Julia was at wit’s end. She has been suffering from insomnia for the past 10 years, since she entered menopause. She keeps waking up after 5 hours, despite trying every over-the-counter and prescription medication available. She has no trouble falling asleep, but is not able to stay asleep for more than 5 hours, typically waking up at 3AM after falling asleep at 10PM. Oftentimes, she has to go to the bathroom when she awakens, but it’s not too much urine. She even saw a behavioral sleep specialist who offered cognitive behavioral therapy for insomnia (CBT-i), which only helped temporarily.
Julia’s history is typical for what’s called sleep maintenance insomnia, where you can’t stay asleep or keep waking up after you’re able to fall asleep. This differs from sleep onset insomnia, where you’re not able to fall asleep within 20 to 30 minutes of getting into bed. The accepted explanation for insomnia is that it’s a complex interaction between poor sleep routines, behavior and thoughts, in addition to a baseline hyperarousal of your brain. Essentially, you can’t shut down your brain when you want to go to sleep.
One of the potential consequences of sleep maintenance insomnia is that with continuous awakenings at AM and not being able to go back to sleep is that your sleep clock becomes advanced, or gets pushed backwards. This could potentially lead to advanced sleep phase syndrome, a condition that’s commonly seen in the elderly. In this condition, you’ll want to go to sleep much earlier in the evening, such as 8PM, rather than at 10PM.
I’ve always wondered why people tend to wake up around 3AM, whether it’s insomnia, nighttime urination, or asthma. The most obvious connection between these three connections is that you spend longer periods of REM sleep (your dream stage), starting around 3AM. Stage REM is also when your muscles are most relaxed, which can predispose you to have breathing problems. I’ve been doing thought experiments about his concept, and I’m convinced that we need to think about sleep maintenance insomnia in a completely different way—perhaps it’s a consequence of a breathing problem.
Before I go over my arguments, a few basic sleep concepts need to be reviewed.
If you see photos or drawing of people sleeping, you’ll often see sleep being depicted as someone sleeping on the back. However, most modern Western people prefer to sleep on their sides or stomach. One of many reasons is that supine (back) sleep will allow the soft tissues of the tongue and soft palate and fall back more due to gravity when supine.
As women go through menopause, throat muscles will relax somewhat due to lowered progesterone levels. This study found that genioglossus muscle (tongue) activity is lower in post-menopausal women compared to pre-menopausal women. This is why women on hormone replacement therapy tend to sleep slightly better.
Your Circadian Rhythm
Another major sleep concept that’s important to understand are two processes that are involved in sleep regulation. The first one is the well-known circadian rhythm. For many of us here on Earth, we are on a 24 hour cycle. The circadian rhythm, which is regulated by light, cycles up and down between two 12-hour intervals. This is called the C process. This is what makes you alert during the day and drowsy at night.
Your Drive for Sleep
There’s another simultaneous sleep-related phenomena called the S process. This is your drive for sleep, which is minimal in the morning when you first wake up, but then increases gradually reaching its peak before you fall asleep. Once you’re asleep, it drops back down to the baseline low level at which point you’ll wake up.
Process S also corresponds to your level of adenosine that builds up in your brain. Adenosine inhibits wakefulness. As the day progresses, adenosine levels slowly increase. Ingesting caffeine from drinking coffee is one way that we block the effects of adenosine.
The Importance of Sleep Stage
Now there’s one more piece to the puzzle that’s critical. This is your sleep cycle. Normally, you’ll cycle between 4 defined stages of sleep: Wake, N1, N2, N3, REM. N1 and N2 are the lighter stages of sleep and N3 is deep sleep. During N1 through N3, your muscles become gradually more relaxed, but in REM sleep (rapid eye movement and dream stage), your muscles are completely relaxed.
You’ll reach deep sleep (N3) in the early part of the night, but as you progress through 4 to 5 sleep cycles (90 to 120 minutes long), N3 gets shorter and shorter and REM becomes longer and longer. Around 3 to 4 AM is when you begin to have longer periods of REM sleep.
