Balloon Angioplasty Lab Report

Balloon Angioplasty
Introduction:
Angioplasty is a technique that broadens a narrow or congested blood vessel using a inflatable catheter. It is used to treat atherosclerosis (blood vessel impediments), and regularly made by an interventional cardiologist, a medical doctor with distinctive training in the handling of the heart, using invasive catheter-based measures. Angioplasty is frequently achieved as a minimally-invasive technique, where a stent is implanted into the blood vessel to preserve it open. A conceivable substitute to heart surgery, it has dependably been shown to diminution indications due to coronary artery disease and decrease cardiac ischemia.
Procedure:
1. An introducer pointer is entrenched into the femoral artery in
the leg. 2. A sheath introducer is placed in the opening to preserve the artery uncluttered and controller hemorrhage. 3.
A controller drain is then strapped through the sheath introducer. Colorants can be inoculated through the guide catheter into the coronary artery to pinpoint and study the polluted artery using x-ray. 4. After reviewing the x-ray image, the cardiologist chooses the type of balloon catheter and plastic coronary guide wire that will be used. 5. The elastic coronary guide rope with radiopaque plastic tip is then introduced into the supervisory catheter and into the coronary artery. 6. Watching through x-ray imaging display, the cardiologist directors the flexible coronary guide wire through the coronary artery to the site of the obstruction. 7. When the stretchy guide wire reaches the obstruction, it is then strapped across the obstacle. 8. A hollow-tipped balloon catheter is then interleaved, using the plastic guide wire as a conduit to the site of the impasse. At this point, the balloon is still collapsed. 9. After the balloon catheter spreads and is strapped inside the obstruction, the balloon is then exaggerated. Inflating the balloon increases the area about it and bandages the plaque accumulation (blockage). The exaggerated balloon also enlarges the artery
wall. 10. A stent (wire mesh tube) occasionally is surrounded to keep the artery wall prolonged. The stent originally is implanted along with the balloon catheter, increases when the balloon is magnified, and left behind in the lengthened position as the balloon catheter is detached. For certain people, heart disease cure can be accomplished without operation. Angioplasty is a non-surgical technique that can be used to open congested heart arteries. Stent appointment is another option that can be done throughout angioplasty. 11. The technique is achieved in the cardiac catheterization workroom by a dedicated cardiologist and a squad of cardiovascular nurses and specialists.
Cardiac catheterization is achieved as part of angioplasty. Next, a sheath is implanted into an artery -- regularly in your groin, but occasionally in the arm. A long, thin, hollow tube, called a catheter, is accepted through the cover and directed up the blood vessel to the arteries nearby the heart. A minor quantity of difference material is injected through the catheter and is cracked with an X-ray as it changes through the heart's hollows, valves, and chief containers. From the cardinal movies of the difference material, the clinicians can tell whether the coronary veins are narrowing and whether the heart valves are active properly.
There are abundant sorts of interventional procedures as below:
Balloon angioplasty:
During this process, a specially intended catheter with a small balloon tip is directed to the point of contraction in the artery.
Stent:
A stent is a tiny metal mesh tube that acts as a scaffold to deliver support privileged your coronary artery. A balloon catheter, positioned over a guide wire, is used to supplement the stent into the lessened coronary artery. Once in dwelling, the balloon tip is exaggerated and the stent enlarges to the size of the artery and grips it open. The balloon is then collapsed and detached while the stent stays in dwelling enduringly. Over a several-week dated, your artery heals around the stent. Stents are usually placed during interventional events such as angioplasty to help retain the coronary artery exposed. Some stents comprise medication and are intended to decrease the risk of obstruction (restenosis).
Atherectomy:
The catheter used in this technique has a hollow chamber on the tip with an open space on one adjacent and a balloon on the other. When the catheter is introduced into the pointed artery, the balloon is exaggerated, assertive the window in contradiction of the fatty material. An edge within the cylinder alternates and shears off any fat that projected into the window. The shavings are caught in a hollow within the catheter and detached. This procedure is recurrent as wanted to permit for better blood flow.

