HRV

Overview:

Heart Rate Variability (HRV) is one of the most promising and popular markers of cardiac autonomic activity because it is an easy measurement. It is usually measured by analyzing the time series of beat-to-beat intervals from ECG (R-R intervals) or arterial pressure tracings.

The European Society of Cardiology and the North American Society of Pacing and Electrophysiology Task Force has defined HRV to describe variations of both instantaneous heart rate and RR intervals (oscillation in the interval between consecutive heartbeats).



Reduced HRV has been commonly used as a marker of reduced vagal activity but since HRV is derived from the ECG, it is not possible to distinguish if this is due to reduced activity in the vagal centers of the brain or from reduced peripheral activity. However, HRV still seems to be a marker of both dynamic and cumulative load, where HRV appears to be sensitive and responsive to acute stress as a dynamic marker of load. For example, under laboratory conditions, mental load such as making complex decisions, and public speech tasks have been shown to lower HRV. As a marker of cumulative wear and tear, HRV has also been shown to decline with the aging process.

Therefore, HRV seems to be a marker of two processes:

  • Frequent activation - short term dips in HRV in response to acute stress
  • Inadequate response - long-term vagal withdrawal, resulting in the over-activity of the counter-regulatory systems

 

Method:

Methods of measuring heart rate variability can be subdivided into time domain and frequency domain measurements.

Overview of HRV analysis methods from an ECG recording, where NN are the normal-to-normal intervals between adjacent QRS complexes.

Time Domain
It is simple to perform using the heart rate at any point in time or the intervals between successive normal complexes and the variables that can be calculated include mean NN interval, mean heart rate, difference between the longest and shortest NN interval. There are several methods to determine the HRV in the time domain.

Statistical Methods
These measures calculated complex statistical time domain measures from a series of instantaneous heart rates or cycle intervals, recorded typically longer than 24 hours. These recording durations should be standardized. The usual or recommended methods include:

  • SDNN (ms)
    • Standard deviation of all NN intervals or square root of variance
    • Reflects all the cyclic components responsible for variability in the period of recording
    • Includes low frequency and high frequency HRV components
    • Not a well-defined statistical quantity for arbitrarily selected ECGs, because the total variance of HRV increases with the length of analyzed recording
  • SDANN (ms)    
    • Standard deviation of the averages of NN intervals calculated over short periods, usually in 5 minutes segments of the entire recording
    • Estimates changes in cycles longer than 5 minutes
  • RMSSD (ms)    
    • Square root of the mean of the sum of the squares of differences between adjacent NN intervals
    • Estimates changes in very short-term cycles
    • SDNN index (ms)
    • Mean of the standard deviations of all NN intervals for all 5-minute segments of the entire recording
    • Measures the variability due to cycles shorter than 5 minutes

Geometric Methods
The series of NN intervals also can be converted into a geometric pattern such as the sample density distribution of NN interval durations sample density distribution of differences between adjacent NN intervals, Lorenz plot of NN or RR intervals. Therefore a method can be use to analyze the variability on the basis of the geometric and/or graphic properties of the resulting pattern.

  • HRV triangular index
    • Total number of all NN intervals divided by the height of the histogram of all NN intervals measured on a discrete scale with bins of 7.8125 ms (1/128 seconds)
  • TINN (ms)     
    • Triangular interpolation of NN interval histogram calculated using minimum square difference
    • Baseline width of the distribution measured as the base of the triangle

Frequency Domain

HRV may also be analyzed in the frequency domain, which provides the amount of variation for different frequencies and is usually calculated from the beat-to-beat interval time series.  Calculation methods may be classified as nonparametric and parametric, which produce similar results in most cases.

Nonparametric

  • simple to use algorithm, usually fast Fourier transform (FFT]
  • has high processing speed

Parametric

  • Smoother spectral components that can be distinguished independent of preselected frequency bands
  • Easy postprocessing of the spectrum and easy identification of the central frequency of each component
  • Accurate estimation of PSD even on a small number of samples
  • Needs of verification of usability, suitability and is more complex

Frequency Bands

  • Short-term Recordings (2 to 5 minutes)
    • High Frequency (HF)
    • Low Frequency (LF)
    • Very Low Frequency (VLF)
  • Long-term Recordings (>24 hour)
    • High Frequency (HF)
    • Low Frequency (LF)
    • Very Low Frequency (VLF)
    • Ultra Low Frequency (ULF)

In humans it was found that:

  • HF (0.15 and 0.4 Hz) is driven by respiration mainly via vagal activity
  • LF (0.04 and 0.15 Hz) is derived from both vagal and sympathetic activity and has been hypothesized to reflect the delay in the baroreceptor loop
  • VLF (0.0033 and 0.04 Hz) has been attributed to physical activity although the origin of VLF is unknown
  • ULF (0 and 0.0033 Hz) mainly varies between night and day  

 

Software:


 

LabChart
LabChart software (for Windows and Macintosh) combines the familiar simplicity of a traditional strip chart recorder with the powerful analysis features of a digital acquisition system. LabChart software and a PowerLab data acquisition unit provide data integrity, easy selection of hardware settings, powerful online and offline analysis, procedure automation, seamless extraction of experimental data and flexible display options. Acquisition and analysis capabilities can be further increased with LabChart Extensions and LabChart Modules. LabChart Modules are available as part of LabChart Pro and LabChart Extensions are free for download from the website for existing LabChart users.

