Abstract: This paper is purposed to investigate the changes in speech formants when humen subjects breathed He-O₂ mixtures at high pressure environment, and the comparisons of the capacities in maintaining voice fundamental frequencies with the eleetromyograms in laryn-geal region during pronunciation under the same conditions. The results are as follows:
When subjects breathed He-O₂ mixtures at high pressure, the vowel formant frequencies shifted upward, particularly the 2nd formant frequencies, such that F_He=(1.2-1.5) F_air.
When subjeets were repeatedly exposed to the He-O₂ mixtures, their capacities in maitaining fundamental frequencies were improved, showing adaptable changes, but the changes of the fornant could not naturally restitute and must be manually modulated.
The duration from occurance of the electromyogram changes to burst of the voice during pronunciation in He-O₂ mixtures was 0.1-0.3 second shorter than in air, and during pronuciation the increases of cular voltage in He-O₂ were less obviously than in air.
The fundamental frequencies of speech, whatever in He-O₂ or in air, were much higher than the frequencies of electromyogram, and were not synchronous with the later.