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ACBT, forced expiration, huffing and autogenic drainage

The active cycle of breathing technique is the most-asked technique in this paper: 7 marks in W16, S23 and S26, 3 marks in S19 and W20, its rationale in asthma (S17), plus FET (W17), huffing vs coughing (W16, S20) and autogenic drainage (S20, W19, and against ACBT in W17). Learn the cycle as a drawing and the physiology behind each part.

Syllabus
Ch 4(a) Bronchial hygiene therapy: forced expiratory technique, ACBT, autogenic drainage
Priority
High yield. In 10 of 20 papers (2016–2026), the most-asked technique.
Asked as
7m W16S17W17S20S23S26 3m W16W17S19W19S20W20W25
Usual split
7-mark description with principle, indications and contraindications; 3-mark components, huff vs cough, AD phases
Checked against
BTS/ACPRC physiotherapy guideline (2009); ACPRC airway clearance leaflets; classic descriptions of ACBT (Pryor) and autogenic drainage (Chevaillier). Full list under Sources.
Content checked
19 October 2026. Next review due October 2027.
My revision

1ACBT: what it is

The active cycle of breathing technique (ACBT) is a flexible cycle of three breathing exercises that the patient does independently to loosen and clear sputum: breathing control, thoracic expansion exercises and the forced expiration technique.

The ACBT cycle

Breathing control, thoracic expansion, breathing control, forced expiration, in a loop Four boxes arranged in a circle with arrows clockwise: breathing control at the top; thoracic expansion exercises, 3 to 4 deep breaths with a 3-second hold, on the right; breathing control at the bottom; forced expiration technique, 1 to 2 huffs then cough, on the left; then back to breathing control. Breathing control always sits between the active parts. Breathing control Thoracic expansion 3–4 deep breaths, 3 s hold Breathing control Forced expiration 1–2 huffs, then cough repeat until huffs are dry twice
Breathing control always sits between the active parts. The order and the number of each part are adapted to the patient (for example, more breathing control in asthma).

2Components and physiological principle (S23)

ComponentHow to do itPhysiological principle
Breathing control (BC)Gentle, relaxed tidal breathing with the lower chest; shoulders and upper chest relaxed; as long as the patient needs between the active partsRest; prevents bronchospasm, fatigue and desaturation that deep or forced breaths can cause
Thoracic expansion exercises (TEE)3–4 deep breaths in, with a 3-second hold (or a sniff) at the top, then a relaxed breath out; the therapist's or patient's hand on the chest wall over the area for feedback; percussion or shaking can be added during themA large lung volume lets air travel through collateral channels (pores of Kohn, canals of Lambert, channels of Martin) and get behind mucus; the hold evens out filling between lung units; expanding one area helps open its neighbours (interdependence)
Forced expiration technique (FET)1–2 huffs (forced breaths out through an open mouth and glottis, like steaming a mirror) from mid to low lung volume, followed by breathing control; a huff or cough from high volume clears secretions that have reached the large airwaysDuring a forced expiration the airways narrow downstream of the equal pressure point, and fast air there shears mucus towards the mouth. Starting from a lower lung volume moves the equal pressure point further out, so a longer huff clears more peripheral airways
What is the equal pressure point?

In a forced breath out, pressure inside the airways falls from the alveoli to the mouth. At some point it equals the pressure outside the airway (the pleural pressure): that is the equal pressure point. Beyond it the airway is squeezed narrower, the air speeds up, and mucus is carried along. At high lung volume this point is in the large central airways; as lung volume falls it moves towards smaller, more peripheral airways. That is why a long, medium-volume huff reaches further than a cough from a full breath.

3Indications and contraindications

Indications

  • Excess or retained bronchial secretions: bronchiectasis, cystic fibrosis, COPD with sputum, chest infection, asthma with mucus plugging.
  • Collapse (atelectasis) and prevention of chest complications after surgery.
  • To make coughing more effective and less tiring; patients who become breathless or wheezy with coughing.
  • Independent daily airway clearance at home (no equipment).

