The differential pressure between high and low pressure is between 30-40 mmHg and is within the normal range. A differential pressure of more than 60 mmHg is called an increased differential pressure, while a differential pressure of less than 20 mmHg is called a decreased differential pressure. Most cases of increased differential pressure are seen in the elderly with atherosclerosis as the main disease, often manifested as a simple increase in systolic pressure, diastolic pressure is often normal, in this case, after correction of atherosclerosis, the differential pressure can often return to normal. The most common disease with reduced differential pressure is constrictive pericarditis, which can be diagnosed with a color Doppler ultrasound examination of the heart. Decreased differential pressure is also seen in patients with peripheral circulation failure or shock, in which case the differential pressure can be restored after correction of the primary disease or rehydration therapy.