[How can one recognize a velum snorer?]

In ten habitually snoring subjects and ten patients with obstructive sleep apnea syndrome, preoperative snoring sounds above a preset sound pressure level were recorded and a frequency spectrum analysis by means of time series Fast Fourier Transformation was performed. All patients underwent uvulopalato-pharyngoplasty after which the snoring sounds were recorded again and analysed under the same conditions. Preoperative frequency spectra in heavy snorers were dominated by a component which results from the movement of the soft palate and uvula and which presents as a low-frequency vibration of 25 to 50 c/s and its harmonics up to several hundred c/s. After UPPP the sound pressure level of the snoring noise in heavy snorers was reduced by 20 to 30 decibels and could not be recorded any more. The frequency spectrum of snoring noises in patients with obstructive sleep apnea syndrome differed from those of heavy snorers. In apnea patients the snoring noise usually consisted of other and higher frequency components which masked the vibration of the soft palate and uvula to a more or less high degree. An extreme degree of masking is reached in snoring noises following apneic episodes when identification of the movement of the soft palate is impossible. After performing UPPP in an apneic patient the low-frequency content of the spectrum below about 400 Hz was reduced dramatically but higher frequency parts were still present. This resulted in only minor reduction of snoring noise sound pressure level. Our results are in agreement with other authors in showing that UPPP is not successful when the site of obstruction is not in the velo-pharyngeal plane.(ABSTRACT TRUNCATED AT 250 WORDS)