The authors have declared that no competing interests exist.
Conceived and designed the experiments: LAL JFY HYL. Performed the experiments: LAL YSC DLW CMC NHC. Analyzed the data: LAL YLL DLW CGH. Contributed reagents/materials/analysis tools: JFY YLN NHC TJF CGH. Wrote the paper: LAL JFY YLL YSC DLW HYL.
Annoying snore is the principle symptom and problem in obstructive sleep apnea syndrome (OSAS). However, investigation has been hampered by the complex snoring sound analyses.
This study was aimed to investigate the energy types of the full-night snoring sounds in patients with OSAS.
Twenty male OSAS patients underwent snoring sound recording throughout 6 hours of in-lab overnight polysomnogragphy. Snoring sounds were processed and analyzed by a new sound analytic program, named as Snore Map®. We transformed the 6-hour snoring sound power spectra into the energy spectrum and classified it as snore map type 1 (monosyllabic low-frequency snore), type 2 (duplex low-&mid-frequency snore), type 3 (duplex low- & high-frequency snore), and type 4 (triplex low-, mid-, & high-frequency snore). The interrator and test-retest reliabilities of snore map typing were assessed. The snore map types and their associations among demographic data, subjective snoring questionnaires, and polysomnographic parameters were explored.
The interrator reliability of snore map typing were almost perfect (
Snore map typing of a full-night energy spectrum is feasible and reliable. The presence of a higher snore map type is a warning sign of severe OSAS and indicated priority OSAS management. Future studies are warranted to evaluate whether snore map type can be used to discriminate OSAS from primary snoring and whether it is affected by OSAS management.
Snoring is the most prevalent symptom and also a principal indicator of obstructive sleep apnea syndrome (OSAS): 51.9% of male Taiwanese individuals older than 15 years having habitual snoring
The power spectrum is a method to simultaneously measure the snore inttensity and frequency. Herzog
(A) & (E) Primarily monosyllabical low-frequency snoring (type 1 snore map). (B) & (F) Duplex low- and mid-frequency snores (type 2). (C) & (G) Duplex low- and high-frequency snoring (type 3). (D) & (H) Triplex low-, mid-, and high-frequency snores (type 4).
According to the concept of “Energy = power × time”, we counted the 6-hour powers of different frequency snoring sounds and found that the patients’ snoring energy types were more easily to be classified. Herein, we defined four energy types (snore map types) of snoring sounds in OSAS patients: type 1 (monosyllabical low- frequency snore,
Twenty consecutive male adult patients with a history of habitual snoring and witnessed sleep apnea, and/or excessive daytime sleepiness were prospectively enrolled from the Sleep Center of the Chang Gung Memorial Hospital in Taoyuan, Taiwan. They had undergone a snoring sound recording accompanied with a standard overnight PSG. Primary inclusion criterion was apnea-hypopnea index (AHI) >5, and secondary criterion was fitting in with snore map type: type 1 (
Demographic characteristics | Snoring questionnaires | Polysomnographic parameters | Severity of OSAS | Snore map type | |||||||||||
No. | Age (yr) | BMI (kg/m2) | NC (cm) | Tonsil size | FTP | Stage | VAS | SOS | SBPS | AHI | AI | HI | SI | ||
1 | 44 | 24.3 | 37 | 2 | IIb | 2 | 10 | 39 | 33 | 38.5 | 0.2 | 38.3 | 19.8 | 2 | 2 |
2 | 46 | 25.5 | 40 | 2 | IIb | 2 | 8 | 49 | 39 | 22.7 | 11.8 | 10.9 | 4.4 | 1 | 1 |
