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The fourth heart sound or S 4 is an extra heart sound that occurs during late diastole, immediately before the normal two "lub-dub" heart sounds (S 1 and S 2).It occurs just after atrial contraction and immediately before the systolic S 1 and is caused by the atria contracting forcefully in an effort to overcome an abnormally stiff or hypertrophic ventricle.
[1] [5] Depending on where the rhythm originates in the AV node, the atria can contract before ventricular contraction due to retrograde conduction, during ventricular contraction, or after ventricular contraction. If there is a blockage between the AV node and the SA node, the atria may not contract at all.
The cochlear amplifier is a positive feedback mechanism within the cochlea that provides acute sensitivity in the mammalian auditory system. [1] The main component of the cochlear amplifier is the outer hair cell (OHC) which increases the amplitude and frequency selectivity of sound vibrations using electromechanical feedback.
The first heart sound, or S 1, forms the "lub" of "lub-dub" and is composed of components M 1 (mitral valve closure) and T 1 (tricuspid valve closure). Normally M 1 precedes T 1 slightly. It is caused by the closure of the atrioventricular valves, i.e. tricuspid and mitral (bicuspid), at the beginning of ventricular contraction, or systole ...
The frequency of a sound is defined as the number of repetitions of its waveform per second, and is measured in hertz; frequency is inversely proportional to wavelength (in a medium of uniform propagation velocity, such as sound in air). The wavelength of a sound is the distance between any two consecutive matching points on the waveform.
There develops a self-perpetuating rapid and abnormal activation. ("Circus Movement" is another term for this.) Conditions necessary for re-entry include a combination of unidirectional block and slowed conduction. [2] Circus movement may also occur on a smaller scale within the AV node (dual AV nodal physiology), a large bypass tract is not ...
Although often regarded as a relatively benign heart rhythm problem, atrial flutter shares the same complications as the related condition atrial fibrillation.There is a paucity of published data directly comparing the two, but overall mortality in these conditions appears to be very similar.
Sound energy causes changes in the shape of these cells, which serves to amplify sound vibrations in a frequency specific manner. Lightly resting atop the longest cilia of the inner hair cells is the tectorial membrane, which moves back and forth with each cycle of sound, tilting the cilia, which is what elicits the hair cells' electrical ...