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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. Porosity

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Presentation Transcript
introduction
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

Characteristics of Vascular Grafts
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

Defects in the graft

Rare

Holes, perforations, rents, slits

Occur during manufacturing and handling

Usually hard to detect

Bleeding and infection

Rare

Usually within first 10 months

Suture line

Interstices of the graft

Graft Failure
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 – Natural Materials
history synthetics
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
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
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, 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
muscular arteries
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
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
Microscopic Structure of Arteries
  • Single layer of endothelial cells
    • Capillaries – major wall component
  • Structure and thickness of other walls depends upon function
elastic arteries
“Elastic Arteries”
  • Wall thickness is relatively thin for the size of the vessel
  • Large arteries
blood
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
Plasma
  • Fluid that transports nutritive materials

Component Percentage

Water 91-92

Protein (fibrinogens, globulins, albumins) 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

blood17
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

Blood Clotting
angioplasty
Angioplasty
  • Opening up plaque-narrowed 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
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

Uses of the Procedure
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