Blood pressure is very important during rest and exercise, as it is blood pressure that
determines the rate at which blood flows through the circulatory path (Brooks, 2005). However,
blood pressure is not constant and can be affected by many factors. Innate factors such radius
and length of the vessel, blood volume, and viscosity of the blood all affect blood pressure.
External influences such as the position of the body in space, exercise, and changes in hormonal
levels also cause blood pressure to change (Donovan, 2009). There are two types of blood
pressure regulation: short term and long term. Short term regulation is controlled by the
sympathetic and parasympathetic nervous systems. Baroreceptors in the aorta monitor and alter
the rate of sensory nerve impulses sent to the cardiac and vasomotor control centers in the brain,
which adjust blood pressure accordingly (Donovan, 2009). Long-term regulation of blood
pressure is accomplished through juxtaglomerular cells in the kidneys, which release certain
enzymes and control sodium and water reabsorption (Donovan, 2009).
This laboratory experiment specifically examined the way that body position affected
blood pressure. During instances where the subject is in a supine position, heart rate is typically
lower, and thus cardiac output diminishes. Because cardiac output is a key determinant of blood
pressure, it is thus assumed that blood pressure should be lower in a supine position when
compared to a standing or sitting position (Brooks, 2005
). Total peripheral resistance also plays a
key role in blood pressure.
If one extends their extremities away from the heart, there is a change
in the force with which the heart must pump to overcome the push of gravity while distributing
blood throughout the body. This increases total peripheral resistance, thus increasing blood
pressure. Gravity also affects venous return to the heart. If venous return is lowered, blood
pressure is ultimately lowered as well, because venous return has direct relationships with end
diastolic volume, stroke volume, and cardiac output (Donovan, 2009).
It is important to study the effect of body position on blood pressure because in clinical