A sleep study, formally known as polysomnography, is a diagnostic test that records various bodily functions during sleep. Healthcare providers use this evaluation to identify or rule out different sleep-related conditions. The study monitors brain activity, heart rate, breathing patterns, blood oxygen levels, and movements of the eyes and limbs. This detailed monitoring provides a complete picture of sleep architecture and disruptions, guiding treatment decisions.
Understanding the Split Night Study
A split night sleep study combines two assessments into a single overnight session: a diagnostic evaluation and a treatment initiation phase. This approach diagnoses obstructive sleep apnea (OSA) and determines appropriate settings for continuous positive airway pressure (CPAP) therapy within the same night. The first part observes sleep patterns to confirm a diagnosis. If criteria are met, the second part focuses on adjusting CPAP pressure to manage the condition.
This consolidated process offers advantages over separate studies, making it more efficient for patients and healthcare systems. Completing both steps in one night reduces the need for multiple appointments, saving time and decreasing costs. The immediate transition to treatment allows individuals to begin addressing sleep issues sooner.
When a Split Night Study is Recommended
A healthcare provider recommends a split night study for individuals with a high likelihood of moderate to severe obstructive sleep apnea. This often includes patients experiencing symptoms such as loud, habitual snoring, observed breathing pauses during sleep, or significant daytime sleepiness. The goal is to provide a swift diagnosis and initiate therapy without requiring a separate CPAP titration study.
This single-night format is convenient for patients, consolidating two potential overnight visits into one. It also contributes to the efficiency of sleep clinics by optimizing bed utilization and reducing waiting lists. The American Academy of Sleep Medicine (AASM) suggests a split night study is appropriate when there is strong clinical suspicion of severe OSA or when severe OSA is detected early in a standard diagnostic study.
What Happens During the Study
Upon arrival at the sleep center in the evening, a sleep technologist will greet the patient and guide them to a private room. The technologist will provide a brief overview of the study and answer any questions before beginning the setup. This involves the painless application of various sensors and electrodes, a process that typically takes about 40 minutes.
Sensors are placed to monitor various functions:
- Electrodes on the scalp monitor brain waves (electroencephalography or EEG) to identify sleep stages.
- Sensors around the eyes track eye movements (electro-oculography or EOG) to distinguish between REM and non-REM sleep.
- Electromyography (EMG) electrodes monitor muscle activity in the chin and legs.
- Electrocardiogram (EKG) sensors on the chest record heart rate and rhythm.
To monitor breathing, sensors are placed near the nose and mouth to detect airflow, and elastic belts around the chest and abdomen measure respiratory effort. A pulse oximeter, often clipped to a finger, continuously measures blood oxygen levels. Some setups may also include a small microphone to record snoring. Once all sensors are in place, the patient can relax until their usual bedtime. A technologist monitors them from an adjacent control room throughout the night.
During the initial part of the night, the study functions as a standard diagnostic polysomnogram, collecting data on natural sleep. If, after a minimum of two hours of sleep, data indicates moderate to severe obstructive sleep apnea, the study transitions to the CPAP titration phase. The technologist gently wakes the patient to apply a CPAP mask, which delivers pressurized air to keep the airway open. The CPAP machine’s pressure is then carefully adjusted to eliminate breathing disturbances like apneas and hypopneas. The patient can still get up to use the restroom if needed, and the technologist will assist with disconnecting and reconnecting the wires.
After Your Study: Results and Treatment
In the morning, the sleep technologist will remove all sensors. The data collected throughout the night is then analyzed by a qualified sleep specialist. A key metric is the Apnea-Hypopnea Index (AHI), which represents the average number of apnea (complete breathing cessation) and hypopnea (partial breathing reduction) events per hour of sleep. Each event must last at least 10 seconds to be counted.
The AHI score helps determine sleep apnea severity: an AHI of less than 5 is normal, 5 to 15 indicates mild, 15 to 30 suggests moderate, and over 30 signifies severe sleep apnea. The sleep specialist interprets this score with other physiological data and the patient’s symptoms to establish a diagnosis. If the study confirmed obstructive sleep apnea and CPAP titration was successful, the patient will likely receive a prescription for a CPAP device for home use. A follow-up consultation with the physician is then scheduled to discuss results and develop a personalized treatment plan.