Real time measurement of RR intervals using a digital signal processor

The accurate measurement of beat to beat intervals is essential for subsequent heart rate variability analysis. Where the ECG is used to derive the intervals, timing can be affected by artefacts such as muscle noise, electrode instability and also shape changes in the QRS complex. Identifying the QRS time by correlation methods can minimize the uncertainty but the method is computationally intensive. We have developed a real time RR interval measurement system using a correlation technique running on a low cost digital signal processor (TMS320C31). Sampling rate is 1 KHz. Timing resolution is +/- 1 ms. The correlation process uses an averaged complex from the actual ECG and has an adaptive noise threshold. The high processing speed of a DSP has proved ideal for accurate RR interval measurement. The system is described and test results with various signal to noise ratios and different types of noise are presented.