Medical Fact of the Day – Heart Swinging
Today's fact comes from a case presented in the New England Journal of Medicine. The 39-year-old woman was being treated for melanoma, a skin cancer, but the disease showed steady spreading. Among other symptoms, her heart rate was 110 and blood pressure 82/64 mmHg (normally 60-70 and 120/80, respectively). This suggested some sort of heart defect, and an echocardiogram was taken to image the heart in action.
This picture, taken from this video, shows the heart swinging within the chest as it beats. Needless to say, this is not normal - the heart usually sits still within its cavity, happily pumping away.
This heart has gone wild. Arrows point to portions of the heart that have collapsed (not a good thing). From Kapoor JR, McConnell MV. NEJM 2009 Oct 29; 361(18):e37.
This happens because the chamber within which the heart usually sits - the pericardium - has filled with fluid when it should be snug against the heart. In this case, the space has filled with fluid because the metastatic cancer spread to the pericardium. The heart now has space to swing about as it beats.
When the pericardium fills with enough fluid, it increases pressure against the heart and can disrupt its normal function, leading to cardiac tamponade. In the picture above, you can see that chambers of the heart collapse after beating, a sign of too much pressure against the walls of the heart.
They eventually sucked out 1.6 liters of fluid, about 160x the amount of fluid usually in the space (10 mL).
Other reasons that pericardial effusion can occur include infection (with viruses, bacteria, or parasites) and inflammatory disorders.
Click here for a video of the swinging heart in action. It's well worth the time.
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Medical Fact of the Day – Why White Coats?
I wore my white coat today to shadow a geneticist in clinic. This made me wonder - why do doctors even wear white coats? It is a recognizable symbol of the medical profession, but how did it start?
WIthout any context, this man looks like a doctor. What a powerful symbol the white coat is.
One answer seems to be that the knee-length coat is indicative of a scientific approach to medicine. It had traditionally been used to ward off chemicals in the laboratory. In the 1900s, scientific medicine competed with homeopathy and traditional remedies, but the development of more powerful drugs established the power of science to treat humans. As a result, doctors adopted the white coat as symbolic of the role of science within medicine and to claim legitimacy in their roles.
Alternatively, my TA in anatomy had a bloodier story. In the early days of surgery, there were very few ways to see inside the patient's body to know exactly what to operate on and where other things were. As a result, the surgeons practiced their procedures on dead bodies right before trying their hand at the real patients. The white coats were thus worn to shield the doctor from the dead body's fluids before transitioning to the live patient. I couldn't verify this story, though it certainly is meaty.
Nowadays, there is debate on the appropriateness of the white coat. Some say it can increase infection and is an unnecessary symbol of medical hubris. However, the white coat has become such a clear marker of the doctor that patients are much more likely to trust physicians wearing the white coat.
Personally, I also find its pockets useful to hold pens, electronic devices, and a stethoscope.
Fun fact: Medical students wear shorter white coats that extend to the waist, while doctors with their MD degrees have longer coats extending almost to the knee. Often patients address me as doctor despite my shorter coat, which is giving me far more credit than I deserve.
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Medical Fact of the Day – The Widowmaker
The heart pumps blood throughout the body through vessels, but it also has its own circulation system. The blood from these coronary arteries supplies the heart with the energy it needs to contract.
One of these vessels is called the left anterior descending branch of the left coronary artery, or the Widowmaker. This artery supplies a large portion of the heart, particularly the section responsible for pumping oxygenated blood to the rest of the body (left ventricle). The reason it's earned its name is that blockage of this vessel is a serious emergency that requires acting within minutes and happens more often in males. Blockage usually causes the heart to pump irregularly or not at all, placing the entire body at risk. The most sensitive organ is the brain, which, if not oxygenated properly, begins dying within five minutes.
This was, unfortunately, the cause of death of Tim Russert earlier this year.
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Medical Fact of the Day – How You Make Antibodies
Over your lifetime you will encounter countless types of pathogens, including bacteria, viruses, and parasites. Additionally, aberrant cells within your body like tumor cells need to be recognized to be killed. Your immune system recognizes all these potential dangers by creating receptors for them - that is, proteins that have a specific shape to recognize other proteins and molecules.
Yet for each type of pathogen, there are countless variants that you might encounter. Over 200 types of viruses can cause the common cold, each expressing different types of proteins that need to be recognized. Furthermore, each individual cell only recognizes one specific shape. How is your immune system able to recognize so many different things?
The answer is an elegant solution to generate diversity called VDJ recombination. Each antibody you make consists of multiple gene segments that are combined together from a much bigger pool. The process is like shuffling three decks of cards and choosing a single card from each deck to create a unique combination for each cell.
One gene from each collection is chosen to form the final product.
For instance, part of the antibody is called the heavy chain. This region contains 65 Variable (V) genes, 27 Diversity (D) genes, and 6 Joining (J) genes. This means there are 65 x 27 x 6 = 10530 combinations. Furthermore, there can be minor modifications in the sequences between genes. Overall, this means that your immune system can recognize billions of different shapes from just a limited set of genes.
The human body really is amazing.
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Medical Fact of the Day – Respirators vs Surgical Masks
In medical school we learn all sorts of interesting facts, and I want to share them with you. I've started the Medical Fact of the Day to share some of the most interesting things I've learned. They won't necessarily come everyday (to avoid making this blog a lecture series) but they will be things I especially want to share.
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Today for Introduction to the Profession we were fitted for respirators, shown below:
This man kindly models proper wearing of the respirator.
These fit so snugly around the mouth that all the air breathed in is filtered through the mask. These respirators are meant to trap all particles in the air down to about 100 nanometers, or smaller than a bacterium and smaller than many viruses. For instance, we would wear them when seeing patients with drug-resistant tuberculosis to prevent being infected ourselves and passing it around the hospital.
I want to contrast these with surgical masks:
More fashionable than we see in the hospital.
You can see these worn around flu season. They were especially notable in Asia during the SARS epidemic and can be quite the fashion item.
These do NOT filter all the air you breathe. It is important to note that they do not protect all that well against inhalation of foreign particles. Instead, they prevent wearers from touching their noses and mouths, and they reduce the spread of droplets when the wearer coughs or sneezes.
For the general public, these can therefore help prevent transmission of disease, especially around flu season, but they are by no means failsafe.
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