Lab 3 – The Mammalian Cardiovascular System
Jessie Schmidt – 4/19/11
Abstract
The aim of this lab was to observe the effects of activity on the human cardiovascular system by
observing blood pressure, heart rate and EKG traces under varying physical exercises. We found that blood
pressure and heart rate increased with increasing physical demand or reduced oxygen supply.
Experiments
Blood pressure: The systolic and diastolic pressure of one group member was measured while lying
down, sitting up, standing and after exercise by using a sphygmomanometer and stethoscope.
Venous circulation: Veins on the hand were observed with the hand held down and then raised above
the head. They were also observed in the feet while standing and then while walking. A pressure cuff was also
applied to the arm, and veins were manipulated by stopping blood flow in the upstream and down stream
directions while pushing blood up or down the vein.
Mammalian EKG: Heart rate and electrocardiogram (EKG) wave components were measured in
response to rest, physical exertion and various breathing exercises including holding one’s breath, breathing out
maximally, and holding one’s breath while tightening the chest muscles as if to breathe out.
Results
Overall, blood pressure increased with increasing physical effort. While no significant change occurred in
blood pressure from lying down to sitting, diastolic pressure increased when the student moved from sitting to
standing, and systolic pressure greatly increased upon physical exertion (Table 1).
Venous pooling was observed to diminish when gravity was reduced from the affected hand, and when
walking ensued. Applying pressure to the arm increased bulging of veins at intervals distal to the cuff. Veins
blocked distally would not refill when emptied “downstream”, but would refill immediately if blocked more
proximally and emptied back “upstream”, suggesting the presence of one-way valves in the veins.
Heart rate increased dramatically after the student exercised, which was correlated with much shorter
durations for the QRS, T, and Q-T intervals of the EKG trace (Table 2). Interestingly, the P wave and P-R intervals
increased in duration after exercise (Table 2). Heart rate also increased for each breath-holding exercise, but
especially when the student was tensing her chest muscles in addition (Table 3).
Discussion
As increased muscle activity from exercise caused increased rates of cellular respiration in our subject,
there was a greater demand for oxygen (O2) to be replenished and carbon dioxide (CO2) and other wastes to be
removed from bodily tissues. The same demand was produced in our subject when they held their breath due to
O2 deprivation to the body and brain. Our subject’s body was able to satisfy this need through faster and
stronger heart beats as seen through the higher heart rate and systolic blood pressure after exercising. The
longer P wave and P-R intervals seen in the post-activity EKG trace could be interpreted as the heart taking more
time to fill the atria with a greater volume of blood before pumping this blood volume at a more rapid rate
through the ventricles followed by a more rapid repolarization time as demonstrated by the shorter QRS and T
intervals. Our subject’s arteries, equipped with thick muscular walls, carried the blood away from the beating
heart, thus experiencing a pulsing sensation that we were able to hear with a stethoscope. This blood then
entered the network of small thin-walled capillaries of the lungs to receive O2 or of the depleted tissues to
distribute this O2. Since capillaries are the main site of gas and nutrient transfer they play a central role in the
circulatory system, yet they are dependent on all other components to be functional. Finally our subject’s blood
returned smoothly back to the heart through the thin-walled veins. As was demonstrated by our results, veins
contain valves and receive pressure from nearby flexing muscles to reduce pooling and promote the return of
blood from parts of the body distant from the heart experiencing greater gravity. In a large organism such as our
subject, the circulatory system is critical for enabling rapid transfer of gasses needed for life, which could never
occur at the rate or diffusion used for transport by a single-celled organism of similar large size.
Table 1. Average blood pressure of a BI-253 student based on three trials for each activity.
Average pressure (mmHg)
Lying down
Sitting
Standing
Post Activity
Systolic
115
117
110
123
Diastolic
71
73
81
85
Table 2. Effects of exercise on the EKG wave form and heart rate of a BI-253 student.
EKG wave segment duration (s)
Heart Rate
(beats/min)
Activity
P
R
T
QRS
P-R
Q-T
Resting
0.09
0.21
0.30
0.24
0.09
0.30
68
Post activity
0.11
0.16
0.19
0.18
0.11
0.19
131
Table 3. Effects of breathing manipulations on the heart rate of a BI-253 student.
Heart Rate (beats/min)
Breathing test
Before test
During test
Hold Inspiration
69
77
Expiration and Hold
62
72
Hold Inspiration while tensing
65
80