The bottom number of your blood pressure reading is your diastolic blood pressure. It is the measure of the pressure of the blood on your vessels between beats, or when the heart is resting as it refills with blood before pumping it out again. According to the American Heart Association, diastolic hypertension, or a bottom number of 90 mm Hg or higher, is most often a concern before age 50. If you have a high diastolic blood pressure, there are several practices that can help you lower the number to the optimum level of less than 80 mm Hg.