Studies on the tubal function have gained much more importance in recent years, because the good tubal function was proved to be one of key point to attain satisfactory result of the reconstructive surgery of the sound conductive system. Although several different methods to evaluate the tubal function have been described, the Eustachian air douche is a most popular clinical procedure to examine the patency of the tube even in these days. Concerning the acoustical properties of the blowing sound, objective analysis has not hardly be made and the true meaning of subjective descriptions regarding to the auscultated sound has not hardly be known. This is the reason why the authors designed to study the acoustical properties of the tubal blowing sound.
As a preliminary experiment, the ordinal procedure of the Eustachian air douche was examined from the acoustical viewpoint. The frequency response characteristics of a standard otoscope was measured as illustrated in Fig. 1. The blowing sound recorded through an otoscope had not any acoustic component above 2kc, which was clearly seen by the soundspectrogram shown in Fig. 2. According to these results, an otoscope in general use was thought to be an acoustical band pass filter, and the inf ormations gained by the auscultation was limited by this frequency characteristics of the otoscope. In order to obtain more extended acoustic component, the authors devised the pick-up and recording method of the blowing sound and performed the soundspectrographic analysis of the recorded sound. The blockdiagram and the frequency response curve of this method were illustrated in Figs. 3 and 4a respectively. It was shown by these figures that the author's method was more favourable to obtain acoustical informations of the tubal blowing sound as compared with the method using otoscope.
The narrow band soundspectrogram and wide band soundspectrogram of a normal blowing sound recorded by the auther's method were presented in Figs 5 a and 5b. The noise pattern up to about 4kc which had at least two main resonant frequency bands, was found to be characteristics of the normal blowing sound.
Several representative abnormal patterns were demonstrated. A characteristic bar illustrated in Fig. 6-a was marked in the case of tubal obstruction. A distinguished vertical striped pattern as shown in Fig. 7 was obtained in the case of tubo-typanal catarrh. Generaly, narrow band soundspectrogram provided more distinctive abnormal pattern.
The spectrum of the blowing sound was found to be another clue for the evaluation of the tubal patency. As an example, the pattern obtained in the case of patulous Eustachian tube was illustrated in Fig. 8. The resonant frequency band around 1kc which was one of characteristics of the normal pattern, could not be recognized in this figure.
Further investigations concerning the orign of the resonant frequency band and the abnormal features will be made to establish the clinical importance of this acoustical method, The availability of the author's method for the evaluation of the tubal function will be discussed in more datails comparing the results of other examinations on the tubal function in the following papers.