The Truth About Snoring
The affliction we have come to know as snoring has been affecting human kind since the beginning of time. Frankly, I am surprised that we have not discovered ancient cave paintings where prehistoric hunters made joking images of one hunter snoring by the fire while his buddies stared sleeplessly into the darkness with nothing to do but see people and animals in the stars and, of course, tell their friend to “Roll Over!”. The clinical importance of snoring on the snorer has only come to light in the last 30 years as diagnostic protocols, home sleep testing devices, medical grade sleep bruxism monitors and therapies have developed to measure and quantify sleep quality and treat the over 100 conditions that take place during sleep that can affect human health. It is high time we started to look at perhaps the most obvious and yet most difficult to quantify clinical parameter, snoring.
First let’s take a look at the definition of snoring so that we all understand what snoring is. The National Sleep Foundation describes snoring as “noisy breathing during sleep”. They go on to describe the physical condition that creates the sound;
“While you sleep, the muscles of your throat relax, your tongue falls backward, and your throat becomes narrow and “floppy.” As you breathe, the walls of the throat begin to vibrate – generally when you breathe in, but also, to a lesser extent, when you breathe out. These vibrations lead to the characteristic sound of snoring. The narrower your airway becomes, the greater the vibration and the louder your snoring.”
Clinicians the world over have used subjective bed partner reports of snoring and snoring volume to begin the diagnosis of sleep disordered breathing, Among the many conditions within sleep disordered breathing is, obstructive sleep apnea, a condition where the tissues of the airway actually collapse and close the airway leading to health risks including heart attacks and strokes.
The question “Do you snore?”. Is included in sleep questionnaires (e.g. Stop Bang and Berlin Questionnaires) and often the very first question. These screeners are used in primary care physician’s offices, dental offices and sleep labs to begin understanding the patients sleep condition. This question can be very difficult to answer, largely because even the patient needs to rely on information from someone else to reply. The importance of snoring in the discussion of sleep quality is critical – not just for the sufferer but also the bed partner. Objectively evaluating, measuring the vibration of airway tissues as well as the volume of the snoring is clearly key to establishing base line sleep disordered breathing diagnosis.
In the early days of sleep science when sleep apnea was just beginning to be objectively measured, it was suggested that since Apnea (no Breath) and Hypopnea (slow or shallow breath) are so similar there should be an index where adding the two conditions together and reporting them per hour of sleep would have value in scoring sleep apnea. Thus, AHI (apnea hypopnea index) was born. Over the last 30 years there have been many who have questioned the value of AHI in describing sleep quality or even severity of the sleep condition. AHI has hung on in the field well beyond its usefulness largely due to its ease of calculation and the fact that insurance companies in the United States use AHI severity (<5 Normal 5 to 15 Mild 15 to 30 Moderate and >30 Severe) to determine if a patient qualifies for treatment. Is it possible that airway narrowing and the increased resistance in the airway could impact patient health and wellness without increasing the patients AHI?
There are a number of great reasons for AHI to maintain its dominance in the diagnostic and reimbursement areas. First of all, consensus in the detection and reporting of apnea and hypopnea is well understood and globally researchers are able to report and comment on each other’s findings. Partial upper airway obstruction is much more nuanced and there is no firm consensus on detection, quantification or clinical impact. The length of each episode of partial airway obstruction is much longer than a typical apnea or hypopnea event. The partial airway obstruction event builds over several minutes. If the event is in fact scored in a sleep study, it is scored as mild apnea which will not merit treatment. There are many fewer arousals during partial airway obstruction so the impact on sleep quality is easily missed. Finally, the key parameter that will identify partial upper airway obstruction in the sleep lab is increased partial pressure of carbon dioxide (CO2); this is rarely measured during an sleep study on an adult patient.