3 | 39 | 26.2 | 41 | 1 | I | 2 | 5 | 53 | 50 | 57.0 | 9.1 | 47.9 | 0.7 | 2 | 4 |
4 | 27 | 25.3 | 38 | 2 | IIa | 2 | 8 | 41 | 33 | 10.3 | 0 | 10.3 | 2.0 | 1 | 1 |
5 | 47 | 31.6 | 42 | 2 | IIa | 2 | 8 | 44 | 33 | 26.3 | 0 | 26.3 | 180.5 | 1 | 2 |
6 | 49 | 28.2 | 42 | 2 | IIa | 2 | 9 | 41 | 33 | 57.5 | 5.8 | 51.7 | 188.6 | 2 | 3 |
7 | 26 | 28.1 | 38 | 2 | IIa | 2 | 10 | 18 | 17 | 32.3 | 6.5 | 25.8 | 110.0 | 2 | 3 |
8 | 39 | 27.5 | 39 | 2 | IIa | 2 | 6 | 56 | 50 | 62.6 | 26.0 | 36.6 | 263.3 | 3 | 3 |
9 | 46 | 29.8 | 41 | 3 | IIa | 2 | 8 | 21 | 22 | 51.4 | 43.8 | 7.6 | 309.6 | 2 | 4 |
10 | 54 | 27.7 | 42 | 3 | III | 3 | 9 | 28 | 28 | 54.8 | 54.1 | 0.7 | 214.8 | 2 | 4 |
11 | 20 | 28.7 | 40 | 3 | I | 1 | 8 | 28 | 28 | 45.0 | 0.4 | 44.6 | 332.7 | 2 | 4 |
12 | 38 | 31.2 | 39 | 2 | IIa | 2 | 8 | 30 | 28 | 104.0 | 13.9 | 90.1 | 520.1 | 3 | 4 |
13 | 41 | 23.8 | 38 | 1 | IIb | 2 | 10 | 23 | 17 | 53.1 | 34.7 | 18.4 | 320.3 | 2 | 1 |
14 | 53 | 24.3 | 37 | 1 | IIb | 2 | 8 | 64 | 17 | 41.3 | 7.2 | 34.1 | 128.5 | 2 | 1 |
15 | 47 | 25.7 | 38 | 2 | III | 3 | 10 | 31 | 17 | 74.8 | 5.3 | 69.5 | 51.0 | 3 | 1 |
16 | 46 | 24.2 | 37 | 3 | IIb | 2 | 6 | 30 | 50 | 59.8 | 54.3 | 5.5 | 251.4 | 2 | 2 |
17 | 28 | 31.1 | 43 | 3 | III | 2 | 8 | 46 | 33 | 77.3 | 70.9 | 6.4 | 148.9 | 3 | 3 |
18 | 39 | 23.3 | 36 | 3 | III | 2 | 7 | 41 | 39 | 25.8 | 0.2 | 25.6 | 11.3 | 1 | 2 |
19 | 39 | 29.3 | 44 | 3 | IIb | 2 | 5 | 39 | 44 | 73.5 | 31.4 | 42.1 | 94.5 | 3 | 3 |
20 | 28 | 27.8 | 40 | 2 | IIb | 2 | 10 | 25 | 22 | 16.3 | 0 | 16.3 | 493.7 | 1 | 2 |
BMI: body mass index. FTP: Friedman tongue position. NC: neck circumference. VAS: visual analogue scale. SOS: snoring outcome survey. SBPS: spouse/bed partners survey. AHI: apnea-hypopnea index. AI: apnea index. HI: hypopnea index. SI: snoring index. OSAS: obstructive sleep apnea syndrome.
All patients completed three snore outcome measures: the VAS, SOS, and SBPS questionnaires. The patients were asked to quantify the average intensity of their snoring using a VAS from 0 (no snoring) to 10 (very severe snoring). The SOS and SBPS are two valid, reliable, and disease-specific outcome measures. The SOS comprised of eight Likert-type items to comprehensively evaluate the duration, loudness, and frequency of snoring, and the SBPS containing another three Likert-type items. The SOS and SBPS were normalized on a scale ranging from 0 (worst) to 100 (best)
Standard overnight PSGs (Nicolet UltraSom System, Madison, WI, USA) were performed in the sleep laboratory to document sleep parameters in each patient. The PSG parameters used in this study were snoring index (PSG-SI), AHI, apnea index (AI), and hypnonea index (HI). All respiratory events were defined as previously described
We used three external measurement microphones (TEDS type 46AE, G.R.A.S. Corp., Holte, Denmark), positioned 100 cm above the patient’s head
The microphone detected sound frequencies between 3.15 and 20,000 Hz. A sound pressure level calibration was performed using a sound calibrator (B&K4321, Brüel & Kjær Corp., Nærum, Denmark) before each test. The intensities of the recorded snoring sounds were collected by portable data cards (PXI 4462, National Instruments Corp., Austin, TX, USA) and processed by digital recording software (Sound & Vibration Toolkit for Labview, National Instruments Corp., Austin, TX, USA) at sample rate of 44,100 Hz. The frequency power spectrum was created by fast Fourier transformation (range, 3.15 Hz–2,000 Hz).
