[Effect of subcutaneous fatty tissue on normal respiratory sounds]

Auscultation is an important, non-invasive and simple measure in the diagnosis of lung diseases that can detect sometimes pathological processes prior to radiography. Attempts have already been made to automatically detect characteristic pathological sounds, but a knowledge of potential influencing factors is a must for correct interpretation. In this study we have investigated the effect of the subcutaneous fat layer on normal lung sounds. This is of importance to determine corrective factors for the automatic detection of bronchial breathing in pneumonia. The lung sounds of 125 healthy people (55f, 70m) were digitally recorded at four different positions of the thorax (3. ICR paravertebral, 7. ICR medioscapular, all left and right). Evaluation was done separately for gender. The subcutaneous fat layer was measured with a Holtain Skinfold Caliper at the identical four recording positions. For a quantitative evaluation of the sounds we calculated the relative power of frequency bands 330-600 Hz and 60-330 Hz and their ratio. The relation between these parameters and the subcutaneous fat layer was analyzed with the Pearson correlation. The results of this study show that the influence of subcutaneous fat layer is negligible and can be ignored in the automatic detection of lung sounds.