As I was preparing this article I was struck by the prevalence of partial upper airway obstruction in women. This condition may be the most common form of sleep disordered breathing in females. It is reported in the scientific literature that partial airway obstruction, and the snoring that goes with it, may result in daytime sleepiness and increased risk of elevated blood pressure by 42% even if other sleep parameters like AHI remain in the normal range. Clearly there is an urgent need to recognize snoring and partial upper airway obstruction as a measurable and treatable form of sleep disordered breathing. Patients with low AHI almost certainly still require treatment.
My grandma is embarrassed that she snores because "it's so unladylike"
— dara (@danadaradelaney) December 27, 2016
Watching Pitch Perfect with my fatherinlaw while my motherinlaw snores in a recliner & my wife looks at her phone, our Christmas tradition
— AverageHeightDrew (@TooTallDrew) December 26, 2016
The need to qualify prolonged partial obstruction is particularly acute. The condition used to be detected in the sleep lab by surface electromyography (EMG) of the diaphragm and intercostal muscles which reflected changes in respiratory effort. This diagnostic protocol has rapidly been replaced with respiratory inductance plethysmography (RIP), a technology which not only allows the monitoring of chest and abdominal movement during sleep but can also be used to calculate, flow and upper airway resistance. This technology will separate the simple snoring patient from the patient with more serious disease.
With tools generally available today such as the Nox T3, type 3 home sleep device, PSG is not required to diagnose partial upper airway obstruction. Prolonged obstruction is usually associated with crescendo snoring. Using a snoring signal from a nasal cannula alone is generally considered to be inadequate because there is no way to differentiate between benign snoring and snoring associated with marked partial obstruction. Much work has been done to combine flow limitation from the nasal prongs and the snore signal to diagnose partial obstruction. It is very clear that snoring is such an important value that there is need for a standardized method of objectively measuring snoring.
It is clear that to achieve an objective diagnosis of partial upper airway obstruction it is critical to collect very accurate snore signals as well as flow limitation from the nasal cannula. Recently there was an excellent study from the University of Iceland where they compared the common methods of measuring this data in order to help develop a best practice that would clear the way to a diagnostic standard for partial upper airway obstruction diagnosis.
Digital Audio for Snoring
- dB(C) weighting was used rather than dB(A) to describe snore events using audio signals.
- The dB(A) weighting attempts to mimic the human ear response to sound. This has the limitation that the audio signal attenuates (reduces) more quickly and has been shown to underestimate snoring in the lower frequencies (<200 Hz)
- dB(C) captures the complete power or loudness of the audio signal.
When the signal from the cannula was compared to piezo sensor on the throat and digital audio collected from the chest it was very clear that the digital audio could, not only, measure sound pressure but also use this information to derive decibels and improve diagnostic accuracy. The discrepancy in clinical value between cannula derived data and recorded and scored digital audio is so clear that some researchers are recommending using digital audio to measure snoring and abandoning the less accurate cannula signal altogether. The literature is still developing in this area but the initial findings are very strong.
So what is the truth about snoring? Clearly research is indicating that the impact of snoring on women and children has much of the same health impact as OSA in men. The primary limitation in objectively measuring and diagnosing snoring related sleepiness has been due to limitations in sleep technologies and scoring algorithms for the snore signal. It stands to reason that the absence of an objective snoring value means that a differential diagnosis is impossible. Recent technological advances in the recording and scoring of snoring as a key indication of sleep quality is now providing the information we need to begin to treat women and children who suffer with partial upper airway obstruction. Snoring can be treated very well by adjusting body position and sleep posture using pillows and devices like SlumberBump and ZZoma pillows, mandibular advancement devices like the dentist fabricated Silent Nite by Glidewell Dental Lab. Key to treatment selection is a differential diagnosis which requires a home diagnostic device that has high quality digital audio recording to measure and quantify the snore signal.
- Prolonged partial upper airway obstruction during sleep – an under diagnosed phenotype of sleep-disordered breathing. Eur Clin Respir J.2016 Sep 6;3:31806.