UNC Health Talk

The Science of Strokes

William Powers, MD, wanted to be a small town doctor, the kind of family physician with a practice set in a refurbished Colonial house, a doctor everyone knew and relied on. Instead, he wound up at Washington University in St. Louis. He became a world-class neurologist who carried out clinical research and conducted an important clinical trial at one of the world’s most prestigious medical schools.

In 2007, after having accomplished nearly all he wanted to as a clinical researcher, Dr. Powers wanted a new challenge. He joined UNC School of Medicine as the H. Houston Merritt Distinguished Professor and chair of the Department of Neurology, the culmination of a career spent improving health care for people who’ve suffered strokes.

Throughout his 34-year career, Dr. Powers has been honored numerous times, including as a Best Doctor in America for 20 years and most recently this February by the American Stroke Association with an award recognizing the best of clinical-based research.

We sat down with Dr. Powers to discuss his path into medicine, why he chose to come to UNC, his research, and what people can do to limit their risk of stroke, a condition that strikes nearly 800,000 people in the United States every year.

What led you to study medicine and focus on neurology?

When I was in high school I set my sights on being president of General Motors because it was the biggest corporation around and I thought it would be wonderful to do. But when I got to college – this will sound trite – I decided I didn’t want to spend my time and apply every effort I had to simply make more money. I wanted to help people. So that’s why I decided to go into medical school. I was planning to become a general practitioner in a small town. But at Cornell, where I went to medical school, they didn’t train general practitioners; they trained specialists. Cornell had one of the best neurology programs in the country, and the neurology residents and faculty were the smartest, most impressive people there. When I took neurology as a third-year med student, I found it fascinating. I stuck with it because I thought it would remain interesting and fascinating for many years, and it has.

Neurology is hard; a bunch of it is straightforward but a lot of it isn’t. Back then and continuing to this day, a lot of neurology is based on patient history and exam.

Neurology is hard; a bunch of it is straightforward but a lot of it isn’t. Back then and continuing to this day, a lot of neurology is based on patient history and exam. It isn’t so much about doing protocols and procedures well over and over. It’s about figuring out what’s wrong. It’s more puzzle than process.

You spent most of your career at Washington University School of Medicine in St. Louis; what led you to join UNC Health Care and the UNC School of Medicine.

I went to Washington University in 1980 immediately after I finished residency. I stayed there for 27 years. For the first 20 years or so I mainly did research. I was fortunate enough to start there right when PET scanning was just being developed. About five places in the world could do PET scans and Wash U. was one of them. So as soon as I got there I had this marvelous tool I could use to study the brain. Well, it turned out I was good at writing grants. So I got lots of funding to do research for many years. And I got to do all sorts of really interesting stuff.

But about eight years ago I pretty much had come to end of all the things I was really fanatical about. I had to write another grant, and I had really good idea, which I was pretty certain would be funded. But I realized that I really had no desire to sit down and write the grant and do the research. I thought maybe it’s time to do something different. I had always wondered what it would be like to be a department chair. Around that time, my younger child was a senior in high school, I was in my mid-50s, and I realized it was either time to leave Wash U. or I’d stay there for my entire career. This job at UNC was open. Actually, I had been offered this job six years prior but decided not to take it because my kids were doing so well at their high school.

What attracted me to UNC was the fact that the neurology department was very good, without any noticeable or difficult issues. But I thought it could be expanded. Plus my wife was willing to move here, which is always a key consideration.

As for that grant idea I had: I wrote half a page summary and gave it to John Morris at Wash U., who wrote the grant and it did get immediately funded. So it was a good idea! We knew that people who have strokes have a high risk of developing dementia within two years, but we really didn’t understand why. John is studying this, but it will be some years before we find out. These kinds of studies often take a long time.

The American Stroke Association annually gives the Feinberg Award to a neurologist who has made significant contributions to patient-based research on stroke. Which of your research discoveries have had the greatest impact on patient care and why?