A snore detection system was designed to separate the snore episodes from environmental (machines, door opening, moving furniture, etc.) and other biological noises (body movements, oral communications, coughs, etc.).
First, recording the environmental sounds of 10 minutes in a study room (silent sleep laboratory) were sampled and analyzed at the beginning of each test, and we found the highest intensity of background noises were relatively constant and occurred between 3.15 Hz and 40 Hz. Using a high-pass filter technique, the interference of background noises and snore episodes was reduced.
Second, a snoring sound detection algorithm was designed based on an adaptive energy threshold. In our previous study
Note that the duration of snoring sound was between 0.6 and 4.0 seconds (blue box) and noise intensity in sound pressure level was general less than 10 dB when frequencies were higher than 450 Hz (green box).
Third, the sensitivity, positive predictive value, and stability of this system for the detection of snores were evaluated. We compared the detection results of ten different 90-minute snoring sounds tested by this system (total detected snore number, 3857) with those snore episodes manually scored by agreement among five careful listeners (total snore number, 3826). The sensitivity and positive predictive value of our detection method were 99.9% and 99.1%, respectively. Moreover, this system was evaluated by the Jury stability test and was considered as “stable” for detecting snores
We simultaneously recorded snoring sounds and PSG for 6 hours during each subject’s natural sleep. We harmonized the time scale and correlated respiratory events and snoring episodes manually by adjusting the time axis of both systems.
(A) Sound intensities of the nine detected snores after an apnea event within one minute. (B) Three dimensional figure showing the power spectrum of each snoring episode. (C) Two dimensional figure showing nine power spectra together. (D) Energy spectrum strengthening the contributions of the predominately loud snoring sounds and helping us to type the snore map.
The previously most popular definition of high-frequency domain of the post-apneic snore was above 800 Hz
Some cases with low amplitude of snoring sound energy needed adjustment of the Y-axis scales for an easier typing.
For snore map typing, we adjusted the highest energy to the upper limit of the Y-axis (
We further analyzed each snore and obtained three independent variables in a 6-hr snoring record: total snoring index (total-SI), total maximal sound intensity (total-Imax [dB]), and total mean sound intensity (total-Imean [dB]). Using frequency filter programs, we calculated the B1-SI, B1-Imax, B1-Imean, B1 peak sound frequency (B1-Fpeak [Hz]) and B1 mean sound frequency (B1-Fmean [Hz]), the B3-SI, B3-Imax, B3-Imean, B3-Fpeak, and B3-Fmean, and the B2-SI, B2-Imax, B2-Imean, B2-Fpeak, and B2-Fmean. Data for each of these acoustic parameters were averaged for all the detected episodes.
