Heart rate unevenness ( HRV ) is a particularly valuable quantitative marker of the flexibility and libra of the autonomic skittish system. significant advances in software programs to mechanically derive HRV have led to its extensive use in psychophysiological research. however, there is a miss of taxonomic comparisons across software programs used to derive HRV indices. Further, researchers report meager details on authoritative signal process decisions making deduction across studies challenging. The draw a bead on of the present study was to evaluate the measurement fidelity of time- and frequency-domain HRV indices derived from three prevailing signal serve software programs normally used in clinical and inquiry settings. Triplicate ECG recordings were derived from 20 participants using identical data learning hardware. Among the time-domain indices, there was strong to excellent symmetry ( ICC avg =0.93 ) for SDNN, SDANN, SDNNi, rMSSD, and pNN50. The frequency-domain indices yielded excellent correspondence ( ICC avg =0.91 ) for LF, HF, and LF/HF ratio, except for VLF which exhibited inadequate parallelism ( ICC avg =0.19 ). rigorous user-decisions and technical specifications for nuanced HRV serve details are essential to ensure measurement fidelity across sign march software programs. A significant challenge exists for researchers who want to compare or synthesize HRV results across studies. In a systematic review on short-run HRV measures, Nunan et alabama. ( 2010 ) found well large variations across studies, specially for frequency-domain variables. These discrepancies were attributed to differences in sketch design and methodology, angstrom good as failure from authors to provide pertinent data on signal action and data clean procedures. The importance of calibration across studies was reinforced by the Task Force ( 1996 ) guidelines in hopes to facilitate the exchange of cognition, allow for comparative results across studies, and avoid conflicting data due to unlike technical and methodological approaches. Following these recommendations for standardization and interpretation of HRV measures, the purpose of the stage analyze was to evaluate the measurement fidelity of HRV indices derived from three overriding signal action software programs most normally used in clinical and research settings among cardiologists, psychophysiologists, and other researchers across diverse disciplines ( MARS, MindWare, Kubios ). Using triplicate ECG data derived from identical data skill hardware, the comparison of HRV indices for time-domain ( i.e., SDNN, SDANN, SDNNi, rMSSD, pNN50 ) and frequency-domain variables ( LF, HF, LF/HF ratio ) was tested. Despite its extensive habit, the comparison between standard calculator HRV software programs has not been systematically evaluated. There is light attest of comprehensive examination comparisons to assess the fidelity of sign process across multiple software programs. Of the only sketch to compare HRV signal processing programs, Jung et aluminum. ( 1996 ) found time- and frequency-domain variables were not comparable across four programs in widespread use at the clock about two decades ago. Jung attributed the bombastic unevenness across programs to different technical specifications, including meter choice methods ( for example, best complex, time-coherent average, extraction ), sampling frequency, interjection, and algorithm. Another significant decision for spectral analyses includes windowing. apparitional windowing involves the application of a window function, of a assign width, to shape the time helping of ECG data by overlapping wave form endpoints in a fluent, continuous way without sharp transitions to minimize edge effects that result in spectral escape for better overall spectral resolution. Hamming or Hanning windows are normally used due to their high quality frequency resolution and reduce spectral escape ( Bloomfield, 1976 ; Harris, 1978 ).

