1.Describe the electrical events occurring in the heart that are responsible for

Question

1.Describe the electrical events occurring in the heart that are responsible for the P wave, QRS complex and T waves of the ECG. What is happening to the myocardium during (1) the PR interval and (2) the ST segment?

2.Question 2: Compare the effect of exercise on the IHR and the periods of ventricular systole (QT) and ventricular diastole (TQ). Which of the periods is changed more in your data and why would one period of the cardiac cycle (systole or diastole) change more than the other? In your answer, indicate what electrical characteristic of the myocardial cell determines why one of the periods changes less than the other (systole or diastole).

3Was the Bainbridge reflex initiated in the subject? In your rationale, describe the expected changes that occur as a result of the Bainbridge reflex (start with deep inhalation and end with the expected change in heart rate that characterizes the Bainbridge reflex) – how does each step in the process lead to the expected change in heart rate: include receptors and ion channels involved.

4Describe the changes in stimulation of the baroreceptor that occur during phase II and phase IV of the Valsalva maneuver. How does that change in baroreceptor activation alter heart rate (be specific for each phase of the response)?

5.What is the source of S1 and S2 detected by the phonocardiogram (what causes the valves to change in that way)? Describe how the pressure wave that travels through the vasculature is generated.

What does the velocity of that pressure pulse wave tell one about vasculature condition?

Explanation / Answer

Answer 1:

The function of the heart is to pump the blood via Pulmonary and systematic pathways in our body system. As the blood is moving in our body system through two pathways, sometimes describes dual pump. Rhythm generator or Sinoatrial node (SA node) or normal pacemaker generates electrical signal, conductor for spreading of signal and myocardium for mechanical pumping of blood are the three types of cells are involved in heartbeat.

The is inherent characteristics of cardiac tissue (tissue system of heart) is rhythmic or automatic instructing the specialized pacemaker or SA nodes to start the electrical signal in the form of depolarization and repolarization in a sequential manner. The signal generated by pacemaker and spreads to ventricular muscles of heart via intermodal pathways and atrial fibres, The bunch of his, Atrioventricular nodes and purkinje fibres. When this depolarized electrical signal reaches the contractile cells, they contract and when the repolarized signal reaches the myocardial cells, they relax. Thus, the electrical signals causing the mechanical pumping of heart. The heartbeat generated as per the rate beats per minutes or BPM and the strength of contraction of heart are modified by sympathetic and parasympathetic nervous system.

The record of electrical signals produced by heart is called Electrocardiogram or ECG involves attaching 10 electrical cables to the body, one to each limb and six across the chest. The electrical signals are recorded in the form of a pattern of baseline broken by P waves, QRS complex and a T wave. The sequence of the event is as follows:

The duration of PR interval is 0.12 – 0.20 seconds, it is the time taken for the impulse to send from SA node to the ventricle. The T waves represent the repolarization of ventricles which begins from the epicardial surface of ventricles and progress inwardly through the ventricular walls to the endocardial surface. The occurrence of T Wave is at the time of last part of the ventricular systole. The onset of the T Wave is the first or abrupt or gradual deviation from the S-T segment; or from the point where the slope of the S-T segment appears to become abruptly of gradually steeper. If the S-T segment is absent, the T Wave begins at the end of the QRS Complete (or the J Point).

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