Question

a) Why would exercise influence the R-R interval? Would a change in R-R interval following a short period of exercise be the same for all people, why/why not?

b) Each component of the ECG waveform is associated with a particular activity during the cardiac cycle. Based on your knowledge of the actions of the heart associated with the P, Q, R, S, and T waves in the ECG, and what actions in the heart generate the lub-dub sounds, when would you expect to hear the lub and dub sounds in relation to the different components of the ECG waveform?

Answer 1

a)

RR nterval is the interval between the peaks of two successive R waves.RR interval is measured for calculating the ventricular rate.

The cardiac output increase in exercise

• In exercise the sympathetic stimulation increasres the heart rate and myocardial contractility,
• Venoconstriction due to sympathetic stimulation increases venous return and EDV

b)

• The P wave represents the arterial depolarization
• The QRS complex repersents ventricular depolarization and consist of 3 waves ie Q ,R,S waves.
• Q wave : The wave of depolarization passes along the bundle branches and purkinje fibers to first excite the interventricular septum,which depolarises from left to right.
• R wave : The wave of depolarisation then spreads from the sub endocardial muscle layer to subepicardial muscle layer ,The deflection in ECG appears as R wave, which is an upward,bigger and sharp wave.
• S wave : The last parts to be depolarized are the portion of the left ventricle and the pulmonary conus.In ECG its a small,negative and sharp wave.
• T wave : Its represents ventricular repolarization

The LUB - DUB is the heart sounds and it is in pairs, The first sound is when the tricuspid and mitral walves closes and the second sound when the pulmonary and aortic walves closes.