Contraindications and precautions

  • Few true contraindications. Not possible in patients who cannot follow instructions (unconscious, confused, very young children).
  • Bronchospasm: lengthen breathing control; stop if wheeze increases.
  • Haemoptysis: avoid vigorous huffing and added percussion; gentle breathing control.
  • Untreated pneumothorax, unstable heart, severe pain after surgery: modify (supported huffing) or avoid forced parts.
  • Fatigue and desaturation: shorter cycles, oxygen as prescribed.

Indications of bronchial hygiene therapy in general (3 marks in W25)

  • Large amounts of sputum (classically more than about 25–30 mL a day) or difficulty clearing it.
  • Mucus plugging with lobar or segmental collapse.
  • Weak or painful cough: neuromuscular disease, after surgery, ventilated patients.
  • Chronic suppurative lung disease (bronchiectasis, cystic fibrosis) as a daily routine.

4Procedure and dose

  1. Explain the purpose; take a bronchodilator first if prescribed.
  2. Position: comfortable sitting, or a gravity-assisted position for the affected lobe if tolerated (see the postural drainage card).
  3. Start with breathing control until relaxed.
  4. 3–4 thoracic expansion breaths with a 3-second hold.
  5. Breathing control.
  6. 1–2 huffs from mid lung volume, then breathing control; when secretions are in the large airways, a high-volume huff or one cough.
  7. Repeat the cycle. Stop when the huff sounds dry and non-productive in two consecutive cycles, or when the patient tires.

Dose: usually 10–30 minutes, once or twice a day in chronic sputum production, more often during an infection. After surgery, a few cycles every hour or two while awake.

Rationale in asthma (S17): breathing control prevents bronchospasm and fatigue; thoracic expansion gets air behind plugs; huffing moves mucus without the coughing fits that narrow sensitive airways; the patient controls the pace and stops if wheeze increases.

5Huffing and coughing (3 marks in W16 and S20)

FeatureHuffCough
GlottisOpen throughoutCloses, pressure builds, then opens suddenly
Pressure in the chestModerateHigh
Lung volumeUsually mid to low: clears smaller, peripheral airwaysHigh: clears large, central airways
ControlVoluntary, graded by the patientReflex or voluntary
Effort and side effectsLess tiring; less airway collapse, bronchospasm, pain and urine leakageTiring when repeated; can cause airway collapse in COPD, bronchospasm, wound pain and stress incontinence
Best forMoving mucus up from the periphery; after surgery (with wound support); unstable airwaysClearing mucus once it reaches the trachea and main bronchi

Teaching a huff: medium breath in, then breathe out fast but not violently through an open "O"-shaped mouth, as if steaming up a mirror; the sound should be a breathy rush, not a cough. A mouthpiece or tube helps keep the glottis open. Support a wound with a pillow or hands.

6Autogenic drainage (7 marks in S20; phases 3 marks in W19)

Autogenic drainage (AD) (Chevaillier, Belgium) uses controlled breathing at different lung volumes to create the highest airflow the airways can take without collapsing, so mucus moves from the small airways to the large ones, where it is cleared with a gentle huff.

The three phases of autogenic drainage

Breathing trace moving from low to mid to high lung volume A lung volume trace. In phase 1, unstick, the patient breathes small breaths near the bottom of the range, low in the expiratory reserve volume. In phase 2, collect, breaths sit in the middle around normal tidal volume. In phase 3, evacuate, breaths move up towards the inspiratory reserve volume, then a huff clears the mucus. Arrows show mucus moving from peripheral to middle to central airways. high low time lung volume resting level (FRC) 1. Unstick 2. Collect 3. Evacuate peripheral middle central
Blue line = lung volume. Each phase shifts the breathing to a higher volume, and the mucus moves from peripheral to middle to central airways, then a gentle huff clears it.
PhaseBreathingEffect
1. UnstickSmall breaths at low lung volume (in the expiratory reserve range)Loosens mucus in the peripheral airways
2. CollectBreaths at mid lung volume (around normal tidal breathing)Gathers mucus in the middle airways
3. EvacuateDeeper breaths at high lung volume; then a gentle huff or coughMoves mucus to the central airways and out

Technique points

  • Sitting upright (or lying); slow breath in through the nose; hold for 2–3 seconds; breathe out through an open mouth and open throat, actively but without forcing, like a sigh, as fast as possible without wheezing or airway squeezing.
  • Feel or hear the mucus crackle to judge which phase to move to.
  • Suppress the urge to cough until mucus reaches the large airways.
  • Sessions usually take 30–45 minutes; the patient learns by feedback over several sessions.

