The cardiovascular system is composed of the heart, blood, arteries, veins, and capillaries in the body. This network of blood vessels can be thought of as a roadmap. There are two major networks of highway systems, arteries and veins.
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The arteries are red and they carry oxygen rich blood away from the heart, while veins are blue and they take de-oxygenated blood back to the heart. Capillaries are small blood vessels that allow for blood to exchange important resources with cells throughout the body. Blood serves as the body's liquid messenger and it carries oxygen, food, and waste.
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The heart is the main organ of the cardiovascular system and it is responsible for pumping or pushing blood throughout the entire body. A child's heart is about the size of a fist and an adult heart is about the size of two fists.
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It is broken down into four distant chambers or compartments. The two upper chambers are called atria and the two lower chambers are called ventricles. There is a left and right side to the heart. Oxygen poor blood is pumped from the right atrium through a valve to the right ventricle and then through another valve into the pulmonary vein. The pulmonary vein is connected to the lungs, which provide blood with oxygen. Once oxygenated, blood is pumped back into the heart through the pulmonary arteries into the left atrium. A valve opens and blood is sent into the left ventricle. From there, blood is sent to the aorta. The aorta offers a network of branches that are responsible for sending oxygenated blood to the rest of the body.
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The heart can be listened to using a stethoscope. And the lub dub sound it makes is caused by the opening and closing of the valves discussed above. The lub can be heart when blood is pushed out of the heart and into the body. The dub is the sound of the heart reloading with blood.
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This vital organ beats about 100,000 times a day, which is equal to about 35 million times each year.
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In an average lifetime a human heart will be almost 2.5 billion times.
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This engine-like wonder never stops, even at rest, the muscles of the heart work twice as hard as leg muscles running at a sprint.
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Heart Health
With all the heart does for the body, it is imperative that the heart remains healthy. There are a variety of problems that can occur with the heart or blood vessels that feed into and out of it. Some major heart problems include cholesterol and plague build up.
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The liver produces cholesterol; it is also found in the meet and dairy products we consume. Too high of cholesterol can lead to endothelial tissue dysfunction, fatty streak build-up, and eventually advanced lesions, also known as atherosclerosis.
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This plaque builds up in the coronary arteries can block blood flow and oxygen to the heart. It can be diagnosed with non-invasive imaging or measuring body fat content. Basic interventions include a healthy diet, exercise, plenty of sleep, and a low stress environment.
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When this does not work stenting is the best option. Doctors often use a balloon angioplasty and stenting to repair this. One of the main issues with this procedure is stenosis and re-stenosis. Stenosis is the natural build up of cells on the stent.
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Engineers are currently working on solutions to this problem. Some possible solutions are making biodegradable stents, coating stents with polymer drugs that release anti-inflammatory drugs, magnetic stents that attract magnetized stem cells to make endothelial cells, and finally tissue engineered blood vessels.
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Cardiologists, or physicians that treat problems within the cardiovascular system, are also extremely interested in helping people recover from heart attacks.
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Heart failure affects more than 5.8 million people in the United States.
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And according to the World Health Organization cardiovascular disease is the leading cause of death worldwide.
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Hundreds of thousands of people suffer from heart attacks each year, also known as a myocardial infarction.
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A heart attack can occur when one or more of the coronary arteries become blocked and blood is thus unable to pass to the necessary heart tissue.
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When this happens, muscle of the heart either dies or is damaged.
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If too much muscle dies, people can develop congestive heart failure.
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Patients with this condition have a difficult time supplying blood to their body, making it extremely difficult to exercise or perform physical labor.
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Physical activity causes people with congestive heart failure to feel symptoms such as, fatigue, swelling of the hands, feet, and abdomen, and shortness of breathe.
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It is extremely important that the left ventricle of the heart work properly because it is this chamber that supplies blood to the entire body.
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Patients with blockages or damages to the left ventricle are often most in need of repair or regeneration therapy.
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Repair and Regeneration of the Heart
Scientists and doctors have had great success in helping patients prevent heart attacks from happening in the first place, but repairing the muscle itself after a heart attack has occurred is a difficult task.
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Recently have observed stem cells at the site of tissue damage after a heart attack.
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These stem cells appear to help the heart repair, but they only last for a few days and are unable to offer more than minor repairs.
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Scientists then became interested in increasing stem cell numbers at the location of tissue damage. Their hope was that these stem cells could help patients' hearts recover after a heart attack.
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And in fact they were right in their hypothesis! Initial trials have shows that stem cells can increase vascularization in the heart, or the number blood vessels in the heart tissue.
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Stem cells also possess the ability to differentiate or become new heart muscle cells.
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And finally stem cells can prevent other heart cells from being damaged and assist in overall recovery.
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The question now becomes how do doctors get stem cells into the heart after a heart attack. Two clinical trials are currently underway to answer just that.
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Both trials are in phase 1, which means researchers are just in the second step of five-step process for getting approval from the FDA for a new therapy or prescription drug.
