High pressure, i.e., systolic blood pressure 110mmHg is within the normal range, and low pressure, i.e., diastolic blood pressure 40mmHg, suggests that the diastolic blood pressure is low, and the reasons for this are physiologic and pathologic reasons. 1. Physiological reasons: the normal adult quiet state blood pressure range is systolic blood pressure 90 ~ 139mmHg, diastolic blood pressure 60 ~ 89mmHg. systolic blood pressure 110mmHg belongs to the normal range, and diastolic blood pressure 40mmHg suggests that the diastolic blood pressure is low. For some people who are weak and thin, and usually have low blood pressure, they may have normal systolic blood pressure and low diastolic blood pressure without obvious symptoms, which does not affect their daily life, which is a physiological reason, and they should strengthen their exercise in normal times without special treatment. 2. Pathological causes: the main factors affecting low diastolic blood pressure are low heart rate and low peripheral resistance. The causes of low heart rate include bradycardia and hypothyroidism. The causes of low peripheral resistance are mainly infections, allergies and other causes. When low diastolic blood pressure occurs or there are obvious clinical symptoms, it is recommended to consult the doctor in time, improve the relevant examination, clarify the cause of the disease, and treat it in time to avoid delaying the condition.