Decreased pulse pressure difference is more common in clinical practice, the most important reasons are the following two: First, the heart rate increases, the main effect is the increase in diastolic pressure, when the heart rate increases the time used for heart contraction will be prolonged, the time used for heart diastole will be shortened, the heart can then shoot more blood into the aorta, the increase in the amount of blood in the aorta leads to higher diastolic pressure, systolic pressure does not change much, the pulse pressure decreases. Second, peripheral vascular resistance increases, which has a significant effect on diastolic pressure. When peripheral vascular resistance increases, the resistance of blood flowing from the aorta to the periphery will increase, and more blood will stay in the aorta, leading to higher diastolic pressure, little change in cardiac contractility, little change in systolic pressure, and eventually a decrease in pulse pressure difference.