In-Lab Sleep Study (Polysomnography)

What Polysomnography Measures

An in-lab sleep study, formally called polysomnography (PSG), records several body systems at once through the night so a physician can see how they interact: something no single measurement can show on its own. A typical recording includes:

• EEG (electroencephalogram): small electrodes on the scalp record brain-wave activity, which is how the recording is divided into sleep stages, including light sleep, deep sleep, and REM sleep, and how arousals are identified.
• EOG (electrooculogram): sensors near the eyes track eye movements, which help distinguish REM sleep from other stages.
• Chin and leg EMG (electromyogram): electrodes measure muscle activity at the chin and, separately, the legs, capturing the muscle relaxation expected during REM sleep and detecting abnormal movements, such as periodic limb movements.
• Airflow: sensors at the nose and mouth detect airflow patterns and interruptions in breathing.
• Respiratory effort: belts around the chest and abdomen record the physical effort of breathing, which helps distinguish obstructive events from central ones.
• Blood oxygen saturation (SpO2): a finger sensor continuously measures oxygen levels, flagging drops that often accompany breathing pauses.
• ECG (electrocardiogram) / heart rate: chest electrodes track heart rhythm throughout the night.
• Body position: a sensor records whether you’re on your back, side, or stomach, since some breathing events are position-dependent.
• Video and audio recording: added when clinically appropriate, most often when a parasomnia or REM sleep behavior disorder is suspected, so unusual movements or behaviors can be reviewed alongside the physiologic data.

Together, these channels give a physician a far more complete picture of sleep architecture and physiology than breathing data alone can provide.

Before the Study

Scheduling typically starts with an evaluation to confirm an in-lab study is the right test for your situation, followed by a scheduled overnight appointment at the sleep lab. You’ll generally be asked to bring comfortable sleepwear, any items from your normal bedtime routine, and anything you’d need for the following morning.

Guidance around medications, caffeine, and daytime napping beforehand is individualized. Our team will review anything specific to your circumstances rather than apply a one-size-fits-all instruction sheet.

During the Study

The steps below outline how a typical overnight visit unfolds, from arrival through morning.

How the Overnight Visit Unfolds

1. 01→Settling InYou arrive in the evening and settle into a private room designed to feel more like a bedroom than a clinical space.↓
2. 02Sensor PlacementA sleep technologist attaches the sensors described above, a process that typically takes some time before the recording begins.↓
3. 03→Signal VerificationThe technologist verifies each signal is recording properly before the study begins.↓
4. 04Overnight RecordingLights go down and the technologist monitors the recording overnight from a nearby station, watching for equipment issues and documenting notable events without disturbing your sleep unnecessarily.

Sleeping with sensors attached is different from sleeping at home, and most patients notice that difference. Even so, the sensors and wiring are designed to allow normal repositioning, and most patients still get a reasonably representative night of sleep: rarely identical to a night at home, but generally sufficient for an accurate reading.

If a sensor loosens or a signal drops out, the technologist can address it without waking you fully.

The Technician’s Role

The overnight sleep technologist is a trained professional responsible for correct sensor placement, real-time signal quality, patient safety and comfort, and accurate documentation of the night’s events. What a technician does not do is interpret or diagnose the study: that assessment happens afterward, once a physician has reviewed the complete recording.

How Scoring and Interpretation Work

After the recording ends, the raw data is scored (broken into 30-second segments, staged by sleep phase, and marked for respiratory, cardiac, and movement events) using standardized criteria maintained by the American Academy of Sleep Medicine.

A physician then reviews the scored study as a whole, in the context of your reported symptoms and medical history, to determine whether a diagnosis is present, such as obstructive sleep apnea, central sleep apnea, narcolepsy, or a parasomnia, and how severe it is. Results and their implications are then discussed with you at a follow-up visit, along with recommended next steps outlined in our broader sleep apnea diagnosis guide.

Common Reasons an In-Lab Study Is Ordered

An in-lab sleep study is generally reserved for situations a simpler test can’t adequately address:

• Suspected obstructive sleep apnea when a home test isn’t sufficient: for example, when a home sleep apnea test was negative or technically inadequate despite ongoing clinical suspicion, or when significant heart, lung, or other medical conditions make in-lab monitoring safer and more reliable.
• Suspected central sleep apnea: because distinguishing central events, in which the brain briefly stops signaling the effort to breathe, from obstructive events, in which the airway itself is blocked, requires the respiratory effort channels only a full PSG provides.
• Suspected narcolepsy: an overnight PSG is the required study the night before a next-day multiple sleep latency test, ruling out other causes of daytime sleepiness and confirming adequate sleep time going into the nap test.
• Suspected parasomnias or REM sleep behavior disorder: video-synchronized PSG allows a physician to directly correlate observed movements or behaviors with brain-wave and muscle-tone data, which is often essential for confirming these diagnoses.
• Other complex or overlapping sleep disorders where breathing, sleep staging, and movement all need to be assessed together in one recording.

Polysomnography vs. Home Sleep Apnea Testing

Comparison table

Dimension	Home Sleep Apnea Test (HSAT)	In-Lab Sleep Study (PSG)
Where It's Done	At home, in your own bed	In a private room at a sleep lab
Supervision	Unattended; you apply the sensors yourself	Technician-attended overnight
What's Recorded	Airflow, breathing effort, oxygen levels, heart rate	All of the above, plus brain waves, eye movements, muscle tone, and video when indicated
Sleep Stages Measured	No	Yes, via EEG and EOG
Typical Use	Adults with a moderate-to-high likelihood of OSA and no complicating conditions	Suspected central sleep apnea, narcolepsy, parasomnias, or an inconclusive HSAT

Neither test is universally “better”: each is matched to a clinical situation. A physician evaluation helps determine which is the right starting point; see our home sleep test vs. sleep study comparison for a closer look at how that decision is made.

Split-Night Studies

A split-night study combines diagnosis and treatment initiation into a single overnight visit. If obstructive sleep apnea is clearly confirmed during the earlier part of the night, the technologist can transition the second portion of the recording to begin PAP titration rather than scheduling a separate night for it.

This approach isn’t suitable for everyone. It depends on how quickly and clearly the diagnosis emerges early in the study, and how much recording time remains to gather useful titration data. When a split-night protocol isn’t appropriate, diagnosis and titration are simply done as two separate overnight studies.

PAP Titration Studies

A PAP titration study is an in-lab night focused specifically on finding an effective pressure setting after obstructive sleep apnea has already been diagnosed, whether by a prior in-lab study, a split-night study, or in some cases an auto-adjusting device used at home.

During the study, the technologist gradually adjusts pressure through the night while the same physiologic channels are recorded, identifying the settings that control breathing events, minimize arousals, and support stable oxygen levels.

Your physician uses this data to finalize your prescription. The specific pressure required is individualized to each patient and is determined by this data rather than a standard number. This titration process directly informs CPAP therapy setup for patients who move forward with PAP treatment.

Local Care

For patients in Frisco, Texas and the surrounding North Dallas–Fort Worth area, the VitalAir Sleep & Lung Center offers physician-directed in-lab polysomnography alongside home sleep apnea testing, so the test ordered actually matches the clinical question being asked. If you’re unsure which study is right for you, a sleep evaluation is the place to start.