睡眠時無呼吸症候群における無呼吸前後の気管音の解析

Abstract

The author analyzed night tracheal sounds from 15 patients with sleep apnea syndrome. The dominant apnea type of the 15 patients was obstructive in nine, central in three and both in three. Tracheal sound was recorded on a video tape recorder through a microphone attached to anterior neck over the trachea. Simultaneously, signals from an ordinary polysomnograph were digitized and recorded on the hard disc of a personal computer. In each patient ten apnea episodes of each type were selected for analysis. The tracheal sounds during three successive breaths preceding and following the apneas were played back and digitized for subsequent analysis. Short-time power spectra were calculated using a fast-Fourier transform successively and displayed as a form of sound-spectrogram. Mean power spectra during the inspiratory and expiratory phases of each breath were separately calculated and compared with those during breaths while awake. In the cases of obstructive apneas, tracheal sounds preceding apneas contained a snoring sound, on the inspiratory phase in about half of the cases and on the expiratory phase in about 20% of them. In most cases resumed breaths after obstructive apneas started with the abrupt emergence of tracheal sound. The resumed trachal sounds were extremely strong (22.2 dB stronger than breath sounds while awake) : in spection of the time expanded waveform revealed a spike with positive deflection followed by any of irregular noise (47%), snore (35%) or normal breath sound (18%). By contrast, in most cases of central apnea normal breath sounds preceded and followed the apneas, and the ratio of snoring in each breath was 0 to 15%. The tracheal sounds were thought to reflect the pathophysiology of the upper airway in sleep apnea. Analysis of tracheal sound recording could be a useful means not only for detection of apnea events but for determining the type of apnea in diagnosis of sleep disordered breathing.