Sunday, February 12, 2012

Know your VEINS

Talk given at Heart to Heart: A Women’s Health Forum on February 4, 2012, Lakewood Ranch FL.

February is Heart Month. You will likely hear a lot about cardiovascular diseases with a special emphasis on risk factors such as smoking, high cholesterol, sedentary lifestyle, and diabetes. One or more of these risk factors may contribute to blood vessel blockage that can have catastrophic consequences such as heart attacks and strokes. However, this is only part of the story. 

The main protagonist in this story is the red blood cell, a microscopic disk-like structure that is partially dissolved in the blood stream. Blood circulates continuously through interconnected tubes we call blood vessels. These blood vessels come in various sizes, and form a vast network spanning thousands of miles if placed end-to-end. Circulating blood, has two diametrically opposite functions, depending on whether blood is going away from the heart or towards it. Blood vessels transporting oxygenated blood from the heart to various organs and muscle groups, are called arteries. Conversely, blood vessels transporting deoxygenated blood rich in carbon dioxide back to the heart are called the veins.

When blood leaves the heart, there are several factors that help circulate this blood to various parts of the body. The pumping action of the heart muscle starts this process. Every single cell of the heart fires synchronously, generating a powerful squeeze (felt as a heart beat) which ejects blood from the heart. Deep breathing in and out contracts and relaxes the diaphragm which in turns creates a pressure differential that aids in the propagation of blood forward. Large blood vessels connected to the heart have muscle cells embedded in the wall. These muscles cells contract and relax with each heart beat and this helps generate the upper (systolic) and lower (diastolic) numbers of a blood pressure reading. Since majority of the body is below the heart, gravity further aids circulation of oxygenated blood to cells and tissues of the body.

Gravity, which aids propagation of oxygenated blood from the heart, becomes a huge impediment to overcome, when blood circulates back to the heart (especially when upright) after delivering oxygen and picking up carbon dioxide. There is no compact and powerful muscular pump such as the heart to jump start the process.  However, the calf muscle mimics this role and consequently it is also called the “second heart”. Walking and running motions utilize the calf muscles, and the resulting contraction and relaxation aids in propagating blood upwards towards the heart. This is one of the reasons why physical activity is so important in keeping blood circulation healthy. In addition, blood pressure exerted by the descending column of blood is transmitted through the tissues to help start the upward movement of blood back to the heart.

As blood moves upwards from the legs to the heart, nature fights gravity through a series of structures within the wall of the blood vessels, called valves. Valves are unique to blood vessels transporting blood back to the heart from the legs. These valves are similar to the locks in the Panama Canal. As a ship moves along the Panama Canal, locks empty and fill. As a ship enters the lock, the gates behind the ship close and the lock fills with water and the ship is raised up. Similarly, as the column of blood inches upwards from the feet to to the heart, valves open and close as blood vessels fill. The Panama Canal connects the Atlantic and Pacific oceans. These oceans may be at the same level, but the land and the lakes in between are not. In fact, ships are raised about 80 feet up during transit through the canal. When we are standing upright, the heart and the legs are not at the same level. Blood needs to be raised up several feet from the legs before reaching the heart. Integrity of these valves is crucial in preventing gravity pulling this column of blood back towards the feet. As blood nears the heart, alternating contraction and relaxation of the diaphragm exerts a suction force that pulls the blood into the heart from where the coordinated pumping action of the heart takes over again repeating this process over and over again.

The valves in the wall of the blood vessels of the legs are very delicate structures. People who have jobs that require prolonged standing, for example teachers, are prone to the effects of gravity exerting pressure on these valves. Pregnancy is another instance wherein there is increased pressure exerted on these valves, mainly due to compression of blood vessels in the pelvis. Some people have an inherited tendency for poor valve function. Obesity is another contributing factor.

Once these valves are damaged, blood is no longer transported in small tight compartments resulting in a larger volume of blood that needs to be accommodated in the veins of the legs. Early adaption to this increased volume of blood is through enlargement of the veins. Since the valves attached to the walls of these veins cannot elongate, as the veins enlarge, the tips of the valves which should normally come together are pulled apart. As more of these valves are pulled apart, the column of blood instead of being series of compartments becomes one large compartment. The pressure at the feet which is the bottom of this compartment is a lot higher than the pressure higher up in the leg. This is similar to increasing water pressure as one dives deeper underwater.

In order to relieve some of this pressure, the body has some inbuilt safety features. Some possibly early tell tale signs of this increasing pressure with the veins are thin blue streaks that appear on the legs. These are called spider veins. As pressure builds up further, a larger outlet may be required. New or dormant preexisting blood vessels open up to accommodate this excess blood and these may appear as ropey structures under the skin called varicose veins.

Initially, there are no symptoms other than an undesirable cosmetic appearance. Since this part of the blood circulation is involved in transport of carbon dioxide, a waste byproduct of normal cellular function, symptoms gradually set in if this blood is not quickly recycled. During the daytime, with prolonged sitting or standing, not much of this is blood is being recycled through the heart. At nighttime, while sleeping in a flat position, gravity is overcome, and blood returns back to the heart. In a flat position, as fresh blood washes out the old blood that has pooled in the veins of the legs, cellular function in legs may cause nocturnal leg cramps. During the night, without gravity to deal with, a healthier circulatory pattern is set up and you wake up with fresh legs. As the day goes on, pressure again builds and this cycle goes on and on.

Gradually over months and years, spider and varicose veins may not be sufficient to accommodate the excess blood. Just as the ground gets saturated and soggy with heavy rain, the tissues then start to swell up with this excess fluid from the blood stream and the ankles and legs start to puff up. Again the pattern here is better first thing in the morning and worse as the day goes on. Along with fluid leaking out of the blood vessels, particles containing iron also come in contact with the skin discoloring it, just as a piece of rusty iron leaves a stain when a piece of cloth comes in contact with it. As a result of this process, soft and supple layers of the skin then becomes tougher and in some cases leathery. In extreme cases, skin breaks down from relentless back pressure. This also usually occurs around the ankles.

Just as the calendar moves forward by a day after completing both daytime and nighttime, every blood cell completes one round trip in its relatively short life span of three months after it has travelled through both the arteries and the veins, with the heart being the start and finish points.

The two left chambers of the heart participate in the better known side of the story involving heart attacks and strokes. The two right chambers of the heart are involved in the lesser known side of the story that starts with spider and varicose veins. Problems (such as strokes and heart attacks) related to blood vessels connected to the left side of the heart, start outside in. For example, a poor diet and lack of exercise influences what goes on inside the blood vessels. On the contrary, in the blood vessels connected to the right side of the heart, problems start inside out. What starts inside the blood vessel is manifested externally, visible on the surface. To keep the heart healthy and whole, it is important not to overlook the importance of the whole story of blood circulation.