Live display Speed using matlab

I am using a Photometrics evolve camera and have had trouble with the speed display of the images as time gets bigger. I am using matlab with the CMMCore library. My initial thought when coming to this problem is the readout frequency of the camera and or the efficiency of my code. The purpose of my code is not to register any picture but just to display and then discard (right away). My code looks like follow:

while (handles.mmc.isSequenceRunning())

           xlim([1 120]);%Identify the X axis
           hold on;
           i=i+1;
           if (handles.mmc.getRemainingImageCount()> 0)
              img1 = handles.mmc.getLastImage;%Recieve the image
            %  img1 = handles.mmc.popNextImage;
              [pixelType] = pixel(handles.mmc);%Define the pixel type, 8or16 bits. In our case it is 16
              [img1] = camprop(handles.mmc, img1,pixelType);%Properties needed by the camera
              img = transpose(img1);%Transpose the matrix to get the right picture

              %%%First signal
              sig(xp) = img(handles.X1,handles.Y1); %Knows the x and y coordinated and plots the signal
              sig(1)=img(handles.X1,handles.Y1); %Define the first value of sig
              %%%Second signal
              sig2(xp) = img(handles.X2,handles.Y2);%Knows the x and y coordinated and plots the signal
              sig2(1)=img(handles.X2,handles.Y2);%Define the first value of sig
              Y =[sig(xp),sig(xp-1)]; %Signal 1 interpolation
              Y2 =[sig2(xp),sig2(xp-1)]; %Signal 1 interpolation
              X = [xp , xp-1];    % X value of signal 1 and 2 which was set in the begining of the while loop
              axes(handles.axes1); % First axes where we will draw the first signal

              %%%Ploting of the first signal 
              %%%%%%White rectangle that updates the signal
              if (xp < 120)
                   rectangle('Position',[xpm1 0 3 3000],'FaceColor','w','EdgeColor','w');
              end
              plot(X,Y);
              hold on; 
              drawnow;

              %%%Potting of the second signal
              xlim([1 120]) %Defining the limit for the X axis
              hold on
              axes(handles.axes2);
              %%%%%%White rectangle that updates the signal
              if (xp < 120)
                   rectangle('Position',[xpm1 0 3 3000],'FaceColor','w','EdgeColor','w');
              end
              plot(X,Y2);
              hold on; 
              drawnow;
              xp = xp+1;
              xpm1 = xpm1+1;
              if (xp > 120)
                  xp = 2;
                   xpm1 = 1;
              end
              tt = tt+1;
           end
            handles.mmc.getImageBufferSize()

      end

Thank you in advance