See our guide below to better understand your WatchPAT sleep study!
Equipment Purpose
Finger Probe Measurements- Pulse oximetry is the measurement of oxygen in the blood. This value is expressed as a percentage of hemoglobin with oxygen bound to it. With normal day-to-day activities, a healthy individual will be greater than 92%.
- Heart Rate is the frequency your heart is beating each minute. 60-100 bpm is considered a normal heart rate. This value will typically increase during a stressful response.
- Peripheral Artery Tone (PAT) Signal detects the change in blood volume in the peripheral arteries. In stressful situations, our body will squeeze our peripheral arteries causing a decrease of blood flow (1).
Wrist Watch Measurement
- Actigraphy is detecting body activity during sleep. This, along with the PAT signal is important in determining what sleep stage the individual is in (1).
Chest Sensor
- Chest Motion is important for determining the presence of breathing efforts. This is paramount in differentiating between obstructive and central sleep apnea
- Snoring statistics are measured by a microphone implanted into the chest sensor. A normal conversation in a calm environment will typically be recorded between 50-60 dB.
- Body Position is important to determine if the severity of events are worse on the left, right or supine (back) or prone (stomach).
Indices Explained
Apnea Hypopnea Index (AHI)
Currently, AHI is the main indicator in determining the severity of sleep apnea. This is the representation of how many times you partially (hypopnea) or completely (apnea) stopped breathing per an hour of sleep. This can be calculated by taking data from multiple sensors to gather the total number of events and dividing it by the “True Sleep Time” (TST).
- AHI <5 = Normal
- AHI 5-15 = Mild Sleep Apnea
- AHI 15-30 = Moderate Sleep Apnea
- AHI >30 = Severe Sleep Apnea
The WatchPAT ONE uses AHI 3% and 4% criteria to further distinguish events. AHI 3% signifies that there was a correlated 3% or more oxygen desaturation during the associated event. An AHI 4% will exclude all 3% episodes and only show the events of 4% or greater.
Furthermore, the WatchPAT is able to distinguish between obstructive and central events. While AHI takes into account all episodes, AHIc is a representation of central events only.
Respiratory Disturbance Index (RDI)
RDI is the total number of respiratory events over the course of the night that disturbed sleep quality. These events include all AHI events but do not need to be associated with such an event. An arousal from sleep can occur due to snoring, or due to airflow reductions that do not meet the standard for an apnea or hypopnea event.
Oxygen Desaturation Index 3% (ODI)
ODI 3% represents the number of times an individual desaturated by 3% over the course of the night. These events can be associated with an AHI, but can occur independently as well.
Cheyne-Stokes Respiration (CSR) %
CSR is a cyclic breathing pattern characterized by periods of deep and rapid breathing, followed by periods of shallow and slow breathing, eventually leading to apneic periods before it resumes again. This type of breathing pattern can be found in central sleep apnea and typically in those who have suffered strokes or have heart failure.
Stages of Sleep
In a sleep lab, your stages of sleep may be broken down into N1, N2, N3 and REM sleep. However, with the WatchPAT ONE, your sleep will be broken down into light sleep (N1 +N2), deep sleep (N3) and REM sleep. In adults, normal sleep typically consists of 5% Stage N1, 50% Stage N2, 20% Stage N3, and 25% REM sleep (2).
Monitoring Time (MT) Vs True Sleep Time (TST)
Total Monitoring Time (MT) refers to the entire duration the device is active. However, relying solely on MT to detect sleep apnea can lead to underdiagnosis or an underestimation of its severity. To ensure accurate diagnosis and assessment, it is crucial to use True Sleep Time (TST)—the actual time spent asleep—as the primary metric for evaluating sleep apnea and its severity (1).
Conclusion
Interpreting a sleep study can be challenging. Fortunately, a qualified sleep doctor is equipped with the expertise to analyze these values in detail, examining every aspect of your sleep report. From identifying the frequency and type of sleep disturbances to understanding how they impact your overall health, the sleep doctor provides a comprehensive interpretation. Based on their analysis, they will offer personalized recommendations and treatment options tailored to your needs. With their guidance, you can take the next steps toward better sleep and improved well-being.