Frequency-domain variables are based on apparitional analysis of RR intervals ( Lahiri et al., 2008 ). Power apparitional density decomposes RR intervals into their cardinal frequency components and provides information on the distribution of world power as a affair of frequency. spectral analyses can include parametric ( autoregressive ; Yule–Walker, Burg ) or nonpara-metric methods ( Fast Fourier Transform, FFT ; Kim et al., 2009 ). FFT is most normally used to calculate the maximum unevenness in kernel period series, based on ranges of frequency-specific oscillations of the RR intervals that reflect different branches of the cardiac organization ( Lahiri et al., 2008 ; Spiers et al., 1993 ). traditionally, the autonomic nervous system ( ANS ) has been thought to be inversely balanced ( i, as one ramify of the ANS increases activeness the other branch decreases activity ) ; however, evidence suggests that parasympathetic and sympathetic outflows are distributed multidimensionally ( Berntson et al., 1991 ). As such, HRV and each of its components are peculiarly valuable quantitative markers that provide information on the flexibility and balance of the branches of the ANS based on heart period series ( Berntson et al., 1997 ; Task Force, 1996 ). The Bland–Altman method acting is used to diagrammatically display the degree of agreement between two techniques on a continuous variable and to assess potential constant and proportional biases ( Bland and Altman, 1986, 2003 ). The differences in the measurements are plotted against the mean values of these measurements. If 95 % of the differences fall within the limits of agreement ( 1 SD ) there is no systematic pas seul across programs ( Bland and Altman, 1986, 2003 ). To detect constant diagonal ( i.e., the average discrepancy between methods of measurements ), the mean bias and limits of agreement are used and should be close to zero. To detect proportional bias, ocular inspection of the diagram graph is normally used ; however, standardized β values can be used to test whether the slope is importantly different than zero ( i.e., when base values are regressed onto mean differences ). To assess measurement fidelity across the three software programs, Intraclass Correlation Coefficients ( ICC ), Pearson Correlation Coefficients, and Bland–Altman statistical methods were computed. An ICC is a measure of agreement between two or more evaluation methods on the same datum that allows for fixed and random effects. Data are assumed to be parametric ( continuous and normally distributed ). ICCs typically range from 0 to 1, but can exceed −1 or 1, which may be attributable to patterns of negative and positive correlations among the methods, limited discrepancy in the data matrix, or no correlations among methods ( Lahey et al., 1983 ). ICCs are categorized as very poor ( 0–0.2 ), fair ( 0.3–0.4 ), control ( 0.5–0.6 ), potent ( 0.7–0.8 ), or excellent ( 0.9–1.0 ; Shrout and Fleiss, 1979 ). ICCs are deemed advantageous over bivariate correlation coefficients as they represent the agreement between two or more methods, and importantly, adjust for the effects of the scale of measurement. In other words, ICCs history for differences in rate order and mean differences between methods ( data centered and scaled using pool mean across methods and standard diversion ), while correlations entirely account for rank order differences ( data centered and scaled using each method ‘s own mean and standard diversion ). Nevertheless, Pearson Correlation Coefficients were computed for comparison purposes. analysis of discrepancy ( ANOVA ) was besides used to test omnibus hateful differences of the HRV parameters, followed by contrasts using match samples t-tests. All data were entered and double-checked by the senior data coordinator and analyzed with IBM SPSS Statistics 20 software ( SPSS, Inc., Chicago, IL ). Data were kept continuous and checked for normality and one-dimensionality using boxplots and histograms. Assumptions of additivity, homoscedasticity, uncorrelated error, and random excerpt of participants were tested ( Shrout and Fleiss, 1979 ). Signal