The Changing Face of Sleep Technology, Part 2
This is the second in a series of articles dealing with the changing landscape of sleep technology. In this article, we’ll take a brief look at our present understanding of sleep as well as review some of the technology we use in our sleep centers.
Present Understanding of Sleep
What once was seen as a state of quiescence, similar to that of being in a coma, is now known to be a very active and essential state. As we look more closely at sleep, we see just how intertwined it is with our health and well being.
Here are a few critical things we know about sleep so far:
(From “Fundamentals of Sleep Technology,” 2nd edition, Chapter 2, pg. 8)
- Sleep is necessary for normal mental and emotional well being
- Sleep disturbances in early childhood make it more likely that person will have trouble with emotional stability, as well as attention and concentration as an adult.
- Sleep is essential for healing
And while sleep medicine has come a long way in the last 20 years, much work is yet to be done. For example, the average medical student spends just under two hours learning about sleep. And most medical students that were surveyed said they had a rather poor understanding of sleep. In fact, some medical schools don’t have any formal training in sleep medicine.
In order to more fully appreciate what we know about sleep disorders, it’s imperative that we have a basic understanding of how the brain functions.
Basic Brain Function Review
The human brain is composed of approximately 100 billion neurons that serve as passageways for electrical signals that travel up to 200 miles an hour to and from the brain. These signals are transferred from neuron to neuron via chemical gaps called synapses, with each neuron containing 1,000 to 10,000 synapses.
Let’s break it down:
There are a group of cells within the hypothalamus called the suprachiasmatic nucleus (SCN). This group of cells receives information about the amount of light entering our eyes and sets our biological clocks. The SCN, in turn, sends signals to the pineal gland, increasing the production of melatonin when it gets dark.
The thalamus interprets information and processes memory from short term to long-term memory. Thalamic activity is quiet during non-REM sleep, allowing us to “tune out” the world. However, the thalamus becomes as active in REM sleep as it is during waking life. The amygdala processes emotions and also becomes active during REM sleep.
GABA is a neurotransmitter in the brain stem that inhibits other neurotransmitters in both the brain and muscles, resulting in our becoming sleepy. GABA also relaxes our muscles. This is especially important during REM sleep as it keeps us from acting out our dreams.
The glymphatic system serves as a waste removal system for the brain. While we sleep, our neural pathways are maintained. Astroglial cells within the brain literally shrink, opening up more space in the brain, which allows toxins to be flushed out. In fact, studies done on mice show that these brain cells shrink by as much as 60 percent during sleep. One of the toxins flushed out during sleep is beta-amyloid, a protein which causes cognitive deficits, such as Alzheimer’s.
Interestingly, this toxic waste removal system is most efficient while sleeping in the lateral position.
Research is also underway to produce technologies that will map individual brain cells and capture complex neural circuit interactions in real time. This research will help us to gain a better understanding of the brain, with the goal of improving treatment for brain
disorders such as dementia. The institutes presently doing this research are The Brain Research through Advancing Innovative Neurotechnologies® (BRAIN) Initiative and the Human Connectome Project.
And, of course, as research continues to advance, our recording equipment must adapt. With that, here’s a rather brief primer on digital recording.
Evolving Sleep Lab Equipment
Analog signals can be compared to a solid line on a graph, while digital signals would be points on a graph. An analog recorder captures the entire signal, whereas the digital recorder captures “bits” of the original continuous signal. In order to digitize analog signals, a sample of the signal is captured at regular intervals. This is known as the sampling rate and is expressed in samples per second or Hz.
The AASM has established sampling rates for acquiring sleep studies. For EEG, EOG, EMG and EKG, for instance, the desired sampling rate is 500 Hz, with a minimum of 200 Hz. According to the Nyquist theorem, which states you should have a sampling rate at least twice the highest frequency you wish to record, this sampling rate is more than sufficient to adequately record these signals, although the actual sampling rate is also limited to the number of pixels on your monitor.
For example, AASM recommends a monitor with at least a 15” screen and a minimum display of 1600 x 1050. The actual width of a 15” monitor is 13.1”, with 1,050 pixels running vertically across the screen. If you’re looking at a 30-second screen, that equates to roughly 80 pixels every 2.3 seconds, or a sampling rate of approximately 35. However, the fastest brainwaves we need to be concerned with are up to 13 Hz, so this should be at minimum sufficient for our needs.
It is crucial to precisely record signals so that an accurate diagnosis can be made, which brings us to the following rather brief perusal through some of the sleep disorders.
At present, there are 74 identified sleep disorders listed in the ICSD-3, falling into the following categories:
- Circadian Rhythm Sleep-Wake Disorders
- Central Disorders of Hypersomnolence (Hypersomnias)
- Sleep-Related Movement Disorders
- Sleep-Related Breathing Disorders
A Few of the Many Treatments for Sleep Disorders:
Insomnia – In some people with insomnia, the frontal cortex stays active, resulting in racing thoughts. Several devices are now available that cool the forehead, purporting to reduce activity in the frontal cortex and reduce insomnia.
