Diff: noisechk.cpp

Revision:

62:8e2fbe131b53

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/noisechk.cpp	Sun Jun 28 03:06:00 2015 +0000
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+/*****************************************************************************
+FILE:  noisechk.cpp
+AUTHOR: Patrick S. Hamilton
+REVISED:    5/13/2002
+  ___________________________________________________________________________
+
+noisechk.cpp: Noise Check
+Copywrite (C) 2001 Patrick S. Hamilton
+
+This file is free software; you can redistribute it and/or modify it under
+the terms of the GNU Library General Public License as published by the Free
+Software Foundation; either version 2 of the License, or (at your option) any
+later version.
+
+This software is distributed in the hope that it will be useful, but WITHOUT ANY
+WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A
+PARTICULAR PURPOSE.  See the GNU Library General Public License for more
+details.
+
+You should have received a copy of the GNU Library General Public License along
+with this library; if not, write to the Free Software Foundation, Inc., 59
+Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+
+You may contact the author by e-mail (pat@eplimited.edu) or postal mail
+(Patrick Hamilton, E.P. Limited, 35 Medford St., Suite 204 Somerville,
+MA 02143 USA).  For updates to this software, please visit our website
+(http://www.eplimited.com).
+  __________________________________________________________________________
+
+This file contains functions for evaluating the noise content of a beat.
+
+*****************************************************************************/
+
+//#include <stdlib.h>
+#include <mbed.h>
+#include "qrsdet.h"
+
+#define NB_LENGTH   MS1500
+#define NS_LENGTH   MS50
+
+int NoiseBuffer[NB_LENGTH], NBPtr = 0 ;
+int NoiseEstimate ;
+
+/************************************************************************
+    GetNoiseEstimate() allows external access the present noise estimate.
+    this function is only used for debugging.
+*************************************************************************/
+
+int GetNoiseEstimate()
+    {
+    return(NoiseEstimate) ;
+    }
+
+/***********************************************************************
+    NoiseCheck() must be called for every sample of data.  The data is
+    stored in a circular buffer to facilitate noise analysis.  When a
+    beat is detected NoiseCheck() is passed the sample delay since the
+    R-wave of the beat occurred (delay), the RR interval between this
+    beat and the next most recent beat, the estimated offset from the
+    R-wave to the beginning of the beat (beatBegin), and the estimated
+    offset from the R-wave to the end of the beat.
+
+    NoiseCheck() estimates the noise in the beat by the maximum and
+    minimum signal values in either a window from the end of the
+    previous beat to the beginning of the present beat, or a 250 ms
+    window preceding the present beat, which ever is shorter.
+
+    NoiseCheck() returns ratio of the signal variation in the window
+    between beats to the length of the window between the beats.  If
+    the heart rate is too high and the beat durations are too long,
+    NoiseCheck() returns 0.
+
+***********************************************************************/
+
+int NoiseCheck(int datum, int delay, int RR, int beatBegin, int beatEnd)
+    {
+    int ptr, i;
+    int ncStart, ncEnd, ncMax, ncMin ;
+    double noiseIndex ;
+
+    NoiseBuffer[NBPtr] = datum ;
+    if(++NBPtr == NB_LENGTH)
+        NBPtr = 0 ;
+
+    // Check for noise in region that is 300 ms following
+    // last R-wave and 250 ms preceding present R-wave.
+
+    ncStart = delay+RR-beatEnd ;    // Calculate offset to end of previous beat.
+    ncEnd = delay+beatBegin ;       // Calculate offset to beginning of this beat.
+    if(ncStart > ncEnd + MS250)
+        ncStart = ncEnd + MS250 ;
+
+
+    // Estimate noise if delay indicates a beat has been detected,
+    // the delay is not to long for the data buffer, and there is
+    // some space between the end of the last beat and the beginning
+    // of this beat.
+
+    if((delay != 0) && (ncStart < NB_LENGTH) && (ncStart > ncEnd))
+        {
+
+        ptr = NBPtr - ncStart ; // Find index to end of last beat in
+        if(ptr < 0)                 // the circular buffer.
+            ptr += NB_LENGTH ;
+
+        // Find the maximum and minimum values in the
+        // isoelectric region between beats.
+
+        ncMax = ncMin = NoiseBuffer[ptr] ;
+        for(i = 0; i < ncStart-ncEnd; ++i)
+            {
+            if(NoiseBuffer[ptr] > ncMax)
+                ncMax = NoiseBuffer[ptr] ;
+            else if(NoiseBuffer[ptr] < ncMin)
+                ncMin = NoiseBuffer[ptr] ;
+            if(++ptr == NB_LENGTH)
+                ptr = 0 ;
+            }
+
+        // The noise index is the ratio of the signal variation
+        // over the isoelectric window length, scaled by 10.
+
+        noiseIndex = (ncMax-ncMin) ;
+        noiseIndex /= (ncStart-ncEnd) ;
+        NoiseEstimate = noiseIndex * 10 ;
+        }
+    else
+        NoiseEstimate = 0 ;
+    return(NoiseEstimate) ;
+    }
+