Studying sleep: technology assesses, alleviates issues

Article By : Brian Dipert

Undiagnosed sleep apnea is rampant, research suggests, and for many represents a life-long and serious impediment.

Back in December, as part of my (first) yearly physical (in more time than I care to admit), the doctor ordered a blood draw for a panel of tests. When the results came back, they suggested an abnormally high hematocrit (volume percentage of red blood cells in blood) level, which the doctor diagnosed (rightly so, as it turns out) as indicative of possible sleep apnea, a “sleep disorder characterized by pauses in breathing or periods of shallow breathing during sleep.”

Folks like me who live at high altitude (I’m at 7,172 feet above sea level, according to the What Is My Elevation? website) tend to have a higher concentration of red blood cells than the population norm, anyway, due to the body’s thin-air counteractions. But in my case, my numbers were well beyond even the high-elevation-adjusted range, and the doctors should know … my primary care provider’s office is located at an altitude of 7,759 feet!

The first step in confirming-or-disproving the diagnosis was a multi-night test using a wrist-mounted pulse oximeter containing resident storage (I’m assuming nonvolatile flash memory, to preclude data loss in case of battery failure). Many of you are already familiar with such devices (here’s a $9.99 home unit that I recently bought and works great), which are briefly clipped to a fingertip (usually at the beginning of a doctor’s visit, along with weight, height, and blood pressure measurements) to assess pulse rate and blood oxygen saturation levels.

Pulse oximeters are conceptually similar to the photoplethysmography optical heart rate sensors you periodically see mention of in teardowns I do for EDN, although since they’re measuring more than just pulse rate, the implementation is more complex (not to mention leveraging different wavelengths of light). Quoting from the Wikipedia entry:

In its most common (transmissive) application mode, a sensor device is placed on a thin part of the patient’s body, usually a fingertip or earlobe, or in the case of an infant, across a foot. The device passes two wavelengths of light [editor note: usually red and infrared] through the body part to a photodetector. It measures the changing absorbance at each of the wavelengths, allowing it to determine the absorbances due to the pulsing arterial blood alone, excluding venous blood, skin, bone, muscle, fat, and (in most cases) nail polish.

The results of the multi-night pulse oximetry test indeed indicated that I was experiencing dozens of breathing and pulse rate “events” each hour while asleep. This all was more than a bit of a surprise to both my wife and me; I’m not obese, for example, which is a common root cause of the obstructive form of sleep apnea in particular. I also don’t mouth-breathe when I sleep, my wife has never noticed interruptions in my breathing, and I hardly ever snore. That all said, the data I saw seemed indisputable, and the doctor concurred.

The next step was two-fold. To give me some immediate relief, the doctor ordered an oxygen concentrator, which works in conjunction with a nasal calluna. Here are a few photos of the Philips Respironics EverFlo unit I used for a few months, taken in the parking lot as I was returning it (hold that thought):

Although (as I understand it … I’m not a doctor, and I don’t even play one on TV) an oxygen concentrator won’t prevent apnea, it ensures that when I am breathing, the air going into my respiratory system is as “pure” as possible, translating into hopeful improved overall health.

In parallel, the doctor ordered a more in-depth sleep study to confirm the initial results. Initially, an on-site overnight study at a sleep center located at the heart of the Continental Divide was requested, at even higher elevation than my residence (9,150 feet above sea level, to be precise) in order to accentuate any apnea symptoms and effects, but my health insurance rejected it due to cost, claiming that my situation wasn’t life threatening. Instead, I did another multi-night home study, this time with the ResMed ApneaLink Air, a more elaborate version of the pulse oximeter I’d used before.

The ApneaLink Air measured respiration three different ways; via a nasal calluna, a fingertip-mounted pulse oximeter, and (since the main unit is strapped to my chest) via an embedded accelerometer that “counts” chest rise-and-fall cycles. Integrated sensors also enable the ApneaLink Air to ascertain my body position whenever vital sign data is being logged; apnea tends to be worse when a person is lying on his or her back or chest, and in fact it turned out that I had notably fewer breathing “events” in a given amount of time when I was sleeping on either side.

Analysis of the ApneaLink Air-captured analytics definitively confirmed the initial sleep apnea diagnosis, complete with a “severe” classification. But what kind of apnea was I suffering from? The earlier-mentioned obstructive form is “caused by complete or partial obstructions of the upper airway … the muscle tone of the body ordinarily relaxes during sleep, and the airway at the throat is composed of walls of soft tissue, which can collapse.” But then there’s central sleep apnea, which is “usually due to an instability in the body’s feedback mechanisms that control respiration” (i.e. neurological versus physical in root cause).