process specifications for detector algorithm and interjection methods were based on nonpayment settings ( adjustable ; refer to ). ocular inspection of the beat-by-beat RR intervals were measured and identified based on template pit and proprietorship algorithm. The sample frequency was based on beat-by-beat RR intervals and mechanically filtered, where RR intervals were divided into 5 min non-overlapping segments. As recommended by Kubios, based on ocular inspection using the graphic interface, an artifact correction degree ( stove from none to very potent ) was selected for each date charge. Each correction flush applies thresholds ( very low : 0.45 s, abject : 0.35 sulfur, medium : 0.25 s, impregnable : 0.15 south, very strong : 0.05 mho ) that are scaled with a heart pace of 60 beats/min. scale is used to adjust for heart rate changes within the recording ( i.e., higher heart pace applies greater thresholds ). High-pass filters on RR time interval series remove all baseline changes from the data file, and from this detrended data, any beats that exceed the respective thresholds are identified as artifacts and removed ( M.P. Tarvainen, personal communication, March 21, 2012 ). Because data clean is limited to this gross classification to detect artifacts, Kubios recommends that artifact correction degree should not be selected blindly, but should include manual ocular inspection and confirmation of the correction level selected within the graphic interface. continuous heart period series were corrected by piecewise cubic spline interpolation method at the default rate of 4 Hz ( adjustable ). Using a window width of 256 sulfur ( window overlap of 50 % ; adjustable ), samples were smoothed anterior to detrending, tapered using a Hanning windowpane, and processed by the Welch ‘s periodogram method. apparitional analyses were performed on a series of RR intervals and were inaugural linearly detrended using a Hanning window and processed by FFT standard office spectrum method acting. All time- and frequency-domain variables were mechanically calculated for each 5 min era and averaged across the entire recording period, except for SDANN and SDNNi, which were manually calculated using standard formula ( Task Force, 1996 ). Signal processing specifications for detector algorithm could be manually overwrite, and included inter-beat-interval determine and automated Minimum Artifact Deviation and Maximum Expected Deviation ( MAD/MED ) algorithm ( Berntson et al., 1990 ). For the present study, 5 min analytic epoch and both detector algorithm were applied. R-peak detection was based on default digital low- and high-pass filters set within appropriate frequency ranges ( 0.05 and 35 Hz, respectively ; adjustable ). Frequency bandwidths were user-defined for LF ( 0.04–0.15 Hz ) and HF ( 0.15–0.40 Hz ). Beat-by-beat ocular inspection of the form, tendency, and length of each QRS building complex datum was displayed on a full graphic interface. electrocardiogram signals were sampled at 1000 Hz and RR filter was automatic ( manual trickle available ). RR intervals that were excluded due to indecipherable signals or recognition error were replaced by cubic slat interjection and resampled at a frequency of 33.33 Hz. For spectral analyses, trending, interpolation rate, interpolation method, and windowing options ( for example, windowpane width and overlapping ) were based on nonpayment settings. Heart period series were linearly detrended, tapered using a Hanning window, and processed by FFT periodogram spectrum method. Time-and frequency-domain parameters were mechanically calculated for each 5 min era across the entire datum file. HRV parameters were then mechanically averaged across the entire record menstruation. Signal action specifications for detector algorithm and interjection methods were based on nonpayment settings ( refer to ). Detector algorithm want at least 5 min of data to calculate HRV indices ( adjustable ). Beat-by-beat ocular inspection of the form, tendency, and length of each QRS complex were measured and identified based on template match and standard Marquette algorithm