HRV
Overview:
Heart rate variability (HRV) refers to subtle beat-by-beat variation in the heart rhythm.
In normal healthy subjects, each heart beat is initiated by the sinoatrial node located in the posterior wall of the right atrium. Myocytes in this area exhibit what is referred to as a leaky conductance across their membranes which results in a regular and uniform discharge of action potentials that cause the heart to contract at a constant frequency.
Ordinarily, however, many factors constantly modulate the autorhythmicity of sinoatrial firing rate.This is achieved by way of the automonic nervous system's two opposing arms: the sympathetic and the parasympathetic (vagal).
By examining heart beat-to-beat variation one therefore effectively gains insight into autonomic nervous system tone. Quantifying sympathovagal tone is one of the major goals of HRV analysis. Example applications in research include:
- Exercise & sympathovagal tone
- Detection of peripheral neuropathy with diabetes
- Temperature stress
- Emotional stress
- Models of anxiety and depression
- Response predictor to antidepressant therapy
- Infant sleeping posture HRV and SIDs
- Risk factor for mortality with heart disease
Method:
Beat Detection
HRV analysis requires a time series of successive heart beat intervals. This can be obtained from pulse recordings, for example using a Finger Pulse Transducer, or, more commonly, from an ECG recording using lead I or II (see Fig. 1 - and also ECG/EKG applications).
Figure 1. Two successive PQRST waves from an ECG recording. HRV analysis requires a time series of successive RR intervals in order to show how the heart rhythm changes over time. The corresponding fiducial point in a pulse-waveform would be the peak in the pressure signal immediately following the ejection phase of each cardiac cycle.
Additional R-waves that may be detected as a result of movement artifacts or arrythmias must be removed from the analysis. This is because HRV is only concerned with external factors (autonomic) that modulate the sinus rhythm.
Missing R-waves as a result of exclusion are normally dealt with by linear interpolation, in which case RR interval is then referred to as NN interval to denote 'normal to normal' beat. This procedure is particularly important for spectral analysis which is very sensitive to the presence of artifacts and arrythmias.
HRV Analysis
Methods of measuring HRV can be subdivided into two broad analytical categories: time domain and frequency domain. Figure 2 summarizes the steps involved:
Figure 2. Flowchart showing key steps involved in processing ECG data for HRV analysis.
Time Domain Analysis
Beat-to-beat variation in the HR series calculated from the RR (or NN) intervals are typically described by several statistical parameters, including (but not limited to):
- SDNN
- Standard deviation of all NN intervals
- Reflects overall variation in the heart beat series
- SDSD
- Standard deviation of the differences between adjacent NN intervals
- Reflects instantaneous variation in the heart beat series
- SDNN:SDSD Ratio
- Ratio between overall to instantaneous variability
- RMSSD
- Square root of the mean of the sum of the squares of differences between adjacent NN intervals
- Reflects overall variation in the heart beat series
- pNN50%
- Number of successive difference of intervals which differ by more than 50 ms, as a proportion of total beat cycles
Frequency Domain Analysis
Spectral analysis on the RR series allows sympathetic and parasympathetic contributions to HRV to be determined. A power spectrum density (PSD) estimate is used to show which frequencies in the RR series contain the HRV power. Since autonomic processes influence heart rate on characteristic timescales, the appearance of the HRV spectrum often reveals three distinct peaks (Fig. 3).
Figure 3. HRV spectral plot from a healthy calm adult male. Three distinct peaks are present in the spectrum: a very low frequency peak (VLF) centered around 0.02 Hz; a low frequency peak (LF) centered around 0.1 Hz; and a high frequency peak (HF) centered around 0.25 Hz. The vertical red lines containing each major peak represent the frequency band ranges for VLF, LF, and HF that have been universally adopted for human studies.
