Mini-Series on Obstructive Sleep Apnea (OSA): Intro to Sleep and OSA Evolution
In honor of Daylight Saving’s Time and losing an hour of sleep this weekend, here begins a mini-series on sleep, particularly focusing on Obstructive Sleep Apnea (OSA). Everyone seems to bring up OSA: friends talking about their parents, patient anecdotes, and super cool people on TV or the radio. It's become a hot topic. I first became drawn to OSA about 15 years ago when I wrote about sleep disorders for my first-ever research paper (I know, how cute). Ever since, I found the concepts of sleep and dreaming fascinating. I worked at a sleep lab in college and landed in Sydney twice to do OSA research during dental school. Did you know that the CPAP machine, a.k.a. the primary non-surgical OSA treatment, originated in Sydney way back when? Well, now you do! You can add that to your list of justifiable reasons to visit.
We spend more than one-third of our lives asleep, yet we still know so little about it. Kind of crazy… Why is sleep so important? Perhaps an easier way to look at this is by thinking, how do you feel when you don’t get enough sleep? Think about those with shift work, jetlag, a late night out/at the office, the stressed out insomniac, or the sleep apneic – they all suffer with the compounding effect of poor sleep. Sleep is a time for body and immune system repair and recovery, it's a chance to recharge. Memory consolidation occurs during the deepest stages of sleep, as well. Simply put, sleep is restorative for the mind and body. When we don’t get enough of it, we feel pretty awful! No fun at all.
These reparative events occur during different phases of sleep. We cycle between two states: REM and non-REM (NREM) sleep. REM stands for “Rapid Eye Movement” – REM sleep is when we dream and occurs about one-quarter of the night. Our voluntary muscles are paralyzed so that we don’t act out our dreams and our eyes roll side to side (hence its name). The brain is essentially in an awake state. Functionally, REM sleep is poorly understood, but the ability to learn complex tasks is hindered without it. Meanwhile, the majority of the night comprises restorative NREM sleep. Growth hormone is released at this time and brain activity slows down. Our drive to sleep is managed by an internal clock, our circadian rhythm. The advent of electricity and our high-tech gadgets today have significantly altered our circadian cycles.
So onto to Obstructive Sleep Apnea (OSA). OSA is highly common, and according to the National Institute of Health, over 12 million Americans have it. This number is likely an underestimation, unfortunately. OSA is chiefly a disease of adulthood, but with our climbing obesity epidemic it may be seen in children. Approximately one-quarter of men and one out of ten women are affected. It is a complex disorder, and it is hard to pinpoint a single cause or etiology. This is what makes OSA challenging to treat. OSA is often a consequence of a combination of loss of muscle tone, decreased relative jaw size, and excess soft tissue. In children, enlarged adenoids and tonsils may be the culprit. Family history and endocrine imbalances such as hypothyroidism or acromegaly are risk factors, as well. Finally, nasal obstruction can also cause OSA – the entire airway needs to be assessed.
OSA occurs when there is a physical impingement on the airway. What is an apnea exactly? An apnea is a complete cessation of airflow, which occurs for at least ten seconds. OSA patients have continued abdominal muscle effort during each apnea episode. Furthermore, the oxygen saturation in the blood decreases < 97%. In severe cases, it can drop way below 80%. This means that your organs are being deprived of oxygen as a result of OSA. This is why OSA is so bad for your body: in severe OSA patients, these apneic events can occur hundreds of times in ONE night. They are not sleeping. No sleep and no oxygen; of course they’ll feel pretty horrible the next day.
I’ve been mentioning OSA severity – this is formally quantified through the AHI or RDI, which stand for Apnea Hypopnea Index or Respiratory Disturbance Index. These indices are very similar, but the RDI includes a few extra measurements. When someone gets a sleep study, the AHI/RDI is used medically to diagnose whether the patient is healthy versus has mild, moderate or severe OSA. So, onto the numbers:
Normal: < 5 events per hour
Mild: 5-15 events per hour
Moderate: 15-30 events per hour
Severe: > 30 events per hour
Please bear in mind that these numbers are for adults, and children should not be having ANY episode of airway obstruction. Snoring is a huge no-no and needs to be addressed appropriately.
Those with OSA are at a significantly higher risk for heart attacks, hypertension, and weight gain since the body goes into a sympathetic nervous system overdrive during these events. As a refresher, this is the “fight and flight mode” stress response (read again my last write-up on stress and the body). In addition, there are unfavorable cognitive changes that include memory loss (not surprising), mood disturbance, and daytime sleepiness. There is a HUGE increase in risk for motor vehicle accidents by up to seven times. Several major accidents have been attributed to OSA, recently a Metro-North train crash in New York. Sadly, most OSA patients don’t even know how rotten they feel and what “normal” is until they are treated. The difference in quality of life can be profound.
Did you know that OSA was first described NOT by a doctor?! Joe in The Posthumous Papers of the Pickwick Club by Charles Dickens, written way back in 1837, had telltale characteristics of OSA. For this reason, OSA was referred to as Pickwickian Syndrome until the late 20th century. Why do we have OSA? OSA is a product of evolution. Interestingly, OSA has been linked to anatomic shifts that enable speech. Basically our airway became elongated and narrowed, increasing airway resistance. This means decreased airflow and at its worst, obstruction. Go back to your physics books if you want to know why, I won't get too science-y on you. The tongue shifted posteriorly, which adds to narrowing and obstruction potential. Then changes in diet and industrialization have a further compounding effect.
Our diet today is soft and full of sugar, which contributes to obesity and unfavorable craniofacial growth. OSA patients tend to be overweight, and may have excess fat in their neck and even in their tongue. This logically contributes to blocking the airway. A healthy neck circumference for males is < 17 inches and for females < 15.5 inches. Go measure your neck! Another fun fact: football players have been shown to have an increased prevalence of OSA (and enlarged neck circumferences). Changes in our diet/craniofacial structure are so interesting especially in relation to orthodontic malocclusion, I will delve into this at a future time!
There are myriad sleep disorders that are similarly captivating. When you have a spare minute look up REM-behavior disorder or YouTube a video of a narcoleptic dog. Stay tuned for more on OSA in kids, diagnostics, prevention, and treatment!