 Blood pressure is the measure of the force generated by the heart against the artery walls. This force is expressed as two numbers, such as 110 over 80 mm Hg (millimeters of mercury). High blood pressure, or hypertension, is blood pressure that consistently reads above 120 over 80 mm Hg (130 over 80 mm Hg if you are a diabetic). Your blood pressure is low if less than 90 over 60 mm Hg (if you're blood pressure falls outside of this range, either too high or too low, you should speak with your primary care physician or cardiologist as soon as possible). High blood pressure causes undue stress to the circulation of key organs, particularly the brain, heart and kidneys. This leads to increased risk of stroke, heart attack and kidney failure. High blood pressure also can cause an aneurysm, a small balloon-like weakening of the artery wall, which can be life-threatening. Hypertension can be especially hard to manage when combined with other disorders, such as diabetes or obesity. Persistent hypertension is one of the risk factors for strokes, heart attacks, heart failure and arterial aneurysm, and is a leading cause of chronic renal failure. The physics of the circulatory system, as of any fluid system, are very complex. That said, there are many physical factors that influence blood pressure. Each of these may in turn be influenced by physiological factors, such as diet, exercise, disease, drugs, etc. Some physical factors are: • Rate of flow of fluid. In the circulatory system, this rate is called heart rate, the rate at which blood (the fluid) is pumped by the heart. The higher the heart rate, the higher the blood pressure. • Volume of fluid. In the case of the circulatory system, this is blood volume, the amount of blood present in the body. The more blood present in the body, the higher the blood pressure. Some research indicates there is a relationship between dietary salt intake and increased blood volume (resulting in higher blood pressure). • Resistance. In the circulatory system, this is the resistance of the blood vessels. The higher the resistance, the higher the blood pressure. Resistance is related to size (The larger the blood vessel, the lower the resistance), as well as the smoothness of the blood vessel walls. Smoothness is reduced by the buildup of fatty deposits on the arterial walls. Substances called vasoconstrictors can reduce the size of blood vessels, thereby increasing blood pressure. Vasodilators (such as nitroglycerin) increase the size of blood vessels, thereby decreasing blood pressure. • Viscosity, or thickness of the fluid. If the blood gets thicker, the result is an increase in blood pressure. Certain medical conditions can change the viscosity of the blood. Note that "blood thinners" such as aspirin affect the viscosity of the blood by reducing platelet clotting. |