The goal of this randomized controlled trial is to learn about the effect of a hydrotherapeutic approach - a temperature-elevating armbath - in people with arterial hypertention. The main question[s] it aims to answer are:

• Can this kind of hydrotherapy lower the blood pressure and therefore be an additional approach to medical treatment in arterial hypertension?
• Besides blood pressure regulation, does this intervention affect sleep quality when being performed at night time or does it affect overall quality of life?

Participants will be advised to perform a temperature-elevating armbath once a day for 30 minutes on at least 5 days per week over 8 weeks.

The comparison group will continue treatment as usual, like continue their medication. 24h blood pressure measurements will be performed at the beginning, after 8 weeks and after 6 months in both groups. The main goal is to evaluate whether the intervention group shows lower blood pressure levels after a certain time of treatment.

After 6 months (end of trial) the control group will be offered to learn the temperature elevating armbath as well.

Arterial hypertension remains one of the most important risk factors in developing a cardiovascular disease. While medical treatment is usually necessary, lifestyle modifications should always be included. Besides physical activity and a balanced diet, there are also therapeutic approaches from the so called classical complementary medicine. One very important part in Europe is hydrotherapy, based on ideas of Sebastian Kneipp and his contemporaries. In hydrotherapy there are various therapeutic approaches that can be used additionally to conventional therapy. Because conventional medical therapy is often associated with unwanted side effects, these additional approaches experience increasing popularity. In arterial hypertension, temperature-elevating armbaths, developed by Kneipps contemporaries Hauffe and Schwenninger, are a hydrotherapeutic approach that is highly recommended. Even though hydrotherapy has been a part of complementary medicine for more than a century now some therapeutic approaches lack of scientific evidence - especially when it comes to their effect on arterial hypertension.

This randomized-controlled trial aims to evaluate the effect of a temperature-elevating armbath among participants with arterial hypertension. 50 participants will be randomized to either an intervention group or waitlist (treatment as usual). All 50 participants will be monitored with three 24-hours ambulatory blood pressure measurements (24h ABPM) at the beginning of the trial after randomization, at 8 weeks and at 6 months.

The intervention group will be advised to perform the armbaths on 5 of 7 days per week for 8 weeks total. Each participant will get a detailed instruction how to perform the armbath and will be handed a diary to document their performance.

After 6 months, each participant of the control group will be offered to be instructed on performing the armbaths as well.

Within the active period of 8 weeks, participants of both groups will be called regularly to ask about their health and whether they have questions regarding the trial.

Inclusion Criteria:

• adult participants (≥18 years)
• diagnosed arterial hypertension, at least stage I, based on the Guidelines of the European Society of Hypertension 2018 (systolic >140 mmHg, diastolic >90 mmHg)
• last change in medication at least 2 months ago
• no planned changes in blood pressure medication within intervention time; changes due to medical reasons (e.g., hypotension, hypertensive emergency) are allowed.
• willingness to perform an armbath on a regular schedule (min. 5x/weeks)

Exclusion Criteria:

• acute psychiatric disease ( e.g., addiction, major depression)
• acute or major physical disease (e.g., cancer diagnosis within the last 5 years, major known cardiovascular diseases, renal or liver dysfunction), acute infection, major neurological diseases (e.g., Parkinsons´ disease, uncontrolled epilepsy)
• secondary hypertension
• pregnancy or lactation period

Blood pressure measurements, Comorbidities, medication