Computed tomography lung volume estimation and its relation to lung capacities and spine deformation

Scoliosis is a three-dimensional deformity which is believed to impact lung function, mechanics of respiratory muscles, lung compliance, etc. It is thus of interest to investigated the relationship between degree of scoliosis in terms of apex rotation or Cobb angle respectively and normalized vital capacity (VC). Furthermore it is interesting to study the possibility of estimating lung volumes (and indirectly lung function) using CT volumetric reconstruction.

The inclusion criteria were consecutive patients for whom surgery was planned and who underwent preoperative low-dose chest CT and preoperative spirometry/plethysmography. Lung capacities were normalized (based upon previous work involving the parameters gender, age, height and smoking). Preoperative CT-scans were used to measure apical rotation and scoliosis. We investigated the relationship between degree of scoliosis in terms of apex rotation or Cobb angle respectively and normalized VC from spirometry 63 patients who had a thoracic scoliosis curve (not necessarily as primary curve). We have tested a method for estimating normalized total lung capacity (TLC) from inspiratory chest CT of a group of 61 patients.

The statistical level of significance used throughout the paper of 0.05. In the first part, we show that the group of 63 patients can, with respect to apical rotation or Cobb angle respectively, be divided into three subgroups in each case respectively, such that, pairwise, the mean of the normalized VC, for the group with higher apical rotation or Cobb angle respectively, is in some sense, at least 9% lower. We also give the result of the more simplistic analysis of subdividing into only two groups which give approximately 13% decrease for the group with higher spine deformation. A linear regression model seems inappropriate, due to the correlation coefficient for normalized VC versus apical rotation or Cobb angle respectively, being -0.53 (or in the case of Cobb angle -0.35). The correlation coefficient between apical rotation and Cobb angles, for the 63 patients, was 0.64. In the second part, the attempted linear regression model for describing the relation between lung volume estimation from inspiratory CT, and the normalized TLC from spirometry/plethysmography yields a correlation coefficient ≈0.71.

In the first part, we show that there is a group subdivision with respect to apical rotation or Cobb angle respectively, whereby groups with a higher degree of thoracic vertebral deviation have, in some sense, a lower normalized VC. We propose that a linear regression model is inappropriate. In the second part, we propose that a linear regression model could describe the relationship between estimations of lung volume from inspiratory CT, and the normalized TLC from spirometry/plethysmography.