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There are still two more sets of clinical trials that would need to be conducted before patients could have access to either of these therapies.
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The drug development stages include: Pre-clinical development – invention of the drug, Phase I – initial safety test, Phase II – tests efficacy in humans using small trials, Phase III - further tests in efficacy in humans using large trials, and Phase IV – post-marketing safety and efficacy studies. All together this process can take anywhere from 9-17 years.
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One therapy involves removing stem cells from the patient's bonne marrow and injecting them directly into the heart.
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Once in the heart, these stem cells can repair heart tissue just like the ones naturally found there after a heart attack.
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On the other hand, the second therapy seeks to use the body's natural repair system and signals, but increase the time and strength of the signals so more stem cells are recruited to the hear to assist in repair.
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Injecting Bone Marrow Stem Cells
Stem cells for this therapy are collected through a bone marrow aspiration or bone marrow transplant.
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The bone marrow is harvested from the hip using a thin needle.
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After the bone marrow is sent to the lab where the bone marrow is centrifuged, separated out, and cleaned.
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The stem cells that are sent back are ready to be injected back into the patient through catheterization.
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Catheters are tubes that are inserted into arteries.
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In this procedure the right femoral artery in the upper thigh is often used to get the stem cells back up into the aorta, across the aortic valve, and then into the left ventricle.
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It is imperative that no arterial wall is punctured; otherwise the patient could suffer internal bleeding.
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Doctors use contrast dye to determine the damaged heart tissue and carefully inject the stem cells to the site.
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Finally, doctors use an echocardiogram to see if any small holes, or perforations were caused during surgery.
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An echocardiogram uses sound wave to produce an image of the heart. Patients who undergo this procedure are carefully monitored for four months to measure results.
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Increasing SDF-1 Signals
The second therapy uses the body's immune system, or built in repair system, to fix the heart.
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As noted above, the heart already sends stem cells to the site of muscle tissue damaged by a heart attack, but too few are sent and they remain for too short of a time.
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Now doctors are seeking to increase the number of stem cells that are sent to the site in need of repair and increase the time they remain there.
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The body sends out this same type of signal when any damage occurs including cuts, bruises, or sprains. This signal called a stromal cell derived factor 1 or SDF-1 signal recruits adult stem cells (stromal cells) to a site in need of repair.
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The problem lies in the fact that the body only produces SDF-1s for a few days after a heart attack and if SDF-1 was injected into the heart it would still only last a short period of time. Scientists therefore needed to figure out a way to get the heart cells to produce more SDF-1 on its own.
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Research has shown though that by injecting a plasmid, or ring of DNA, with specific instructions to produce SDF-1, heart cells can make more SDF-1 themselves.
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Initial research on mouse hearts shows that SDF-1 plasmids injected into cells can cause the to continue to release the signal for up to 20 days after the original injection.
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In this procedure the right femoral artery in the upper leg is again used to inject the plasmids up into the aorta, across the aortic valve, and then into the left ventricle using catheterization.
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The same precautions are used to make sure the arterial walls are not punctured, contrast dye is also used to find damaged heart tissue, and an echocardiogram again checks for perforations or tears.
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Patients that undergo either procedure require careful monitoring for four months.
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Aortic Aneurysm Repair
An aneurysm is a balloon-like bulge in an artery.
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Arteries are blood vessels that carry oxygen-rich blood to the body and they therefore have generally thick walls.
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However, extreme pressure can weaken the walls and cause and aneurysm. When an aneurysm grows large enough it can rupture and cause dangerous internal bleeding.
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images/2014/4/14.04.10.03.jpg
Figure 3. Diagram of an aortic aneurysm. Section A shows a normal aorta. Section B shows a thoracic aortic aneurysm (located behind the heart). Section C shows an abdominal aortic aneurysm located below the arteries that supply blood to the kidneys. Based on public domain photo courtesy of the National Institute of Health, 2010.
Most aneurysms occur in the aorta, the main artery that carries blood from the art to
the rest of the body.
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An aneurysm that occurs in the chest portion of the aorta is called an thoracic aortic aneurysm, while an aneurysm found in the abdominal cavity is called an abdominal aortic aneurysm (See Figure 3).
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About 13,000 Americans die each year from aortic aneurysms.
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When found in time, doctors can often treat aneurysms with medicine or surgery. During surgery, weakened or damaged parts of the artery are replaced (open abdominal or open chest repair) or reinforced (endovascular repair).
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During open abdominal or open chest repair the aneurysm is removed and that section of the aorta is replaced with a graft (stent) made of material such as Dacron or Teflon.
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During endovascular repair the aneurism is not removed.
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Instead, a catheter is used to insert a graft into the aorta to provide strength.
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Once the stent reaches the site of the aneurysm it is expanded and fixed in place. This graft helps to reinforce the weak section of the aorta and hopefully prevent it from breaking. This endovascular procedure does not work for all aneurysms though, it depends on their location and size.
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