Figure: Illustrating how ORP is measured and representative ORP values and patterns observed during wakefulness and sleep.
Figure: Top left, example of a 3-sec EEG epoch and the power values in the different frequency ranges for that very epoch. Each value is assigned a rank (0 to 9) based on its location within the total range found in 430,000 3-s epochs in development PSGs obtained from patients with a wide spectrum of sleep disorders. Each range was divided into 10 deciles.
Delta power in the example 3-s epoch was 202 μV2 and that placed it in rank 8 of the delta range. Powers in the other frequencies are located in ranks 4, 1, and zero of their respective ranges. This results in a 4-digit number of 8410.
There are 10,000 possible 4-digit numbers.
The probability (0-100%) of epochs with each number occurring in wake epochs or during arousals is determined from a look up table established from these probabilities in the development PSGs (right panel). The probability for each 4-digit number is divided by 40 (last column), which is the % of wake epochs in the development files. Thus, an ORP of 2.5 indicates a 100% probability that the pattern of the 3-sec epoch occurs in wake epochs or during arousals, while an ORP of zero indicates that the pattern invariably occurs during epochs scored visually as sleep.
Note: Epochs with low values in the first two digits of the 4-digit number and high value of the 4th digit (e.g., 0008, 0009) are almost always found in epochs staged wake (% awake >90); hence have an ORP near 2.50, while those with high values in the first two digits and low value of the 4th digit (e.g., 9990. 9991) are almost never seen in stage wake or in arousals; hence have a very low ORP. (Reference 2)
Relevant References:
How do Epochs with Different ORP Look and how ORP architecture differs from conventional sleep architecture?
Figure: Records from one subject from the Sleep Heart Health Study.
A) Nine 30-second EEG tracings representing EEG patterns receiving ORP values spanning the entire ORP range (0.00-2.50). Epochs with ORP >1.75 are typically scored as wake (1) but exhibit a wide spectrum from full wakefulness with high ORP (top panel) to patterns with micro-sleep, which do not meet the criteria of sleep. Likewise, a wide range of patterns can be identified in epochs typically scored as NREM sleep. The figure shows ORP values ranging from 0.36 to 1.77 within stage N2.
B) Conventional sleep stages in the same subject showing normal values.
C) ORP-based architecture in which % of epochs occurring within each ORP decile is illustrated. (Reference 2)
Relevant References:
ORP vs. Sleep Stages Across the Night
Figure: Typical pattern of ORP in normal sleep. ORP data are presented as the average of 30-second epochs. Note that ORP is constantly changing throughout the sleep period in slow cycles (sleep cycles) and as a result of transient awakenings (aw) and long arousals (Lar). Short arousals (e.g., <9 seconds) have little impact on average ORP in the epoch. Fast oscillations in 30-second ORP are only in small part related to brief arousals but mostly reflect real changes in the average of the ten 3-second ORP values within each 30-second epoch (1).
Note: ORP tends to increase across the night (2), reflecting the cumulative restorative function of sleep.
The dotted vertical lines show that most of the range of sleep depth occurs during stage N2, such that stage N2 does not represent a unique or narrow range of sleep depth, whereas stage N3 occurs only when sleep is very deep (3).
Relevant References:
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