The purpose of PLB is to create back-pressure inside airways to splint them open; moving air thus takes less work.
[2] Breathing through pursed lips on both exhalation and inhalation is one of the signs that health workers use to detect possible chronic obstructive pulmonary disease (COPD) in patients.
COPD Canada suggests that using PLB has positive effects in treating stress- and anxiety-related disorders.
[3] Pursed-lip breathing increases positive pressure generated in the conducting branches of the lungs.
[4] This can hold open bronchioles in patients with high lung compliance, such as those with emphysema.