function output = pnna(rr, alpha)
%
% output = pnna(rr,alpha)
%
% OVERVIEW: finds the fraction of consecutive beats that differ by
% more than a specified time.
% Setting <alpha> to 50 msec will make this equivalent to pnn50
% 50 msec is the default value of <alpha>
% When no arguments are given, the program documents itself%
%
% INPUT:
% rr - is a vector containing RR intervals in seconds
% alpha - is a number which specifies the limit of successive
% differences in milliseconds (50 ms by default)
% OUTPUT:
% pnna - Probability of intervals greater alpha ms or
% smaller -alpha ms (e.g., alpha = 50 ms)
% REPO:
% https://github.com/cliffordlab/PhysioNet-Cardiovascular-Signal-Toolbox
% SOURCE: Adapted from Kaplan Tools
% See: http://www.robots.ox.ac.uk/~gari/CODE/HRV/
% AUTHORS: Adriana Vest <adriana.vest@gmail.com>
% COPYRIGHT (C) 2016 AUTHORS (see above)
% LICENSE: This code (and all others in this repository) are under
% the GNU General Public License v3
% set default parameters
if nargin < 2
% assume alpha is in millisecs
alpha = 50;
end
dif = diff(rr);
% pnnalpha is the fraction of differences larger than alpha
output = sum( abs(dif) >= alpha/1000 )/length(dif);
end