Active cycle of breathing (ACBT): how to clear phlegm

What is the active cycle of breathing?

Coughing is the body’s way of clearing phlegm, but repeated hard coughing is tiring, can make the airways narrow and often brings up little. The active cycle of breathing technique, usually shortened to ACBT, was developed by UK physiotherapists as a gentler, more effective way to clear the chest. It has three parts, which you repeat in a cycle:

• Breathing control. Gentle, relaxed breathing that gives you a rest and stops your airways tightening.
• Deep breaths. Slow, full breaths that get air behind the phlegm, through small side-channels between the air sacs, so there is something to push it out with.
• Huffs. Fast, open-mouthed breaths out that squeeze the air out and carry the phlegm up towards your throat, where a single cough can clear it.

The steps above show the standard cycle. Your physiotherapist may change the number of deep breaths or huffs, or add a hold at the top of each deep breath, to suit your chest.

When should you use it?

• Every day, if you have bronchiectasis or COPD with a lot of phlegm, at the times your physiotherapist suggests.
• More often during a chest infection or flare-up, when there is more phlegm to clear.
• Before you go out or before bed, so your chest is clear when it matters.

Sitting upright works well for most people. Some people clear more lying on their side, or in other positions that use gravity to drain particular parts of the lungs. These are called gravity-assisted or postural drainage positions; learn them from a physiotherapist rather than guessing, as head-down positions don’t suit everyone.

What the research shows

A systematic review of 24 studies in people with conditions that produce a lot of phlegm found that ACBT cleared more phlegm, during and up to an hour after a session, than conventional chest physiotherapy, oscillating devices or no treatment. The reviewers rated the overall body of evidence as good, though individual studies varied in quality. Most measured how much phlegm came up in the short term; there is much less evidence on longer-term outcomes, such as the number of chest infections.

UK guidance backs it. NICE recommends that people with COPD who have excessive phlegm are taught the active cycle of breathing or how to use a positive expiratory pressure device. The British Thoracic Society’s bronchiectasis guideline recommends that people are taught an airway clearance technique by a respiratory physiotherapist, and ACBT is one of the main options. We grade it as moderate.

Common mistakes

• Coughing instead of huffing. Save coughing for when the phlegm is right at the top. Repeated hard coughing is tiring and can tighten your airways.
• Huffing from your throat. A huff should be open and breathy, like misting a window, not a sharp noise in your throat.
• Skipping breathing control. The rest periods are part of the technique. They stop you getting wheezy or tired.
• Carrying on too long. When two huffs in a row are dry and your chest feels clear, stop.

Make it easier or harder

• Easier: take two or three deep breaths instead of four, and spend longer on breathing control between each part.
• Adapted: if you have a lot of thick phlegm, your physiotherapist may combine ACBT with a hand-held positive expiratory pressure device, nebulised salt water, or exercise, which also helps loosen phlegm.