Abstract
By means of the X-ray CT (computed tomography) images, the body compositions on the cranial border plane of the sternum, the midpoint plane of the sternum and the xiphoid plane of the sternum were studied in 26 adult humans (10 males, 16 females) . On the each plane, the following items were measured; the cross-sectional area of the subcutaneous fatty layer, the muscle and bone layer and the thoracal cavity, the sagittal diameter of the thorax and the thoracal cavity, the transverse diameter of the thorax and the thoracal cavity. And about the each component, the differences in the sexes and in the body types and the changes due to the aging were discussed. The following results were obtained. 1) Total cross-sectional area of the thorax; in both sexes, the total areas were in the order D-type>C-type>A-type on the each plane. On the comparison between the body types, in male D and C-type, the areas were in the order on the xiphoid>on the midpoint>on the cranial border. In male A-type and in all females, the areas were in the order on the midpoint>on the xiphoid>on the cranial border. 2) Ratio of the each component; in the all types, the ratios were in the order the muscle and bone layer>the subcutaneous fatty layer>the thoracal cavity on the cranial border and were in the order the thoracal cavity>the muscle and bone layer>the subcutaneous fatty layer on the midpoint and on the xiphoid in both sexes. The differences between the muscle and bone layer and the subcutaneous fatty layer showed the tendency to decrease in the order A-type, C-type, D-type. 3) Changes due to the aging; in males, on the each plane, the muscle and bone layer reduced apparently and the differences from the subcutaneous fatty layer decreased with aging. In over 60 years of age, on the xiphoid plane of the sternum, the both layers were approximately equal. The difference of the ratio between the thoracal cavity and the subcutaneous fatty layer changes reversely. In females, no differences with aging were observed on the each plane. 4) Comparison of the sagittal and the transverse diameter of the thorax and the thoracal cavity; both diameters of D-type were larger than that of the other types in both sexes. In the D-type, on the cranial border, the sagittal diameter of the posterior part in males and that of the anterior part in females tended to increase. And on the midpoint, the sagittal diameters of the both parts in males and that of the anterior part in females showed the same tendancy. On the xiphoid plane, the sagittal diameters of the both parts were larger in D-type than that of the other types in both sexes. Furthermore, in males the transverse diameter was also larger than that of the other types. 5) Changes of the diameter of the thorax with aging; in males, the tendencies to increase with aging were observed in the sagittal diameters of the both parts but not in the transverse diameter. In females, no changes with aging were observed in the sagittal and the transverse diameter. 6) From the results stated above, for the factors of the increase or decrease of the cross-sectional area in the thorax, the change of the diameter of the thoracal cavity affected rather than that of the thickness of the thoracal wall. In addition, the subcutaneous fatty layer caused by the decrease of the muscle and bone layer with aging affected mostly.