Frequency bands in human HRV studies
There are five frequency bands for measuring spectral power that have been adopted for use in human HRV studies. Two of these relate to sympathetic and parasympathetic cardiac drive:
- HF (0.15 - 0.4 Hz) is driven mainly via parasympathetic innervation of the heart
- LF (0.04 - 0.15 Hz) is driven mainly by sympathetic innervation of the heart
Power within a very low frequency brand may also be present, but would only be revealed where recordings last for several hours:
- VLF (0.0033 - 0.04 Hz) - autonomic activity influenced by thermoregulation and humoral system activity
For recordings lasting 24 hours or more, power within an ultra-low frequency band will also be seen:
- ULF (0 - 0.0033 Hz) - autonomic activity related to the circadian rhythm
Frequency bands in rat HRV studies 1
The average heart rate of the rat is much higher than in human (~300 bpm) and so the effects of autonomic modulation on SA node firing occur on different timescales. For this reason the LF and HF bands are defined differently:
- LF (0.04 - 1.0)
- HF (1.0 - 3.0)
1. Kuwahara, M., Yayou, K., Ishii, K., Hashimoto, S., Tsubone, H., & Sugano, S. (1994). Power spectral analysis of heart rate variability as a new method for assessing autonomic activity in the rat. Journal of Electrocardiology, 27(4), 333-7.
Software:
The LabChart Advantage:
(may require additional Modules and Extensions)
- LabChart data files can be marked with events using the Comments feature
- Parameters such as heart rate, and RR interval can be calculated and displayed in real-time using LabChart's Cyclic Measurements function and the Data Pad
- Macros can automate many tedious and repetitive analysis tasks
- Automated extraction of data from recordings using online Timed Add to Data Pad or offline using Multiple Add to Data Pad
- The LabChart HRV Module enables real-time or offline analysis of HRV parameters such as SDNN, pNN50, and LF/HF as well as several graphical plots
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
The HRV Module (Windows and Macintosh) provides a comprehensive set of tools for the analysis and display of variation in the interval between heartbeats in human and animal ECG recordings.
It provides:
- Detection and analysis of R waves and RR interval variation in real-time or offline
- Includes or excludes ectopic beats from analysis
- Adds R waves or remove artifacts from analysis
- Exports data analysis
- NN Intervals, RR Intervals, Spectrum NN Intervals & Report
- HRV Analysis Plots
- Poincaré Plot, Tachogram & Spectrum
- Period Histogram and Delta NN Histogram
- Frequency-domain analysis:
- High frequency (HF) spectral power - a measure of vagal (parasympathetic) tone
- Low frequency (LF) spectral power - a measure of sympathetic tone
- LF/HF ratio - sympathovagal balance
- Time-domain analysis:
- Average HR, RR range, SDNN, SD of delta NN, RMSSD, pNN50
- Full HRV report generated containing all time and frequency domain parameters
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:
PowerLab Data Acquisition Systems
The PowerLab is a high-performance data acquisition unit capable of recording at speeds of up to 400,000 samples per second continuously to disk (aggregate). PowerLab units are compatible with instruments, signal conditioners and transducers supplied by ADInstruments, as well as many other third-party companies. In addition to standard single-ended BNC inputs, 4 differential Pod ports are also available for direct connection of Pod signal conditioners and appropriate transducers. Research PowerLab units include:
- PL3504 PowerLab 4/35 - 4 Channels
- PL3508 PowerLab 8/35 – 8 Channels
- PL3516 PowerLab 16/35 – 16 Channels
Research Systems
Wireless ECG in Small Animals
PL3516B109 Telemetry Small Animal Foundation System: A wireless monitoring system for physiological signals including intravascular or intralumen pressure signals, biopotentials such as ECG, EMG, EOG or EEG signals. Suitable for small conscious animals > 200 g (especially in rats). Note: Telemeters purchased separately.
Signal Conditioners
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:
FE132 Bio Amp
- A single channel, differential amplifier that is suitable for recording a range of biopotentials including Lead I, Lead II or Lead III ECG
- Supplied with a MLA2340 3 Lead Shielded Bio Amp Cable
- Supplied with MLA2503 Shielded Lead Wires (3 snap-on)
- A dual channel, differential amplifier that is suitable for recording 2 independent biopotentials that share a common ground. In ECG recordings, any two of Lead I, Lead II or Lead III configurations can be recorded
- Supplied with an MLA2540 5 Lead Shielded Bio Amp Cable
- Supplied with MLA2505 Shielded Lead Wires (5 snap-on)
- A dual channel, differential amplifier that also includes an isolated stimulator suitable for mild electrical stimulation of human subjects (i.e. Evoked EMG studies).