Descriptive statistics were calculated for baseline subject characteristics and results are reported with mean ± standard deviation. Summary statistics for the cut-off frequencies (Lines 1 and 2) of the snore spectrum and the snore map types were also calculated with the
All cases | Type 1 | Type 2 | Type 3 | Type 4 | ||||||||
( |
( |
( |
( |
( |
Total | 1–2 | 1–3 | 1–4 | 2–3 | 2–4 | 3–4 | |
Demographic characteristics | ||||||||||||
Age | 38±9.1 | 42.8±9.8 | 40.8±7.8 | 36.2±9.4 | 39.4±12.6 | 0.681 | 0.599 | 0.249 | 0.530 | 0.396 | 0.753 | 0.751 |
BMI (kg/m2) | 26.9±2.8 | 24.9±0.8 | 26.2±3.5 | 28.8±1.4 | 28.7±1.9 | 0.040 |
1.00 | 0.009 |
0.009 |
0.175 | 0.251 | 0.917 |
NC (cm) | 39.5±2.2 | 38.1±1.1 | 38.4±2.5 | 41.1±2.5 | 40.5±0.8 | 0.071 | 0.670 | 0.045 |
0.020 |
0.093 | 0.206 | 0.528 |
Tonsil Size | 2.2±0.7 | 1.6±0.5 | 2.4±0.5 | 2.4±0.5 | 2.4±0.9 | 0.182 | 0.058 | 0.058 | 0.121 | 01.00 | 0.817 | 0.817 |
FTP | 2.7±0.9 | 3.0±0.7 | 3.0±0.7 | 2.6±0.9 | 2.0±1.2 | 0.278 | 1.00 | 0.371 | 0.131 | 0.371 | 0.131 | 0.262 |
Stage | 2.1±0.4 | 2.2±0.4 | 2.0±0.0 | 2.0±0.0 | 2.0±0.7 | 0.808 | 0.317 | 0.317 | 0.606 | 1.00 | 1.00 | 1.00 |
Snoring questionnaires | ||||||||||||
VAS | 8.1±1.6 | 8.8±1.1 | 8.2±1.8 | 7.6±2.1 | 7.6±1.5 | 0.684 | 0.504 | 0.382 | 0.238 | 0.595 | 0.665 | 0.828 |
SOS | 37.3±12.5 | 41.6±16.1 | 35.7±8.3 | 40.2±13.8 | 31.8±12.3 | 0.599 | 0.602 | 0.917 | 0.251 | 0.402 | 0.465 | 0.347 |
SBPS | 31.7±11.3 | 24.5±10.8 | 35.6±10.1 | 35.6±12.8 | 31.1±10.8 | 0.352 | 0.133 | 0.190 | 0.335 | 1.00 | 0.337 | 0.395 |
Polysomnographic parameters | ||||||||||||
AHI | 49.2±23.4 | 40.4±25.3 | 33.3±16.8 | 60.6±17.7 | 62.4±23.7 | 0.119 | 0.754 | 0.175 | 0.175 | 0.047 |
0.076 | 0.465 |
AI | 18.8±22.0 | 11.8±13.5 | 10.9±24.2 | 28.1±26.5 | 24.3±23.3 | 0.210 | 0.340 | 0.347 | 0.251 | 0.074 | 0.115 | 0.917 |
HI | 30.4±23.0 | 28.6±24.8 | 22.4±12.3 | 32.5±17.3 | 38.2±36.0 | 0.810 | 0.917 | 0.602 | 0.917 | 0.251 | 0.465 | 0.754 |
SI | 182.3±157.0 | 101.2±132.7 | 191.3±198.1 | 161.0±67.8 | 275.6±189.4 | 0.432 | 0.347 | 0.251 | 0.251 | 0.917 | 0.465 | 0.175 |
OSAS severity | 2.0±0.7 | 1.8±0.8 | 1.4±0.5 | 2.6±0.5 | 2.2±0.4 | 0.055 | 0.419 | 0.151 | 0.421 | 0.032 | 0.095 | 0.310 |
BMI: body mass index. FTP: Friedman tongue position. NC: neck circumference. VAS: visual analogue scale. SOS: snoring outcome survey. SBPS: spouse/bed partners survey. AHI: apnea-hypopnea index. AI: apnea index. HI: hypopnea index. SI: snoring index. OSAS: obstructive sleep apnea syndrome.
Significance was assessed by a Kruskal Wallis test.
