Day: July 16, 2025

• COV (Coefficient of Variation): <10% for adults, <15% for children (R5 parameter)
• Repeat at least 3 tests for a valid session.
• Coherence: >0.85 ensures signal reliability

PulmoScan’s software incorporates reference equations from multiple published studies covering a range of ethnicities, enabling results to be compared against the most relevant population norms for each patient. The software displays Z-scores and percent predicted values for comparing the oscillometry test parameters, but the ERS technical standards [1] recommend using Z-scores from reference equations [4, 5]. PulmoScan software flags values beyond the upper limits of normal or ULN (1.645 Z-score) and grades severity automatically, supporting consistent, evidence-based interpretation. 

Step 2: Start with R5: Total Airway Resistance

• R5 (resistance at 5 Hz) reflects the total resistance from central and peripheral airways.
• ↑ R5 suggests overall airway narrowing, as in asthma, COPD, or acute bronchoconstriction.
• Normal R5 means total airway resistance is within expected limits — but you must still check small airway parameters.

Step 3: Assess Small Airway Resistance: R5-R20

• R20 (resistance at 20 Hz) primarily reflects large/central airways.
• R5-R20 isolates peripheral airway resistance.
• ↑ R5-R20 means small airway narrowing, often the earliest sign of obstructive lung disease.
• A normal R20 but elevated R5-R20 can point to isolated small airway disease, which spirometry often misses.

 Step 4a: Look at X5: Small Airway Reactance

• X5 (reactance at 5 Hz) reflects the elastic and inertial properties of peripheral airways.
• More negative ↑ X5 values mean stiffer, less compliant small airways.
• Seen in restriction (fibrosis, interstitial lung disease) and in severe small airway obstruction (asthma, COPD).

Step 4b: Review AX: Area under the Reactance curve

• AX is the integrated area under the reactance curve from 5 Hz to Fres (resonant frequency or zero-crossing).
• ↑ AX indicates greater small airway dysfunction and can amplify findings from X5.
• AX is highly sensitive to early changes in the small airways.

Step 5: Identify the Pattern

Obstructive

• ↑ R5, ↑ R5–R20, ↑ X5, ↑ AX
• Seen in asthma, COPD, bronchiolitis

• Normal- R20, ↑ R5–R20, ↑ X5, ↑ AX
• Often early asthma/COPD

Restrictive 

• Normal/slightly ↑ R5, normal R5–R20, markedly ↑ X5, ↑ AX
• Seen in fibrosis, ILD, hyperinflation

Obstructive with central airway component

• ↑ R5, ↑ R20, ↑ X5, ↑ AX
• Normal R5–R20
• Seen in asthma

For more disease cases, please refer to the examples provided in Gupta et al., 2021[2].

Step 6: Use Within-Breath Parameters for Deeper Insight

PulmoScan can analyze inspiratory vs. expiratory phases within each tidal breath, revealing patterns invisible to whole-breath averages. These within-breath parameters help detect flow limitation:

Expiratory Flow Limitation (EFL)

• Defined as markedly higher expiratory resistance/reactance compared to inspiration.
• EFL is a hallmark of COPD, severe asthma, and other obstructive diseases.
• Mechanism: During expiration, small airways collapse prematurely, trapping air.
• Oscillometry signal:
  • R5 (exp) markedly higher than R5 (insp)
  • More negative X5 (exp) than X5 (insp)
  • Often seen with dynamic hyperinflation.

Inspiratory Flow Limitation (IFL)

• Characterized by higher inspiratory resistance/reactance compared to expiration.
• Suggestive of restrictive mechanics, including upper airway restriction, interstitial lung disease, and chest wall disorders.
• Mechanism: Increased stiffness or structural limitation reduces inspiratory compliance.
• Oscillometry signal:
  • R5 (insp) markedly higher than R5 (exp)
  • X5 more negative during inspiration.

Why It Matters:

• Whole-breath results may appear borderline or normal, but within-breath analysis can reveal dynamic airway behavior that guides diagnosis and therapy.
• EFL detection can prompt earlier COPD intervention.
• IFL patterns can push work-up toward restrictive or neuromuscular causes rather than obstructive disease.

Step 7: Bronchodilator Reversibility with PulmoScan

PulmoScan can test reversibility without repeated forced maneuvers. Per ERS guidance, a significant change is:

• R5 ↓ by ≥40%
• X5 ↑ by ≥50%
• AX ↓ by ≥80%

By combining whole-breath parameters with within-breath flow limitation analysis, PulmoScan helps clinicians move beyond a simple “normal/abnormal” report and toward a nuanced, physiology-driven interpretation that can:

• Detect early disease
• Differentiate between obstructive and restrictive mechanics
• Identify dynamic airway collapse or stiffness patterns
• Track patient response over time, in the clinic or at home.o