Abstract Heart rate variability analysis is used to provideinformation about the autonomous nervous system control-ling the heart rate. There are many factors that affect the heartrate variability, internal and external to the human body. Inthis paper, we compare the heart rate variability parametersof 19 male volunteers while listening and not listening toQuran within the same group. The results of this researchare presented in a form of statistical analysis in addition tointroducing variability displays called circle plots for bettervisualization of the compared data sets.
Keywords ECG · HRV · RR interval
A. Al-Zaben: In leave from Yarmouk University, Jordan.
A. Al-Zaben (B)Electrical Engineering Department, Engineering College,Salman Bin Abdualziz University,Al-Kharj, Saudi Arabiae-mail: [email protected]
H. HamadElectronic Engineering Department, Hijjawi Collegefor Engineering Technology, Yarmouk University,Irbid, Jordan
A. Alfahoum · W. SaefanBiomedical Systems and Medical Informatics Department,Hijjawi College for Engineering Technology,Yarmouk University, Irbid, Jordan
1 Introduction
Heart rate variability (HRV) is the beat to beat intervalrecorded over some period of time. When using the electro-cardiograph (ECG) as the source of this signal, then it is thetime between consecutive R’s (known as R–R interval). HRVand the corresponding R–R intervals are random. Therefore,certain parameters are used to study the changes in the HRV.According to the Task Force of the European Society ofCardiology and the North America Society of Pacing andElectrophysiology, these parameters can be divided into timedomain and frequency domain parameters [1]. Time domainparameters considered in this paper are: mean of the R–Rinterval, standard deviation (SDNN) of the R–R intervals,the root mean square of the difference between successiveadjacent R–R intervals (rMSSD). In frequency domain, thefollowing parameters are considered: low frequency power(aLF), high frequency power (aHF), total power (aTotal),the corresponding power percentages (pLF and pHF), thevalue of the frequency where the low frequency peak occurs(peakLF), the value of the frequency where the high fre-quency occurs (peakHF), and the ratio of the low frequency
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power to that of the high frequency (LF/HF). There are alsononlinear methods that can be used in the analysis of theHRV signal, among these the Poincare plot which gives twoparameters SD1 and SD2 in addition to providing a tool forvisual inspection.
The HRV is related to the autonomous nervous systemwhich controls many functions of health in the body. Theautonomous nervous system is divided into the sympatheticnervous system which is responsible for increasing heart rate,and the parasympathetic nervous system which is responsiblefor decreasing heart rate. Therefore, all the previous parame-ters can be related to parasympathetic or sympathetic activ-ities. In this sense, the SDNN mostly reflects the very-low-frequency fluctuations in heart rate behavior and it correlatesto the total HRV power [2]. The rMSSD correlates morewith the parasympathetic (vagal) activity (high frequencypower) [2,3]. The LF Power in range 0.04–0.15 Hz repre-sents a mixed influence of sympathetic, parasympathetic andbaroreflex activities [3], while HF power in range 0.015–0.4 Hz represents the parasympathetic activity [3], and thisHF band represents the respiratory sinus arrhythmia due toparasympathetic cardiovascular activity. On the other hand,the total power intervals represent the global activity of theautonomic nervous system. The LF/HF ratio represents tosome extent sympathovagal balance [3], and variability isused to indicate changes in the autonomic nervous system.
The HRV parameters are studied in the literature underdifferent conditions, namely mental stress, panic disorder,smoking, diabetes, and many other factors. In a study of theHRV and HR in healthy volunteers [4], the authors studied allthe HRV parameters. They found that all parameters, exceptfor PNN50 and HF, were higher in men than women. Gen-der difference was confined to age categories <40 years. Themajority of HRV parameters decreased with age. In a short-term HRV study [5] of the HRV in students during examina-tions, the mean beat to beat interval was significantly lower atthe time of examination, SDNN and total spectral power weresignificantly reduced during examination, and LF, HF and theLF/HF ratio were not significantly different. In a study of theeffect of music therapy on HRV [6], the authors found thatthe following parameters VLF, LF, HF increase significantlyafter music treatment, while the LF/ HF ratio has no signifi-cant change. In addition, they suggested that relaxing musiccan increase the activity of parasympathetic nervous system.In a study on the vagal modulation and aging [7], the mainfindings were that senior competitive athletes have increasedoverall HRV and vagal modulation of HR when comparedwith their sedentary counterparts. HRV parameters had a pos-itive correlation with aerobic fitness and a negative correla-tion with obesity. Time–Frequency study [8] of HRV signalin prognosis of Type 2 diabetic autonomic neuropathy foundthat SDNN, rMSSD, NN50 count, pNN50 count, Triangularindex were significantly decreased in DM patient group com-
pared to normal controls. Mean heart rate of the DM patientswas significantly higher than that of the control group. VLFpower, LF power, LF % power, HF power of the HRV dataof DM patients were significantly lower than control group.There was no significant difference in LF peak, HF peak, andLF/HF ratio. In a another comparative study of music and softtissue massage on heart rate variability [9], there was no sta-tistically significant difference in LF/HF between the fourintervention studies. In addition, for each of the interven-tion studies, there was no statistically significant differenceamong pre-intervention, intervention and post-intervention.In the sub-group of low heart rate responders, an increasein LF/HF indicating sympathetic dominance in response tomassage was found. In Power spectral study [10] of HRVduring mental workload, they found that there were signif-icant group differences for the LF components at the taskperiods. There were also significant group differences forthe HF components at the pre-task period, task periods, andpost-task period. There were significant differences for theLF/HF ratio between Type As and Type Bs not only dur-ing the task periods but also during the resting period. It isfound [11] that HRV was negatively associated with smok-ing, C-reactive protein, white blood cell count, blood sugarand triglyceride concentration, female gender, and diabetes.Physical activity was strongly associated with higher heartrate variability.
