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.

Objective: To determine the effect of a device slowing breathing (Resperate©) on office systolic blood pressure (SBP) in diabetic patients with treated hypertension with moderate BP control.

Study design: A randomized, double-blind, controlled trial.

Study population: Patients with type 2 diabetes mellitus, over 18 years old and a baseline systolic blood pressure between 140-160 mm Hg.

Intervention: One group receives treatment with a breathing device (Resperate©) and the other group receives treatment with a "control" breathing device. The latter device does not try to alter the breathing pattern.

Main study parameters/endpoints: The effect of the breathing device on SBP is the main study parameter. Secondary endpoints include diastolic blood pressure (DBP) and quality of life.

Inclusion Criteria:

• known T2DM,
• over 18 years old,
• known hypertension with a systolic BP (SBP) between 130-170 mm Hg at the previous visit to the internal outpatient department and at the last visit to the internist (which is the same day as baseline measurement) and treated with one or more anti-hypertensive drugs, which have not been changed for the preceding three months. At baseline the SBP should be between 140-160 mm Hg, measured by the investigator.

Exclusion Criteria:

• patients with orthostatic hypotension,
• known heart failure (NYHA III-IV) and/or patients with pulmonary disease (for example asthma, chronic obstructive pulmonary disease and pulmonary fibrosis),
• patients with insufficient knowledge of the Dutch language to understand the requirements of the study,
• additional criteria were hospitalization in the past 3 months, deafness, blindness and cognitive abilities deemed insufficient for operation of a study device.