Nasal Pressure Should Be Used to Diagnose RERAs
Nasal pressure transducers are the recommended sensor for diagnosing Respiratory Effort-Related Arousals (RERAs), not thermistors. 1 The American Academy of Sleep Medicine (AASM) guidelines explicitly state that flattening of the inspiratory portion of the nasal pressure waveform is the surrogate marker for airflow limitation that defines RERAs. 1
Why Nasal Pressure is Superior for RERA Detection
Technical Requirements for RERA Scoring
RERAs are defined by inspiratory flow limitation patterns that appear as flattening of the nasal pressure waveform, which thermistors cannot adequately detect. 1
The nasal pressure signal must be recorded as either a DC signal or an AC signal with a low-frequency filter setting (cutoff frequency ≤0.03 Hz) to properly visualize the flattening characteristic of flow limitation. 1
At higher filter settings (e.g., 0.1 Hz), the ability to demonstrate airflow flattening is significantly impaired, making RERA detection unreliable. 1
Thermistor Limitations
Thermistors are designed to detect temperature changes between inhaled and exhaled gas, making them suitable only for detecting complete or near-complete airflow cessation (apneas). 1
Thermistors are insensitive to the subtle airflow changes and flow limitation patterns that characterize RERAs. 2
The AASM guidelines explicitly state that oronasal thermal sensors are the recommended sensor for apnea detection, but nasal pressure is recommended for hypopnea and RERA detection. 1
Clinical Algorithm for RERA Diagnosis
Diagnostic Polysomnography
Use nasal pressure transducer as the primary airflow sensor with appropriate filter settings (≤0.03 Hz low-frequency cutoff). 1
Score a RERA when: 1
- A sequence of breaths lasts ≥10 seconds in adults
- Progressive flattening of the inspiratory nasal pressure waveform is present
- The sequence terminates in an arousal from sleep
- The event does not meet criteria for apnea or hypopnea
Include a thermistor simultaneously for apnea detection, but do not rely on it for RERA identification. 1
PAP Titration Studies
During PAP titration, use the PAP device flow signal (not nasal pressure under the mask) to detect flow limitation and RERAs. 1
Thermistors placed under PAP masks are explicitly not acceptable for detecting respiratory events during titration. 1
Supporting Evidence Hierarchy
Research Validation
Nasal pressure transducers detect significantly more respiratory events than thermistors alone, particularly when the apnea-hypopnea index (AHI) is <50. 2
In one study, nasal pressure detected 90% of thermistor-identified events, while thermistors detected only 62% of nasal pressure-identified events when AHI <50. 2
Nasal cannula/pressure transducers provide non-invasive detection of flow limitation events with excellent interscorer reliability (ICC=0.96), comparable to esophageal manometry for RERA detection. 3
In pediatric populations, nasal pressure transducers detected all respiratory events identified by thermistors, but thermistors detected only 84% of transducer-defined events. 4
Critical Technical Pitfalls
Filter Settings
Failure to use appropriate low-frequency filter settings (≤0.03 Hz) is the most common error that prevents adequate RERA detection. 1
High-frequency filter settings should be set to 100 Hz to allow detection of snoring oscillations superimposed on the nasal pressure signal. 1
Signal Quality
Nasal pressure signals may show decreased amplitude during mouth breathing, which can affect event detection. 1
Nasal cannulas dislodge more frequently than thermistors, requiring vigilant monitoring during studies. 4
The non-linear characteristics of nasal pressure (proportional to flow squared) can be corrected with square root transformation for more accurate flow estimation. 1
Pediatric Considerations
- For pediatric RERAs using nasal pressure, additional criteria include: 1
- Discernible fall in signal amplitude
- Duration of at least 2 breath cycles
- Accompanying snoring, noisy breathing, or elevated CO2
- Termination by arousal