Significance was tested using a 2-sided Mann-Whitney
A value of
In our new snoring sound analytic method, the interrater reliabilities for the raters were found to be significant to determine the Line 1 (
Type 1 | Type 2 | Type 3 | Type 4 | |||||||||
( |
( |
( |
( |
Total | 1–2 | 1–3 | 1–4 | 2–3 | 2–4 | 3–4 | ||
Total | SI | 273.8±217.3 | 401.6±336.5 | 200.6±78.8 | 373.2±134.8 | 0.346 | 0.602 | 0.917 | 0.251 | 0.249 | 0.917 | 0.047 |
Imax (dB) | 64.9±6.1 | 70.7±6.4 | 72.3±4.5 | 78.9±5.3 | 0.014 |
0.175 | 0.076 | 0.009 |
0.465 | 0.047 |
0.028 |
|
Imean (dB) | 50.2±4.4 | 52.6±3.2 | 56.5±3.9 | 59.5±3.8 | 0.018 |
0.465 | 0.047 |
0.016 |
0.076 | 0.028 |
0.251 | |
Fpeak (Hz) | 120.0±27.4 | 128.0±29.5 | 116.0±194.5 | 122.0±43.8 | 0.657 | 0.277 | 0.658 | 1.000 | 0.501 | 0.381 | 0.435 | |
Fmean (Hz) | 726.0±554.0 | 832.0±530.2 | 1370.0±242.4 | 1668.0±436.8 | 0.072 | 0.465 | 0.142 | 0.076 | 0.094 | 0.028 |
0.465 | |
B1 | SI | 261.6±222.9 | 375.0±347.0 | 163.0±69.8 | 304.4±146.1 | 0.595 | 0.754 | 0.465 | 0.602 | 0.465 | 0.917 | 0.117 |
Imax (dB) | 59.0±3.5 | 63.1±5.1 | 60.0±4.6 | 66.7±6.6 | 0.173 | 0.117 | 0.754 | 0.094 | 0.175 | 0.347 | 0.175 | |
Imean (dB) | 46.1±2.1 | 47.9±4.2 | 47.4±1.0 | 48.8±3.7 | 0.488 | 0.465 | 0.251 | 0.251 | 0.917 | 0.602 | 0.175 | |
Fpeak (Hz) | 250.0±34.6 | 270.0±22.3 | 236.0±53.7 | 252.0±40.9 | 0.661 | 0.290 | 0.672 | 0.915 | 0.287 | 0.462 | 0.673 | |
Fmean (Hz) | 112.7±18.2 | 137.3±22.3 | 116.1±17.4 | 116.5±37.9 | 0.216 | 0.076 | 0.754 | 0.917 | 0.117 | 0.117 | 0.465 | |
B2 | SI | 255.2±139.0 | 418.8±271.3 | 231.4±82.0 | 418.2±114.7 | 0.127 | 0.251 | 0.917 | 0.117 | 0.117 | 0.917 | 0.028 |
Imax (dB) | 58.0±7.3 | 68.2±5.4 | 61.9±2.6 | 76.4±6.5 | 0.007 |
0.047 |
0.1117 | 0.016 |
0.076 | 0.076 | 0.009 |
|
Imean (dB) | 44.3±3.2 | 47.9±3.9 | 45.2±1.2 | 51.6±4.6 | 0.044 |
0.251 | 0.251 | 0.016 |
0.347 | 0.175 | 0.028 |
|
Fpeak (Hz) | 828.0±49.2 | 786.0±73.3 | 844.0±8.9 | 848.0±4.5 | 0.126 | 0.118 | 0.700 | 0.881 | 0.105 | 0.044 |
0.439 | |
Fmean (Hz) | 424.9±56.2 | 430.6±97.7 | 413.2±71.2 | 468.9±89.7 | 0.832 | 0.917 | 0.917 | 0.602 | 0.754 | 0.602 | 0.251 | |
B3 | SI | 358.0±133.0 | 327.8±204.4 | 363.2±48.5 | 555.6±138.6 | 0.069 | 0.917 | 0.754 | 0.047 |
0.917 | 0.076 | 0.009 |
Imax (dB) | 61.9±10.8 | 66.1±8.9 | 72.0±4.5 | 76.9±4.8 | 0.064 | 0.465 | 0.175 | 0.028 |
0.347 | 0.076 | 0.076 | |
Imean (dB) | 43.3±4.1 | 44.2±4.1 | 49.4±4.7 | 52.8±3.3 | 0.011 |
0.602 | 0.076 | 0.009 |
0.117 | 0.009 |
0.175 | |
Fpeak (Hz) | 1992.0±13.0 | 1950.0±111.8 | 1734.0±267.1 | 1980.0±28.3 | 0.037 |
0.700 | 0.020 |
0.638 | 0.041 |
0.700 | 0.026 |
|
Fmean (Hz) | 1209.9±158.9 | 1242.9±178.2 | 1215.9±124.2 | 1237.8±81.6 | 0.881 | 0.754 | 0.465 | 0.754 | 0.465 | 0.602 | 0.465 |
SI: snoring index. Imax: maximal sound intensity. Imean: mean sound intensity. Fpeak: peak frequency. Fmean: mean frequency. B1: the band between 40 Hz and 300 Hz. B2: the band between 301 Hz and 850 Hz. B3: the band between 851 Hz and 2000 Hz.
