Question

1- Explain the changes in heart rate between conditions.  Describe the physiological mechanisms causing these changes.

2- Are there differences in the cardiac cycle with the respiratory cycle (“Start of inhale-exhale” data)?

3- What changes occurred in the duration of systole and diastole between resting and post-exercise?

4- In the normal cardiac cycle, the atria contract before the ventricles. Where is this fact represented in the ECG?

5- What is meant by “AV delay” and what purpose does the delay serve?

6- What is the isoelectric line of the ECG?

7- Compared to the resting state, do the durations of the ECG intervals and segments decrease during exercise?  Explain

Answer 1

1. Heart increases during exercise as compared to in resting state. As during exercise body cell need more energy and oxygen there heart needs to pump blood at fast rate.heart rate increases during stress as adrenaline causes heart to pump more blood to meet body needs
2. Cardiac cycle is performance of heart from one heartbeat to next. It consists of diastole in which heart relaxes to fill followed by systole in which cardiac muscles contract to pump blood. Wheras respiratory cycle is one repetition of the pattern of inhalation, oxygen carbon dioxide exchange and exalation.
3. there is much decrease in diastole time as compared to resting. Less time is there between systole and diastole as heart needs to pump fast. Cardiac cycle gets shorter.
4. p wave precedes qrs segment
5. atrioventicular node delays impuses by .09 sec . This is important as this delay ensures that atria have ejected their blood into ventricles first before the ventricles contract
6. Isoelectric line is a straight line on the ECG paper where there is no positive or negative charges of electricity to create deflections.
7. changes in ecg during exercise:   RR interval decreases , P-wave amplitude and morphology undergo minor changes , Septal Q-wave amplitude increases, R-wave height increases from rest to submaximal exercise and then reduces to a minimum at maximal exercise, The QRS complex experiences minimal shortening, J-point depression occurs, Tall, peaked T waves occur (high interindividual variability), ST segment becomes upsloping, QT interval experiences a rate-related shortening , Superimposition of P waves and T waves on successive beats may be observed