Diagnostic percussion: an investigation using electronic measurement techniques
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Medical percussion, because of its simplicity, is an extremely useful diagnostic aid. Yet it is poorly understood. Confusion exists both in the terminology and in the description of the various percussion sounds. In addition, the sound pressure waveforms presently in use are found to be unsatisfactory. A special purpose tape recording system, which was constructed to allow automatic retrieval of the waveforms onto chart paper is described. Percussion sounds are first examined qualitatively. Preliminary observational studies of the waveshapes reveal the types and ranges of the sounds. No important features of these waveshapes are found to be obscured by quiet room noise. Subjective descriptions of the sounds are reviewed. Results of Pourier analysis are correlated with judgements of frequency content. Other descriptions - intensity, duration, tactile sensation - are examined while producing a physical explanation of the sound pressure waveshape. Two fundamental physical components are isolated. A four parameter model for quantitatively describing percussion sounds is proposed. The validity of the model is verified visually and acoustically with simulated waveforms; an electronic simulator being designed for this purpose. A sound reproduction system, developed to enable the transient percussion sounds to be reproduced, is discussed. Computer-automated parameter measurement is used. Tape-recorded sounds are fed directly to the computer and the four parameters of each sound analysed are tabulated on the computer's teletype without any human intervention other than the initial setting up of equipment. It is shown that 'resonant* sounds of varying quality can be satisfactorily quantified and that differences between sounds can be measured. Variation in parameters due to changing the lung volume and to moving the percussion position down the chest are measured. Also, sounds from several healthy subjects are compared. Success in detecting diseased tissue in the lung is achieved using this four parameter measurement technique.