Image of the bloodstream in the left ventricle of the heart, with regular Doppler technology to the left side, and «Blood Speckle Tracking» to the right side.(Photo: Annichen Søyland Daae)
The beauty of a swirl: We continuously reveal the secrets of the heart
SHARE YOUR SCIENCE: The heart is perhaps the most romanticised, and most studied human organ. The blood flow in the heart has fascinated physicians and researchers for decades, and our understanding of the cardiac mechanics are ever evolving.
Annichen SøylandDaaePhD Candidate at Faculty of Medicine and Health Sciences, NTNU
For the past 70 years, physicians have
used ultrasound in the examination of the heart, and these seven decades have
given us an enormous development of the method. Ultrasound of the heart, or echocardiography,
is a complex examination as it involves moving tissue and muscle and moving
Already in the 16th century Leonardo da Vinci described the possibility of swirls of blood, or vortices, in the aorta above the aortic valve.
Since the 1970’s we have used the Doppler
technology to get an impression of the blood flow, and even though the
ultrasound probe and scanner has evolved, the theory behind is the same today
as was used 50 years ago.
Soundwaves and the Doppler effect
Sound is pressure variations and
propagates as waves – and this is why we talk about sound waves or pressure
waves. The frequency is the number of oscillations per second of the sound
Imagine the sound of an ambulance as it
moves towards you and the change in the siren as it passes and moves away. This
is the Doppler effect. More specific the Doppler effect is the change in
frequency of a soundwave when the source of the wave, i.e. a siren, is moving
relative to the person that perceives the sound.
In echocardiography, we utilise the
Doppler effect to estimate velocities of both the contracting and relaxing
cardiac walls and the moving blood pool within, as these move towards and away
from the ultrasound probe.
The ultrasound wave is reflected towards the probe
when it hits blood and tissue, and when these are in motion the Doppler effect
arises with different frequencies of the waves that are transmitted and
received, and this difference is measurable!
The Doppler technology is heavily limited
by the angle of the blood relative to the ultrasound beam.
To be sure that our
measurements are accurate, we are dependent on the ultrasound beam being well
aligned with the flow direction, if not we will get a measurement of the
velocity of the blood that is lower than the real velocity. And if the angle is
too big, we will not get a measurement at all.
Flow perpendicular to the beam is
impossible to interpret and flow that is not aligned with the beam is a
challenge as well.
Visualizing complex blood flow is therefore not possible
with the Doppler technology, and clinicians are dependent on interpretation
rather than objective measurements.
Vortices and da Vinci
Already in the 16th century
Leonardo da Vinci described the possibility of swirls of blood, or vortices, in
the aorta above the aortic valve.
During the last 50 years researchers have dug
deeper into this, and with fluid mechanics and models of the heart it has been
shown that the anatomy of the heart will create a more complex blood flow than
what we can see with Doppler technology alone.
The role of the vortex in normal heart
function is to stop the blood colliding with itself, thus preserving the
momentum and energy, and avoiding unnecessary loss of pressure and speed of the
There is extensive research throughout the world today on different
methods for vortex imaging and parameters linked to the formation of vortices
in the ventricles of the heart.
Tracking the blood
In 2018, we conducted a study in healthy
volunteers to test a new method, first developed for kids, in adults. The
method is called Blood Speckle Tracking (BST), and with this we can measure
the movement of the blood in all directions inside the heart.
As opposed to the
Doppler technology it is not dependent on the angle of the ultrasound beam. The
motivation was to be able to visualise complex blood flow and vortices with
Blood Speckle Tracking is promising as an
addition to the standard clinical methods in children, and the aim of the study
was to further develop the method so that it could be used in adults.
challenge in adults when compared to children is that the heart is located
deeper into the body, and that the ultrasound waves thus must penetrate deeper
into the tissue.
We managed to adapt the method for adults,
and from the study we could map the blood flow throughout the whole heart
contraction (known as the cardiac cycle), describing the function of the blood
flow and how it relates to the appearance and movement of the inside of the
The results show a fascinating swirling
pattern inside the heart, helping the muscle of the heart during the cardiac
cycle so that the heart avoids using excessive force to pump blood to all parts
of out body, thus conserving energy.
Changes in the blood flow
To better understand the normal physiology
of the blood flow within the heart will in turn give a better understanding of
how this will change with different heart diseases, and in 2020 we conducted a
study in patients with heart disease.
In this study we had two groups of
patients with heart failure. One of the groups had a dilated left main chamber
with weakened muscle and impaired function, and the other one had thickened and
stiff muscle which leaves little room for the blood in the left main chamber.
The first results from this study give us
the impression is that the blood flow is changed, and that the vortices change
with different heart diseases.
Our hope for the BST-method is that it can
be a supplement to the Doppler technology, and that the methods together can
help us better understand the spectrum of heart diseases. Maybe the method can
be used to target medical treatment of heart failure – to fix the broken swirl.