for QRS pronounce. ECG data was sampled at diverse rates resulting in QRS timing at different resolutions ( 1024 samples/300 s ) and RR percolate was automatic ( manual of arms filter available ). The removal of artifacts was based on a 20 % change from the previous bespeak as a criterion ( Kleiger et al., 1987 ). In cases where artifacts and excluded RR intervals were mechanically filtered and identified as indecipherable signals, the remaining acceptable beats were used to replace the datum points via cubic slat interpolation method acting. At least 4 acceptable R-peaks were needed in order for slat interpolation to identify the continuous affair between two middle R-peaks. If there was no datum in the first gear segment ( e.g., noise ), then RR interval series were interpolated from the default heart rate of 70 beats per minute ( adjustable ). Beat-by-beat intervals with approach millisecond measurement of continuous ECG data were required for data cleaning. Missed or unidentified R-peaks by each respective platform ‘s detector algorithm were manually relabeled ( refer to ; data cleaning section ). In junction with each software course of study ‘s automated cleaning operation, pre-defined clean guidelines adhering to the recommendations in the adept committee reputation were used by a aim research worker to accurately discriminate QRS complexes ( Berntson et al., 1997 ). If an R-peak was automatically detected, but upon ocular inspection was not found to be accurate, ≥2 shortstop inter-beat-intervals were added to retain the integrity of the heart period series. If an R-peak was not mechanically detected, the postdate guidelines ( in social station order ) were applied : 1 ) RR time interval distance from cleaned ECG recording sample was measured, 2 ) R-peak was estimated from remaining datum points, and 3 ) long R-peak were split into ≥ 2 adequate RR intervals ( Berntson et al., 1997 ). ECG Holter tapes were converted and digitized into Waveform Audio ( WAV ) version using a high-grade contemporary dual capstan deck unit. WAV files were imported into shareware software for recording and editing audio files ( Audacity® v.1.2 ; hypertext transfer protocol : //audacity.sourceforge.net ). The accelerate of the sound recording signal was resampled and the duration, flip, and frequency were optimized to yield clear high-quality ECG signals. then, using a 4-channel high-level interface module in the BioNex 2SLT Chassis Assembly ( MindWare Technologies Ltd., Columbus, Ohio, USA ) and the Biolab 3.0 data acquisition software ( 16-bit A/D conversion ) the resampled digital data files were imported ( sampled at 250 ks/s rate ), converted, and formatted into MindWare ( MW ) files, while preserving the integrity of the signal. One set of sensitive MW formatted data files were imported into MindWare® HRV Scoring Module v.3.0.17 ( MindWare Technologies Ltd., Columbus, Ohio, USA ). A duplicate sic was converted into ASCII textbook files and imported into Kubios® HRV v.2.0 ( University of Eastern Finland, Kuopio, Finland ; Niskanen et al., 2004 ). It is important to note that all software programs were used without applying any ad hoc custom-made act changes ( i, all default settings and specifications were maintained ). The only exception was the adaptation of the default option frequency bandwidths for LF and HF in MindWare ; these were adjusted in accord with the Task Force ( 1996 ) guidelines. Signal processing and default specifications are outlined below for each software program. ECG Holter tapes undergo identical serve procedures for each software program. Triplicate ECG datum signals were derived from each of the 20 recordings. Each triplicate ECG recording was cleaned by a qualify detective and independently car scored with all three signal process software programs rigorously adhering to both Task Force ( 1996 ) guidelines and manufacturer specifications ( described in contingent below ; visualize ). ECG data was derived from a modified Lead II shape using disposable, pre-gelled snap eloquent chloride electrodes. Electrode resistance was minimized ( < 10 knockout ) by precleaning the