度下的心肺生理参数测量的准确性。使用随行生理参数监测系统SensEcho与心肺功能测试系统METALYZER 3B型(CORTEX)同步采集28名健康志愿者(17名男性和11名女性)在站立、躺下、Bruce跑台运动等多种运动状态下的心肺生理参数,利用Bland-Altman分析、相关性分析等方法,从群体和个体角度对比分析两类设备测量得到的心率和呼吸率参数。群体分析结果显示,两种设备采集的心率、呼吸率数据箱图高度一致,心率差值为(-0.407±3.380)次/分,呼吸率差值为(-0.560±7.047)次/分,差异很小,受试者各阶段心率、呼吸率Bland-Altman图显示mean±2SD之间所占比例分别为96.86%、95.29%,均大于95%;个体分析结果显示,全过程心率和呼吸率数据的相关系数均大于0.9。本研究表明在多种运动状态下,随行生理参数监测系统SensEcho能够准确测量人体心率和呼吸率等关键心肺生理参数,在各种强度的运动状态下都能保持很好的稳定性,能够满足运动状态下的连续生理信号采集和分析应用。     

A method of constant stimuli for examining heartbeat detection: Comparison with the Brener-Kluvitse and Whitehead methods

A method of constant stimuli (MCS) for measuring heartbeat detection was examined by comparing performance on this method with the Brener and Kluvitse (BK) method and a variant of the Whitehead (WH′) method. All methods required subjects to judge the simultaneity of heartbeat sensations and tones, and each yielded measures of judgment precision and of the temporal location of heartbeat sensations relative to the electrocardiogram R-wave. Both measures were found to be significantly correlated across tasks. A greater proportion of subjects met criteria for classification as heartbeat detectors on the MCS (54%) and BK (50%) tasks than on the WH’task (33%). In the MCS and BK tasks, subjects judged tones presented 100–300 ms after the R-wave to be most simultaneous with heartbeat sensations. Intratask correlations showed that only the MCS procedure yielded stable measurements of both judgment precision and temporal location. The MCS procedure possesses commendable psychometric properties and provides a simpler means than the BK procedure of examining heartbeat detection.     

全数据库评估概率密度函数法利用R-R间期检测房颤精度

研究整个MIT-BIH心律失常数据库评估概率密度函数法利用R-R间期检测房颤的精度。研究发现正常窦性心律含较多早搏时[（早搏次数/总心搏次数）>9.3%],识别房颤的精度下降到约70%;左束支传导阻滞含较多早搏时,识别房颤的精度下降到约80%;而房颤心电中频繁早搏对辨别房颤精度影响很小,仍达91%。可见该算法适用于区分关联性强的序列与关联性弱的序列。正常窦性心律和左束支传导阻滞心律相邻R-R间期关联性强,频繁早搏使其相邻R-R间期关联性减弱,从而降低识别房颤的精度;而房颤相邻R-R间期无关联性,频繁早搏对检测精度无影响。尽管数据库中有种类繁多的心律失常,且伴有频繁的早搏,算法全数据库共约110 000次心跳辨别房颤精度达82%~86%。     

第一产程胎心监护异常226例的相关因素分析

目的探讨第一产程胎心监护异常的相关因素,提示处理措施。方法2004年1月1日至2004年12月31日对深圳市宝安区妇幼保健院226例第一产程胎心监护异常的相关因素进行回顾性分析。结果第一产程胎心监护异常为综合因素所致,胎儿高危因素为91.59%,母体高危因素为65.49%,产程处理因素为42.92%。结论第一产程胎心监护异常主要与胎儿因素、母体因素有关,提高产前检查质量,加强产程监护,正确选择分娩方式极为重要。     

Detection of the third heart sound using a tailored wavelet approach

The third heart sound is normally heard during auscultation of younger individuals but disappears with increasing age. However, this sound can appear in patients with heart failure and is thus of potential diagnostic use in these patients. Auscultation of the heart involves a high degree of subjectivity. Furthermore, the third heart sound has low amplitude and a low-frequency content compared with the first and second heart sounds, which makes it difficult for the human ear to detect this sound. It is our belief that it would be of great help to the physician to receive computer-based support through an intelligent stethoscope, to determine whether a third heart sound is present or not. A precise, accurate and low-cost instrument of this kind would potentially provide objective means for the detection of early heart failure, and could even be used in primary health care. In the first step, phonocardiograms from ten children, all known to have a third heart sound, were analysed, to provide knowledge about the sound features without interference from pathological sounds. Using this knowledge, a tailored wavelet analysis procedure was developed to identify the third heart sound automatically, a technique that was shown to be superior to Fourier transform techniques. In the second step, the method was applied to phonocardiograms from heart patients known to have heart failure. The features of the third heart sound in children and of that in patients were shown to be similar. This resulted in a method for the automatic detection of third heart sounds. The method was able to detect third heart sounds effectively (90%), with a low false detection rate (3.7%), which supports its clinical use. The detection rate was almost equal in both the children and patient groups. The method is therefore capable of detecting, not only distinct and clearly visible/audible third heart sounds found in children, but also third heart sounds in phonocardiograms from patients suffering from heart failure.     

