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The Split Night Sleep Study: Challenges and Problems

To someone who may be suffering from obstructive sleep apnea (OSA), the two-night overnight/nocturnal polysomnogram (NPSG) plus continuous positive airway pressure (CPAP) Titration Study is considered the gold standard of sleep studies.

But what if, for some reason, you are unable to devote two nights at a sleep clinic? For example, an insurance provider may only choose to cover one night, leaving you to pay the full bill for the other. Or you may find it difficult to sleep in the unfamiliar environs of the sleep study center. Or other personal, financial, or work-related issues may make it difficult to commit to the two-day, non-contiguous window required for the NPSG/Titration studies.

A compromise option is available to diagnose and to treat obstructive sleep apnea: the split night sleep study. However, like most compromises, it solves one problems but potentially creates more serious issues, including possibly missing out on gathering the most complete information about your OSA and being unable to asses the correct treatment for your individual sleep impairment.

What is Obstructive Sleep Apnea?

Obstructive sleep apnea (OSA), commonly called sleep apnea , or simply apnea , is a condition that occurs when a persons upper airway becomes so obstructed during sleep that they actually stop breathing.

OSA is most often caused by the most natural of all occurrences: when you sleep, all of your muscles relax, including those in your throat. If those throat tissues relax too far, or are heavier than your neck can support, they may end up squeezing your windpipe shut.

Since you are asleep, you are completely unaware that your own neck is choking off your air. Fortunately, our bodies are capable of rescuing us by waking us up every time this occurs: this restores our waking muscle tone, lifts the relaxed muscles off our throats, and allows us to gasp for air successfully. Unfortunately, this interrupts our sleep and then when we almost immediately fall back into it, the apnea cycle repeats, sometimes hundreds of times in a single night.

OSA is measured by using the Apnea-Hypopnea Index (AHI): an hourly measure of the number of completely blocked instances of breathing ( apneas ) and partially blocked instances ( hypopnea ). An apnea lasts at least ten seconds; reduces blood oxygen levels up to 4%; and literally forces a person to be jolted awake by their autonomic nervous system, which interprets a full-blown apnea as being choked to death.

What are Polysomnogram and Titration Studies?

The ideal solution for diagnosing and treating obstructive sleep apnea is to study your sleep for two nights. The first night is to diagnose whether or not you actually suffer from OSA and how severe your condition may be; the second night is to carefully test and calibrate the most effective treatment:

  • You spend your first night in a professional sleep clinic, during which time your body is measured, analyzed, and studied by an experienced sleep technician.
  • The next morning, your results are passed onto a certified sleep doctor, qualified to make an informed diagnosis of the severity of your condition, and give the most data-backed recommendation on how to treat your apnea-afflicted sleepless nights.
  • You then spend your second night (likely non-sequential) in the sleep clinic for the CPAP Titration Study. For this, you will don a PAP (positive airway pressure) device that will be used to determine the proper air pressure settings (titration) that will best relieve your sleep apnea.

What is a split night sleep study?

A split-night sleep study consolidates both polysomnogram and titration sessions into a single night.

  • Standard Nocturnal Polysomnogram NPSG
    • A successful NPSG requires a minimum of two full hours of actual sleep.
    • During this period, about a dozen electrodes and straps will be attached to your body, and measure specific body functions such as heart rate (EKG electrocardiogram), brain activity (EEG electroencehpalogram), and muscle tone.
    • Obstructive sleep apnea is generally diagnosed when the sensors record interrupted breathing and lowered blood oxygen levels.
  • CPAP Titration Study
    • Once the NPSG is complete, the sleep technician will instruct you to don the PAP device to measure and test titration settings.
    • Your sleep will be interrupted with instructions to change positions and to answer questions about comfort and sleep habits.
    • The technician will adjust the titration remotely. Too low a setting, and snoring and apnea will persist too high, the patients sleep may be disturbed, and central apneas may be caused.
    • The CPAP titration study may not be possible to complete if the NPSG takes longer than 4 hours, due to difficulties sleeping or other issues.

What are the limitations and challenges of a split night study?

From many perspectives, the split night sleep study may appear to be the most practical, economical, and efficient means of completing polysomnogram and titration tests. However, before choosing to do a split night study instead of the two-night NPSG + CPAP Titration option, there are several issues to consider.

  • Incomplete information . Rather than collating the biometric information on a full 8-hour night of sleep, the split night study only gathers two hours of data.
  • Missed REM sleep data . REM sleep, or rapid eye movement sleep, is the sleep stage during which your body is at its most relaxed. This is also when any episodes of sleep apnea are at their most severe. Unfortunately, REM sleep occurs most often during the second half of your nights sleep meaning in a split-night study, all of this data is not recorded. This could result in a significant underestimation of just how severe your sleep apnea may be.
  • Limited time windows . Eight hours in a sleep study bed may seem to be plenty of time, but in reality, there is only about a three-hour window to complete the NPSG phase of testing. If the required data is not gathered within that window, the second part of split-night testing, the CPAP Titration Study, cannot be completed and could require a return for a second night of testing.
  • Lost information . In the two-hour baseline for the NPSG in a split night study, studying the effect of body position on breathing may need to be sacrificed in order to proceed to the titration study. In addition, during the titration phase, there may not be enough time to ensure that breathing has been corrected in all sleep positions and sleep stages.
  • Insufficient sleep time . While some patients may have no trouble getting comfortable in the sleep center, many patients will experience difficulty getting to sleep at all in the unfamiliar environment. They may not complete the required two hours of sleep until more than half the night has passed, making it impossible for the sleep technician to proceed to the titration study.

Most importantly for the patient, an interrupted, incomplete sleep study may give an unfavorable first impression of CPAP therapy. Although a patient in a split-night study will enjoy the benefits of sleeping with a CPAP device to alleviate their apneas, they will only be using it for as little as one or two hours at the end of a long night of sleep study.

In contrast, dedicating a full night for a CPAP titration study allows the sleep technician to test, adjust, and instruct the patient in the first few hours of their sleep period. Once they have determined the best titration level for the patient, they leave them to sleep the rest of the night in apnea-free bliss which may result in the patient waking the next morning to find themselves surprisingly rested, even with less than a full nights sleep.

No matter which kind of sleep study you choose, it has been shown through several studies that even an imperfect titration study can effectively treat obstructive sleep apnea. Your doctor may order an additional study if necessary, and can help you with adjusting your CPAP therapy pressure at any time.

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