From microphones to piezoelectric and cannulas, sleep techs and other experts explain how they work and the pros and cons of each technology.
By Alyx Arnett
Habitual snoring, affecting 22% to 44% of middle-aged men and 13% to 28% of middle-aged women, is the most common symptom of obstructive sleep apnea (OSA).1,2 Loud and frequent snoring may indicate increased upper airway resistance and pharyngeal collapsibility.3,4
“Snoring is an alarm that something is wrong with breathing during sleep and often the chief complaint from a bed partner,” says Michael Sauve, BSc, RPSGT, clinical sleep technologist at Braebon Medical Corp, a manufacturer of snore sensors, though not everyone who snores has sleep apnea.
The AAST requires monitoring snoring for standard polysomnography (PSG)—the gold standard for diagnosing OSA.5 The American Academy of Sleep Medicine (AASM) updated its manual for scoring sleep and associated events last year to recommend monitoring snoring in children, while it remains optional for adults.6
The three most commonly used types of snore-monitoring technologies during PSG are microphones, piezoelectric sensors, and nasal pressure transducers (cannulas)7—all of which also are recommended by the AASM.8
Sleep techs and manufacturers of snore sensors explain the science behind the different types, what’s available in each category, and how to pick the sensor that best meets specific needs.
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Microphones | Piezoelectric | PVDF | Nasal Pressure Transducers | Clinical Significance of Snoring
Microphones: A Pioneer in Snore Detection
The microphone was an early entrant to the snore monitoring category. In early sleep labs, techs would mount a microphone over the top of the bed, and decibel meters gauged how loudly the patient was snoring, according to Todd Eiken, RPSGT, FAAST, vice president of product development at sensor manufacturer Dymedix Diagnostics.
Eiken remembers that some sleep labs also would buy inexpensive headphones, remove the earpiece covers, tape the headphones to a person’s neck, and wire them to a PSG to monitor snoring. While the technology has advanced to better suit sleep study patients, the basic concept remains: Microphones measure snore based on sound.
Microphones are usually battery-powered and provide a quantitative signal in decibels.
Many snore microphones, like those manufactured by SleepSense, attach to patients’ necks. SleepSense’s microphone responds to snoring and other sounds in the audio range picked up through the skin and converts them to a small analog voltage.
Others are placed on a patient’s face close to the source of snoring, like Braebon’s snore microphone, which uses electret condenser microphone technology. Placement just above the nasion is optimal, says Sauve.
Braebon’s Q-Snor kit offers a non-contact solution for snore analysis with a microphone that can be mounted on the wall behind the patient or hung above. “Since the chief complaint from a patient’s bed partner is snoring, quantifying the actual level of snoring intensity as mild, moderate, severe, or loud is important for treatment options; however, being able to provide a decibel number for snoring level is best,” says Sauve. “If the clinician is looking to detect the severity of snoring, a microphone remains the better option.”
Microphones can be good for picking up other respiratory sounds a clinician may want to monitor. “I have heard in some instances on very small pediatric patients that some labs do like to use the microphones to pick up any other sounds that may happen when the child’s breathing,” says Sarah Paddock, director of sales and marketing at SleepSense. SleepSense’s snoring microphones’ frequency response is tailored to snore monitoring and respiratory sounds.
The microphone’s sensitivity is also its downfall, as it can pick up ambient and environmental noise. “If a CPAP machine is going in the background, or any kind of noise, it would show up,” says Eiken. “It would appear as though it was a snore, but it really wasn’t. It was just a noise in the room.”
Piezoelectric Sensors Pick Up the Vibes
Piezoelectric sensors detect snoring based on vibrations. Unlike microphones, piezoelectronic sensors are “not going to pick up those ambient sounds,” says Paddock.
A piezo disc contains crystals on a film, which vibrate when snoring occurs and convert mechanical energy into an electrical signal. These sensors do not require an external power source, says Sauve.
SleepSense’s piezo snore sensors are designed with a small bump on the side that faces the patient’s skin. The bump concentrates vibrations at the sensor’s center, says Paddock. The design ensures the sensor maintains constant contact with the skin, even if the patient moves.
According to Sauve, if a quantitative decibel level is not needed, then a piezo sensor is a good option. “They could only estimate the intensity from the technologist’s observations,” he says.
A piezo sensor has to be placed near the snoring vibrations, usually the neck. However, some people have obstructions that cause snoring to occur in the nasal areas, rather than back in the throat where the sensor could pick it up. Eiken says, “In other words, there’s a challenge to try and place the sensor based on the type of snoring the patient has. Oftentimes, you don’t know what kind of snoring the patient will have until they fall asleep, and of course, it’s not ideal to have to go in and adjust it and wake the patient up once they’ve fallen asleep.”
Piezo sensor signal quality also depends on patient weight, and some overweight patients may show poorer-quality signals. In addition, signal quality may vary with sleeping position. In Sauve’s experience, movement and electrocardiogram artifact are more frequently observed with piezo snoring sensors than with a snore microphone.