Cutting Balloon: The cutting inflatable catheter has a singular balloon tip with small blades. When the inflatable is inflated, the razorblades are triggered. The small edges score the panel, and then the balloon wrappings the fatty material into the artery wall.
Mechanics of Balloon Fabrication
Angioplasty balloons, such as those described above, are fabricated by first designing a tube that is extruded in certain dimensions. This tube is then crystallized so that only a small length is left amorphous, and then the tube is free-blown into a balloon in a machine designed for that purpose. Lastly, the balloon is heat-set. All of these processes are carefully controlled in order to achieve a balloon that meets the necessary standards. Tube Design
The design of the extruded tube is important because it dictates the final 2.4.2 Tube Crystallization
After extrusion, tubes with a specific inner and outer diameter are obtained. For a
5mm balloon, the tube wall is approximately 0.020” thick. The tubes are then crystallized except for a small segment in the center. Placing the tubes on a heated block with a gap in the center allows them to crystallize except for the section above the gap. This amorphous section is the only part of the tube that will expand during the free-blowing procedure. Its length can be manipulated in order to influence the dimensions of the balloon. For PET, the temperature of the heating block and the amount of time used are related to the known melting and glass transition temperature of the material as determined by Golike and Cobbs, in Eq. 3.19      
 
        −
      − −
=−
2
2
1
0
2
1
1
1
log
TT T
T
b
TT b b t m m g (3)
Where the variables are defined as follows: t1/2 = the total time between the start of heating and the halfway point of crystallization T = the temperature the polymer is being heated at Tg = the glass transition temperature of the polymer (~70°C for PET) Tm = the melting temperature of the polymer (~265 °C for PET) b0 = 1.97 b1 = 137 b2 = 1.03
Balloon Heat-setting
After a repeatable free-blow process is determined, and balloons of the correct size and shape are fabricated, the balloons must be subjected to a final, heat-setting procedure. This procedure is necessary to anneal the balloon and to relax it so as to alleviate any shrinking that may occur during sterilization. In order to do this, the balloon must be exposed to a temperature higher than the sterilization temperature, but lower than its melting temperature because of the ability of many polymers to remember their heat history.
Stress Models and Yielding Behavior
For the purpose of stress analysis, an angioplasty balloon can be approximated as a cylindrical thin-walled pressure vessel because the thickness of its wall is less than one tenth of its diameter. Figure 2.12 illustrates the stresses acting on such a vessel. Only normal stresses are present because the conditions of symmetry exclude the existence of any shearing stresses in the planes of the sections, as shearing stresses would cause an incompatible distortion of the vessel.
An equation for the circumferential, or hoop, stress can be derived by summing the forces in the radial direction and setting them equal to 0, as seen in Equation 5. t pr
=1 σ (5)
In addition, the equation for the longitudinal stress is found by equating the force developed by the internal pressure and the force developed by the longitudinal stress in the walls, resulting in Equation 6.
t pr 22 = σ (6)
In both Equation 5 and 6, p is the internal pressure of the vessel (created by a contained gas or fluid), r is the inner radius of the vessel, and t is the thickness of the wall. The hoop and longitudinal stresses are assumed to be constant throughout the wall of the vessel.27 These stresses can be compared to calculated yield stresses in order to predict if the vessel will yield under given pressures at given thicknesses. Yield criterion developed by both von Mises and Tresca both propose to calculate these stresses using different methods. While the Tresca criterion predicts more conservative values, the von Mises criterion has been shown to be more accurate for states of biaxial stress, such as those experienced by an angioplasty balloon.28 Because of this, the von Mises criterion was used for this investigation. The von Mises yield criterion is based upon the Maximum Energy Failure
Theory, which states that failure is caused by the component of strain energy that
results in a change in shape, rather than the component that causes a change in volume. This theory is based on the observation that materials can be loaded with extremely high hydrostatic pressure, even exceeding their apparent strength, without failure.29 The equation for the von Mises yield criterion is as follows:
( ) ( ) ( ) [] 2 1 2 31 2 23 2 12
2 1 σσ σσ σσ +−+−=−Y (7)
Where Y is the tensile yield strength, and σ 1, σ 2, and σ 3 are the principle stresses. For a cylindrical thin-walled pressure vessel, such as an angioplasty balloon, combining
Equation 7 with Equations 5 and 6, and knowing that σ 3 = 0, gives the following simplified equation (with all variables previously defined):
     
       
==
t pr
YY 2 3 or 2 3 1 σ (8)
In a polymeric material, yielding occurs when, under an applied stress, the chemical bonds within the polymer are stressed. As the stress increases, the bonds begin to break and small microcracks form, which coalesce into larger cracks. After these cracks are initiated, they propagate to failure. The way that these cracks form is related to the mechanisms by which the polymer must dissipate the energy of the applied stress, which is a function of the geometry, mode of loading, and material properties of the polymer, such as crystallinity and orientation.

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