Heart Rate Variability Logger

Heart Rate Variability Logger is an app that lets you record, plot and export time and frequency domain Heart Rate Variability (HRV) features.

Main Features:
- extracts, plots, stores and exports time and frequency domain heart rate variability features (AVNN, SDNN, rMSSD, pNN50, LF, HF, LF/HF)
- configurable time window for feature extraction (30 seconds to 5 minutes)
- automatic RR-interval correction (configurable)
- event annotation
- data export/storage on SD card and Dropbox (csv format, exports heart rates, rr intervals, events and computed features)
- records data even when the app is in the background
- handles recordings longer than 10 hours

HRV Logger requires at least Android version 4.3 and Bluetooth 4.0. HRV Logger was tested using Polar H7, Armour39, mio alpha and two Samsung S3 (i9300 and mini) running android 4.3.

Detailed description:
Time window:
The time window used to compute features can be configured choosing between 30 seconds, 1, 2 or 5 minutes. Windows of at least 2 minutes should be used when using low frequency features (LF). Given the non-constant frequency at which RR-intervals are received, a buffer of RR-intervals is used to collect 30 seconds to 5 minutes of data, on which features extraction is executed.

Features:
The following features are extracted from RR-intervals:
- Mean of beat-to-beat intervals (AVNN),
- Standard deviation of beat-to-beat intervals (SDNN),
- Square root of the mean squared difference of successive RRs (rMSSD),
- Number of pairs of successive RRs that differ by more than 50 ms (pNN50),
- Low frequency power (LF, 0.04-0.15 Hz),
- High frequency power (HF, 0.15-0.40 Hz),
- Low to High frequency power ratio (LFHF).

Interpolation:
Since RR-intervals come at non-constant frequency, they are linearly interpolated before frequency analysis. After interpolation, a hamming window is applied.

RR-intervals correction:
RR-Intervals correction prevents artifacts due to ectopic beats or motion from affecting features computation, as often reported in literature for HRV analysis.

It is advised to keep RR-interval correction to 20%, meaning that every RR-interval which differs by more than 20% from the previous one, will be discarded. HRV Logger provides three options, the correction can be completely disabled, in case you are interested in looking at PVCs or other events. By default the correction is set to 20%. The third and last setting is 50%, which is a less aggressive correction, since every RR-interval which differs by more than 50% from the previous one, will be discarded.

Data format:
All files are in csv format, making it easy to import them in other tools. Four files are exported for each recording, including timestamped HR, RR-intervals, extracted features and annotated events.

Overview on HRV:
The cardiovascular system is mostly controlled by autonomic regulation through the activity of sympathetic and parasympathetic pathways of the autonomic nervous system. HRV analysis attempts to assess cardiac autonomic regulation through quantification of sinus rhythm variability. The sinus rhythm times series is derived from RR intervals (R peaks of the QRS complex derived from the electrocardiogram (ECG)), by extracting only normal (NN) intervals.

Since HRV aims at quantifying autonomic regulations, it can be used as marker of sympathetic or parasympathetic predominance, and therefore become relevant in many applications. In athletes for example heavy training is responsible for shifting the cardiac autonomic balance toward a predominance of the sympathetic over the parasympathetic drive, and HRV analysis attempts to quantify this shift.

Other applications span from stress monitoring during public speaking or daily life, assessment of pathological conditions and even emotional regulation during financial decision-making (trading).

Find out more at this link: http://www.marcoaltini.com/2/post/2013/12/heart-rate-variability-logger-app-details.html