Inclusion Criteria:  Age ≥ 18 Ability and willingness to give informed consent to participate in the study  Exclusion Criteria:  Atrial fibrillation Active pacing of the heart by a cardiac pacemaker (i.e. no intrinsic heart rate) Clinically pre-established cardiovascular disease (e.g. arterial hypertension or systolic heart failure) In-patient stay in the hospital within the last 4 weeks prior to the study examination date