Application to biomedical signals 181
root of the mean squared difference of successive RRs, the number of pairs of suc-
cessive RRs that differ by more than 50 ms (so called NN50), the proportion of NN50
divided by total number of NNs (pNN50). These markers and other tools helpful in
HRV quantification may be found in PhysioNet [Goldberger et al., 2000].
The series of RR intervals can also be represented by density distribution of RR
interval durations or density distribution of differences between adjacent RR inter-
vals. In construction of the density distribution a reasonable number of RR intervals
is needed. In practice, recordings of at least 20 minutes (but preferably 24 hours) are
recommended to ensure correct performance. The discrete scale ...