血壓的工作原理 How Blood Pressure Works

• Your blood vessels will be 95,000 kilometers long if you line them up.
• They carry 7,500 liters of blood that's being recycled everyday.
• The blood delivers oxygen and precious nutrients like glucose and amino acids.
• The heart beats 70 times a minute and at least 2.5 billion times during an average lifetime.

Blood pressure: pressure that is exerted by the blood upon the walls of the blood vessels. It rises and falls with the phases of the heartbeat.

Normal blood pressure: 120/80 mm Hg

Systolic pressure (收縮壓) : 90-120 mm Hg

Diastolic pressure (舒張壓) : 60-80 mm Hg

Several things can affect the force on the walls of blood vessels. For example, the properties of the fluid, extra fluid, and narrower blood vessels. A high salt diet promotes water retention (保水性). Extra fluid (多余的液體) increases the blood volume and blood pressure. Stress (壓力) releases hormones (激素), like epinephrine and norepinephrine, that constrict key blood vessels, increasing the resistance to flow and raising the pressure upstream.

Blood vessels have elastic fibers in their walls which make them resilient (有彈性的). But when the blood pressure constantly rises above 140/90 mm Hg, hypertension (高血壓), it can cause serious health problems like atherosclerosis (動脈粥樣硬化) . Atherosclerosis is when fatty materials buildup in the walls of blood vessels. When the plaque (the fat) ruptures, a blood clot will form inside the blood vessel which will narrow the vessel or completely block the flow of oxygen and nutrients to cells. This may lead to heart attacks or strokes.

Dangerously narrowed blood vessels can be widened by a procedure called an angioplasty. Doctors will thread a wire through the vessel to the site, and place a deflated balloon catheter over the wire. When the balloon is inflated, it forces the passageway to widen again. Stents, rigid tubes, can also be placed in a vessel to hold it open.

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