Friday, July 14, 2006

Artery Disease and Ribbon Microphones

Get ready for a tour though a fake artery. Actually this is a plastic model of a heart artery, also known as a coronary artery, that was provided by the drug company that made Zocor, to physicians. Doctors find it helpful to have models and pictures to explain various diseases to their patients.

This is a model of a diseased artery, one that is affected by the disease known as atherosclerosis. Atherosclerosis (say it five times fast) is a diffuse disease that affects the entire arterial circulation system in humans. Everybody has it to some extent. The cutaway shows yellow colored plaque in the artery. Plaque is the term used to describe the buildup of lipid (fatty) material and calcium that can clog an artery and result in obstructive diseases, and cause shortness of breath, starve the heart muscle of oxygen, which it needs, and even trigger a fatal heart attack.

The typical notion is that a blockage or plug of some sort forms inside the artery. Even this model seems to show that, and it also shows a brown material, which is a blood clot inside the artery. Blood clots can form inside an artery and can completely cut off blood flow. That can cause a sudden and acute heart arrest, and death.

But the model is not quite right.

It shows the three layers of an artery - intima, media and adventitia - corresponding to inside, middle, and outside, of a normal artery. That's ok in a normal segment, but it is not what the diseased artery looks like. The medial layer is often gone altogether, and replaced by a pool of liquid, fatty material. The model doesn't show that condition, which is termed Vulnerable Plaque. Ultrasound images show us that arterial disease is more complex than was commonly appreciated, and spreads over large areas of the artery.

Vulnerable Plaque is a real killer
and is more prevalant than many people think. That fat-rich liquid is nasty - it actually causes a clot when the plaque cracks open (which it can do any time) and spills into the blood. Then the clot stops the flow of blood completely, and the heart tissue, starved of oxygen it needs, dies. So too the patient.

Our group developed IVUS, which is a way to look inside heart arteries. We did this in the late 80's and the early 90's and today it is a successful business that is larger than the entire market for music recording microphones. IVUS uses a small microphone-like catheter - a tiny tube that is inserted into the heart - to make a sonar scan of the artery, so doctors can put in stents or decide if surgery is needed.

Now we are experimenting with new microphone materials, and have come up with a more sensitive technology that will eventually be used in studio recording microphones. The technology involves the use of nanomaterials, such as carbon nanotubes.

We hope to use the same microphone technology as a sensor to detect that bad actor - Vulnerable Plaque. Today, there is no way to detect it. We think that we have found a way to listen for the sound of Vulnerable Plaque so that clinicians can do something about it before it causes a potentially fatal heart attack.

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