PVDF: a Piezo Subcategory
Within the piezo sensor category are PVDF—polyvinylidene fluoride—sensors. PVDF has piezo properties that not only respond to movement or vibration but also thermal properties that respond to temperature changes. The flexible film harnesses these stimuli to create measurable electrical energy.
Dymedix’s disposable PVDF snore sensor with adhesive backing allows for multiple placement locations during testing. The thermal properties of PVDF are utilized in an airflow sensor.
“PVDF can be either a standalone sensor placed on the neck—or even the suprasternal notch is oftentimes a good place to pick up snoring activity—or our airflow sensor is capable of detecting snore at the same time,” says Eiken.
Dana Burger-Dipzinski, vice president of business services at ElectraMed Corporation, says combination products that incorporate snore and airflow make it more comfortable for the patient by reducing attachments. “Patient comfort typically means better study results,” she says, adding that she’s seen a trend toward disposable sensors, snore included.
Nasal Pressure Transducers
A cannula connected to a pressure transducer detects snoring by capturing high-frequency pressure changes through a derived and filtered signal. A high-pass (low-frequency) filter eliminates the slower respiratory waveforms, thereby isolating and displaying the faster-moving snoring waveforms.
“The snoring vibrations within the airflow signal can be picked up, filtered out, and you can create two channels from a nasal cannula,” says Eiken. “You can get the airflow that you would normally be recording and the snore events as well.”
Auto-adjusting CPAP machines use this method, Eiken adds, since snoring while on CPAP indicates that the applied airway pressure is insufficient.
High-quality pressure transducers are differential in nature, battery-powered, and highly stable and linear, says Sauve.
SleepSense’s pressure transducers use a piezo membrane to generate a small voltage in response to pressure changes and acoustical input. They can be used with any brand of pressure cannula.
Most PSG systems can use the nasal cannula, says Eiken, making them compatible with most systems and nixing the need for an individual snore sensor. The issue, he says, is they can be uncomfortable. “Most people don’t like nasal cannula,” he says.
A study comparing the types of sensors also found this method inferior, suggesting that “the use of the cannula as a snore sensor be discontinued.” Of the methods studied—a microphone on a patient’s chest, two overhead microphones, a piezoelectric sensor, and nasal cannula—the authors determined that a microphone on a patient’s chest picked up the most snore events.7
Clinical Significance of Snoring
While various techniques exist to detect snoring, research indicates they don’t measure snore the same, which poses a challenge for future research into the clinical significance of snoring.7,2
As it stands, the correlation between snoring and OSA severity based on apnea–hypopnea index (AHI) is still unclear—a knowledge gap that Eiken says has led to varying opinions regarding the significance of counting snore events during a sleep study.9
“A person could have, let’s say, a total of 2,100 snoring events during a PSG, and another person could have, let’s say, 45,” says Eiken. “What is the value of those numbers? It’s up in the air in terms of whether there’s really any useful information because there’s no standard.”
Eiken says some laboratories don’t record snoring and rely on the technologist’s observations. “The technologist will just report in their comments at the end of the study: Yes, the patient snored quite a bit, frequently, infrequently, or whatever it was,” he says.
Future research that draws connections between quantified snoring and OSA severity could enhance its clinical utility in decision-making. By establishing clear correlations, snoring could potentially emerge as a valuable diagnostic marker for OSA.
References
- Nakano H, Hirayama K, Sadamitsu Y, et al. Monitoring sound to quantify snoring and sleep apnea severity using a smartphone: proof of concept. J Clin Sleep Med. 2014 Jan 15;10(1):73-8.
- Kim SG, Cho SW, Rhee CS, et al. How to objectively measure snoring: a systematic review. Sleep Breath. Published online. 2023 July 8.
- Maimon N, Hanly PJ. Does snoring intensity correlate with the severity of obstructive sleep apnea? J Clin Sleep Med. 2010;6(5):475-8.
- Rowley J. Snoring in adults. UpToDate. Updated 2023 Jan 6.
- AAST Technical Guideline. Standard polysomnography. Updated 2021 December. Available at https://www.aastweb.org/Portals/0/Docs/Resources/Guidelines/AAST%20PSG%20Guideline%20Final.pdf.
- The AASM manual for the scoring of sleep and associated events. Summary of updates in version 3. 2023 February. Available at https://aasm.org/wp-content/uploads/2024/02/SummaryofChanges_Document_3-1.pdf.
- Arnardottir ES, Isleifsson B, Agustsson JS, et al. How to measure snoring? A comparison of the microphone, cannula and piezoelectric sensor. J Sleep Res. 2016;25(2):158-68.
- The AASM manual for the scoring of sleep and associated events. The 2007 AASM scoring manual vs. the AASM scoring manual v2.0. 2012 October. Available at https://aasm.org/wp-content/uploads/2017/11/Summary-of-Updates-in-v2.0-FINAL.pdf.
- Chiang JK, Lin YC, Lu CM, et al. Snoring index and neck circumference as predictors of adult obstructive sleep apnea. Healthcare (Basel). 2022 Dec 15;10(12):2543.
Photo caption: SleepSense’s piezo snore sensor responds to snoring and other sounds in the audio range picked up through the skin.
Photo credit: SleepSense