Hypoglossal Nerve Stimulation – This is a surgically implanted device that activates the hypoglossal nerve, which, in turn, stimulates the genioglossus muscle, which controls tongue movement, resulting in the tongue being pulled forward, thus opening the airway.
Negative air pressure – Known as CNEP (Negative External Pressure) or Continuous Negative Air Pressure (CNAP), there are different versions of this type of treatment. However, they all produce the same effect: opening the airway by using a gentle suction to pull the tongue forward.
Oral Appliances – Although CPAP remains the most effective way to treat sleep apnea, oral appliances have been proven to successfully manage OSA, as well. When compared with CPAP, oral appliances tend to cause more dental changes, though mild, whereas CPAP tends to cause symptoms such as nasal congestion, rhinorrhea and eye irritation.
REMEDE – This is a transvenous neurostimulation device for treatment of Central Sleep Apnea (CSA). It stimulates the phrenic nerve, which causes the diaphragm to move.
Of course, insurers will continue to be a major driver of healthcare. Therefore, I’ve included a brief summary of some of the more basic concepts of this rather complex system.
The Changing Face of Insurance
In the U.S., the insurance industry has been predominantly based on a fee-for- service payment system. However, this tends to raise healthcare costs. That’s because physicians receive a fee for each service they provide, resulting in a tendency to order more procedures than may be necessary. In fact, according to some reports, healthcare costs in the U.S. are about double what they are in other developed countries (although other factors play into this increased rate).
However, other types of insurance, such as the Affordable Care Act (ACA), are based more on a pay-for-performance approach, and therefore are more patient-focused. But while the ACA offers coverage to more Americans, it still leaves many without insurance; thus, is not true universal healthcare, which by definition covers everyone.
Then there’s the single-payer system, which is a system whereby all healthcare is covered by a single entity, as opposed to a multipayer system. Single-payer systems tend to be more cost effective than multipayer systems. There are many variations of single-payer systems, primarily in other countries.
In the sleep center, in an effort to keep medical costs down, home sleep apnea testing (or HSAT) is becoming more common. Therefore, I’ve included the following brief review of HSAT.
Home Sleep Apnea Testing (HSAT)
As you probably already know, there are different levels of HSATs based on the number of channels recorded. They are designated Type II, Type III and Type IV by the Center for Medicare & Medicaid Services (CMS), and standards and guidelines for their use are designated by the American Academy of Sleep Medicine (AASM).
However, these guidelines were established back in 1994; since then, there have been a number of new testing devices developed, many of which don’t fit within established criteria for the Type II, Type III and Type IV designations set by CMS. More recently, an evaluation system has been developed by the AASM that more closely matches the capabilities of present day equipment. This system is known as SCOPER (Sleep, Cardiovascular, Oximetry, Position, Effort and Respiratory) and is intended as a guide to evaluate equipment. There are also HSAT equipment guidelines and scoring and reporting parameters outlined in the current version of the “AASM Scoring Manual.”
In addition, research shows that portable monitoring using HSAT followed by auto- titration is a very efficient way to treat patients with obstructive sleep apnea. In fact, when compared with an in lab PSG and CPAP titration, HSAT followed by auto-titration gave similar results with only a few minor differences. However, HSAT does have limitations and therefore is not recommended for everyone. Let’s take a look at who does, and who doesn’t, qualify.
Patients with a low probability of OSA don’t qualify. This is because HSAT does not monitor sleep, and therefore could give a falsely low AHI. Also, patients with a high probability of OSA but with known or suspected comorbidities don’t qualify, for obvious reasons.
Patients who do qualify are those suspected of moderate to severe OSA without comorbidities, and those who can’t make it to an in-lab study because of immobility, safety or critical illness.
Other limitations include not only variability in sensors, but also variability in defining apneas and hypopneas. Additionally, HSAT equipment is not standardized. The technology has also become available to many physicians who are not trained in sleep. Ideally, HSAT should only be used and interpreted by sleep medicine physicians.
In addition, compliance with today’s treatment options is low. So, although patient education is important and effective, we will need to come up with more efficient, cost-effective treatment options that patients will use.
An article from the Sleep Research Society (SRS) states that while sleep centers have quadrupled, most patients with sleep apnea are neither diagnosed nor receiving treatment. This could mean that current testing equipment and treatment options may not be sufficient. At the same time, however, these very services are being targeted for budget cuts by CMS.
The future of sleep medicine will be interesting indeed.
In our first article, we looked at the history of sleep medicine. This article focused on where we are presently with sleep medicine. In my next article, I’ll take you on a trip into the future and show you what a sleep study might look like sometime soon.