Blood pressure is the force exerted by the walls of an artery on the blood. We distinguish in practice systolic blood pressure, a value which reflects the blood pressure during systole, the period of contraction of the cardiac ventricles which ejects blood into the vessels, and diastolic blood pressure at the time of diastole, when the heart chambers fill with blood. In practice, the systolic blood pressure is the high value and the diastolic blood pressure is the low value measured by the doctor during the consultation. Diastolic hypertension is when the pressure is above 90 mm or 9 cm of mercury. Diagnosis is confirmed in cases of high values on 2 of the 3 measurements taken on successive consultations during a period of at least 3 months. Sometimes these values can be confirmed by self- measurements, made by the patient at home, because blood pressure is often higher at the doctor's office than at the patient's home.