The AcqKnowledge software includes a fully-automated Heart Rate Variability analysis tool. The algorithm conforms to the frequency domain algorithm guidelines as published by the European Heart Journal.
There are two methods for extracting the RR intervals from the ECG signal:
A modified Pan-Tompkins QRS detector
Events located in the file - ECG QRS Peak event
The RR intervals are re-sampled to a continuous sampling rate in order to extract frequency information.
Cubic-spline interpolation is used to generate this continuous time-domain representation of the RR intervals.
The frequency information is extracted from the RR intervals and analyzed to produce standard ratios. Power sums are reported in units of sec2/Hz. A Welch periodogram is used to generate the Power Spectral Density (equivalent to Transform > Power Spectral Density).
The software reports values for the typical HRV frequency bands, including: Very Low Frequency, Low Frequency, High Frequency, and Very High Frequency ranges. The analysis also includes values for the overall ratios: Sympathetic, Vagal and Sympathetic - Vagal balance. The ratio values and frequency band results can be plotted into a Journal file or exported for further analysis.
AcqKnowledge also inlcudes a Poincare plot option that will display either selected areas of the data, or the entire file. The Poincare plot is an X/Y plot of the RR intervals in seconds. One axis displays the RR interval and the other axis displays the interval delayed by one beat.