skin with rubbing alcohol swab. The active electrode ( and its derivative/dZ ) was placed on the right clavicle next to the sternum over the first rib between the two collarbones. The second electrode was placed on the left mid-clavicular line at the apex of the kernel over the ninth rib. The ground electrode was placed near the lowest possible right rib batting cage on the abdomen. Additional dZ electrodes were placed over the right fourth intercostal quad at the sternal edge, the fifth intercostal space at the left axillary line, and on the sixth ridicule in the mid-clavicular line. To reduce potential violations of stationarity, the ECG acquisition procedure was standardized and kept reproducible for all recordings ( Berntson et al., 1997 ). The cogitation was reviewed and approved by the St. Justine Hospital Institutional Review Board ( # 2040 ). Twenty Holter tapes with sensitive ECG data were randomly chosen from an ongoing study of healthy young person participants between the ages of 8 and 11 ( M old age =9.93 years, SD =1.02 ; 55 % male ). The dispatch research protocol is described elsewhere ( Lambert et al., 2011 ). All ECG recordings were reviewed by a board-certified cardiologist ; no cardiovascular pathology was identified ( i.e., bradycardia, fibrillation, premature contraction ). During the standardize protocol conducted in a hospital place setting, continuous raw ECG data were acquired using the 8500 Marquette MARS Holter monitor ( GE Marquette Medical Systems, Milwaukee, Wisconsin, USA ), digitized ( 128 Hz ), and recorded on a frequency modulated cassette recorder. The Holter monitor incorporated a quartz-derived, binary time channel that was mechanically zeroed at the begin of the recording. ECG skill began in the dawn between 8 and 9 am and lasted approximately 2.5 h. Bland–Altman plots and analyses were conducted to assess measurement fidelity for each HRV parameter paired by software programs ( 30 plots not depicted for parsimony ). For each HRV parameter, the differences between each of the pair software programs were plotted against the average values of these measurements. coherent with the recommendations outlined by Bland and Altman ( 1986, 2003 ), data were log-transformed anterior to the calculation of limits of agreement when heteroscedasticity was present. There was no tell of changeless or proportional biases for any of the time-domain variables : SDNN ( Bias avg =0.02, [ Limits of Agreement avg =−0.03, 0.08 ] ; β avg = −0.07 ), SDANN ( Bias avg =0.04, [ −0.05, 0.14 ] ; β avg =0.05 ), SDNNi ( Bias avg = 0.03, [ −0.06, 0.13 ] ; β avg =−0.16 ), rMSSD ( Bias avg =0.09, [ −0.00, 0.19 ] ; β avg =0.07 ), and pNN50 ( Bias avg =0.07, [ −0.09, 0.25 ] ; β avg =− 0.06 ). similarly, no ceaseless or proportional biases were observed for the frequency-domain variables : VLF ( Bias avg =0.70, [ 0.43, 0.96 ] ; β avg = −0.00 ), LF ( Bias avg =0.10, [ −0.02, 0.22 ] ; β avg = −0.19 ), HF ( Bias avg =0.13, [ −0.01, 0.29 ] ; β avg =0.22 ), and LF : HF ratio ( Bias avg =0.10, [ −0.02, 0.22 ] ; β avg = −0.11 ). all in all, the results from the ICCs and Bland–Altman analyses were congruous. ICCs were computed to compare the fidelity of HRV scoring across the software programs ( see ). Among the time-domain indices, there was potent to excellent symmetry across all software programs for SDNN ( ICC avg =0.96 ; radius avg =0.97 ), SDANN ( ICC avg =0.93 ; roentgen avg =0.88 ), SDNNi ( ICC avg =0.96 ; r avg =0.97 ), rMSSD ( ICC avg =0.80 ; gas constant avg =0.93 ), and pNN50 ( ICC avg =0.98 ; radius avg =0.99 ). Among the frequency-domain indices, there was excellent parallelism across all software programs for LF ( ICC avg =0.90 ; roentgen avg =0.94 ), HF ( ICC avg =0.91 ; gas constant avg =0.96 ), and LF/HF ratio ( ICC avg =0.95 ; gas constant avg =0.93 ). however, VLF exhibited poor commensurateness ( ICC avg =0.19 ) ; these findings may be largely attributable to the significant hateful floor differences observed across software programs ( see ). Pearson coefficients revealed moderate correlations for VLF when hateful flat differences are not considered ( r avg =0.83 ).

