function [SDANN, SDNNI] = CalcSDANN(windows_all, tNN, NN, HRVparams)
% [SDANN, SDNNI] = CalcSDANN(windows_all, tNN, NN, HRVparams)
%
% OVERVIEW: Calculates SDANN and SDNNindex for all segments
% of a specified constant length with no overlap.
%
% INPUT: windows_all :
% NN : a single column of NN (normal normal) interval
% data in seconds
% tNN : the time indices of the rr interval data (seconds)
% HRVparams : settings struct, including segment length - the
% length of the interval requested
% (it is defaulted at 5minutes == 300 seconds)
% NOTE: seglength must be specified in the same units as <times>
%
% OUTPUT: SDANN : standard deviation of the averages of values
% SDNNI : mean of the standard deviations of all values
%
% REPO:
% https://github.com/cliffordlab/PhysioNet-Cardiovascular-Signal-Toolbox
% ORIGINAL SOURCE AND AUTHORS:
% Main script written by Adriana N. Vest
% Dependent scripts written by various authors
% (see functions for details)
% COPYRIGHT (C) 2016
% LICENSE:
% This software is offered freely and without warranty under
% the GNU (v3 or later) public license. See license file for
% more information
%%
if nargin<3
error('not enough input arguments!');
end
segmentlength = HRVparams.windowlength;
for i = 1:length(windows_all)
if ~isnan(windows_all(i))
idx = find(tNN >= windows_all(i) & tNN < windows_all(i) + segmentlength);
nn_win = NN(idx);
sm(i) = mean(nn_win); % mean of each segment
sstd(i) = std(nn_win); % stdev of each segment
else
sm(i) = NaN;
sstd(i) = NaN;
end
end
% Remove NaN values from calculation
seg_mean = sm;
seg_stdev = sstd;
idxrem = find(isnan(sm));
seg_mean(idxrem) = [];
seg_stdev(idxrem) = [];
SDANN = std(seg_mean); % stdev of means of each segment
SDNNI = mean(seg_stdev); % mean of stdevs from each segment
end