Almost everyone has been affected by cardiovascular disease in one way or another. According to the World Health Organization, cardiovascular diseases are the number one cause of death worldwide. NASA’s goal is to keep astronauts heart healthy during their space flight missions, and biomedical research that aims to prevent heart disease is an important part of the NASA Human Research Program.
Stuart Lee, who received his doctorate of philosophy in kinesiology and exercise science, serves as a lead scientist at NASA’s Cardiovascular and Vision Laboratory and studies the effects of spaceflight on the cardiovascular system. He hopes his work inspires people on Earth to protect their cardiovascular health as well.
“One of the things that we hope spaceflight research does is help people understand that cardiovascular health is not just about running marathons, climbing mountains or traveling in space,” said Lee. “It includes maintaining a healthy lifestyle so that you get to spend more time with the people you care about.”
Cardio Ox, one of the laboratory’s most recent investigations that Lee leads, will continue unraveling how spaceflight affects the cardiovascular physiology of crew members aboard the International Space Station.
“There is still a lot to be learned studying the cardiovascular system,” said Lee.
Cardio Ox promises to help scientists determine whether specific markers of physiological stress increase during spaceflight, and if vascular structure and function are compromised. To do this, Lee and his team will measure the structure and function of crew members’ carotid and brachial arteries, as well as biomarkers of oxidative stress and inflammation in their blood and urine.
Oxidative Stress is Totally Radical
Blueberries, strawberries, raspberries and other common edibles have been touted as antioxidant super foods. But what are antioxidants and why are they important?
Antioxidants neutralize a set of oxygen-containing molecules (oxidants), also called free radicals that are naturally produced in the body by metabolism. Free radicals have one or more unpaired electrons, which makes them highly reactive with other molecules. To balance their own electrons, they “steal” electrons from other molecules, and thus can damage DNA and membranes in your cells, changing their ability to function. An imbalance between oxidants and antioxidants is called oxidative stress. Biomarkers of DNA damage is one of the many measures that investigators are collecting in crew member blood and urine to study oxidative stress and inflammation.
Oxidative stress can result from either increased free radical production or decreased antioxidant availability. Like other familiar forms of stress, oxidative stress can contribute to illness. Along with other maladies, oxidative stress has been associated with cardiovascular diseases like atherosclerosis (deposits of plaque and fatty material on the inner arterial wall), heart failure and other neurodegenerative and inflammatory diseases.
Because arterial structure and function (control of blood flow) can be influenced by oxidative stress, scientists at the Cardiovascular and Vision Laboratory are studying vascular health in the laboratory and during spaceflight. Ultrasound experts on the ground use remote guidance, two-way video and audio communication between the ground and the orbiting laboratory, to help crew members conduct ultrasounds of their own brachial and carotid arteries during their missions to see if spaceflight causes any change in the arteries.
The Vascular System: Vessels of Health
Arteries are made up of three cell layers: an outer layer (tunica externa), a middle layer (tunica media) and an inner layer (tunica intima). The intima is one cell layer thick and serves as the messenger part of the artery. It senses what is going on in the blood vessel and sends signals to the media layer, made up primarily of smooth muscle cells. The signals determine whether the media layer “flexes its muscle” and constricts the vessel or expands through smooth muscle relaxation. If the messaging is working properly, the vessel will expand when there is an increase in blood flow. This is called vasodilation and it is important for exercise, for example, so you can increase blood flow to your muscles when they need it.
Oxidative stress can affect those signals by interfering with a molecule called nitric oxide, which is what the intima sends as its signal to the media. A decrease in vasodilation can happen when the smooth muscle cells do not respond to the nitric oxide or because the body is not releasing enough nitric oxide to affect the smooth muscle cells. Cardio Ox studies both of these.
Give me a Brachial!
To measure an artery’s ability to vasodilate, investigators place a blood pressure cuff around the lower part of the crewmember’s arm and increase the cuff’s pressure to temporarily block the blood flow to the lower arm. When the cuff’s pressure is released, they use ultrasound to determine whether the brachial artery vasodilates properly when the blood rushes back into the lower arm. The increase in blood flow is the stimulus for the intima to release nitric oxide to the media.
“That gives us an indication of vascular health,” said Lee. “If the artery does not dilate normally in response to this increase in blood flow that is a good predictive indicator of atherosclerosis.”
The second vascular functional test determines whether the artery’s smooth muscle cells are reacting properly to any nitric oxide that is released by the intima. During this test, crew members are provided nitroglycerin, the same medication that is used to treat the symptoms of chest pain, or angina. The nitroglycerin is an alternate for nitric oxide provided in a controlled dose.
“During the cuff procedure, if vasodilation is impaired, the effect may result from either a decrease in nitric oxide release or from a decreased responsiveness of the media to the nitric oxide. If vasodilation is impaired in response to the sublingual nitroglycerine, then we know the problem is with the responsiveness of the smooth muscle cells to the nitric oxide,” said Lee.
Measurements of the carotid artery, which is particularly sensitive to changes in blood flow and is often the site where the atherosclerosis is first detected, are collected in the same testing sessions as those measurements of the brachial artery.
“It’s one of the first places it shows up because it’s so close to the heart,” said Lee. “It also sees some of the higher pressures when a person is standing up because you are driving blood up into the head.”
Ultrasounds of the carotid determine whether there is increased thickness of the media which indicates higher than normal pressure and can be associated with vessel damage or onset of atherosclerosis.
Not Missing a Beat
Cardio Ox investigators are “pouring” their hearts into the study, making it unique in several respects.
A total of 12 crew members will participate in the study. Cardio Ox is also one of the ten Twins Study investigations for the One Year Mission in which NASA astronaut Scott Kelly participated.
Investigators are collecting the biomarkers, in collaboration with the NASA Nutritional Biochemistry Laboratory’s Biochem Profile investigation, pre-flight, in-flight and post-flight. In-flight collection occurs on each participating crew member’s flight days 15 and 60, and within two weeks of the mission end.
“We want to capture a response curve,” said Lee. “Picking a couple of different time points like we are doing here gives us an opportunity, in a limited sense, to determine if oxidative stress, inflammation, and vascular adaptations are an early or late in-flight phenomena and, if so, whether they can be corrected by countermeasures.”
In addition to studying astronauts, the controlled environment of the space station also helps make this cardiovascular study unique.
“We know things like inactivity, nutrition, stress, and changes in sleep habits contribute to the development of cardiovascular disease in people on earth,” said Lee. “The advantage of this model is that, although the crew members are free living, in some ways it’s a more controlled environment than in other Earth-based studies and we have more information about what they do every day on-orbit.”
The team is receiving data as part of NASA medical requirements testing, so they will receive information about crew exercise habits, nutrition information and some information about their sleep habits.
“Because they are in a closed environment, as it were, we are able to get multiple measurements,” said Lee. “There aren’t that many prospective studies out there where you would have this much information about your subject and their environment.”
Investigators are also studying crew members for up to five years after they return from space. This makes the investigation one of the longest-duration life science studies. The investigation began in 2013 and is not expected to end until 2022, five years after the final participating crew member returns from space.
Getting To the Heart of the Matter
The investigation’s results will help determine if there are cardiovascular risks associated with long-duration spaceflight and to develop countermeasures, if needed, as well as understanding crew cardiovascular status in the years after their return to Earth. Whether the returning crew members are marathon runners, mountain climbers or just want to make sure they are healthy enough to spend more time with the people they care about, Lee hopes this and future cardiovascular studies will inspire them and others to take their cardiovascular health to heart.
Filed Under: Aerospace + defense
