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These programs derive pNNx, time domain measures of heart rate variability defined for any time interval x as the fraction of consecutive normal sinus (NN) intervals that differ by more than x. Conventionally, such measures have been applied to assess parasympathetic activity using x = 50 milliseconds (yielding the widely-cited pNN50 statistic).
This program takes as standard input an annotation interval list, containing intervals in seconds and the (beat and non-beat) annotations that terminate each interval; and outputs on standard output each unique NN increment (x) in milliseconds, and the percentage of NN interval increments (pNNx) greater than x.
Options for pnnlist may include:
This shell script invokes ann2rr(1) and pnnlist to obtain pNNx statistics using a beat annotation file as input. The input file must be specified using the -r record and -a annotator arguments.
Options for pNNx may include any of those usable with pnnlist, as well as:
These commands are functionally identical:
ann2rr -r nsrdb/16265 -a atr -A -i s8 -w | pnnlist
pNNx -r nsrdb/16265 -a atr
Each of these commands reads the atr (reference) annotations for MIT-BIH
Normal Sinus Rhythm Database (nsrdb) record 16265 (downloading them directly
from PhysioNet if the annotation file has not previously been downloaded
into a local nsrdb directory. These commands will then print each unique
NN interval increment in milliseconds along with the percentage of intervals
greater than that value. Both of the examples above produce the same output;
the first few lines are shown below:
It may be necessary to set and export the shell variable WFDB (see setwfdb(1) ).
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Updated 8 March 2019