- Supplied with an MLA2540 5 Lead Shielded Bio Amp Cable
- Supplied with MLA2505 Shielded Lead Wires (5 snap-on)
- Supplied with MLADDB30 Recording Bar Electrode
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 MLA0115/S ECG 12 Lead Switch Box (with a ML132 Single Bio Amp) or MLA0115/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)
- A fully isolated, 16 channel stand-alone biological amplifier that consists of 8 modules, with each module containing two channel amplifiers that share a common ground input
- Electrodes are NOT supplied and must be ordered separately
- Suitable electrodes and lead wires include the:
- MLAWBT9 Flat EEG Electrodes for recording ECG, EEG, EOG and EMG
- MLA0315 Lead Wires (unshielded, 5 snap on)
- MLA1010B Disposable ECG Electrodes
The following ADInstruments' biological amplifiers for use with animals (i.e. pithed toad, or anaesthetized rat/mouse) only:
FE136 Animal Bio Amp
- An isolated, high performance and software-controlled differential amplifier
- Has three 2mm input sockets allow the direct connection of electrodes to this amplifier
- Supplied with MLA1215 Animal Bio Lead Wires
- Also suitable for use with
Transducers and Accessories
Finger-Pulse Transducer
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 (MLA0115/S or MLA0115/D)
- Quickly change between limb and augmented limb leads (I, II, II, aVR, aVL, aVF) and precordial leads (V1 - V6) on Ch1 in LabChart
- Lead II is recorded on Ch2 by default
Bio Amp Cables & Lead Wires
- MLA1340 3 Unshielded Lead Bio Amp Cable
- MLA1540 5 Unshielded Lead Bio Amp Cable
- MLA2340 3 Shielded Lead Bio Amp Cable
- MLA2540 5 Shielded Lead Bio Amp Cable
Leads compatible with both shielded (MLA2340 & MLA2540) and unshielded (MLA1340 & MLA1540) cables:
- MLA1505 Unshielded Lead Wires (5 alligator clip)
- MLA0311 Unshielded Lead Wires (1 m, 10 Snap on)
- MLA0310 Unshielded Lead Wires (1.8 m, 10 snap on)
- MLA1203 Needle Electrodes (29 gauge, 5)
Leads compatible with shielded cables (MLA2340 & MLA2540) only:
- MLA1605 Shielded Lead Wires (5 alligator clip, 25 cm)
- MLA1610 Shielded Lead Wires (5 Micro-Hooks)
- MLA1615 Shielded Lead Wires (5 Alligator Clip, 100 cm)
Leads that directly connect to the Dual Bio Amp
Leads that directly connect to the Animal Bio Amp
Electrodes
- MLA1010 Disposable ECG Electrodes (100)
- MLA1010B Disposable ECG Electrodes (1000)
- MLA700 Reusable ECG Electrodes
- MLA710 Chest ECG Electrodes (suction)
Wireless Biopotential Telemeters
Wireless biopotential telemeters are suitable for measuring ECG (and other types of biopotentials) plus temperature in small laboratory animals ≥200 g (ideally suited to rats).
Single lead wireless EEG:
Dual lead wireless EEG
Moderate weight loss improves heart rate variability in overweight and obese adults with type 2 diabetes.
Sjoberg N, Brinkworth GD, Wycherley TP, Noakes M, Saint DA., Journal of Applied Physiology, 1060-1064, 2011
A mouse model of high trait anxiety shows reduced heart rate variability that can be reversed by anxiolytic drug treatment
S Gaburro, O Stiedl, P Giusti, S B. Sartori, R Landgraf
and N Singewald, International Journal of Neuropsychopharmacology, 1341-1355, 2011
Heart Rate Variability Dynamics for the Prognosis of
Cardiovascular Risk
Ramirez-Villegas JF, Lam-Espinosa E, Ramirez-Moreno DF, Calvo-Echeverry PC, Agredo-Rodriguez W., PLoS ONE, e17060, 2011
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.
