No Spacer, Poor Coordination — Most Dose Lost in the Throat
Without a spacer, fast pMDI sprays mostly hit the throat, not the lungs.
- ~10%: Lung deposition, no spacer (typical poor-technique pMDI use)
- ~80%: Oropharyngeal deposition (swallowed, not inhaled)
- ~30 m/s: Plume exit velocity (too fast for small airways)
- ~50%: Patients with poor technique (even after being shown once)
Why coordination fails
Actuation and inhalation must start within the same fraction of a second.
The cold-freon effect
Cold spray on the palate makes many patients stop inhaling mid-puff.
Where the dose goes
Large fast droplets impact the throat wall by inertial deposition.
Spacer Chamber Slows the Plume Before It Reaches the Mouth
A holding chamber lets propellant evaporate so particles arrive smaller and slower.
- ~20-30%: Lung deposition with spacer (roughly double bare pMDI)
- ~20%: Oropharyngeal deposition (large droplets trapped in chamber)
- low: Coordination requirement (timing errors matter far less)
- children, elderly: Recommended for (anyone with weak coordination)
Chamber physics
A spacer gives propellant time to evaporate before inhalation.
Slower plume velocity
Particles drift instead of jetting straight into the throat.
Single slow breath
One slow, deep inhalation draws the dose from the chamber.
Exhaling Too Soon Undoes an Otherwise Good Inhalation
Particles that reach deep airways can still be breathed straight back out.
- ~2 s: Hold in this scenario (far short of recommended time)
- ~30-40%: Lung dose lost to early exhale (relative to a full hold)
- gravity: Settling mechanism (needs still air time to work)
- frequent: Common patient behavior (especially with breathless patients)
Sedimentation takes time
Small particles settle by gravity only during quiet breath-holding.
Early exhale carries particles out
Airflow reversal sweeps unsettled particles back toward the mouth.
A silent, invisible error
Patients often feel they inhaled correctly despite exhaling too soon.
A Full 10-Second Hold Maximizes Particle Settling
Ten seconds of stillness lets aerosol particles settle deep in small airways.
- 10 s: Recommended hold time (or as long as comfortable)
- +30-40%: Lung dose gain vs 2 s hold (relative improvement)
- small airways: Particle settling zone (bronchioles and alveolar ducts)
- ~4-5 s: Minimum useful hold (below this, gains are small)
Why ten seconds
Most respirable particles finish settling within about ten seconds.
Still air, no turbulence
A held breath removes airflow that would resuspend particles.
Comfort matters
Even a shorter comfortable hold beats no hold at all.
Spacer, Slow Inhale, and Hold — the Full Correct Sequence
Combining all three steps delivers the highest and most reliable lung dose.
- ~35-40%: Best-case lung deposition (spacer plus full technique)
- ~10%: Worst-case lung deposition (no spacer, poor coordination)
- 3: Technique steps that matter (spacer, slow breath, 10 s hold)
- ~3-4×: Relative improvement possible (best technique vs worst)
Shake and prime
A shaken canister and primed actuator ensure a consistent dose.
Slow steady inhale
A slow inhale keeps particles suspended long enough to travel deep.
Hold, then breathe normally
Hold ten seconds, then resume normal breathing before a second puff.