基于指端脉搏波视频信号的心率稳定检测算法

目的:研究一种基于脉搏波的稳定检测心率的算法。 方法:提出一种基于快速独立成分分析（FastICA）算法处理指端脉搏波视频信号。首先通过手机摄像头采集手指视频,在每帧图片中提取感兴趣区域（ROI）,根据每个区域中像素灰度值的变化得到血液容积变化的时序曲线;然后通过对ROI进行RGB通道分离和FastICA后,分别选取红、绿色分量与盲源分离后的估计信号进行相关性分析,筛选出相关性最大的作为后续提取心率的信号,并与波峰法测得的心率进行对比,得到一种稳定的心率检测算法,并利用SPSS软件做相关性分析。 结果:选取R、G通道信号的一致性在95%以上,基于FastICA的算法与统计波峰法获取心率的一致性在95%以上。 结论:FastICA算法能够有效地提高心率测量的稳定性,实验结果验证了该方法的可行性和有效性,对于基于脉搏波的人体生理参数获取具有重要意义。     

A new approach for detection of leg movement using segmental electrical impedance changes

The purpose of this paper is to provide a new approach for detection using bio-impedance. This impedance is measured by the four-electrode method. As the impedance changes resulting from ankle, knee, and hip movements depend on electrode placement, we determined the optimal electrode configurations for these movements by searching for high correlation coefficients, large impedance changes, and minimum interference in ten subjects (age: 20?±?4). Our optimal electrode configurations showed very strong relationships between the ankle joint angle and ankle impedance (γ?=???0.913?±?0.03), between the knee joint angle and knee impedance (γ?=?0.944?±?0.02), and between the hip joint angle and hip impedance (γ?=?0.823?±?0.08). This study showed that lower leg movement could be easily measured by the impedance measurement system with two pairs of skin electrodes.     

两种计算正常成年人短时心率变异性方法的比较研究

目的利用光电容积脉搏波法分析心率变异性,为通过心率变异性(heart rate variability,HRV)参数表征自主神经系统的变化提供新的研究方法。方法对46个健康成年受试者分别同步采集自主呼吸状态下的心电信号和光电容积脉搏波信号,利用二阶差分极大值提取心电图的RR间期,搜索脉搏波极大值提取脉搏波主波波峰间期PP,然后计算通用HRV参数SDNN、RMSSD和LF/HF,并利用回归的统计学方法结合Bland-Altman随机分析法对这两种方法获取的HRV结果进行比较。结果两种方法计算得到的心率变异性参数结果的Pearson相关系数分别为0.998、0.995和0.992,均显著相关(P0.01),Bland-Altman分布图也均在一致性区间内,说明这两种方法在计算心率变异性上具有一致性。结论利用光电容积脉搏波法分析心率变异具有可行性。     

A new method for qualitative and quantitative evaluation of tooth displacement under the application of orthodontic forces using magnetic sensors

The purpose of this study was to develop a new method for the quantitative and qualitative measurement of tooth displacement under load and to clarify the relationship between the force system acting on a tooth and a resultant movement. A combination of eight magnetic sensors and a magnet was employed to measure three-dimensional displacement. Two sets of sensors and a magnet were placed in front and at the back of a front tooth subjected to orthodontic forces. Magnets and sensors were fixed to the subject tooth and posterior teeth, respectively. Sensors detected displacements of two magnets extended from the subject tooth separately in real time. The tooth trajectories projected on the sagittal plane were studied. From displacements of two magnets, angle of tooth rotation, the position of center of rotation and the amount and direction of displacement of an arbitrary point on the tooth could be calculated with high accuracy. Also, the location of center of resistance could be determined. It was found that the center of rotation is moving substantially even with a small difference in the level of force application. Furthermore, a small amount of displacement of the center of resistance was observed with varying the force magnitude.