A Comparison of Systolic and Diastolic Blood Pressure
To compare systolic and diastolic blood pressure, you need to first know how your heart functions. Your heart functions by pushing blood and oxygen out in to the body through the vessels known as arteries. The heart contracts to  pump blood to the body through the arteries. Each contraction may be referred to as a beat. The heart then rests between beats. Sometimes the heart has to work harder in the pumping of the blood. This increase in pressure is known as the level of blood pressure.

Now, there are two types of blood pressures as mentioned above: systolic blood pressure that is the pressure when the heart contracts and diastolic blood pressure when the heart relaxes. The blood pressure is at the highest during systolic blood pressure when the heart beats pumping the blood and blood pressure shrinks during diastolic blood pressure when the heart rests between beats.   

During high blood pressure, your heart pushes huge amount of blood through your arteries. But if you have obstruction or plaque in your arteries, it prevents the arteries from expanding when your heart contracts, leading to rise in your blood pressure. It is important to understand the significance of these two types of blood pressure. It is systolic blood pressure, which is a more important indicator of heart attack or stroke risk. Rise in diastolic blood pressure does not point to any susceptibility in heart attack risk

Usually, blood pressure- both systolic and diastolic are measured in millimeters of mercury i.e. mmHg. A person’s blood pressure changes frequently depending on temperature, diet, posture, medication use, activity and physical state. When the blood pressure reaches 140/90 or higher, the person is suffering from high blood pressure. It is also possible to compare systolic and diastolic blood pressure by comparing the values of mercury in the different stages of blood pressure. This is shown below: 

Category             Systolic (Top number)        Diastolic (Bottom number)   
Normal                Less than 120                   Less than 80
Pre-hypertension      120-139                       80-89   
Stage 1-                     140-159                   90-99
Stage 2-                 160 or higher                100 or higher (all in mmHg)   

As can be seen from the above, stage 1 and stage 2 hypertensions are the more lethal ones. Your risk of hypertension is augmented when you are suffering from high blood cholesterol, diabetes, obesity etc. Hypertension is a condition which needs prompt and effective treatment.