Engr. Hinesh Kumar (Lecturer) 1 Phonocardiography

Definition 2 Phonocardiography is the recording of heart sounds. The heart. like any mechanical pump, produces characteristic sounds as it beats. These are the sounds the physician hears with a stethoscope. Certain heart murmurs produce sounds in the 1000-Hz range, and some frequency components exist down to 4 or 5 Hz.

Heart Sounds Generation 3 The first heart sound is generated at the end of atrial contraction, just at the onset of ventricular contraction. This sound is generally attributed to movement of blood into the ventricles, the atrioventricular (AV) valves closing, and the abrupt cessation of blood flow in the atria. The second heart sound corresponds to the closing of the aortic and pulmonary valves.

Cont… 4 Third heart sound corresponds to the cessation of ventricular filling. Fourth heart sound is correlated to the atrial contraction. This last sound has a very low amplitude and a low- frequency component.

Cont… 5 The phonocardiograph transducer is a contact or air- coupled acoustical microphone held against the patient's chest (shown in fig). Various types of microphones are used, but most are the piezoelectric crystal or dynamic type of construction.

Cont… 6 The crystal microphone generally costs less and is more rugged than the dynamic type. Also, the crystal microphone produces a larger output signal for a given level of stimulus The dynamic microphone uses a moving coil coupled to the acoustical diaphragm. The dynamic microphone is used when it is desirable to have a signal frequency response similar to that of the medical stethoscope. An air-coupled microphone with a 2-s time constant is often used in apex phonocardiography.