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The mean velocity in the aorta varies over the cardiac cycle. During systole the mean velocity rises to a peak, then it falls during diastole. This pattern is repeated with each squeezing pulse of the heart. The highest velocities are found at the exit of the valve during systole.
Typically, blood flow velocities in the common carotid artery are measured as peak systolic velocity (PSV) and end diastolic velocity (EDV). In a study of normative men aged 20-29 years, the average PSV was 115 cm/sec and EDV was 32 cm/sec. In men 80 years and older, the average PSV was 88 cm/sec and EDV was 17 cm/sec. [7]
One parameter to quantify this difference is the pulsatility index (PI), which is equal to the difference between the peak systolic velocity and the minimum diastolic velocity divided by the mean velocity during the cardiac cycle. This value decreases with distance from the heart. [20]
A Wiggers diagram modified from [1]. A Wiggers diagram, named after its developer, Carl Wiggers, is a unique diagram that has been used in teaching cardiac physiology for more than a century.
In ultrasound it is usually measured from the velocity gradient SR = (v 2 - v 1)/L where v 2 and v 1 are the myocardial velocities at two different points, and L is the instantaneous distance between them. This is thus equivalent to the velocity difference per length unit (the spatial derivative of velocity) and has the unit s −1. Strain is ...
The peak mitral annular velocity during early filling, e' is a measure of left ventricular diastolic function, and has been shown to be relatively independent of left ventricular filling pressure. [ 12 ] [ 13 ] [ 14 ] If there is impaired relaxation ( Diastolic dysfunction ), the e' velocity decreases.
The horizontal axis of Guyton diagram represents right atrial pressure or central venous pressure, and the vertical axis represents cardiac output or venous return.The red curve sloping upward to the right is the cardiac output curve, and the blue curve sloping downward to the right is the venous return curve.
The slope of ESPVR (Ees) represents the end-systolic elastance, which provides an index of myocardial contractility. The ESPVR is relatively insensitive to changes in preload, afterload, and heart rate. This makes it an improved index of systolic function over other hemodynamic parameters like ejection fraction, cardiac output, and stroke volume.