Do respiratory effort-related arousals (RERAs) correlate with periodic respiratory disturbance index (pRDI) on Watchpat?

Relationship Between RERAs and pRDI on WatchPAT

Yes, respiratory effort-related arousals (RERAs) directly contribute to the periodic respiratory disturbance index (pRDI) on WatchPAT, as the pRDI includes apneas, hypopneas, and RERAs per hour of sleep.

Understanding RERAs and RDI

RERAs are defined by the American Academy of Sleep Medicine (AASM) as:

• A sequence of breaths lasting ≥10 seconds
• Characterized by increasing respiratory effort or flattening of the inspiratory portion of the nasal pressure waveform
• Leading to arousal from sleep
• Not meeting criteria for apnea or hypopnea 1

The Respiratory Disturbance Index (RDI) is a comprehensive metric that includes:

• Apneas (≥90% drop in airflow for ≥10 seconds)
• Hypopneas (≥30% decrease in airflow with either ≥3% oxygen desaturation or an EEG arousal)
• RERAs 2

RERAs and WatchPAT Technology

WatchPAT is a home sleep testing device that uses peripheral arterial tone (PAT) signal along with actigraphy and pulse oximetry to detect sleep-disordered breathing. Unlike traditional polysomnography (PSG), WatchPAT doesn't directly measure EEG to detect arousals. Instead:

1. WatchPAT identifies autonomic nervous system activations through changes in the PAT signal
2. These autonomic activations correlate with cortical arousals seen on EEG
3. The device's algorithm can detect respiratory events that cause these autonomic activations

Correlation Between RERAs and pRDI

The pRDI reported by WatchPAT specifically includes:

• All apneas and hypopneas (which would be counted in the AHI)
• Events that resemble RERAs, detected through autonomic activations

Research evidence supports that:

• RERAs are associated with marked increases in cardiac sympathetic modulation 3
• These sympathetic activations can be detected through peripheral arterial tone changes
• Even without oxygen desaturation, RERAs contribute significantly to sleep fragmentation and sympathetic activation 4

Clinical Significance

The inclusion of RERAs in the pRDI is clinically important because:

1. Comprehensive assessment: The AASM recommends that "respiratory events that include arousals should be captured either by scoring hypopneas using the RECOMMENDED AASM Scoring Manual criteria or optionally by reporting an RDI" 1

2. Symptom correlation: Arousals, not hypoxemia, better predict hypersomnia in patients with OSA 1

3. Treatment implications: Patients with a high RERA index, even with a normal AHI, may experience significant sympathetic activation during sleep 3

Recent Changes in Scoring Rules

It's important to note that recent changes in hypopnea definitions have affected the relationship between RERAs and RDI:

• The newer AASM hypopnea definition includes events with ≥30% reduction in airflow for ≥10 seconds with EITHER a 3% oxygen desaturation OR an arousal
• This change has resulted in many events previously scored as RERAs now being classified as hypopneas 5
• In studies using the 3% hypopnea rule, RERAs contribute only about 4.3% to the RDI, while with the 4% rule, RERAs contribute about 27.7% 5

Practical Implications

When interpreting WatchPAT results:

• A difference between the pRDI and pAHI primarily represents events that cause autonomic activations without significant oxygen desaturation
• These events are physiologically similar to RERAs detected on PSG
• The pRDI provides a more complete picture of sleep-disordered breathing than pAHI alone, especially in patients with upper airway resistance syndrome or milder forms of OSA

In conclusion, RERAs are a significant component of the pRDI on WatchPAT, and understanding this relationship is crucial for accurate diagnosis and appropriate treatment of sleep-disordered breathing.