Normal Exhalation in the COPD Airway
COPD weakens the scaffolding that keeps small airways open.
- Small bronchi: Collapse point (no cartilage support)
- Reduced: Elastic recoil (emphysema destroys septa)
- <2 mm: Airway diameter (most vulnerable zone)
- Forced exhale: Trigger (raises pleural pressure)
Why small airways collapse
Emphysema destroys elastic tissue tethering airways open.
Dynamic airway compression
Forced exhalation pressure squeezes floppy bronchioles shut.
Equal pressure point
Collapse point shifts upstream as airflow speeds up.
Air Trapping and Hyperinflation
Airways shut before alveoli finish emptying, trapping stale air.
- ↑ 150%: Residual volume (vs healthy lung)
- ~55-65%: Air trapped (of tidal breath)
- Hyperinflated: Chest state (flattened diaphragm)
- Dyspnea: Symptom (breathlessness on exertion)
Premature airway closure
Collapsed segments seal before alveolar air fully escapes.
Rising residual volume
Trapped air stacks breath over breath, lungs stay overfull.
Flattened diaphragm
Hyperinflation blunts diaphragm mechanics, work of breathing rises.
Pursed-Lip Breathing Begins
Exhaling through lightly pursed lips adds resistance at the mouth.
- Narrowed: Lip gap (candle-blowing shape)
- 1:2 to 1:4: Inhale:exhale ratio (slow prolonged exhale)
- Reduced: Airflow speed (gentler than forced exhale)
- Slightly ↑: Mouth pressure (builds resistance)
The pursing maneuver
Lips form a narrow opening, like gently blowing out a candle.
Resistance at the mouth
Narrowed opening slows exiting air, raising downstream pressure.
Voluntary slow exhale
Patients extend exhale time instead of forcing air out fast.
Back-Pressure Holds Airways Open
Resistance at the lips raises pressure back through the airway tree.
- 4-14 cmH2O: Back-pressure (depends on pursing)
- Pneumatic splint: Effect (props airway walls)
- Shifts downstream: Equal pressure point (toward mouth)
- ↓ Sharply: Collapse risk (walls stay open)
Pneumatic splinting
Back-pressure pushes outward on airway walls from inside.
Equal pressure point shifts
Collapse point moves toward the mouth, away from fragile airways.
Pressure gradient control
Slower flow lowers the pressure drop across weak airway segments.
Reduced Trapping, Easier Breathing
Slower, more complete exhalation improves ventilation efficiency.
- ~15-20%: Air trapped (down from ~60%)
- ↓ to 10-12: Respiratory rate (breaths per minute)
- ↓ 2-4 points: Dyspnea (Borg) (reported relief)
- Improved: Oxygen saturation (better gas exchange)
More complete emptying
Fuller exhale leaves more room for the next fresh breath.
Slower breathing pattern
Fewer, deeper breaths replace rapid shallow panting.
Everyday clinical use
Patients use pursing during exertion, stairs, and flare-ups.