The average distance of the 20 ECG recordings was 131 min ( SD= 46 ). All ECG recordings were inspected manually to review flower detection and to identify and remove artifacts. manual editing took approximately 25 min per ECG recording. Recordings were found to be of excellent timbre ; over 90 % of data were analyzable, artifact meter did not exceed 1500 south ( 5.2 % ), and no recordings were found to exceed 20 % noise or ectopic beats .

4. Discussion

recent advances in the automatize analyses of HRV offers an accessible and alone access for quantifying the effects of sympathetic and parasympathetic nervous system branches of the ANS. Despite testify of the dependability of HRV parameters across different recording devices, measurement protocols, and maneuvers ( Dietrich et al., 2010 ; Faulkner et al., 2003 ; Pinna et al., 2007 ; Sandercock, Shelton and Brodie, 2004, 2005, 2003 ), there is no available information on the fidelity of commercially available signal processing software programs presently in consumption ( Jung et al., 1996 ). The bearing of the present report was to evaluate the measurement fidelity of HRV indices derived from three normally used signal action software programs. Following rigorous calibration ( i.e., data collection, march, cleaning ), excellent measurement fidelity for time-domain variables ( for example, SDNN, SDANN, SDNNi, rMSSD, pNN50 ) was observed across programs. excellent symmetry was besides observed for LF, HF, and LF/HF proportion. Poor correspondence was found for VLF ; however, examination of the Pearson correlation indicates a moderate affiliation across software programs. The excellent comparison for HRV variables is probably attributable to similar sign processing techniques and pivotal user-defined specifications across software programs ( i.e., R-peak detection algorithm, identical analytic epoch length ). For case, the use of algorithm analogue to the Pan-Tompkins for the recognition of QRS complexes was apparent across all software programs ( Pan and Tompkins, 1985 ). As such, the ECG sign is passed through an automated low- and high-pass percolate to remove make noise. After filtering, the signal passes through derivative ( to obtain QRS slope ), squaring ( to emphasize higher frequencies ), and window integration phases ( to identify wave form patterns ), where last, a threshold method is applied and R-peaks are detected. As for the frequency-domain variables, windowing options ( i.e., width and overlap ) and frequency bandwidths must besides be taken into retainer ( Task Force, 1996 ). In the present study, all software programs applied linear detrending method, cubic slat interpolation, with similar windowing ( Hamming and Hanning ) and spectrum methods ( Periodogram and Welch ‘s periodogram ). User-defined data reduction decisions can have meaning implications on the automatic analysis of HRV parameters. Short analytic epoch ( e.g., 1 minute ) and recording durations ( < 18 h ) may fail to capture the wide spectrum of components or underlying circadian cycle ( Massin et al., 2000 ; Task Force, 1996 ). For case, the lowest frequency that can be assessed with 1 min is 0.016 Hz ( G. Berntson, personal communication, December 15, 2011 ), indicating that it does not quantify the entire spectrum of VLF components. therefore, to capture data at the lowest frequency, larger analytic era durations must be chosen ( for example, 3 to 5 min ; Task Force, 1996 ). Further, the established physiological components and frequency bandwidth ranges are less chiseled for VLF, as compared to HF and LF ( Berntson et al., 1994 ; Cacioppo et al., 1994 ). analytic epoch length, recording durations, and frequency bands should be consistent when making comparisons of HRV. Given that technical specifications for data cleaning vary across programs, it is essential to know whether programs allow for manual inspection ( i.e., some permit coincident automatic and manual clean and editing decisions ). For case, MindWare offers users much flexibility to visually inspect and adjust RR fiducial points and identify crucial event markers ( for example, during tasks ). In line, Kubios suggests visually inspect data and applying an automated artifact correction based on gross categorization levels ( for example, humble ). Given the sensitivity of certain HRV parameters ( for example, rMSSD ; Salo et al., 2001 ), the flush of gross artifact correction may be appropriate for some variables, while less appropriate for others. Taken together, these specific user-defined decisions likely account for the especial commensurateness across software programs. The portray study yields original findings indicating the robust comparison for HRV across normally used bespeak process programs. While proprietorship detector and interpolation algorithms are typically set, the excellent parallelism across software programs is largely attributable to apparently nuanced, however meaning decisions. These include decisions related to the modification of finical user-defined and nonpayment settings ( for example, analytic epoch duration, frequency-bandwidths ), use of clean tools ( for example, survival of appropriate artifact correction grade ), and implicit in procedures in each software plan ( e.g., removing partial inter-beat intervals prior to data psychoanalysis ). prior to selecting bespeak march software, the conceptualization and sympathy of HRV physiologic indices is imperative. There is growing pastime and advancements using neuroimaging techniques ( for example, functional magnetic resonance imaging ) to better understand neurobiological ( brain–body ) interactions ( c.f., Gianaros and Sheu, 2009 ; Gianaros et al., 2004 ). For example, HF has been associated with activeness within the ventral anterior cingulate ( Matthews et al., 2004 ), back tooth cingulate cortex ( O'Connor et al., 2007 ), amygdala, periaqueductal gray, and the hypothalamus in reply to somatosensory stimuli ( Gray et al., 2009 ) and isometric line use ( Napadow et al., 2008 ). Given the evidence of an association between the brain and the ANS ( i.e., parasympathetic nervous system and charitable activeness ), these promising inquiry directions underscore the importance of purposeful and informed choice of HRV parameters. Consider, if the research doubt centers around assessing parasympathetic nervous system natural process, it is necessary to select HRV parameters that validly reflect this activity in the ANS ( for example, HF, pNN50, rMSSD ; Task Force, 1996 ). This in become will immediately impact decisions related to methodological design and measurement issues, including the recommended commemorate distance to capture parasympathetic activity ( for example, 1 minute ), and an campaign to minimize non-stationarity across conditions and participants, peculiarly for frequency-domain variables ( Task Force, 1996 ). other decisions may include whether recordings will be partitioned by job or time interval ( for example, baseline vs. tax, sleep vs. wake state ). similar issues were articulately raised in a exhaustive review by Nunan et alabama. ( 2010 ) investigating normative HRV values from short-run recordings in healthy adults. Taking these pivotal methodological decisions into consideration will facilitate comprehensive systematic comparisons across studies and promote advance the field .