There are many different explanations on what causes us to wake up prematurely in the morning, but it’s probably a combination of these three processes, along with sunlight that arrives in the morning. When you’re about to wake up, your circadian (wake forces) are beginning to increase from its lowest point, your sleep drive (S) is at its lowest point, and you’re most likely in REM sleep, when muscles are most relaxed, leading to possible obstructed breathing. This can be a natural, normal waking mechanism. Notice that in many cases you’re waking up during a dream in the morning. Adding sunlight is another cue for you to wake up.
In addition, the lowest point in the circadian cycle is called the singularity. It typically occurs around 2 hours before your natural wake up time. It’s also the time when your core body temperature is at its lowest. On the C&S figure, notice that this dip is about 2 hours before wake time. We also know that as core body temperature rises, you’re more likely to wake up.
In the figure below, I’ve juxtaposed the hypnogram (sleep stages) underneath the C&S figure during 8 hours of sleep.
All of the above is assuming that you have normal upper airway anatomy and you are able to wake up after sleeping 7 to 8 hours without any problems. However, if you have upper airway narrowing due to large tonsils or small jaws with dental crowding, you’re more likely to partially or totally stop breathing, whether it’s for 3 seconds or 25 seconds. Totally obstructed breathing for more than 10 seconds is called an apnea if detected during a sleep study. A breathing pause for less than 10 seconds won’t be counted as a formal respiratory event (apneas, hypopnea or RERA) but will most likely be counted as an arousal.
We also know that obstructed breathing is more likely to occur during REM sleep, especially when you’re on your back. If you have more narrow upper airways, then the higher the likelihood of more frequent breathing pauses around 3-4 AM, when you’re in longer periods of REM sleep. If you add the various other factors mentioned above (circadian factors, sleep drive, sleep position, sleep stage, light, etc.), then you’re more likely to wake up around this time.
One of the hallmarks of insomniacs is the inability shut down the brain when going to sleep, or after a nighttime arousal. It think you’ll agree with me that waking up due to choking and breathing pauses can be a major cause of physiologic, emotional and psychological stress.
Some of you may have to go to the bathroom to urinate. This is a common condition (nocturia) in people with obstructive sleep apnea or upper airway resistance syndrome due to a hormone (atrial natriuretic peptide) that’s created by your heart in response to stimulation from obstructed breathing, leading to more urine production. Some of you are able to go back to sleep, but some of you can’t fall back asleep. Whether or not you can fall back asleep may depend on how violently you woke up. If you just had a 30 second choking episode, this will lead to a major stress response, with heart rate blood pressure elevations. It’s unlikely you’ll be able to fall back asleep.
Putting the pieces together
In medicine, and especially sleep medicine, we like to categorize medical conditions into separate categories. It assumes that obstructive sleep apnea is completely different from insomnia. However, when it comes to these two conditions, there is compelling evidence that there can be a great deal of overlap when it comes to presenting symptoms.
One example of this overlapping phenomenon is a study performed by Dr. Barry Krakow. He and his colleague reviewed 218 patients with prescription medication resistant insomnia, and 75% were found to have obstructive sleep apnea based on formal sleep studies.
Julia eventually made her way to find me and not surprisingly, she was found to have moderately obstructive sleep apnea (AHI 20). She began using CPAP, and finally able to sleep for 7 hours again like she used to when she was in her teens. Looking back on her history, she suffered a shoulder about 8 years ago. This forced her to sleep on her back, when she normally preferred to sleep on her side. She began to gain weight later, and began to snore heavily.
This alternative explanation for sleep maintenance insomnia may seem a bit fat fetched for traditional sleep scientists, but looking at this from a sleep-breathing standpoint, it makes a lot of sense. How many of you keep waking up much earlier than your preferred time? What have to tried so far? Please enter your responses in the text box below.