Exercise 31 Conduction System of the Heart
and Electrocardiography
Be able to describe the conduction system of the heart.
Be able to identify the P, QRS and T waves in a normal ECG and describe what is
happening in the heart during each wave.
You will be instructed in the use of the Logger Pro ECG monitor in class.
The following is from Dr. Buchanan's lab, which we will modify somewhat.
purpose: To investigate human cardiac and responses under a variety of conditions.
Materials and Methods: You will be using the Logger Pro computer assisted data collection system to record EKGs. From these recordings heart rate, magnitude of ventricular depolarization and the P-T interval can be determined. EKG recordings of each person in your group will be recorded under 5 different conditions.
General Instructions:
Detailed instructions for setting up and using the recording equipment will be
given in lab. A couple of suggestions. If nothing seems to work, try
shutting down the Logger Pro software (make sure you’ve saved all your data!!)
and restart the
computer. Data recording rates need to be set fairly high (~100 pts/sec).
However, if you
need to record for several minutes, you made need to reduce the sampling rate in order to complete the
recording.
Safety: Students who are pregnant or who have any medical condition that might be stressed by these exercises are unconditionally excused. They are not allowed to do parts 3 & 4 of this lab. When you set up the data collection parameters, collection times need to be set in seconds (NOT minutes). For example, instead of typing in "6 min", use "480 sec". If you enter the collection time in minutes, the program automatically changes the sampling rate to "samples/min". This has a significant impact on the accuracy of your data.
Data Recording
: You will be recording the EKG of each individual under the following conditions:1. Control
Record each individual’s EKG while they are setting quietly. These records will serve as the control. It is important the subject being recorded moves as little as possible. You should record under these conditions for 2 minutes. When you analyze the data do so in 20 sec intervals. The end result will be that you will have data from 6, 20 sec control intervals for each individual.2. Supine
Use the same protocol as for the control, but have the subject lie quietly during the recording. Do not begin the recording until the subject has been lying quietly for 5 minutes.3. CO2 enriched air
Record EKGs while each individual is breathing into a plastic bag. Rebreathing the same air results in alveolar air that is enriched in CO2 and somewhat depleted in O2. Based on results so far, it looks like most people can breathe into the bag for between 3 and 4 minutes. (Although there is significant inter-individual variation). Therefore, try recording continuously for 9 minutes. Each subject should breathe into the bag as long as they can, you will need to record continuously during that time and for 4-5 minutes after the subject has returned to breathing normal air.4. After exercise
Record EKGs for 4 minutes immediately after the end of an exercise regime. In
order to try to standardize the amount of exercise done, we will "walk the
stairs". Be careful, but you are to climb as quickly as possible up to the 5th
floor, down to the 1st floor and back up to the lab on the 4th
floor. Each subject will be timed—start the timer as soon as they leave the room
and stop the timer when recording starts. Since the goal of this part of the
experiment is to investigate the effects of fairly strenuous exercise on human
physiology subjects should try to complete the circuit safely, but as quickly as
possible. As soon as the subject returns to the lab, quickly hook the leads up
and begin recording their EKG as soon as possible. Record EKGs
from the subject for 6 minutes after they have returned to the room. Practice
setting up the recording devices so that you can get begin recording as
quickly as possible. If you waste much time setting up the recording devices,
subject will begin to recover and the information you collect will be
inaccurate.
5. Noxious Sensory Stimulus (cold)
This is described in exercise 33A. Take readings
for 3 minutes.
For each condition analyze your data in 20 sec. intervals, making note of the heart rate, average magnitude of ventricular depolarization and average length of P - T interval. Compare these data with what you (or another group) obtained for blood pressure readings.
Additional information:
In addition to the EKGs from each subject you should also report each individual’s
1. Age
2. Approx. weight 3. Sex4. Approx. height
5. Exercise time (in sec).
6. Other pertinent information: Please note all subjects that are trained athletes or smokers.