The technique called resonant breathing biofeedback teaches how to recognize and control involuntary heart rate variability (HRV).
A study by Sutarto et al. assessed the effect of resonant breathing biofeedback among manufacturing operators. Depression, anxiety and stress significantly decreased.
A first overall meta-analysis by Goessl VC et al. (24 studies, 484 individuals, 2017) indicates ''HRV biofeedback training is associated with a large reduction in self-reported stress and anxiety''.

Biofeedback therapists use pneumograph biofeedback with patients diagnosed with anxiety disorders, asthma, chronic pulmonary obstructive disorder (COPD), essential hypertension, panic attack, stress and dysfunctional breathing*.

FLOW, like other pneumographs, uses a flexible sensor band that is placed around the chest, abdomen, or both.
* Dysfunctional breathing patterns include clavicular breathing (breathing that primarily relies on the external intercostals and the accessory muscles of respiration to inflate the lungs), reverse breathing (breathing where the abdomen expands during exhalation and contracts during inhalation), and thoracic breathing (shallow breathing that primarily relies on the external intercostals to inflate the lungs). Dysfunctional breathing behaviors include apnea (suspension of breathing), gasping, sighing, and wheezing.