For as long as humans have been, well, human, our bodies have been working. Pumping blood, digesting food, running, sleeping, healing. In life we never stop—if we stopped, we’d be dead. One of the first things that drew me to study physiology was how our bodies are constantly keeping us alive, and most of the time we don’t give a second thought about how.
 
Despite how presumably static human bodies have remained the past few thousand years, our understanding of human physiology is constantly changing and adapting because our methods of understanding are changing. I want to focus most specifically on cardiovascular physiology, which is my love, and your heart.
 
By now, we’ve all heard that exercise training, like running, is good for your heart. What is absolutely bonkers to me is that this is a concept that we have had to learn. In the United States in the 1950s and 60s, people didn’t go jogging. Serious athletes – your college track stars and Olympians – would run and train their bodies, but regular people? They would have to be crazy to slap on an old pair of shoes and go running. Seventy years is really not that long ago, but jogging was so unusual and unheard of at the time that people in cars would intentionally run joggers off of the road. It took a while for it to catch on, but thankfully, people today know exercise is good for them, even if they don’t like to do it.
 
Around the same time that recreational exercise entered the mainstream, the first coronary bypass surgeries began taking place. These involve taking veins from the legs and using them to circumvent blockages in coronary arteries, the blood vessels that deliver blood to the heart itself. The surgery makes sure that blood still gets to the heart muscle so the heart keeps beating. It’s one of a handful of surgical interventions still regularly used today to keep hearts beating. Naturally, doctors advised cardiac patients who had heart attacks or surgeries to not put strain on their hearts, so this population avoided the jogging boom that was sweeping the U.S. However, thoughtful cardiologist began to find that cardiac patients who jogged felt better and stayed healthier. The stress of exercise was strengthening their hearts. And ever since we learned this, we’ve been trying to understand how and why. 
 
All of this has been one long introduction into why my research matters. For years, treating the large vessels has been the obvious choice. They are easy to image and easy to handle; blockages here are easily evident. It is no surprise, however, that any intervention we perform on the large vessels is only treating symptoms; the real problem starts on a much smaller scale in the microvessels. More and more research connects microvascular dysfunction with diseases such as coronary artery disease, diabetes, and hypertension. When these tiny microvessels can’t dilate properly, they become unable to deliver blood to an organ when it needs it the most. In the heart, this can lead to a heart attack when you suddenly ramp up your heart rate – think an exciting football game or shoveling snow after sitting around all winter. In a 2018 review¹, Allaqaband discusses the role of large coronary vessel function compared to coronary microvascular function and finds that negative cardiac events are more dependent on microvascular dysfunction. These tiny blood vessels can make or break blood flow to the heart, and yet we primarily monitor and treat large vessels.
 
The work I do examines the role of microvessels in cardiovascular health. Exercise training, such as running or jogging, causes molecular changes in large and small coronary blood vessels—these molecular changes are protective against disease. Because of the current limitations of science and medicine, exercise training creates changes that pharmaceuticals and surgical intervention have yet to match. Microvascular dysfunction is associated with most metabolic diseases, cardiovascular diseases including stroke, and even is a long-term effect of chemotherapy. Therefore, it is not only important to promote exercise to preserve microvascular function, but it is essential that more microvascular research be undertaken. Our bodies are resilient and constantly trying to heal the damage that we unknowingly inflict. Exercise training activates specific vasodilation pathways to make sure our blood vessels can still dilate and still deliver enough blood to our hearts when other vasodilation pathways are damaged by disease.
 
Our lab only examines the role of exercise in cases of cardiovascular ischemia, when the large blood vessels are blocked. However, the information we gain contributes to a greater body of microvascular research that paints a picture of what coronary microvascular function looks like in health and disease in humans. In the future, my hope is that coronary bypass surgery will become a relic as we shift towards less invasive, and more specific and preventative measures to treat microvascular issues, and keep hearts beating.
 

1. Allaqaband H., Gutterman D., Kadlec A. Physiological Consequences of Coronary Arteriolar Dysfunction and Its Influence on Cardiovascular Disease. Physiology (Bethesda). 2018;33(5):338-347. doi:10.1152/physiol.00019.2018

 
– Kalen Johnson
 
Kalen is a doctoral candidate in the College of Veterinary Medicine and Biomedical Sciences.