中等度騒音と職業性難聴との研究—（第1篇）中等度騒音下従業員の聴力自覚症と聴力検査成績との統計的観察

　緒言

　周知の如く，騒音が騒音下従業員の聴覚及び全身に及ぼす影響に就ては，重騒音，中等度騒音を問わず，幾多先哲により種々の研究が発表されている。余は中等度騒音の影響及び実態に就て卿かにても知見を加えんと考え，聴力損失を1/4（a＋2b＋c）式より算出し，（但し，500c/sの損失値をa db，1,000c/sの夫をb db，2,000c/sの夫をC dbとす），中等度騒音下従業員の自覚症と聴力検査成績との統計的観察の研究を既に施行し，既に発表中であるが，今回1/4（a＋2b＋d）式（但し，500c/sの損失値をadb，1,000c/sの夫をbdb，4,000c/sの夫をddbとす）を使用し，前回の成績と比較検討し，且つ松浦の重騒音下従業員の自覚症と聴力検査成績との統計的観察の夫（1958年）とも併せ比較検討し，梢々興味ある成績を得たので，茲にその成績の大要を報告する次第である。

　The effect of hearing among individuals who are engaged in a workshop constantly exposed to medium degree noise is studied. Hearing loss calculations are made by a formula, 1/4(a+2b+c);(provided that:Loss of 500c/s is considered as a db, that of 1,000 c/s as b db and 2,000 c/s as c db). The results of this examination is compared to the next examination which was slightly differed by adopting a formula, 1/4(a+2b+d) where 500 c/s loss is considered as a db, 1,000 c/s as b db and 4,000 c/s as d db.

　Two hundred seventy four employees 548 ears constantly exposed to medium degree noise of 60 to 100 phon in loudness were studied for hearing acuity by means of 51B audiometer ; objective results and the subjective sensation of hearing abilities were also studied in comparison.

　The subjective and the objective hearings were not necessarily in agreement;in some the gap between the two was cosiderable. There were 11.7% of the total number who considered themselves to be normal but showed a loss of hearing. Subjectively normal individuals suffering tinnitus as the only symptom showed a hearing loss among 20.5%. On the other hand, those who considered themselves as slightly hard of hearing were by objective test found to be normal by 35.1%. Subjective loss with tinnitus showed a normalcy of 27.3%. The loss hearing increased proportionately with the increase of age particularly beyond the age of 41.