File content as of revision 62:8e2fbe131b53:

/*****************************************************************************
FILE:  analbeat.cpp
AUTHOR: Patrick S. Hamilton
REVISED:    5/13/2002
  ___________________________________________________________________________

analbeat.cpp: Analyze Beat
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 determining the QRS onset, QRS offset,
  beat onset, beat offset, polarity, and isoelectric level for a beat.

  Revisions:
    4/16: Modified to prevent isoStart from being set to less than ISO_LENGTH1-1
   5/13/2002: Time related constants are tied to BEAT_SAMPLE_RATE in bdac.h.

*****************************************************************************/
#include <mbed.h>
#include "bdac.h"
//#include <stdio.h>
//#include <stdlib.h>

#define ISO_LENGTH1  BEAT_MS50
#define ISO_LENGTH2 BEAT_MS80
#define ISO_LIMIT   20

// Local prototypes.

int IsoCheck(int *data, int isoLength);

/****************************************************************
    IsoCheck determines whether the amplitudes of a run
    of data fall within a sufficiently small amplitude that
    the run can be considered isoelectric.
*****************************************************************/

int IsoCheck(int *data, int isoLength)
    {
    int i, max, min ;

    for(i = 1, max=min = data[0]; i < isoLength; ++i)
        {
        if(data[i] > max)
            max = data[i] ;
        else if(data[i] < min)
            min = data[i] ;
        }

    if(max - min < ISO_LIMIT)
        return(1) ;
   return(0) ;
    }

/**********************************************************************
    AnalyzeBeat takes a beat buffer as input and returns (via pointers)
    estimates of the QRS onset, QRS offset, polarity, isoelectric level
    beat beginning (P-wave onset), and beat ending (T-wave offset).
    Analyze Beat assumes that the beat has been sampled at 100 Hz, is
    BEATLGTH long, and has an R-wave location of roughly FIDMARK.

    Note that beatBegin is the number of samples before FIDMARK that
    the beat begins and beatEnd is the number of samples after the
    FIDMARK that the beat ends.
************************************************************************/

#define INF_CHK_N   BEAT_MS40

void AnalyzeBeat(int *beat, int *onset, int *offset, int *isoLevel,
    int *beatBegin, int *beatEnd, int *amp)
    {
    int maxSlope = 0, maxSlopeI, minSlope = 0, minSlopeI  ;
    int maxV, minV ;
    int isoStart, isoEnd ;
    int slope, i ;

    // Search back from the fiducial mark to find the isoelectric
    // region preceeding the QRS complex.

    for(i = FIDMARK-ISO_LENGTH2; (i > 0) && (IsoCheck(&beat[i],ISO_LENGTH2) == 0); --i) ;

    // If the first search didn't turn up any isoelectric region, look for
    // a shorter isoelectric region.

    if(i == 0)
        {
        for(i = FIDMARK-ISO_LENGTH1; (i > 0) && (IsoCheck(&beat[i],ISO_LENGTH1) == 0); --i) ;
        isoStart = i + (ISO_LENGTH1 - 1) ;
        }
    else isoStart = i + (ISO_LENGTH2 - 1) ;

    // Search forward from the R-wave to find an isoelectric region following
    // the QRS complex.

    for(i = FIDMARK; (i < BEATLGTH) && (IsoCheck(&beat[i],ISO_LENGTH1) == 0); ++i) ;
    isoEnd = i ;

    // Find the maximum and minimum slopes on the
    // QRS complex.

    i = FIDMARK-BEAT_MS150 ;
    maxSlope = maxSlope = beat[i] - beat[i-1] ;
    maxSlopeI = minSlopeI = i ;

    for(; i < FIDMARK+BEAT_MS150; ++i)
        {
        slope = beat[i] - beat[i-1] ;
        if(slope > maxSlope)
            {
            maxSlope = slope ;
            maxSlopeI = i ;
            }
        else if(slope < minSlope)
            {
            minSlope = slope ;
            minSlopeI = i ;
            }
        }

    // Use the smallest of max or min slope for search parameters.

    if(maxSlope > -minSlope)
        maxSlope = -minSlope ;
    else minSlope = -maxSlope ;

    if(maxSlopeI < minSlopeI)
        {

        // Search back from the maximum slope point for the QRS onset.

