SLEEPstudy Workflow and metrics

The SleepImage system is operator-independent with metrics and workflow suggestions based on automatic analysis of ECG data collected during sleep. The primary metrics can be explained as follows: • Sleep Quality Index (SQI) is a summary index of sleep duration, sleep stability and sleep pathology.17,18,19,20,21

• Sleep Apnea Indicator (SAI) is a measure of Cyclic Variation of Heart Rate (CVHR) detecting oscillations in cardiac intervals that are often associated with prolonged cycles of sleep apnea. 22,23 • Stable sleep (HFC) is driven by the parasympathetic nervous system (Rest & Digest), dominated by integrated activity around individual respiratory cycles. Heart rate slows down and speeds up in synchrony with respiration. Characterized by stable breathing, high vagal tone and non-cyclic alternating pattern on the electroencephalogram, high delta power and blood pressure dipping, stable sleep may be considered to be “effective” NREM sleep. Effective sleep enables the normal functions of sleep, such as recovery and restoration processes. • Unstable sleep (LFC) is driven by sympathetic nervous system (Fight & Flight), it is dominated by low frequency cycling of respiration and heart rate, with tidal volume fluctuations, cyclic variation in heart rate, a cyclic alternating pattern, electroencephalogram low delta power and stable (non-dipping) blood pressure. Unstable sleep may be considered “ineffective” NREM sleep, sleep that fails to accomplish the normal functions of healthy sleep. • Using SQI together with SAI and biomarkers for sleep pathology called elevated Low Frequency Coupling broad-band (eLFCbb) and elevated Low Frequency Coupling narrow-band (eLFCnb), it is possible to identify the presence of SDB and categorize it as either obstructive or non-obstructive sleep apnea.17,18,19,20,21 The workflow to identify the presence of sleep disorders, using the SleepImage system can be demonstrated in Figure 2.

Clinical Example

Figure 2: Suggested workflow protocol for objective sleep screening

38 DSP | Spring 2017

The subject is a 57 year old male, BMI>35, with a history of daytime somnolence, snoring and waking up gasping or choking for air. In addition to the above-mentioned metrics, the SleepImage system provides a spectrographic picture of the sleep parameters. A frontal view of the spectrogram presents