Live capture: Floating stone shrine in the galaxy
Knowledge base
What happens in the body during relaxation, and what research currently says about it. This section covers the basics of HRV and EEG and the current state of research on meditation, slow breathing and immersive relaxation, with a source for every key point.
Heart rate variability (HRV) basics
The definition, how ECG and optical measurement differ, common indicators such as RMSSD and SDNN, the debate over LF/HF, how breathing affects the values, and six common misconceptions.
EEG basics
How the bands from delta to gamma are usually interpreted, findings from meditation and relaxation research, how headband devices differ from hospital equipment, and eye movement and muscle artifacts.
Research review
37 studies across 10 topics: HRV measurement standards, slow breathing and biofeedback, meditation and mindfulness, immersive VR relaxation, natural environments, sleep, the validity of wearables, and workplace interventions.
Glossary
- Heart rate variability (HRV)
- How much the interval between successive heartbeats varies. It is shaped by the autonomic nervous system, breathing and blood pressure regulation, and is best compared with your own values under the same conditions.
- RR interval / NN interval
- The time between two successive heartbeats. Once abnormal beats are removed, the intervals are called NN intervals. They are the raw data for calculating HRV.
- RMSSD
- The root mean square of successive differences between beat-to-beat intervals. It is commonly used to observe short-term, vagally mediated changes.
- SDNN
- The standard deviation of beat-to-beat intervals over a period. It reflects overall variability and depends heavily on recording length.
- pNN50
- The percentage of successive intervals that differ by more than 50 milliseconds.
- HF (high-frequency power)
- Power in the 0.15–0.40 Hz band, related to breathing and vagal regulation. When breathing is very slow, this activity moves into the LF band.
- LF (low-frequency power)
- Power in the 0.04–0.15 Hz band. It is influenced by sympathetic and parasympathetic activity and the baroreflex together, so it is not a pure sympathetic index.
- LF/HF
- The ratio of LF to HF power. It was once regarded as the "sympathovagal balance", but its meaning is still debated in the research literature.
- Respiratory sinus arrhythmia (RSA)
- The normal pattern in which the heart beats slightly faster during inhalation and slightly slower during exhalation. It is the main source of HF power.
- Resonance breathing
- Slowing the breath to about six breaths a minute, so that the breathing rhythm comes close to the rhythm of blood pressure regulation and heart rate oscillations grow larger. HRV biofeedback often uses this approach.
- Photoplethysmography (PPG)
- Optical sensing of the pulse, used by watches and armbands. It measures pulse rate variability, which comes close to ECG measurement at rest and diverges more during movement.
- Electroencephalography (EEG)
- Electrical activity of the brain recorded at the scalp. It is usually analyzed in frequency bands such as delta, theta, alpha, beta and gamma.
- Alpha waves
- About 8–12 Hz. Prominent during awake rest with the eyes closed, and reduced when the eyes open or attention turns to a task.
- Theta waves
- About 4–8 Hz. They can rise during meditation and also with drowsiness, so interpretation has to tell the two apart.
- Artifacts
- Signals from sources other than the brain, such as blinking, muscle activity and the heartbeat, which can inflate power in certain bands.
- Meta-analysis
- A statistical method that pools results from multiple studies to estimate the overall size of an effect.
These definitions are based on the literature cited in the HRV and EEG articles. For the indicators and six-axis radar used in Mandala Hub reports, see Measurement and research.
How this relates to Mandala Hub
Mandala Hub uses wearables to record HRV and EEG during relaxation, so you can see how your values change from before the session to during the journey. This section explains where those numbers come from and what they mean, so you can read your report with more confidence.