ARUP; ISBN: 978-0-9562121-5-3 - CMBBE 2012 - Cardiff University

4.2 Partial thrombosis versus Patent false lumen
A false lumen with a partial thrombosis is a serious issue for clinicians, as patients
under such conditions might be exposed to more risk than those with a patent false
lumen [9]. A direct comparison on the force magnitude between the cases of a fully
patent false lumen and a partial thrombosis is not appropriate, since the areas subject to
hydrodynamic pressure are different for each case. Consequently, it is more sensible to
discuss the pressure in the present comparison. Pressure inside the false lumen is
another critical parameter to cause the further expansion of the aortic walls. In Table 1,
the systolic pressures of various dissecting aneurysm sizes inside the false lumen for the
fully patent and partially thrombosed cases are 120.48-120.74 mmHg and 124.91-
125.02 mmHg respectively. The absolute difference of the systolic pressure between
these two scenarios is greater than 4 mmHg.
Furthermore, we shall also consider the mean arterial pressure (MAP) [15]. This is an
important quantity in the determination of the mean pressure in an artery, defined by
1
MAP DP (SP DP) , (2)
3
where DP = diastolic pressure; SP = systolic pressure. Swelling from 40 mm to 80 mm,
the mean arterial pressures of the patent false lumen are in the range of 94.71-94.81
mmHg, while the mean arterial pressures in the false lumen with partial thrombosis
become 95.98-96.01 mmHg (see Table 1). This increases 1.20-1.29 mmHg when the
false lumen changes from the patent state to partial thrombosis.
Table 1 Systolic and mean arterial pressures inside the false lumen
Aneurysm Systolic Pressure (mmHg) Mean Arterial Pressure (mmHg)
Size
(mm)
Patent
Lumen
Partial
Thrombosis
Difference
Patent
Lumen
Partial
Thrombosis Difference
40 120.48 125.01 4.53 94.71 96.00 1.29
50 120.51 124.96 4.45 94.72 95.99 1.27
60 120.62 124.91 4.29 94.77 95.98 1.21
70 120.66 124.95 4.29 94.78 95.99 1.21
80 120.74 125.02 4.28 94.81 96.01 1.20
5. CONCLUSIONS
In practice, a false lumen with a greater area means further weakened wall, resulting in
an even greater risk of rupture. The present work shows that the hemodynamic force
acting on the false lumen wall increases by 73%, as the aortic dissection size changes
from 40 mm to 80 mm. Moreover, the blood pressure is also affected by the dissection
size. For the false lumen with partial thrombosis, both systolic and mean arterial
pressures are higher than those of the false lumen without thrombus formation. These
findings are critical for clinicians in determining the need for surgical intervention. To
gain further insights into the pathophysiology of TAD, we will next pursue an in-vitro
experimental investigation using dissection phantoms fabricated with rapid prototyping
techniques. The fluid-structure interactions of these phantoms will be measured with
high-frame-rate ultrasound imaging methods that can provide millisecond-range
temporal resolutions. It is anticipated that such an investigation will allow us to more
rigorously assess how different biomechanical factors may play a role in TAD