[Evaluation of air segment plethysmography using computer tomography]

The measurement of tissue volume in the calf area carried out by computer-tomography and planimetry showed a nearly elliptic form, an average bony part of 9.9 ml (9.3%), and an average tissue volume of 97.7 ml (90.7%). When compared with the tissue volume approximation (cylinder formula) the tissue volumes thus specified were too large. The error, depending on the circumference of the calf, was about 5 to 15%. There was a difference of 5% between the venous capacity measured by computer-tomography on the one hand and air segment plethysmography on the other. The reason for this is found in the varying density of veins in the examined area. The application of the sensor on the skin caused an average reduction of 5.4% in total volume and thus in the blood volume of about 59% in the examined area. The pressure-dependent venous capacity was measured with and without application of the sensors on the skin and controlled by computer-tomography. The results showed an average difference of only 2.1%. Thus it is obviously unimportant for the results of the investigation presented, if the venous capacity is measured on the basis of the reduced total volume caused by the application of the sensors on the skin. With regard to the computer-tomographical and planimetrical control and the error of measurement discussed, the results suggest a sufficient precision of the venoextensiometry measuring the pressure-dependent venous capacity.