Motility 2: High-Resolution Manometry and the Chicago Classification v4.0
Episode keywords: high-resolution manometry, Chicago Classification v4.0, integrated relaxation pressure IRP, distal contractile integral DCI, distal latency, Chicago Classification decision tree, EGJ pressure, Clouse plot

Episode Summary
High-resolution manometry replaced 4–8 point sensors with 36 solid-state sensors spaced 1 cm apart, producing color-coded pressure topography Clouse plots that display the entire esophagus simultaneously. This episode teaches the three new metrics — IRP, DCI, and distal latency — and walks through the complete Chicago Classification v4.0 decision tree from the IRP branch point through every diagnosis. The CCv4.0 changes from v3.0 are explicitly board-tested.

Key Topics

• The three HRM metrics:
  • Integrated Relaxation Pressure (IRP): Lowest mean EGJ relaxation pressure over a 4-second window following swallow. Normal: supine median <15 mmHg; upright median <12 mmHg (Medtronic system). IRP is gate one of the entire CCv4.0 decision tree.
  • Distal Contractile Integral (DCI): Volume of the pressure topography "mountain" in smooth muscle — height (mmHg) × length (cm) × duration (sec). Normal: 450–8,000 mmHg·cm·sec. Below 100 = failed swallow. Above 8,000 = hypercontractile.
  • Distal Latency (DL): Time from swallow onset to the contractile deceleration point. Normal: ≥4.5 seconds. Short DL (<4.5 sec) = premature/spastic contraction.
• The CCv4.0 decision tree:
  • Elevated IRP + 100% failed peristalsis → Achalasia (subtype by body response)
  • Elevated IRP + preserved peristalsis → EGJOO (clinically inconclusive without confirmatory testing)
  • Normal IRP + 100% failed peristalsis → Absent contractility
  • Normal IRP + premature contractions (DL <4.5 sec, ≥20% swallows) → DES
  • Normal IRP + DCI >8,000 (≥20% swallows) → Hypercontractile esophagus
  • Normal IRP + >70% ineffective or ≥50% failed swallows → IEM
• What CCv4.0 changed from v3.0: Positional testing now required (supine AND upright). Clinically inconclusive category introduced for DES, hypercontractile esophagus, IEM, and EGJOO. Symptoms plus confirmatory testing required for diagnosis.

Board Pearls

Board trap: DCI and DL measure different things. DCI = contraction strength (how hard). DL = contraction timing (how early). DES is a timing disorder, not a strength disorder.

High-yield: IRP is always gate one. Ask yourself: is the IRP elevated or normal? Every subsequent decision branches from that answer.