Sleep Study Signals and Measurement
Oxygen Saturation –
ARES captures blood oxygen
saturation and pulse rate using reflectance pulse oximetry. The
ARES oximeter was designed specifically for the diagnosis of
OSA, which involves the detections and quantification of brief
desaturations and resaturations. It measures oxyhemoglobin
saturation in 0.1% increments rather than the typical 1%, which
allows identification of small but important changes in
Airflow (nasal pressure) –
Changes in air pressure
are measured with a pressure transducer connected to the nasal
opening via a nasal cannula. Decreases and increases in flow of
50% or more are automatically identified and marked as hypopneas
and cessations of airflow for at least 10 seconds are marked as
Pulse Rate –
ARES uses reflectance
pulse oximetry to measure pulse rate. Limited smoothing of pulse
rate signal increases capability of ARES Insight software to
recognize brief changes in pulse rate (e.g.,
Brady-tachycardias). These changes in pulse rate are recognized
markers of arousal.
Snoring is recorded with a
calibrated acoustic microphone so that the level of loudness can
be precisely quantified. Changes in snoring patterns and
crescendo snoring are automatically recognized and used as
markers of a respiratory-related arousals.
Head Position/Movement –
Head position indicates
the position of the pharynx and is used to determine the
positionality of obstructive events. Understanding the influence
of position on the severity of the OSA is useful in making
treatment decisions. Head movement is measured using
accelerometers similar to those used for actigraphy. Head
movement is a unique signal identified by ARES as a marker of
respiratory related arousal.
ARES measures sleep
behaviorally by combining the detection of subtle movements
through actigraphy, with variability of the airflow signal and
recognition of snoring.
ARES distinguishes REM
from NREM using EEG, EOG and EMG signals derived from two
electrodes placed at FP1 and FP2 on the forehead.
Apnea/Hypopnea Index (AHI)
ARES determines AHI by
adding the number of apneas and hypopneas per hour, where there
is a 4% oxygen desaturation.
Index (RDI) –
ARES measures RDI by
adding the number of apneas and hypopneas per hour, where the
hypopneas require a 1% oxygen desaturation/resaturation and at
least one behavioral arousal indicator.