Significance was assessed by a Kruskal Wallis test.
Significance was tested using a 2-sided Mann-Whitney
A value of
The differences in the B2-Imax between type 1 and type 2 reached a statistical significance. Type 2 had a significant higher B3-Fpeak than type 3. Type 3 and type 4 were significantly different in the total-SI, B1-SI, B2-SI, B3-SI, and B2-Imax. Type 3 patients had higher mean total-Imean B2-Fpeak, and lower B3-Fpeak than type 1 patients. The total-Imax, total-Imean, B2-Imax, B2-Imean, B3-SI, B3-Imax, and B3-Imean were particularly higher of type 4 patients than type 1 patients. Type 2 and type 4 were different in the total-Imax, total-Imean, total-Fmean, B2-Fpeak, and B3-Imean.
(A) A scatter plot of body mass index (BMI) versus snore map type. (B) A scatter plot of neck circumference versus snore map type. (C) A scatter plot of apnea-hypopnea index versus snore map type. (D) A scatter plot of severity of obstructive sleep apnea syndrome (OSAS) versus groups of snore map type. After adjustment for BMI and neck circumference, snore map type 3–4 was significantly associated with severity of OSAS (
We further explored the associations of acoustic parameters and subjective questionnaire scores among these OSAS patients. After adjustment for BMI and neck circumference, the total-Fpeak was independently associated with the VAS score (
We further categorized the subjects into the snore map type 1–2 group and the snore map type 3–4 group (Table 4). The snore map type 3–4 group had significantly higher BMI, neck circumference, AHI, AI, and severity of OSAS than the snore map type 1–2 group. Among acoustic parameters, the snore map type 3–4 group had remarkably higher total-Imax, total-Imean, B3-Imax, and B3-Imean. After adjustment for BMI and neck circumference, snore map type 3–4 was marginally significantlycorrelated with AHI (
Group | Demographic characteristics | Snoring questionnaires | Polysomnographic parameters | Severity of OSAS | ||||||||||||||||||||
Age (yr) | BMI (kg/m2) | NC (cm) | Tonsil Size | FTP | Stage | VAS | SOS | SBPS | AHI | AI | HI | SI | ||||||||||||
Type 1-2 | 41.8±8.4 | 25.6±2.5 | 38.3±1.8 | 2.0±0.7 | 3.0±0.7 | 2.1±0.3 | 8.5±1.4 | 38.6±12.4 | 30.0±11.5 | 36.9±20.6 | 11.4±18.5 | 25.5±18.7 | 146.3±165.9 | 1.6±0.7 | ||||||||||
Type 3-4 | 37.8±10.6 | 28.8±1.6 | 40.8±1.8 | 2.4±0.7 | 2.3±1.1 | 2.0±0.5 | 7.6±1.7 | 36.0±13.1 | 33.3±11.4 | 61.5±19.7 | 26.2±23.6 | 35.4±26.8 | 218.3±147.1 | 2.4±0.5 | ||||||||||
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0.287 | 0.005 |
0.009 |
0.185 | 0.081 | 0.584 | 0.287 | 0.677 | 0.645 | 0.019 |
0.049 |
0.364 | 0.257 | 0.014 |
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Type 1-2 | 337.7±275.4 | 67.8±6.7 | 51.4±3.8 | 318.3±281.3 | 61.0±4.7 | 47.0±3.2 | 337.0±220.8 | 63.1±8.1 | 46.1±3.9 | 342.9±163.3 | 64.1±9.6 | 43.8±3.9 | ||||||||||||
Type 3-4 | 286.9±138.2 | 75.6±5.8 | 58.0±3.9 | 233.7±131.2 | 63.4±6.4 | 48.1±2.7 | 324.8±136.1 | 69.1±8.9 | 48.4±4.6 | 459.4±141.0 | 74.5±5.1 | 51.1±4.2 | ||||||||||||
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0.940 | 0.010 |
0.002 |
0.705 | 0.571 | 0.326 | 1.000 | 0.151 | 0.151 | 0.131 | 0.023 |
0.002 |
BMI: body mass index. FTP: Friedman tongue position. NC: neck circumference. VAS: visual analogue scale. SOS: snoring outcome survey. SBPS: spouse/bed partners survey. AHI: apnea-hypopnea index. AI: apnea index. HI: hypopnea index. SI: snoring index. OSAS: obstructive sleep apnea syndrome. Imax: maximal sound intensity. Imean: mean sound intensity. B1: the band between 40 Hz and 300 Hz. B2: the band between 301 Hz and 850 Hz. B3: the band between 851 Hz and 2000 Hz.
