Investigating Factors that Affect Heart Rate and Blood Pressure
Blood pumped through blood vessels is always under pressure. This
pressure is highest in the arteries closest to the heart and gradually
decreases as the blood travels around the body. Blood keeps moving
around the body because there are differences in pressure in the blood
vessels. Blood flows from higher-pressure areas to lower-pressure
areas until it eventually returns to the heart. Blood pressure is
controlled by three things: heart rate, stroke volume and peripheral
resistance. Generally, when heart rate increases, blood pressure
rises, and vice versa. A number of things affect heart rate, such as
body's temperature, nervous system, hormones, medications, and
diseases, etc. The amount of blood pumped out of a ventricle with each
heartbeat is called stroke volume. When you're resting, stroke volume
is about the same as the amount of blood that veins carry back to the
heart. But under stressful conditions, the nervous system can increase
stroke volume by making the heart pump harder. Width of arteries also
affects the blood pressure. Blood traveling in narrower vessels meets
more resistance than blood traveling through a wider vessel. Depending
on what a person is doing, the amount of blood the heart pumps varies
enormously. Yet the blood pressure normally remains pretty stable.
That's mainly because the body adjusts the resistance of the arteries,
either widening or narrowing them as appropriate, to prevent the blood
pressure from swinging wildly. This ability to regulate the width of
the blood vessels is called the peripheral resistance. Most of the
resistance to blood flow in the circulation occurs in the
small-diameter arteries called arterioles. These arterioles are
especially important in the immediate regulation of blood pressure.
Generally, a change in any factor that may cause the blood pressure to
rise is balanced by a change in another factor. This is how the body
keeps blood pressure in a normal range.
The purpose of this lab is to identify the difference between blood
pressure and heart rate, and to analyze the factors that may affect