The authors statistically studied the respiratory function in 138 cases of silicotics by means of principal component analysis. The respiratory function tests were spirography (%VC, FEV₁%), measurement of the lung volumes (%TLC, %FRC, %RV, RV%), CO diffusing capacity by single breath method, (%DL_CO, DL_CO/VA), flow volume curve(%V₅₀, %V₂₅, V₅₀/V₂₅), the analysis of arterial blood gas(%PaO₂, PaCO₂, pH, %A-D_O2) and mechanical properties (%Pel at TLC, Cst(1), Cdyn/Cst(1), R_L, R_T).
According to the factor loading with values higher than 0.4 in each principal component, the significance of each principal component can be determined. The first principal component, Z₁, included FEV₁%, %V₅₀, %V₂₅, R_L, R_T, and RV% as the factor loading with higher value and may be considered as the obstructive impairment factor. Because %TLC, %FRC, %RV, Cst(1), %Pel at TLC and %DL_CO showed higher values, Z₂ was suggested to be the factor of restrictive impairment or over-inflation, Z₃, the disturbance of diffusing capitacity with hypoxemia, and Z₄ the impairment of small airway. In other words, the disturbance of respiratory function in silicosis may be constructed by the above described principal components.
The principal component scores (PCS) are weighed by the various respiratory functions. If we compare two PCS with each other on the graph, the characteritics of the functional disturbance may be easily demonstrated. Lastly, we investigated the relationships between the grading of the findings on chest X-P and the PCS.
The relation between the profusion of the small opacities and Z₁, the obstructive impairment, and Z₂, the restrictive impairment, and between the extent of the large opacities and Z₁, obstructive impairment, was statistically significant.