 |
| Fig.3.1 |
During systole,
blood is ejected through the open aortic valve cusps. In normal
individuals, the velocity rapidly rises to a peak somewhere in the
first one-third of systole and then falls back to baseline during
the remainder of this portion of the cardiac cycle. A normal flow
velocity profile and its relationship to electrocardiographic events
is shown in Figure 3.1. Note that the rise in velocity begins just after the QRS complex.
There are various indices, or measurements, that can be made from
the spectral recording which help to characterize systolic functional
characteristics. These are demonstrated in the idealized spectral
velocity in Figure 3.2. These flow profiles are characterized by
a peak velocity (in cm/s), the maximum velocity reached during systole.
This measurement is easily obtained from the inspection of the spectral
tracing. The time to reach peak velocity (or "time to peak") is
another component of the systolic profile which helps to characterize
systolic ejection and is measured in seconds. Left ventricular ejection
time is the duration of the systolic flow velocity recording. These
time durations are also easily measured directly from spectral recording.
 |
| Fig.3.2 |
The peak acceleration is a more complex measurement and usually
requires the assistance of an automated, computerized device. It
is found on the upstroke and is the maximum acceleration expressed
in centimeters per second. Likewise, measurement of the flow velocity
integral usually requires computer assistance and is the area under
the spectral flow velocity tracing.
2004