4.1. Post-hoc observations

4.1.1. Kubios

several researchers report using an understudy strategy to clean data prior to using Kubios by deleting aberrant inter-beat intervals less than 300 and greater than 1200 ms ( c.f., Capa et al., 2011 ; Li et al., 2009 ; Rodríguez-Colón et al., 2011 ; Timonen et al., 2006 ). Data were re-analyzed with Kubios after applying this normally reported data cleaning scheme. Post-hoc analyses revealed no meaning differences across software programs for both time- and frequency-domain variables when this data clean strategy was applied ( data not shown for meanness ) .

4.2. Strengths and limitations

The first limit of the show study was the consumption of short-rather than long-run recordings ( i, 3 vs. 24 heat content ). however, many studies typically record for similarly short durations. In keeping with the recommendations by the Task Force ( 1996 ), the stage learn adhered to a rigid protocol for the skill, recording, collection, clean, and analyses of the data under standardize settings to minimize measurement error. The second gear limit was the habit of only three software programs for comparison. These programs were intentionally selected due to their omnipresent use within clinical and research settings among psycho-physiologists, cardiologists, and general researchers. however, it is authoritative to recognize there are extra commercially available adenine well as investigator-created software programs ; however, their inclusion was beyond the setting of the give study. future comparisons should be conducted using other software programs. The third base limit was the judgment of lone time- and frequency-domain variables. Geometric ( for example, trilateral shapes of Lorenz plots ) and nonlinear methods ( for example, detrended fluctuation psychoanalysis, approximate information ) can besides be used to analyze HRV ( Pincus, 1995 ; Porta et al., 2001, 2007 ; Richman and Moorman, 2000 ; Task Force, 1996 ; Voss et al., 2009 ). however, these methods largely depend on the preciseness of equipment ( i.e., obtain appropriate issue of RR intervals ), recording length ( i.e., preferably 24 heat content for geometric methods ), and capability of these advanced analyses in software programs. Time- and frequency-domain variables are traditional HRV parameters reported in the majority of studies ; therefore, the comparison of these specific parameters was deemed peculiarly crucial to inform future comparisons and syntheses across published studies ( Task Force, 1996 ). last, all ECG recordings were derived from a Holter monitor manufactured by GE Marquette, the same manufacturer of MARS software plan. however, it is improbable that having a coarse manufacturer created any bias for the MARS software analyses. In fact, a major military capability of the present study was the consumption of identical ECG recordings in triplicate for the three software programs. In other words, each software plan analyzed the exact same ECG datum. frankincense, these findings are generalizable to the scenario quite coarse in research and clinical settings when hardware and software manufacturers differ .

