Do snoring sounds arouse the snorer?

Abstract

Study objectives: Respiratory cycle-related electroencephalographic (EEG) changes (RCREC), especially in delta and sigma frequencies, are thought to reflect subtle, breath-to-breath inspiratory microarousals that are exacerbated in association with increased work of breathing in obstructive sleep apnea (OSA). We wondered whether snoring sounds could create these microarousals, and investigated whether earplugs, anticipated to alter snoring perception, might affect RCREC.

Design: Randomized controlled trial.

Setting: An accredited, academic sleep laboratory.

Patients: Adults (n = 400) referred for suspected OSA.

Interventions: Subjects were randomly assigned to use earplugs or not during a night of diagnostic polysomnography.

Results: Two hundred three of the participants were randomized to use earplugs. Earplug use was associated with lower RCREC in delta EEG frequencies (0.5-4.5 Hz), although not in other frequencies, after controlling for potential confounds (P = 0.048). This effect of earplug use was larger among men in comparison with women (interaction term P = 0.046), and possibly among nonobese subjects in comparison with obese subjects (P = 0.081). However, the effect of earplug use on delta RCREC did not differ significantly based on apnea severity or snoring prominence as rated by sleep technologists (P > 0.10 for each).

Conclusions: This randomized controlled trial is the first study to show that perception of snoring sounds, as modulated by earplugs, can influence the cortical EEG during sleep. However, the small magnitude of effect, lack of effect on RCREC in EEG frequencies other than delta, and absence of effect modulation by apnea severity or snoring prominence suggest that perception of snoring is not the main explanation for RCREC.

Keywords: Polysomnography; RCREC; computer-assisted signal processing; earplugs; obstructive sleep apnea; respiratory cycle-related EEG changes; snoring; sound.

Figure 1

Computation of respiratory cycle-related electroencephalogram (EEG) changes (RCREC). The variation of the EEG signal power is computed for a specific frequency band during each respiratory cycle. The nasal-oral thermistor signal is filtered (A) and divided into four time segments based on maxima, minima, and their midpoints. A digital band-pass filter is applied to the measured EEG signal (B) to produce a time series for the targeted frequency band. This signal is squared to produce a time series that shows variation of the relevant EEG power (C). The mean frequency-specific EEG power is then computed for each of the four respiratory cycle segments as defined in (A). The mean power for each segment is normalized by the mean frequency-specific power over the entire respiratory cycle. One is subtracted from each result to derive the measures shown for each of the four segments (D). The segment-specific EEG powers are averaged over many respiratory cycles to obtain the average measure for each of the four respiratory segments (E). The subject's RCREC, on this sleep study, is computed as the difference between the maximum and minimum mean relative EEG powers for each of the four respiratory segments. The RCREC thus reflects the average extent to which EEG power varies in synchrony with the respiratory cycle.

Figure 2

Delta respiratory cycle-related electroencephalographic (EEG) changes (RCREC) was lower when earplugs were used than when they were not used by men (A), but among women no such association emerged (B). Plots show median and 10^th, 25^th, 75^th, and 90^th percentiles, as well as some (not all) outliers.