Chen YF, Huang XY, Chien CH, Cheng JF. The effectiveness of diaphragmatic breathing relaxation training for reducing anxiety. Perspect Psychiatr Care. 2017;53(4):329-336. doi:10.1111/ppc.12184
Diaphragmatic breathing significantly reduces subjective (questionnaire) and physiological (heart rate, breathing rate) indicators of anxiety in patients with mild-to-moderate anxiety.