The QRS complex. QRS complex represents depolarization of

The purpose of this lab
was to see the effect of exercise on
duration of ECG components and we hypothesized that increasing the activity
level would decrease P-R interval, T-P segment, and R-R interval duration and
make no changes in QRS complex duration and QRS complex amplitude. After
running this experiment, we found out that there was a small decrease in QRS
complex duration which opposed our hypothesis (but we found out later that our
hypothesis was right and there was a problem in our experiment results) and then
we conclude that as the activity level increases, ECG intervals and segments duration
would decrease and there would be no changes in QRS complex duration. We also observed
an increase in heart rate after exercise.

As
we learned in class, T-P segments represents the time from the end of
ventricular repolarization to the onset of atrial depolarization and R-R
interval represents the time between two ventricular depolarizations which is
called one cardiac cycle. The sympathetic nervous system which is the subgroup of
autonomic nervous system, releases the hormone Norepinephrine which accelerates
heart rate by increasing the slope of rising portion of the cardiac myocyte action
potential during phase 0 and by activating the ?1 adrenergic receptors in the heart
and decreasing K+ permeability (Gordan, Gwathmey and Xie, 2015). Then
autorhythmic cells start to depolarize because of the reduced efflux of
potassium and the interior membrane potential becomes less negative, depolarize
really slow and generate the pacemaker potential. Pacemaker currents of SA node
cells (action potential initiators) bring action potential to threshold faster
than AV node cells increase the firing rate and make the heart beats faster per
minute. In another hand the parasympathetic nervous system releases the
hormone Acetylcholine to slow down the heart rate by increasing K+ permeability.

We
did learn in class that P-R segments represents the time interval between the
AV node and the ventricular myocardium. Sympathetic stimulation of the AV node decreases
the regular delay of conduction through the AV node which decreases the time interval
from atrial to ventricular contraction. As AV nodal conduction velocity increases,
the P-R interval of ECG decreases (Carruthers et al., 1987). As we noticed in
our experiment, there was not any changes in QRS complex. QRS complex
represents depolarization of the right and left ventricles and also atrial
repolarization. There two bundle branches that come to a point to make a lot of
Purkinje fibers, which stimulate individual groups of myocardial cells to
contract. The movement of action potential through the ventricular myocardium makes
the QRS complex on the ECG. Purkinje fibers and ventricular myocardium get
activated together and they do not depend on heart rate during our experiment,
so there would be no change in QRS complex if heart rate increases.

Some
of the limitations in this experiment could be problems with the machine, being
smoker, fitness level, health, gender, age, subject’s energy level for the day,
sudden weakness during the experiment, etc.