        for(i = maxSlopeI;
            (i > 0) && ((beat[i]-beat[i-1]) > (maxSlope >> 2)); --i) ;
            *onset = i-1 ;

        // Check to see if this was just a brief inflection.

        for(; (i > *onset-INF_CHK_N) && ((beat[i]-beat[i-1]) <= (maxSlope >>2)); --i) ;
        if(i > *onset-INF_CHK_N)
            {
            for(;(i > 0) && ((beat[i]-beat[i-1]) > (maxSlope >> 2)); --i) ;
            *onset = i-1 ;
            }
        i = *onset+1 ;

        // Check to see if a large negative slope follows an inflection.
        // If so, extend the onset a little more.

        for(;(i > *onset-INF_CHK_N) && ((beat[i-1]-beat[i]) < (maxSlope>>2)); --i);
        if(i > *onset-INF_CHK_N)
            {
            for(; (i > 0) && ((beat[i-1]-beat[i]) > (maxSlope>>2)); --i) ;
            *onset = i-1 ;
            }

        // Search forward from minimum slope point for QRS offset.

        for(i = minSlopeI;
            (i < BEATLGTH) && ((beat[i] - beat[i-1]) < (minSlope >>2)); ++i);
            *offset = i ;

        // Make sure this wasn't just an inflection.

        for(; (i < *offset+INF_CHK_N) && ((beat[i]-beat[i-1]) >= (minSlope>>2)); ++i) ;
        if(i < *offset+INF_CHK_N)
            {
            for(;(i < BEATLGTH) && ((beat[i]-beat[i-1]) < (minSlope >>2)); ++i) ;
            *offset = i ;
            }
        i = *offset ;

        // Check to see if there is a significant upslope following
        // the end of the down slope.

        for(;(i < *offset+BEAT_MS40) && ((beat[i-1]-beat[i]) > (minSlope>>2)); ++i);
        if(i < *offset+BEAT_MS40)
            {
            for(; (i < BEATLGTH) && ((beat[i-1]-beat[i]) < (minSlope>>2)); ++i) ;
            *offset = i ;

            // One more search motivated by PVC shape in 123.

            for(; (i < *offset+BEAT_MS60) && (beat[i]-beat[i-1] > (minSlope>>2)); ++i) ;
            if(i < *offset + BEAT_MS60)
                {
                for(;(i < BEATLGTH) && (beat[i]-beat[i-1] < (minSlope>>2)); ++i) ;
                *offset = i ;
                }
            }
        }

    else
        {

        // Search back from the minimum slope point for the QRS onset.

        for(i = minSlopeI;
            (i > 0) && ((beat[i]-beat[i-1]) < (minSlope >> 2)); --i) ;
            *onset = i-1 ;

        // Check to see if this was just a brief inflection.

        for(; (i > *onset-INF_CHK_N) && ((beat[i]-beat[i-1]) >= (minSlope>>2)); --i) ;
        if(i > *onset-INF_CHK_N)
            {
            for(; (i > 0) && ((beat[i]-beat[i-1]) < (minSlope>>2));--i) ;
            *onset = i-1 ;
            }
        i = *onset+1 ;

        // Check for significant positive slope after a turning point.

        for(;(i > *onset-INF_CHK_N) && ((beat[i-1]-beat[i]) > (minSlope>>2)); --i);
        if(i > *onset-INF_CHK_N)
            {
            for(; (i > 0) && ((beat[i-1]-beat[i]) < (minSlope>>2)); --i) ;
            *onset = i-1 ;
            }

        // Search forward from maximum slope point for QRS offset.

        for(i = maxSlopeI;
            (i < BEATLGTH) && ((beat[i] - beat[i-1]) > (maxSlope >>2)); ++i) ;
        *offset = i ;

        // Check to see if this was just a brief inflection.

        for(; (i < *offset+INF_CHK_N) && ((beat[i] - beat[i-1]) <= (maxSlope >> 2)); ++i) ;
        if(i < *offset+INF_CHK_N)
            {
            for(;(i < BEATLGTH) && ((beat[i] - beat[i-1]) > (maxSlope >>2)); ++i) ;
            *offset = i ;
            }
        i = *offset ;

        // Check to see if there is a significant downslope following
        // the end of the up slope.

