Physiological basis for each airway clearance technique
| Ventilation | Expiratory airflow | Oscillation | |||||
| Interdependence | CV | Breath hold | Huffing# | PEFR/PIFR >1.1 | PEFR >30–60 L·min-1 | ||
| Active cycle of breathing techniques | Thoracic expansion exercises utilise interdependence | Thoracic expansion exercises utilise CV | Sometimes used with this technique if hypoventilating | Uses forced expirations at different levels | Ratio 2.8 | Average 302 L·min-1 with huffing | No |
| Autogenic drainage | No | Yes, with breath hold | Uses 3-s breath hold with each breath | Only used to clear secretions from larger airways if needed | Yes; emphasis is on slow inspiration and increased velocity on expiration | 40–70 L·min-1 Depends on level of breathing and degree of airway obstruction | No |
| PEP | No | As PEP is maintained within the airways over 12–15 breaths, use of CV is maximised | Not necessary as PEP is maintained within the airways over 12–15 breaths | Used at end of each cycle of 12–15 breaths | No Ratio 0.47 | No Average 26 L·min-1 | No |
| Oscillating PEP with Flutter | Oscillations at 3–5 Hz may play a role, but frequency used in Flutter is >5 Hz | Yes with breath hold | Uses 3-s breath hold with each breath | Used at end of each cycle of 8–10 breaths | Ratio 1.15 | Average 68 L·min-1 | 2–32 Hz Most often uses 6–26 Hz |
| Oscillating PEP with Acapella | Oscillations at 3–5 Hz may play a role, but frequency used in Acapella is >5 Hz | As a PEP is maintained within the airways over 12–15 breaths, use of CV is maximised | Not necessary | Used at end of each cycle of 12–15 breaths | No Ratio 0.64 | Average 35.4 L·min-1 Within PEFR range needed, but would depend on viscoelastic and viscosity properties of secretions | 10–18 Hz |
| HFCWO | Oscillations at 3–5 Hz may play a role, but frequency used in HFCWO is >5 Hz | No | No | Interspersed with HFCWO | Yes, expiratory flow rate is much higher than inspiratory flow rate | Average 120 L·min-1 | 5–25 Hz |
CV: collateral ventilation; PEFR: peak expiratory flow rate; PIFR: peak inspiratory flow rate; PEP: positive expiratory pressure; HFCWO: high-frequency chest wall oscillation. #: each technique incorporates huffing, as used in the forced expiration technique, with the exception of autogenic drainage.