Abstract:
Heart rate is the number of ventricular contractions per minute. SA node able to generate action potential with rate 70-80 beats/minute in young adult. The normal heart rate in children is high (80 – 140 beats/minute according age). When SA node does not generate action potential, AV node (at rate of 40 – 60 beats /minute) and Purkinje fiber (at rate of 15 – 40 beats /minute) can generate action potential.
Normocardia: It is a normal heart rate, varies between 60 and 90 beats/min.
Tachycardia: It refers to a fast heart rate, is more than 100 beats/min.
Bradycardia: It is a heart rate less than 60 beats/min.
Stimulation of the sympathetic nervous system activates B1 receptors in the SA node by norepinephrine which increases inward Na ion current, and increases the rate of phase 4 depolarization. That mean the SA node is depolarized to threshold more frequently (increase heart rate).
Stimulation of parasympathetic nervous system activates muscarinic receptors by acetylcholine (Ach) in the SA node which decreases inward Na ion current and decreases the rate of phase 4 depolarization. That mean SA node is depolarized to threshold less frequently (decreased heart rate).
The cause of heart sound is the cushioning effect of blood. First heart sound corresponds to closure of AV valves (mitral and tricuspid valves). When the AV valves close during contraction of ventricles, they bulge backward toward the atrium until the chordae tendineae abruptly stops the back bulging. The elastic tautness of the valves then causes the back bulging. The surging blood to bounce forward again in to each receptive ventricle, by this the first heart sound is produced. It is accentuated in the mitral valve stenosis because prolonged diastolic filling through narrowed valve.
Murmurs or bruits are abnormal sound heard in various parts of CVS. Blood flow is laminar and non-turbulent (silent) up to critical velocity. Above this velocity and beyond an obstruction, blood flow is turbulent (creates sound).