Transcript Vascular Grafts - Auburn University

Vascular Grafts, Stents, and
Meshes
Introduction
• Arterial diseases
– Major medical problem world-wide
– One of the main causes of death in the US
• Surgical reconstruction
– Does not deal with the causes of disease
• Not fully understood
– Solve problems caused by symptoms
Characteristics of Vascular
Grafts
• Porosity
– Essential component
– Long-term patency
– Permit ingrowth of cells
(fibroblasts)
• Necessary for uniform and
satisfactory bonding of the
internal lining
• Compliance
– Must be matched to the
properties of the artery
• Occlusion of the replacement
• High shear stress at suture
line
• Turbulence of blood flow with
local stagnation
• Biodegradability
– Control hemorrhage
– Low porosity during
implantation/high porosity
during healing
– Enables patient’s cells to
replace the graft with natural
tissue
Graft Failure
• Dilitation
– Permanent enlargement of
graft diameter due to
pulsing stresses
– Most frequent mechanical
failure
– 35 months after
implantation
• Suture failure
– Mismatch of compliances
– Suture material failure
– 30-50 months after
implantation
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•
Defects in the graft
–
–
–
–
Rare
Holes, perforations, rents, slits
Occur during manufacturing and
handling
Usually hard to detect
Bleeding and infection
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–
–
–
Rare
Usually within first 10 months
Suture line
Interstices of the graft
History – Natural Materials
• 1906 to 1916
– First documented case
of veins used to
replace human
arteries
• 1940s
– Arterial grafts from
young, dying persons
used
(allograft/homograft)
– Degenerative changes
– Rejection
– Abandoned in the
1950s
• 1950’s
– Carotid artery from
cow
(heterograft/xenograft)
was initially successful
– Development of
complications
• 1976
– Tanned umbilical vein
graft
– Still used for lower
extremity
revascularization
History - Synthetics
• During WW I (1914-1918) paraffin-coated
Ag tubes introduced
• Also, paraffin-coated glass, aluminum,
polyethylene, and steel mesh
– Inert
– Non-porous
– Compliance
Cardiovascular System
• Blood vascular
system
– Distributes nutritive
materials, oxygen, and
hormones
– Removes cellular
waste products of
metabolism and
carbon dioxide
– 60,000 miles
(http://www.cardio.bayer.com/en/heart_vascular/vascular/)
Heart
• Modified blood vessel
serving as a double
pump
– 2 sides, left and right
heart
– Atria and ventricles
• Atria – reservoirs
• Ventricles - pumps
Arteries, Capillaries, and Veins
• Arteries
– Carry blood from the heart
to the extremities
– Pulsating pressure
• Capillaries
– Major location of biological
interchange
– Meshwork of fine tubules
• Veins
– Return blood from
extremities to heart
– Constant pressure
Pressure/Area Profile
Muscular Arteries
• Parts of the body under varying conditions
require different amounts of blood
• Supply arteries must be able to vary the
size of their lumina
– Walls consist of smooth muscle fibers
– Controlled by autonomic nerve system
Arterioles
• Blood delivered to capillaries under
reduced pressure because walls thin to
allow nutrient/waste transfer
• Narrow arteries (<100 μm or less) with
thick, muscular walls
Microscopic Structure of
Arteries
• Single layer of
endothelial cells
– Capillaries – major
wall component
• Structure and
thickness of other
walls depends upon
function
“Elastic Arteries”
•
•
Wall thickness is relatively thin for the size of the vessel
Large arteries
Blood
• Belongs to group of tissues called
connective tissue
• 7% of total body weight
• 5 ℓ in average adult
• Formed elements (55%)
– Red cells, white cells, platelets
• Plasma (45%)
– Imparts fluid properties to blood
Plasma
• Fluid that transports nutritive materials
Component
Water
Protein (fibrinogens, globulins, albumins)
Percentage
91-92
7-8
Other solutes: Small electrolytes (Na+, K+ , Ca2+, Mg2+, Cl-, HCO3 -, PO4 3-, SO4
2-) Nonprotein nitrogen substances [NPN] (urea, uric acid, creatine, creatinine,
ammonium salts) Nutrients (glucose, lipids, amino acids) Blood gasses (oxygen,
carbon dioxide, nitrogen) Regulatory substances (hormones, enzymes)
1-2
Blood
Component
Number or percentage
Red blood cells (erythrocytes)
4-5x106/mm3
White blood cells (leukocytes)
6000-9000/mm3
Agranular leukocytes:
Lymphocytes
30-35% (of leukocytes)
Monocytes
3-7% (of leukocytes)
Granular leukocytes:
Neutrophils
55-60% (of leukocytes)
Eosinophils
2-5% (of leukocytes)
Basophils
0-1% (of leukocytes)
Platelets (thrombocytes)
2-4x105/mm3
Blood Clotting
• Discontinuity in
endothelial lining
– Leads to deposition of
proteins
– Leads to platelet
aggregation
– Followed by adhesion
of other platelets
• Coagulation initiated
by factors in plasma
• Cascade of at least
13 plasma proteins
• Last step is
conversion of
monomer fibrinogen
to fibrin through
action of plasma
enzyme thrombin
creating a fibrous
network that traps
blood cells
Angioplasty
• Opening up plaquenarrowed artery
without doing major
surgery
• Catheter w/balloon tip
inserted into coronary
or major leg or arm
artery
• Inflation of balloon
– often repeatedly
– stretches artery wall
– disrupts plaques
Stents
• wire mesh
• Used in 70-90% of all
angioplasty
procedures
• keeps the vessel
open after widening
• placed onto balloon
prior to insertion
• permanently attached
as balloon inflates
Uses of the Procedure
• Open narrowed or
blocked coronary artery in
patients suffering from
angina – alternative to
bypass surgery
• Open a blocked artery in
the pelvis, leg, or arm –
peripheral arterial
disease
• Control blood pressure in
renal hypertension –
caused by narrowing of
one or both arteries
supplying kidneys
• To keep blood vessel
grafts open in patients
undergoing hemodialysis
– most have a graft
between a artery and vein
in the arm to easily draw
and replace blood
• maintain blood flow to the
brain by keeping open the
carotid artery