In this paper, we compare the HRV at rest to that obtainedwhile listening to Quran. The authors in [12] studied the effectof Quran as part of a whole study and as a verification oftheir software development. Here, we present the completestatistical analysis of the HRV parameters. In addition, wepresent the use of data displays called circle plots [13] forvisual inspection of the variability as an alternative to theScatter plot or the Poincare plot. Circle plots [14] use thecircular (ϕ, r ) coordinate system, ϕ ordinates are assigned tothe reconstructed data such that the points are at equal angulardistance dϕ, where dϕ = 2π/n, n is the total number of theR–R intervals. For the reconstructed plot, r = 1 is assignedfor all data points, which results in the unity circle centered atthe origin. For each R–R interval, the angular distance ϕi forthe ith data point is at i(2π/n), and the radial distance r is setfrom the origin at a ratio of the value of the R–R interval to R–R intervals mean. Once the circles plot is constructed, it canbe used to establish a preliminary view of the R–R intervalsvariability around the mean. In other words, the dispersionof the points from the unit circle reflects the degree of heartrate variability.
2 Method
A total of 19 healthy male university students at the age of20–22 years are volunteered to participate in this study. After
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Table 1 Paired samples t-test results
Paired samples test
Paired differences t d f Sig. (2-tailed)
Mean Std. deviation Std. error mean 95 % Confidence intervalof the difference
taking a written consent, the ECG (lead II and lead III) isrecorded for each subject for a period of 20 min while atrest and 20 min while listening to Quran through a headsetthat has good isolation from outside noise. The subjects weredivided into two groups. In the first group, the rest ECG wasrecorded in one day and the listening ECG was recorded ina different day but around the same time of the day knowingthat the HRV parameters do not change. In the second group,the rest ECG was recorded for 20 min followed by another 20min while listening to Quran. The two groups are statisticallytreated as one group consisting of all subjects at rest as thecontrol set (group A) and while listening to Quran as thevariation group (group B).
The ECG signal is pre-processed and furthermore visuallyinspected for ectopic beats or any abnormalities. The HRVsignal is then constructed from the ECG by detecting the Rwaves and then forming the R–R intervals. Any abnormal R–R intervals were removed from the signal. We used the HRVanalysis routines available at [15] to obtain the time domain,frequency domain, SD1, and SD2 parameters.
3 Results and Discussion
A normality test of the data distribution is applied on each ofthe parameters to determine the significant test to use. Thefollowing parameters were found to be normally distributed:Mean, SDNN, SDANN, and rMSSD, therefore, paired sam-ples t test is used to test for the significance. The other para-meters (aLF, aHF, aTotal, pLF, pHF, LF/HF, peakLF, peakHF,
SD1 and SD2) were found to be not normal and hence theWilcoxon test is used. The results of the significant test areshown in Tables 1 and 2, where the subscript A represents thedata obtained while at rest and the subscript B refers to thedata obtained while listening to Quran . From the table wecan conclude the following: there is no significant differencebetween the means of the R–R intervals (or the heart rate),i.e., there is no change in the mean heart rate before listeningand while listening. There is a significant reduction in theSDNN, rMSSD while listening to Quran, meaning that theHRV is reduced while listening. There are no changes in thefrequencies where the low and high peak power occur, whilethere is a significant reduction of all other parameters (aLF,aHF, aTotal). The reduction in the LF, HF powers confirmswith that obtained in [12]. However, the HF power in nor-malized value (pHF) does not show a significant change. Theimportant conclusion that can be inferred from the table isthe following: while listening to Quran, heart rate does notchange significantly while there is a reduction in the heartrate variability, and reduced LF power indicating reducedsympathetic activation.
In most cases studied in the literature, there is a change inthe mean heart rate combined with a change in the LF, HF, orboth. However, reduced variability has been found as a resultof listening to Quran without change in the mean heart rate.Therefore, we believe that the conclusion found in [2] is validhere and can be stated that lower sympathetic activity andlow lower frequency power may provide protection againstarrhythmias and against the development of coronary heartdisease.
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Fig. 1 Circle plots of selected subjects: for each subject, the red (left) is the rest R–R interval, the blue (right) is the R–R intervals while listening
The variability can be seen visually using the circle plotsshown in Fig. 1 where the more the dispersed points thelarger the variably. These plots are examples of the subjects’HRVs before and while listening to Quran, where we can seethat the plot to the left is more dispersed than the one to theright for each subject indicating reduced variability or morespecifically (SDNN).
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