How to create respiratory curve (plot) from two segmented CT scans?

Dear all,

I know, that this problem isn´t your specialization, but I try, if there is any specialist in this topic. I have two CT scans of thorax (exhale and inhale). I segmented this images, so I got coordinates for each image. I subtracted these two sets of points (two cells) from each other and I got one cell array (1237x2 double). Now I would like to create respiratory curve from that, I know that axe X is time, but I don´t know, how get axe Y. I tried this, because this combination seemed to me the most logical:

grayImage1 = dicomread('000048.dcm');
grayImage2 = dicomread('000086.dcm');
[rows, columns, numberOfColorChannels] = size(grayImage1);
if numberOfColorChannels > 1
  % Máme barevný obraz, musíme ho převést na černobílý = vybereme zelený kanál
  grayImage1 = grayImage1(:, :, 2); % zelený kanál
end
[rows, columns, numberOfColorChannels] = size(grayImage2);
if numberOfColorChannels > 1
  % Máme barevný obraz, musíme ho převést na černobílý = vybereme zelený kanál
  grayImage2 = grayImage2(:, :, 2); % zelený kanál
end
figure(1)
subplot(2,2,1)
imshow(grayImage1, [])
subplot(2,2,2)
imshow(grayImage2, [])

thresholdValue = 900
binaryImage_dech1 = grayImage1 > thresholdValue;
% Odstranění okolí.
binaryImage_dech1 = imclearborder(binaryImage_dech1);
% Vyplnění otvorů.
binaryImage_dech1 = imfill(binaryImage_dech1, 'holes');
% Vymazání menších otvorů.
 binaryImage_dech1 = bwareaopen(binaryImage_dech1, 1150);
%Roztažení binárního obrazu pro přesnější segmentaci
se = strel('line',5,100);
binaryImage_dech1= imdilate(binaryImage_dech1,se);

binaryImage_dech2 = grayImage2 > thresholdValue;
% Odstranění okolí.
binaryImage_dech2 = imclearborder(binaryImage_dech2);
% Vyplnění otvorů.
binaryImage_dech2 = imfill(binaryImage_dech2, 'holes');
% Vymazání menších otvorů.
 binaryImage_dech2 = bwareaopen(binaryImage_dech2, 1150);
%Roztažení binárního obrazu pro přesnější segmentaci
se = strel('line',5,100);
binaryImage_dech2= imdilate(binaryImage_dech2,se);

subplot(2,2,3)
imshow(binaryImage_dech1, [])

subplot(2,2,4)
imshow(binaryImage_dech2, [])

figure(2)
subplot(2,2,1)
imshow(grayImage1, []);
title('Segmentace okolí'); 
axis image;% Ujištění, že se obraz po zvětšení okna nezdeformuje.
hold on;
boundaries1 = bwboundaries(binaryImage_dech1);
numberOfBoundaries = size(boundaries1, 1);
for k = 1 : numberOfBoundaries
  thisBoundary1 = boundaries1{k};
  plot(thisBoundary1(:,2), thisBoundary1(:,1), 'r', 'LineWidth', 2);
end

figure(2)
subplot(2,2,2)
imshow(grayImage2, []);
title('Segmentace okolí'); 
axis image;% Ujištění, že se obraz po zvětšení okna nezdeformuje.
hold on;
boundaries2 = bwboundaries(binaryImage_dech2);
numberOfBoundaries = size(boundaries2, 1);
for k = 1 : numberOfBoundaries
  thisBoundary2 = boundaries2{k};
  plot(thisBoundary2(:,2), thisBoundary2(:,1), 'r', 'LineWidth', 2);
end

thisBoundary1_bigger = [thisBoundary1; zeros(5,2)];
thisBoundary1_bigger = [zeros(5,2); thisBoundary1];
dech = thisBoundary2 - thisBoundary1_bigger

figure(3)
plot(dech(:,2))

I attach two CT scans in zip for this code.

Thank you for your time and answers.