I’d say there are two. I led a group of studies to find out what happens when a major artery supplying the brain gets blocked. We know that when it first gets blocked it can cause a stroke. But we also know that there are other blood vessel channels that help blood get around the blockage to supply the part of the brain that the vessel normally would have supplied. And we know that the ability of those channels to carry blood varies a lot from person to person. Yet, we couldn’t figure out who had good collateral channels by doing conventional CTs or angiograms.

Beginning in the 1980s, with PET scans, we were able to distinguish patients with blocked arteries who had great collateral channels from those patients with poor collateral channels. We defined and categorized them. Then we followed these patients for several years and proved that the ones with poor collaterals identified by PET were at higher risk of stroke. This was probably the biggest influence my work has had on the field of stroke – using PET to define the importance of collateral channels.

The second major discovery had to do with the sort of stroke that occurs when a small artery inside the brain bursts and causes a clot.

The second major discovery had to do with the sort of stroke that occurs when a small artery inside the brain bursts and causes a clot. This accounts for about 5 to 10 percent of all strokes. The clot in the brain destroys part of the brain as it expands. Up until about 10 years ago, it was widely believed that the clot also compressed the blood vessels in the brain surrounding it and cut off part of the blood supply. It was thought patients could get more brain damage because of the low blood flow. If that theory were true, then doctors should be very careful when lowering a patient’s blood pressure because you could make things worse by reducing the blood flow even more.

This was debated for many years without data. We did two studies in the early 2000s to address it. One study looked at whether there was a reduction in blood flow in the area around the clot that put you at risk for further brain damage. A second study looked at what happened to blood flow if you abruptly dropped pressure.

We found that there was a reduction in blood flow but it was because tissue was damaged and didn’t need the blood, not because the vessels were compressed. And if you dropped the pressure, then blood flow didn’t change. So there was no danger from this.

This assuaged fears in the field and paved the way for people to study if lowering pressure was actually beneficial for people with that particular kind of stroke.

From 2002-2010, you led a study to find out if surgery to bypass a blocked artery to the brain would lower the risk of having a second stroke. What led to this study and what were the results?

Basically, this goes back to two things that happened a long time ago. One was the development of the surgery, which is not trivial. You drill a hole in the skull, free up the vessel from the scalp, and guide it through the hole to attach it to a small vessel on the surface of the brain. This procedure became quite popular in the 1970s. But it wasn’t clear if it actually benefited most patients. The second was our observation that people with blocked arteries and poor collateral channels, identified by PET scans, have a high risk of stroke, as I mentioned before.

It turned out that the surgery worked in the sense that if you create another way to get blood to flow to that part of the brain it reduces risk of stroke.

We did a randomized study at 49 centers around country over eight years. It turned out that the surgery worked in the sense that if you create another way to get blood to flow to that part of the brain it reduces risk of stroke. But the surgery itself causes so many strokes that it completely negates the positive results we saw. So then we tried to figure out if there was any way we could identify the patients who would have stroke from surgery so in the future we could just operate on the ones who wouldn’t. We did an exhaustive analysis to identify particular characteristics shared by patients who had a stroke from surgery. We looked at everything we could think of, even various characteristics of surgeons, but we couldn’t pinpoint anything.

About 800,000 people in the United States suffer a stroke every year. What are the best things people can do to reduce risk of stroke throughout their lives?

When we see someone with a stroke and we want to prevent another one, there are several things we do. We put them on medicine – aspirin or a similar drug – to reduce the body’s ability to form clots. If they have high blood pressure we treat it. If they smoke we advise them to stop. We also treat cholesterol and diabetes, though those two things have turned out to be much less important in stroke prevention than they are for heart disease.

Really, smoking and high blood pressure are the main concerns. Smokers have a much higher risk of stroke than do people who never smoked. But here’s the thing smokers should know: if they quit, then in three to five years their risk of stroke drops back to the level of people who have never smoked.

The other most important thing is get your blood pressure checked regularly. If it’s high, go to your doctor, and if medications are prescribed, take them. One of the most tragic things we see is when people knew they had high blood pressure, but they didn’t take their meds or follow up with their doctor, and then we see them in the hospital with a stroke.