Blood pressure readings are notated as the systolic pressure over the diastolic pressure. The systolic pressure number is the highest pressure reading when the heart is in a state of contraction. The diastolic pressure number is the highest pressure reading when the heart is in a state of relaxation. So, the typical normal blood pressure reading is 120/80 (measured in millimeters of mercury). This is a standard normal value, but some people have slightly lower readings and some have slightly higher readings, but these are still normal blood pressure readings.
The physiology of blood pressure is a little more complex. Blood pressure is determined by a relationship of two independent things. The first thing is the cardiac output which is the amount of blood volume that the heart pumps in a minute of time. The second thing is the peripheral vascular resistance which is determined by the internal blood vessel diameter, the length of the blood vessel, and the viscosity of the blood. All of these things combined together account for the levels of pressure in the blood vessels. When you consider just how high the pressure can actually get, you understand the amount of damage that can be done to surrounding tissues. Now, this damage doesn’t happen right away, but sustained high levels of blood pressure will do damage over time.
Many things can control why blood pressure levels can be high or low such as genetic factors, endocrine factors, and other disease processes such as hyperlipidemia and diabetes. In people who have high blood pressure, the increased force of blood flow from the heart on the artery walls may cause them to develop thicker, stronger structures. This is why so many different blood pressure medications exist as there are many different targets that can be approached to try to lower blood pressure. Medications can act directly at the blood vessel level, at the level of the kidney, at the level of the heart, or even at the level of the central nervous system. Gaining some understanding of the physiologic aspects of blood pressure can make it understandable that blood pressure is a dynamic and complex concept.