4.3. Recommended strategies

Although there are an increasing number of studies investigating HRV, the methodological, measurement, and technical specifications are not systematically applied in the field. These discrepancies add confusion to the rendition of HRV and hinder progress in the sphere because findings can not be synthesized. Hence, to maximize measurement fidelity researchers must be aware of these subtle, so far pivotal very well details when using software programs. Two recommend strategies are provided .

4.3.1. Equipment and software specifications

Differences across user-defined choices and specifications of software programs may contribute to HRV discrepancies across studies. Researchers should report specific information about the recording equipment, sign ( pre ) march software, software applications, and features selected ( for example, sampling rate of 250–500 Hz or higher, RR interval filter characteristics, R-peak signal detection and interjection algorithm ). Further, if frequency-domain variables are analyzed, extra information on the apparitional decomposition method acting, apparitional windowing, window overlap, and the define compass of frequency bandwidths should be specified.

4.3.2. Data reduction and cleaning

Data reduction and cleanse decisions anterior to HRV analysis ( either by default or adjustable settings ) should be explained and justified. For model, because the removal of erroneous beats or the unintentional removal of normal beats may affect the analysis and the comparison of HRV parameters ( Berntson et al., 1997 ; Berntson and Stowell, 1998 ; Xia et al., 1993 ), the rationale for any exclusion criteria should be clearly stated. furthermore, to facilitate systematic comparisons and synthesis of data, it is important to provide complete information on data reduction decisions. These include justification for how the data were segmented or partitioned for aggregating ( for example, conditions, tasks, restraint vs. clinical groups ), cleaning ( for example, duration of analytic era ), and analyzing ( for example, night vs. sidereal day ). Complex cogitation designs ( for example, multiple discreet intervals ) may warrant use of software that permits greater flexibility for user-specifications and manual of arms clean ( i.e., Mindware ). Regardless of what equipment or software is used, drift artifacts, technical bankruptcy, or poor data quality can seriously contaminate the integrity of the data. Despite the crucial tax of manually cleaning data, specific procedures and decision rules are rarely reported. basic information on the RR time interval mistake identification, removal, criteria ( for example, thresholds ), and correction procedures should be provided .

4.4. Future research

future studies should assess the measurement fidelity of time- and frequency-domain HRV variables with longer recordings ( for example, 24 henry ), under differing conditions ( for example, day vs. night ), and in reception to standardized challenges ( for example, stress test, cold vasoconstrictor reactivity ). Additional geometric methods ( i.e., HRV triangular index ) should besides be considered. Further, comparisons could be made for HRV parameters derived from different recording hardware and then analyzed with different software programs, as this would be a more ecologically valid contemplation of the divers practices across the research field. The contribution of the deliver study highlights the importance of providing sufficient detail about the sign acquisition hardware, the bespeak process software, and the overall procedures used to derive HRV variables. last, given that guidelines to specify standard definitions of HRV terms and measurement methodology were published about two decades ago ( for example, Task Force, 1996 ; Berntson et al., 1997 ), there is deservingness in the marriage proposal of updating the critical considerations in HRV analyses ( for example, Nunan et al., 2010 ) .

4.5. Conclusion

The introduce report demonstrated that rigorous decisions and specifications for subtle details are instrumental in the acquisition of excellent measurement fidelity across three normally used HRV signal process software programs. specifically, signal work, data scavenge, analysis, and interpretation specifications must be meticulously selected to enhance the preciseness of HRV data and should not be lowball. Given the significance and value of comparing and synthesizing results across studies, it is all-important for researchers to understand and accurately report the technical specifications applied for HRV analyses .

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