Rationale: Hypertension is an important risk factor of cardiovascular disease, especially in patients with type 2 diabetes mellitus (T2DM). A relatively recent development for the treatment of hypertension is the use of breathing exercises. The investigators' previous studies with a breathing device did not show any positive results. However, these studies and other trials investigating the effects of breathing devices had not a double-blind design. Therefore, the investigators want to perform a randomized, double-blind, controlled trial in a population of T2DM patients.