diameter of the blood vessel is small as compared to the pulse
This is justified during the large part
cardiac cycle. At peak flow rates in early systole however, the ratio of
vlc is large (but not exceeding
turbulence may ensue to produce
Reynolds number from eqn. (3.1.12) is seen to vary with body length
dimensions, or the diameter
the aorta. One question immediately
arises is that the resulting Reynolds numbers calculated for large
mammals, such as the horse, show that turbulence may occur for a large
the systole in the aorta. But this may not necessarily be the
case. It has been well documented that turbulence may not exist even for
Reynolds number greatly exceeding the critical value of
It is only
established that for Reynolds number under
turbulence does not
Again, this value was established under steady flow
conditions in rigid tubes.
arterial blood flow
occurs mostly in diastole.
In systole during
ventricular ejection, the aorta distends as a reservoir to accommodate the
flow as described by the classic windkessel model of the arterial system.
In concert with the pulsation, this compliance of the aorta acts to protect
the peripheral vascular beds from sudden surges in pressure and flow.
The compliance, defined as the ratio of change in volume due to a
change in pressure,
is proportional to body weight.
larger volume change occurs in
a larger mammal and the longer effective length of the
aorta and a much slower heart rate, all help to reduce the tendency
of turbulence to reside in too large
Elastic and Viscoelastic Properties
Many investigators have examined elastic properties of arteries. It is found
that the stress-strain or length-tension relationship is nonlinear and thus
does not obey Hooke's law. Arterial elasticity increases with extension and