It is well known that there are many causes of sleep disruption through the night, and patients rarely exhibit just one. Simply addressing sleep disordered breathing (SDB) may not result in good long term sleep. Other issues can range from an inferior bed, a disruptive sleep environment, incorrect medication, pain, incorrect positive airway pressure (PAP), insomnia, and many more.
For the nearly 70 million Americans who suffer from sleep disorders, sleep offers little chance to rest. In the United States, sleep deprivation and disorders carry a price tag of more than $100 billion annually in lost productivity, medical expenses, sick leave, and property damage. The National Highway Traffic Safety Administration estimates that 71,000 injuries each year are related to drowsy drivers.
As a result of these staggering numbers and the increasing awareness of sleep disorders, it has been suggested that sleep should be one of the “vital signs” of health together with temperature, blood pressure, respiration rate, pulse, pain, and BMI (body mass index).
Adequate sleep has been defined as regularly sleeping 6-8 hours per night. Clinicians now believe that sufficient slumber is a critical factor in health and health-related behaviors across all ages. It is not enough to simply spend these hours in bed. The quality of sleep is just as, if not more important than, the quantity.
How is quality of sleep defined? For the sleep specialist, “good” sleep may be defined as sleep that has normal efficiency, organized sleep architecture, and the absence of any sleep disruptions. For the patient, good sleep may mean waking up in the morning feeling refreshed and not feeling sleepy during the day.
How do we currently measure “good sleep?” One way is with an in-lab PSG test, which is often necessary but also expensive. A second way is through home sleep testing (HST), although most of these devices measure parameters that only detect sleep apnea. A third, purely subjective way we measure sleep, is to simply ask patients how they are sleeping. This last approach is akin to asking them whether they feel heavier or lighter instead of having them step on a scale.
In addition, if your patients have never slept well, how do they know they slept well last night versus sleeping a bit better than the night before? This leaves us with the sleep lab but how can we expect a patient to sleep “normally” and collect a representative night of sleep quality when there are so many cables and equipment attached to them, not to mention we are asking them to sleep in a strange environment – with a camera watching them all night – which takes us back to home sleep testing.
All of this information points to the need for a simple and objective measure of sleep quality that is cost effective enough to use on patients regularly without being specific to a particular condition, in much the same way a scale will objectively measure weight. What’s needed is a “scale” that objectively measures sleep quality or sleep health.
Enter Robert Thomas, MD, and his colleagues at the Beth Israel Deaconess Medical Center, a teaching school of Harvard Medical School, who have taken a different approach to examining sleep—seeking to objectively measure sleep quality using cardiopulmonary coupling (CPC).
The principle behind this technology, is the understanding that stable NREM (non-rapid eye movement) sleep is characterized by a cardiac rhythm known as sinus arrhythmia. During stable sleep, high vagal tone modulating a healthy heart results in characteristic heart rate variability in which the heart slows and speeds up in synchrony with very regular respiration. This is what Thomas calls stable sleep
But not all heart rate variability is synchronized with normal respiration. Repetitive sleep disruptions, which could be caused by SDB, pain, a noisy sleeping environment, periodic limb movement syndrome (PLMS), restless legs syndrome (RLS), or anxiety, to name a few, can cause the heart rate and breathing rate to vary. This bradytachyarrhythmia is well recognized in polysomnograms.
These recurring disruptions can be seen as infrequently as once every 2 to 3 minutes, or as often as 1 to 3 times every minute, so they are difficult to see in a normal PSG test. However, if we look at the data in terms of frequency we can see these changes occurring over sometimes long periods of time. It’s like being too close and not seeing the forest for the trees. This is unstable sleep.
Thomas also identified that there is little overlap between stable and unstable sleep, so they can be easily displayed and differentiated from each other. This makes interpretation much easier. The concept of stable and unstable sleep is central to CPC.
The result of Roberts’ CPC is a new, low cost, patient centered system call SleepImage that measures stable vs. unstable sleep. This test-anywhere device weighs less than an ounce, sits barely detectable on the patient’s chest, and also records actigraphy, body position, ECG, and snoring. It is fully integrated with a secure website and delivers a simple and easy-to-understand “picture of sleep” that identifies stable and unstable sleep to produce an objective measure of sleep quality.
There are many practical uses for the device, and because of its simplicity, researchers have been able to expand the identification and understanding of sleep beyond conventional sleep diagnostic practices. In the sleep lab, the CPC technology can be used to help identify complex sleep apnea, a disorder that may make conventional CPAPs intolerable for patients.
As a home sleep test, the SleepImage system can be used as a very low cost screener for patients that complain of poor sleep. The SleepImage will quickly and cost effectively validate whether an in-lab PSG or some other course of action is necessary and more importantly allow the physician to monitor sleep quality after intervention to ensure that the patient is complying with therapy or if there is another co-morbid condition that is continuing to cause poor sleep quality.
Perhaps the most noteworthy benefit of this technology is its ease of use, requiring little or no instruction to the patient, with automated analysis and easy-to-understand graphic results.
SleepImage is FDA cleared, and affords an objective measure of sleep quality that not only provides a picture of your patient’s sleep, but also assists in tracking sleep trends over time—offering an accurate measure of the effectiveness of a given therapeutic choice. So the next time you ask patients how they slept last night, why not have an objective way to validate the answer?
Click for more information about SleepImage.