Significance was assessed by a Kruskal Wallis test.
A value of
This is the first study investigating OSAS patients’ snoring using the snoring energy spectrum. The findings suggest that there are at least four different energy types of the snoring sounds (snore map types) that are fairly associated with the severity of OSAS. The fine reliabilities of snore map measuring indicate that snore map typing represents a simple trustworthy way to classify the energy pattern of each OSAS patient’s snoring in nature sleep. Notably, snore map type cannot be differentiated by current subjective snoring questionnaires. These different distributions of snoring map may reflect the multiple vibrating sites of the upper airway, including contributions from the velum, tongue base, pharyngeal wall, and epiglottis.
Perez-Padilla and coworkers firstly described that most of the power of snoring noise was below 2,000 Hz, and patients with OSAS had residual energy at 1,000 Hz, whereas the nonapneic snorers did not
Beck et al. found that there are two distinctly different patterns of snoring sound waveform by using power spectrum as follows: complex-waveform snore and simple-waveform snore. They found that brief airway closure induce collide of the airway walls and produce complex-waveform snores, whereas simple-waveform snores result from oscillation of a patent airway lumen
In our study, we tried to simplify the formant distribution, pitch density, and running variance of snoring sounds by snoring energy spectrum typing. For this purpose, we developed a semi-automatic graphical user interface to automatically detect full-night snoring energy and to manually decide which type of snore map is based on audio and visual perception. Snore map type 1 (
Miyazaki et al. found that the lower frequency snoring sound (fundamental frequency [ff] = 102.8±34.9 Hz) is characteristic of the soft palate obstruction and the higher frequency snoring sound (ff = 331.7±144.8 Hz) resulting from the tonsil/tongue base obstruction according to the intraluminal pressure of the upper airway
Currently, there is no standard method for snoring acquisition. Therefore, some of those previous studies used ambient microphones placed at a specific location, some others used contact microphones or sensors usually placed at the trachea. In addition, the sampling frequencies and filtering bands were usually different. Accordingly, caution must be taken when comparing our results with the results of those other studies. Aside from those outlined above, this preliminary study has other limitations. Although this study enrolled patients with four different energy types of their snoring sounds, this snore map typing method should be further validated in the patients with primary snoring, and in the peer norms. Besides, the effect of nasal obstruction, a crucial factor of snoring
In conclusion, there are plenty of publications that have addressed the spectral analysis of snores, in subjects with and without OSAS. This study further supported the importance of analysis of the full-night snoring sounds. The highest intensity of the special-band snores (40 Hz–2,000 Hz or 851 Hz–2,000 Hz) and the mean frequency of total-frequency and high-frequency snoring sounds are reliable snoring sound parameters to predict the AHI among male OSAS patients; however, these predicators could not be measured by current subjective questionnaires appropriately. Snore map types can be classified easily and reliably, and are fairly related to the severity of OSAS. The clinical values of snore map typing such as differentiation of primary snoring and OSAS in larger populations and changes after OSAS treatment needs a further investigation.
The authors would like to thank Mrs. Shin-Jao Lee, Department of Otolaryngology, Chang Gung Memorial Hospital, Taoyuan, Taiwan, for assisting in data collection.