Flow and Pressure

Considerations

When fluid mass is subject to force in the form of a pressure, it will first resist movement
because of its inertia and viscosity. In a pressure driven system the pressure rises faster
than the fluid moves; the pressure will peak before the fluid velocity peaks. However, when
one simultaneously measures pressure and flow in the aorta, the peak flow markedly
precedes the peak pressure. This phenomenon was observed as early as 1860 by Chauveau
and Lortet and, as reported by McDonald 7, it contradicts the law of inertia in the pressure
propulsion concept. (See Fig. 2.) While this phase relationship actually confirms the
momentum propulsion principle, it nevertheless remained a source of conjecture for a
considerable period of time in the 1950s until it was `rescued' with the help of elaborate
mathematical modeling for oscillating flow.

An observation in favor of the concept of the blood having its own momentum was reported
by Noble 8 in 1968. By simultaneous pressure measurements in the left ventricle and the
root of the aorta of a dog, he demonstrated that the pressure in the left ventricle exceeds
the aortic pressure only during the first half of the systole and that the aortic pressure is
actually higher during the second half. He found it paradoxical that the ejected blood from
the ventricle continues into the aorta despite the positive pressure gradient. The erroneous
concept of left ventricular pressure exceeding the aortic pressure during entire systole
proposed by Wiggers in 1928 is still depicted in many modern texts of physiology. (See Fig.
3A and B.) Noble proposed that this type of pressure pattern could be a result of
momentum flow; however, this idea was overshadowed by the edifice of pressure
propulsion.

The concept of pressure propulsion sent physiologists and scientists from diverse fields on a
crusade that resulted in numerous hypotheses and theories about the cardiovascular
system mechanics. The saying that, "fluid dynamists in the nineteenth century were divided
into hydraulic engineers who observed what could not be explained and mathematicians
who explained things that could not be observed," still stands true to this very day.
Embryological Observations
Steiner 6 indicated that embryology provides the clues for solving the problem of the
circulation. In relation to this, Bremer 9 performed a remarkable series of observations of
blood circulation in the very early chick embryo before the formation of the heart valves. He
described the two streams of spiraling blood with different forward velocities in the single
tube stage heart. Nevertheless, the blood is noted to have a definite direction of flow within
the conduits and moves without an apparent propelling mechanism. These streams spiral
around their own longitudinal axes and around each other. The streams appear to be a
considerable distance apart, do not fill their vessels, and appear to be in discontinuous
segments.

In a movie made by Bremer of the beating embryonic heart, one observes that the spiraling
blood is boosted by the pulsating heart without creating turbulence in the blood. This
suggests that the momentum transfer occurring between the heart and blood is in phase;
the heart must somehow sense the motion of the blood and respond to it in turn with a
spiraling impulse at the same velocities as the blood, thereby combining blood and heart
momenta.

It is assumed that heart muscle layers have the same velocity distribution pattern as the
concentric streams of a free vortex to enable heart and blood motions to couple in multivelocity
phase. It was significant to observe that the movement of the heart occurred with
minimal inward motion of the heart wall. That the streaming of the blood can be observed
before the functioning of the heart is supported by observations that the circulation in the
early chick embryo is maintained for around 10 minutes after the heart had been excised 10.
Moreover, the inherent mobility of the blood was highlighted by Pomerance and Davies 11,
who found an embryo that lived to term without a heart but was born dead and grossly
disfigured. Thus, the composite view of the embryonic cardiovascular system tells us that
the blood is not propelled by pressure, but rather moves with its own biological momentum
and with its own intrinsic flow pattern.