The phrase "use it or lose it" is used in many different ways; in terms of our own bodies, the phrase can have tremendous implications. Research has shown the more we use our brains (i.e. reading, learning, studying), the more dendrites will extend from our nerve cell membranes. These dendrites form a network that is the "hardware" of our intelligence; when we do not use this network, we will "lose" these dendrites, and thus our brainpower! The same principles apply to many other parts of the body, including our bones, muscles, and even our reproductive organs!
How does this apply to our circulatory system, and how are these principles used to our advantage in surgery?
I was fortunate to be able to watch Dr. Karwowski and his team perform a lower limb bypass surgery, the first "invasive" vascular surgery that I saw. When you think "bypass" in vascular surgery, it is essentially redirecting blood flow from one artery or vein to another. The surgery focused on the arteries shown below:
The patient had a large thrombus within their left iliac artery, blocking the artery by 95%. The thrombus formed on a polymer graft with the iliac artery; while this graft's intention was to help improve the blood flow, it ended up being an ideal site for the formation of a thrombus. Since the blockage was near the groin, the patient had poor circulation throughout the whole leg and foot, causing foot and leg ulcers. The circulation was so poor that the patient was at risk of losing his left leg. Again, "use it or lose it"; if the circulatory system within that leg was not used properly, it would become dysfunctional. Without proper nutrient distribution throughout the leg, it might have been lost.
What approaches could be used to restore blood flow through the patient's leg?
Unfortunately, the thrombus could not be removed without destroying the artery. Other arteries within the leg were not viable replacement options, as the patient had atherosclerotic plaques within the arteries. The approach used by Dr. Karwowski was something that caught me by surprise; he wanted to take a vein from the left leg and use it as an artery. How would this work? The following things were flowing through my head.
- Veins have valves to prevent backflow of blood, while arteries do not.
- The vein being used was not the same diameter as the artery being used.
- The endothelial cells that comprise that vein are very different from those within the artery.
How was this going to work out?
The result was fascinating; since the veins have valves that are one-directional, he simply "flipped" the vein over. Such a technique would make the vein like an artery; the valves would always stay open, allowing arterial blood flow. Could these very different cells handle the new blood flow, and could they compensate for the difference in diameter? Dr. Karwowski told me that the cells would "arteriolize"; in response to the new blood flow patterns, the cells forming this vein will actually engineer the vessel to become more like an artery. The surgery ended up being a success; the vein was able to handle the new blood flow patterns, and normal circulation returned to the patient's left leg.
However, it is worth noting that a bypass is one of the last options that are desired in vascular surgery. The scar left was tremendous; a deep incision was made within the patient's leg, from his groin to his knee. The patient had a recovery period of 6 weeks within the hospital ahead, and the such a large wound poses a huge risk of infection.
It was also interesting to note that Dr. Karwowski said this bypass would only last for 5-7 years. While such a vein can arteriolize, it will not last forever. There are only so many blood vessels within the body that can be used for a bypass; better solutions are needed for such problems.
On the research side of things, Dr. Karwowski stated that the creation of an engineered blood vessel (currently being worked on at Yale: http://www.technologyreview.com/biotech/19693/) is the "Holy Grail" of vascular surgery. While such a solution currently seems far away, it is an area of great need that can use more funding and researchers. Future Cornell BMEs, take note!
I will finish off with a few food and karaoke suggestions:
Patsy's Pizzeria: Look no further for great pizza; located on 69th and 2nd avenue, Patsy's provides a very unique, coal-oven baked pizza made with fresh ingredients. It stands out from the rest of the pizzerias on the upper east side.
For Pete's Sake: Located right around the block from Olin Hall, Pete's has free, awesome karaoke on Thursday nights! It is becoming a Thursday tradition for Cornell BME students.
I hope to do better next time!