the first heart sound occurs during the isovolumic contraction phase of the cardiac cycle.
the first heart sound occurs during the isovolumic contraction phase of the cardiac cycle.
during which phase of the cardiac cycle does the first heart sound occur?
isovolumic contraction
the cardiac cycle involves four major stages of activity: 1) "isovolumic relaxation", 2) inflow, 3) "isovolumic contraction", 4) "ejection". (see wiggers diagram, which presents the stages, label-wise, in 3,4,1,2 order, left-to-right.) moving from the left along the wiggers diagram shows the activities within four stages during a single cardiac cycle. (see the consecutive panels labeled, at bottom-right, "diastole" then "systole").
cardiac cycle
one of the simplest methods of assessing the heart's condition is to listen to it using a stethoscope. in a healthy heart, there are only two audible heart sounds, called s1 and s2. the first heart sound s1, is the sound created by the closing of the atrioventricular valves during ventricular contraction and is normally described as "lub". the second heart sound, s2, is the sound of the semilunar valves closing during ventricular diastole and is described as "dub". each sound consists of two components, reflecting the slight difference in time as the two valves close. s2 may split into two distinct sounds, either as a result of inspiration or different valvular or cardiac problems. additional heart sounds may also be present and these give rise to gallop rhythms. a third heart sound, s3 usually indicates an increase in ventricular blood volume. a fourth heart sound s4 is referred to as an atrial gallop and is produced by the sound of blood being forced into a stiff ventricle. the combined presence of s3 and s4 give a quadruple gallop.
cardiac physiology