A pilot study on the effects of heart rate variability biofeedback in patients with depression and in healthy subjects - Siepmann, M; Aykac, V; Unterdorfer, J; Petrowski, K; Mueck-Weymann, M (Applied Psychophysiology and Biofeedback, 2008)
doi: 10.1007/s10484–008–9064-z.