Indications, advantages and disadvantages

  • Indications: bronchiectasis, cystic fibrosis (from about 8–12 years), COPD with sputum; patients whose airways collapse or wheeze with forced techniques; patients with cough-induced incontinence.
  • Advantages: independent, no equipment, gentle (less airway collapse, bronchospasm and desaturation), can be done anywhere quietly.
  • Disadvantages: hard to learn; needs concentration and good body awareness; time-consuming; not for young children or confused patients (a therapist-assisted form exists for infants).

ACBT and autogenic drainage are compared in a table on the bronchiectasis page (W17, 7 marks).

7Exam corner

Past questions (MUHS, 2016–2026)

  • 7-mark questionsActive cycle of breathing technique (W16). Rationale of ACBT in bronchial asthma (S17). Compare ACBT and autogenic drainage in bronchiectasis (W17). Indications and phases of autogenic drainage (S20). ACBT: physiological principle, indication and contraindication (S23). Describe ACBT (S26).
  • 3-mark questionsHuffing and coughing techniques (W16). Forced expiratory techniques (W17). ACBT (S19, W20). Difference between huffing and coughing (S20). Phases of autogenic drainage (W19). Three indications of bronchial hygiene therapy (W25).

Answer skeleton: ACBT, 7 marks (S23 wording)

  1. [1] Definition and the cycle drawing.
  2. [2.5] Each component: how to do it and its principle (collateral ventilation, equal pressure point, rest).
  3. [1.5] Indications.
  4. [1] Contraindications and precautions.
  5. [1] Dose and end point; advantages (independent, no equipment, adaptable).

Test yourself

3 mName the three components of ACBT with one purpose of each.

Breathing control: rest, prevents bronchospasm and fatigue. Thoracic expansion exercises: get air behind mucus through collateral ventilation. Forced expiration technique (huffs): moves mucus from smaller to larger airways.

3 mName the three phases of autogenic drainage and the lung volume of each.

Unstick (low lung volume), collect (mid, tidal volume), evacuate (high lung volume), followed by a gentle huff.

MCQA huff from low lung volume clears mainly:A. The tracheaB. Peripheral (smaller) airwaysC. The nasal passagesD. The pleural space

B. At low lung volume the equal pressure point lies further out, in the smaller airways.

MCQACBT should be stopped or changed when:A. The huff sounds wetB. Wheeze increasesC. The patient is sittingD. Breathing control lasts more than 20 seconds

B. Increase breathing control and stop forced breaths if wheeze increases.

 Sources

  1. MUHS BPTh syllabus (2012) and MUHS IV BPTh question papers 2016–2026 (muhsonline.com, unofficial archive; Dhole Patil College of Physiotherapy past-paper page).
  2. Bott J, et al. Guidelines for the physiotherapy management of the adult, medical, spontaneously breathing patient (BTS/ACPRC). Thorax 2009;64 Suppl 1:i1–51.
  3. Association of Chartered Physiotherapists in Respiratory Care (ACPRC). The active cycle of breathing techniques; Autogenic drainage (patient leaflets). acprc.org.uk
  4. Pryor JA, Webber BA, et al. Evaluation of the forced expiration technique as an adjunct to postural drainage. BMJ 1979.
  5. Structure and classical content: Pryor & Prasad, Physiotherapy for Respiratory and Cardiac Problems (2008); Main & Denehy (2016); Frownfelter & Dean (2022).

Educational notes for exam preparation. Not medical advice.

Version 1. Content checked 19 October 2026. Next review October 2027.