        for(;(i < *offset+BEAT_MS40) && ((beat[i-1]-beat[i]) < (maxSlope>>2)); ++i);
        if(i < *offset+BEAT_MS40)
            {
            for(; (i < BEATLGTH) && ((beat[i-1]-beat[i]) > (maxSlope>>2)); ++i) ;
            *offset = i ;
            }
        }

    // If the estimate of the beginning of the isoelectric level was
    // at the beginning of the beat, use the slope based QRS onset point
    // as the iso electric point.

    if((isoStart == ISO_LENGTH1-1)&& (*onset > isoStart)) // ** 4/19 **
        isoStart = *onset ;

    // Otherwise, if the isoelectric start and the slope based points
    // are close, use the isoelectric start point.

    else if(*onset-isoStart < BEAT_MS50)
        *onset = isoStart ;

    // If the isoelectric end and the slope based QRS offset are close
    // use the isoelectic based point.

    if(isoEnd - *offset < BEAT_MS50)
        *offset = isoEnd ;

    *isoLevel = beat[isoStart] ;


    // Find the maximum and minimum values in the QRS.

    for(i = *onset, maxV = minV = beat[*onset]; i < *offset; ++i)
        if(beat[i] > maxV)
            maxV = beat[i] ;
        else if(beat[i] < minV)
            minV = beat[i] ;

    // If the offset is significantly below the onset and the offset is
    // on a negative slope, add the next up slope to the width.

    if((beat[*onset]-beat[*offset] > ((maxV-minV)>>2)+((maxV-minV)>>3)))
        {

        // Find the maximum slope between the finish and the end of the buffer.

        for(i = maxSlopeI = *offset, maxSlope = beat[*offset] - beat[*offset-1];
            (i < *offset+BEAT_MS100) && (i < BEATLGTH); ++i)
            {
            slope = beat[i]-beat[i-1] ;
            if(slope > maxSlope)
                {
                maxSlope = slope ;
                maxSlopeI = i ;
                }
            }

        // Find the new offset.

        if(maxSlope > 0)
            {
            for(i = maxSlopeI;
                (i < BEATLGTH) && (beat[i]-beat[i-1] > (maxSlope>>1)); ++i) ;
            *offset = i ;
            }
        }

    // Determine beginning and ending of the beat.
    // Search for an isoelectric region that precedes the R-wave.
    // by at least 250 ms.

    for(i = FIDMARK-BEAT_MS250;
        (i >= BEAT_MS80) && (IsoCheck(&beat[i-BEAT_MS80],BEAT_MS80) == 0); --i) ;
    *beatBegin = i ;

    // If there was an isoelectric section at 250 ms before the
    // R-wave, search forward for the isoelectric region closest
    // to the R-wave.  But leave at least 50 ms between beat begin
    // and onset, or else normal beat onset is within PVC QRS complexes.
    // that screws up noise estimation.

    if(*beatBegin == FIDMARK-BEAT_MS250)
        {
        for(; (i < *onset-BEAT_MS50) &&
            (IsoCheck(&beat[i-BEAT_MS80],BEAT_MS80) == 1); ++i) ;
        *beatBegin = i-1 ;
        }

    // Rev 1.1
    else if(*beatBegin == BEAT_MS80 - 1)
        {
        for(; (i < *onset) && (IsoCheck(&beat[i-BEAT_MS80],BEAT_MS80) == 0); ++i);
        if(i < *onset)
            {
            for(; (i < *onset) && (IsoCheck(&beat[i-BEAT_MS80],BEAT_MS80) == 1); ++i) ;
            if(i < *onset)
                *beatBegin = i-1 ;
            }
        }

    // Search for the end of the beat as the first isoelectric
    // segment that follows the beat by at least 300 ms.

    for(i = FIDMARK+BEAT_MS300;
        (i < BEATLGTH) && (IsoCheck(&beat[i],BEAT_MS80) == 0); ++i) ;
    *beatEnd = i ;

    // If the signal was isoelectric at 300 ms. search backwards.
/*  if(*beatEnd == FIDMARK+30)
        {
        for(; (i > *offset) && (IsoCheck(&beat[i],8) != 0); --i) ;
        *beatEnd = i ;
        }
*/
    // Calculate beat amplitude.

    maxV=minV=beat[*onset] ;
    for(i = *onset; i < *offset; ++i)
        if(beat[i] > maxV)
            maxV = beat[i] ;
        else if(beat[i] < minV)
            minV = beat[i] ;
    *amp = maxV-minV ;

    }