😴 CPAP Pressure Titration Simulator

The Collapsing Pharyngeal Airway

Sleep relaxes throat muscles, letting soft tissue collapse the airway.

• >30: Untreated severe AHI (events per hour)
• ~1 B: Adults with OSA (worldwide, mostly undiagnosed)
• 10–40 s: Apnea duration (per obstructive event)
• >3–4%: Oxygen desaturation (drop defines a scored event)

Why the airway collapses

Sleep drops pharyngeal muscle tone sharply. Negative inspiratory pressure pulls soft walls inward. Tongue base and soft palate fall backward. The lumen narrows or closes completely.

The Starling resistor model

The pharynx acts like a collapsible tube. Inspiration creates suction downstream of narrowing. Low critical closing pressure means easy collapse. Airflow stops despite continued breathing effort.

A fully collapsed airway with continued effort defines an obstructive apnea.

Consequences of untreated events

Each event ends in a brief arousal. Sleep architecture fragments, deep stages are lost. Repeated desaturation strains the cardiovascular system. Daytime sleepiness and hypertension risk both rise.

Partial Splinting at Low Pressure

A little positive pressure props the airway open, but not enough.

• 4 cmH2O: Typical starting pressure (titration protocol minimum)
• ≥30%: Hypopnea airflow drop (vs. baseline breathing)
• ~15–25: Residual AHI at low P (events per hour)
• 1–2 cmH2O: Pressure step size (per titration increment)

Pneumatic splint, partially applied

Positive pressure pushes air into the pharynx. Walls widen slightly but still flutter shut. Full apneas become shorter, partial hypopneas instead.

Hypopnea vs. apnea

Hypopnea means reduced, not absent, airflow. Snoring vibration often persists at this pressure. Arousals still fragment sleep, just less severely.

Low pressure trades apneas for hypopneas — improvement, not resolution.

Why titration continues upward

A tech raises pressure in small steps. Each step is held for several minutes. Events are counted until pressure suffices.

Most Obstructions Resolve

At moderate pressure the splint mostly overcomes tissue collapse.

• 8–10 cmH2O: Typical moderate range (common effective band)
• ~70–90%: AHI reduction (from baseline severity)
• Marked: Snoring reduction (walls vibrate far less)
• ~60%: Patients resolved here (of typical titration studies)

Splint force nears collapse force

Applied pressure now approaches critical closing pressure. Walls stay apart through most of the breath. Occasional brief narrowing can still occur.

Watching the airflow trace

The flow signal becomes rounder, less flattened. Flow limitation — a plateaued inspiratory shape — fades.

A flattened flow trace signals residual partial obstruction, even without a scored event.

REM sleep still challenges the splint

Muscle tone drops further during REM sleep. Higher pressure is often needed in REM. Titration protocols test pressure across sleep stages.

The Optimal Pressure Point

A single pressure now holds the airway open all night.

• <5: Target AHI (events per hour, normalized)
• 6–14 cmH2O: Typical optimal pressure (varies by patient anatomy)
• >90%: Oxygen saturation (sustained throughout sleep)
• Normalized: Arousal index (sleep architecture restored)

Defining the optimal pressure

Optimal pressure eliminates apneas, hypopneas, and snoring. It is the lowest pressure achieving that goal. Higher than needed adds discomfort without benefit.

Pneumatic splinting explained

Continuous positive pressure acts as an air stent. It counteracts negative inspiratory suction directly. The lumen cross-section stays open, unobstructed.

CPAP is a pneumatic splint, not a mechanical ventilator — it holds tissue open, it does not breathe for the patient.

From study to prescription

The optimal pressure becomes the take-home prescription. Auto-titrating devices can also track nightly need. Follow-up confirms sustained control over months.

When Pressure Goes Too High

Excess pressure trades one problem for new ones.

• CO2 washout: Central apnea trigger (over-ventilation suppresses drive)
• >24 L/min: Mask leak threshold (typical unintentional leak limit)
• ~5–15%: Treatment-emergent CSA (of titration patients)
• Common: Comfort complaints (aerophagia, dry mouth, leak noise)

Central apnea emerges

Too much pressure over-ventilates the lungs. Falling CO2 removes the drive to breathe. Breathing pauses occur despite an open airway.

Mask leak and arousal

High pressure forces air past the mask seal. Leak noise and airflow can wake the patient. Comfort drops even as obstruction stays resolved.

Central apnea at high pressure looks identical on a flow trace to central apnea from other causes — context matters.

Backing off to the true optimum

Titration steps back down once overshoot appears. The lowest effective pressure is the real target. This defines the final optimal prescription.