A conventional (or unconventional) continuous positive airway pressure (CPAP) machine is intended to treat obstructive sleep apnea. But it won’t relieve the symptoms of central sleep apnea, and may in fact worsen them. Nonetheless, not wanting to further delay the process with further clarifying tests, the doc and I decided to roll the dice and try a conventional CPAP first, relying on the fact that obstructive sleep apnea is the most common form of the affliction.

My unit is once again from Philips Respironics, this time called the DreamStation. It normally (and controversially so) transmits encrypted data to both your doctor and your insurance provider (to ensure treatment regiment compliance … I need to use mine a minimum of 21 days per month, at four hours minimum per day, in order to keep coverage active) via an EV-DO cellular connection. A Wi-Fi module is also available, and worst case there’s a user-removable memory card that can be shipped out every few months. Bluetooth Low Energy connectivity to an iOS or Android device allows for user viewing of a data subset (which is also uploaded to the “cloud” for web browser retrieval purposes).

Here are a few photos of the main device, accompanied by a quarter for dimension comparison purposes:

The DreamStation is quite small and lightweight, and can actually be half the size shown if you disconnect the optional humidifier section (the back half). Because it’s an approved medical device, it doesn’t count against your carry-on luggage allotment if you take it with you when you travel. It’s also nearly silent when in use; much quieter than its oxygen concentrator predecessor (which wasn’t loud by any means, either). And a variety of accompanying “mask” options was offered to me:

I went with the simplest and most comfortable “nasal pillow” approach, since as previously mentioned, I don’t breath out of my mouth and a fuller-face-covering design therefore isn’t necessary. My transition to using the CPAP was effortless (it doesn’t hurt that I’ve long been able to fall asleep pretty much anywhere, at the drop of a hat); others report it taking weeks-to-months to get used to the mask, and some folks never do (oral appliances are an alternative, particularly with minor-to-moderate apnea cases).

Bottom line: how well is the DreamStation working? Great! First off, here are some screenshots of the initial installation of the DreamMapper app for iOS, which is normally formatted to run on a smartphone but I have installed on my “Retina” iPad mini 2 (therefore the “full screen” option at bottom right of the images):

And here’s the overview screenshot after the second full night of use:

The Apnea–Hypopnea Index (AHI) is “used to indicate the severity of sleep apnea.” My measurement that second night (5.6) fell barely within the mild sleep apnea range of 5-15. One week later, my AHI was 3.7. And more generally, after only two weeks of use, my energy level is notably higher, my head is clearer, and my wife is appreciating the resurrected healthy glow of my skin (which neither of us had admittedly realized had faded, until after it returned and the contrast was obvious).

I’ll have more data to share in my next post in this series. For now, however, I’ll conclude with a strong encouragement to follow in my footsteps and get your sleep quality checked out if at all in doubt. Undiagnosed sleep apnea is reportedly rampant and for many, represents a life-long impediment. Quoting Wikipedia:

People with sleep apnea have problems with excessive daytime sleepiness (EDS), impaired alertness, and vision problems. Obstructive sleep apnea (OSA) may increase risk for driving accidents and work-related accidents. If OSA is not treated, people are at increased risk of other health problems, such as diabetes. Death could occur from untreated OSA due to lack of oxygen to the body Moreover, people are examined using “standard test batteries” to further identify parts of the brain that may be adversely affected by sleep apnea, including those that govern:

  • “executive functioning,” the way the person plans and initiates tasks
  • paying attention, working effectively and processing information when in a waking state
  • using memory and learning.

Due to the disruption in daytime cognitive state, behavioral effects may be present. These can include moodiness, belligerence, as well as a decrease in attentiveness and energy. These effects may become intractable, leading to depression.

There is evidence that the risk of diabetes among those with moderate or severe sleep apnea is higher. There is increasing evidence that sleep apnea may lead to liver function impairment, particularly fatty liver diseases. Finally, because there are many factors that could lead to some of the effects previously listed, some people are not aware that they have sleep apnea and are either misdiagnosed or ignore the symptoms altogether.

Stay tuned for my next post, which will discuss my experiences with an in-depth personal sleep monitoring system. Until then, I welcome your thoughts!

Brian Dipert is Editor-in-Chief of the Embedded Vision Alliance, and a Senior Analyst at BDTI and Editor-in-Chief of InsideDSP, the company’s online newsletter.

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