WPF Native Chart Control and continuous updating

using System;
using System.Windows;
using System.Windows.Media;
using System.Windows.Shapes;
using System.IO;
using System.Collections.ObjectModel;
using System.ComponentModel;
using System.Windows.Threading;
using System.Collections.Specialized;
///// this is the real realtime graph 
namespace RealTimeGraph
{
 /// <summary>
 /// Interaction logic for MainWindow.xaml
 /// </summary>
 public partial class MainWindow : Window
 {
  public string FullNamePath = @"C:\KarlSample\RealTimeGraph\michael-forks20101201-200256";
  //public string FullNamePath = @"C:\SessionDataTest\michael-forks20101201-200256A";
  private double xmin = 0;
  private double xmax = 1600;
  private double ymin = 850;
  private double ymax = 950;
  private BackgroundWorker _bw = new BackgroundWorker();
  Polyline pl;
  ObservableCollection<Point> Obdatapoints = new ObservableCollection<Point>();
  public MainWindow()
  {
   InitializeComponent();
   _bw = new BackgroundWorker();
   _bw.DoWork += new DoWorkEventHandler(_bw_DoWork);
  }

  void _bw_DoWork(object sender, DoWorkEventArgs e)
  {
   int count = 0;
   string wrkString = null;
   double[] values = new double[4];
   StreamReader sr = new StreamReader(FullNamePath);
   while ((wrkString = sr.ReadLine()) != null)
   {
    System.Threading.Thread.Sleep(500);

    if (wrkString.StartsWith("\""))
    {
     wrkString = sr.ReadLine();
    }
    else
    {
     values = ParseTextStream(wrkString);
     Point pt = new Point(count, values[0]);
     Obdatapoints.Add(pt);
     count++;
    }
   }
  }

  void Obdatapoints_CollectionChanged(object sender, System.Collections.Specialized.NotifyCollectionChangedEventArgs e)
  {
   //GraphCanvas.Children.Clear();
   this.Dispatcher.Invoke( DispatcherPriority.DataBind, new Action(()=>{
    pl = CreateNewPolyLine(Obdatapoints);//(NormalizePoint(pt)) in the CreatePolyLineMethod
    GraphCanvas.Children.Add(pl);
   })); 
  }

  public double[] ParseTextStream(string wrkString)
  {
   // MessageBox.Show(wrkString);
   string[] stringSeparators = new string[] { "," };
   string[] sresult = new string[10];
   double[] result = new double[4];
   sresult = wrkString.Split(stringSeparators, StringSplitOptions.None);
   result[0] = Double.Parse(sresult[1]); //EDM
   result[1] = Double.Parse(sresult[2]);  //HR
   result[2] = Double.Parse(sresult[7]);  //BVP
   result[3] = Double.Parse(sresult[8]); //HRV
   return result;
  }

  private Point NormalizePoint(Point pt)
  {
   Point result = new Point();
   result.X = ((pt.X - xmin) * GraphCanvas.Width / (xmax - xmin));
   result.Y = GraphCanvas.Height - (pt.Y - ymin) * GraphCanvas.Height / (ymax - ymin);
   return result;
  }

  public void chartGrid_SizeChanged(Object sender, SizeChangedEventArgs e)
  {
   if (pl == null) return;
   GraphCanvas.Width = graphGrid.ActualWidth;
   GraphCanvas.Height = graphGrid.ActualHeight;
   GraphCanvas.Children.Clear();
   GraphCanvas.Children.Add(pl);
   // AddChart();
  }

  public Polyline CreateNewPolyLine(ObservableCollection<Point> obdpts)
  {
   Polyline pltemp = new Polyline();
   pltemp.Stroke = Brushes.Red;
   pltemp.StrokeThickness = .5;
   foreach (Point pt in obdpts)
   {
    pltemp.Points.Add(NormalizePoint(pt));  //(NormalizePoint(pt))
   }
   return pltemp;

  }

  private void Window_Loaded(object sender, RoutedEventArgs e)
  {
   Obdatapoints.CollectionChanged += new NotifyCollectionChangedEventHandler(Obdatapoints_CollectionChanged);
   _bw.RunWorkerAsync();
  }
 }
}