Heart Rate Variability (HRV) Module (Windows or Macintosh)
The MLS310 HRV Module provides a comprehensive set of tools for the analysis and display of variation in the interval between heartbeats in human and animal electrocardiogram recordings.

It provides:

  • Detects and analyzes of R waves & RR interval variation in ECG real-time or offline recordings
  • Includes or excludes ectopic beats from analysis
  • Adds R waves or remove short artifacts from analysis
  • Exports data analysis
    • NN Intervals, RR Intervals, Spectrum NN Intervals & Report
  • Automated HRV Analysis Windows
    • Poincaré Plot, Tachogram & Spectrum
    • Period Histogram & Delta NN Histogram

GLP and 21 CFR Part 11


For those researchers working within a laboratory requiring GLP and 21 CFR Part 11 compliance the GLP Client and GLP Server are available for use with LabChart (Windows only) and PowerLab data acquisition systems. For more information, visit the Good Laboratory Practice application page or contact your nearest ADInstruments representative.
 

Hardware:

A PowerLab data acquisition system can be used with other brands and models of amplifier to record the ECG/EKG, provided they have a suitable analog output (Maximum ±10 V).

PowerLab Data Acquisition Systems

The PowerLab is a high-performance data acquisition unit suitable for a wide range of research applications. Typical applications include human and animal physiology, pharmacology, neurophysiology, biology, zoology, biochemistry, and biomedical engineering. Units are compatible with instruments, signal conditioners and transducers supplied by ADInstruments, as well as many other brands. In addition to standard single-ended BNC inputs, differential Pod ports are also available for direct connection of Pod signal conditioners and appropriate transducers. These units include:

Research PowerLabs


Telemetry ECG/Biopotential Foundation System
This ML870B99 Telemetry ECG/Biopotential Foundation System comprises of hardware and software to record and analyze one biopotential signal such as ECG EMG, EOG or EEG, as well as body temperature, from conscious animals.

The system includes:

  • The ML319 TR Scheduler Pod and LabChart Scheduler Extension that allows the user to program recording periods as well as record data from up to 12 individual transmitters/animals.
  • Uses implantable wireless transmitters
  • Requires no special caging due to independent frequency transmission
  • Suitable for small or large animals
  • Allows long-term, stress-free recording


Transmitters are purchase separately and the recommended transmitters are:

Bio Amplifiers

The ECG biopotentials are typically very small in amplitude (mV). Therefore accurate recording, display and analysis of an ECG require a suitable bioamplifier. ADInstruments offer a range of Bio Amplifiers, when connected a PowerLab data acquisition unit and, are certified safe for use with humans or used with animals. These bioamplifiers are fully software-controlled using LabChart or Scope. The following ADInstruments' biological amplifiers are fully isolated for connection to human or animal subjects:

ML132 Bio Amp

ML135 Dual Bio Amp

ML408 Dual Bio Amp/Stimulator


If a Dual Bio Amp is used to record any two signals of Lead I or Lead II or Lead III, then the Arithmetic function of the LabChart software can be used to generate aVR, aVL, and aVF signals simultaneously on different channels. The MLA0114/S ECG 12 Lead Switch Box (with a ML132 Single Bio Amp) or MLA0114/D ECG 12 Lead Switch Box (with a Dual Bio Amp) can be used to record all 12 ECG leads as shown in multi-lead recording.

ML138 Octal Bio Amp

  • A differential amplifier that consists of eight electrically isolated differential input AC amplifiers
  • A shared ground connection across all eight inputs.
  • Supplied with two packets of MLA0310 Lead Wires (1.8 m, 10 snap on)


GT201/F 16 Channel Bio Amp

The following ADInstruments' biological amplifiers for use with animals (i.e. pithed toad, or anaesthetized rat/mouse) only:

ML136 Animal Bio Amp

ECG Switch Boxes

  • For multi-lead recordings, ADInstruments Bio Amps (Bio Amp, Dual Bio Amp, Dual Bio Amp/Stim) can be used with the ECG Switch Boxes (MLA0114/S or MLA0114/D) to quickly change between Lead I, II, II, aVR, aVL, aVF, and V1 - V6 lead configurations
  • Only one lead configuration is recorded at any one time
  • For the V1 - V6 configurations, the position of the chest electrode must be changed, which is most easily done by using MLA710 Chest ECG Electrodes (suction)
  • Not suitable for use with the Multiple Channel Bio Amps


Accessories

Bio Amp cables:


Leads compatible with both shielded (MLA2340 & MLA2540) and unshielded (MLA1340 & MLA1540) cables:


Leads compatible with shielded cables (MLA2340 & MLA2540) only:


Leads that directly connect to the Dual Bio Amp


Leads that directly connect to the Animal Bio Amp


Electrodes:

 

Effects of endurance training on resting and post-exercise cardiac autonomic control
K Yamamoto, M Miyachi, Y Saitoh, A Yoshioka and S Onodera, Med & Sci in Sports and Exercise, 1496-1502, 2001

Study of heart rate variability signals at sitting and lying postures
R Acharya U, N Kannathal, L M Hua and L M Yi, Journal of Bodywork and Movement Therapies, 134-141, 2000

Heart rate variability analysis: a useful assessment tool for diabetes associated cardiac dysfunction in rural and remote areas
A C Flynn, H F Jelinek and M Smith, Australian Journal of Rural Health, 77-82, 2005

Citations Database


The material on this page is provided in good faith and believed accurate at the time of writing. No responsibility will be taken, or liability accepted, for damages arising from the use of information herein. Readers are urged to check with respective manufacturers the accuracy of all product related information.

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