INTRODUCTION
Heart sounds are the sounds produced by mechanical activities of Heart during each cardiac cycle.
Heart sounds are produced by:
1. Flow of blood through cardiac chambers. 2. Contraction of cardiac muscle.
3. Closure of valves of the heart.
Heart sounds are heard by placing the ear over the chest or by using a stethoscope or microphone. These sounds are also recorded graphically.
Different HEART SOUNDS
Four heart sounds are produced during each cardiac gde. First and second heart sounds are called classical heart sounds and are heard by using the stethoscope. These two sounds are more prominent and resemble the spoken words 'LUB, (or LUBB) and 'DUBB" (or DUP), respectively
Third heart sound is a mild sound and it is not heard by using stethoscope in normal conditions. But it canbe heard by using a microphone. Fourth heart sound is an inaudible sound. It becomes audible in pathological conditions only. This sound is studied only by graphic registration, i.e. the phonocardiogram.
IMPORTANCE OF HEART SOUNDS
Study of heart sounds has important diagnostic value in clinical practice because alteration in the heart sounds indicates cardiac diseases involving valves of the heart.
FIRST HEART SOUND
First heart sound is produced during isometric contraction period and earlier part of ejection period
■CAUSES OF FIRST HEART SOUNDS
Major cause for first heart sound is the sudden and synchronous (simultaneous) closure of atrioventricular valves. However, some other factors are also involved Four types of factors are responsible for the production of the first heart sound.
1. Valvular Factor
Synchronous closure of atrioventricular valves set up the vibrations in the valvular leaflets and chordae tendineae. These vibrations are mainly responsible for the production of the first heart sound.
2. Vascular Factor
Rush of blood from the ventricles into aorta and pulmonary artery during ejection period is also responsible for the production of the first heart sound.
3. Muscular Factor
Myocardial tension and the contraction of ventricular muscle during isometric contraction and the ejection periods also add to the production of the first heart sound.
4. Atrial Factor
Vibrations produced by the atrial systole aiso play a role in the production of the first heart sound.
CHARACTERISTIS OF FIRST HEART SOUNDS
First heart sound is a long, soft and low-pitched sound. It resembles the spoken word 'LUBB'. The duration of this sound is 0.10 to 0.17 second. Its frequency is 25 to 45 cycles/second.
SECOND HEART SOUND
Second heart sound is produced at the end of protodiastolic period.
CAUSE OF SECOND HEART SOUNDS
Second heart sound is produced due to the sudden and synchronous closure of the semilunar valves.
CHARACTERISTICS OF SECOND HEART SOUNDS
Second heart sound is a short, sharp and high-pitched sound. It resembles the spoken word 'DUBB' (or DUP). Duration of second heart sound is 0.10 to 0.14 second. is frequency is 50 cycles/second.
