Over the past 20 years, most of the U.S. military’s active conflicts have been fought in mountainous areas of the Middle East. Because the air contains less oxygen at higher altitudes than it does at lower ones, that means a hard workout for a soldier’s heart and lungs. Once the heavy gear a soldier typically carries is added to the mix, the situation becomes even more extreme.
Understanding how load carriage affects the cardiac performance and endurance of individuals at high altitudes is a research interest for Maj. Dan Baur, Ph.D., assistant professor of human performance and wellness (formerly physical education), and his wife, Capt. Katherine “Katie” Baur, an instructor in the same department.
This summer, Cadets Abaigeal Doody ’23 and Beverley Buchanan ’23, both majoring in biology, worked under the Baurs’ direction in their Summer Undergraduate Research Institute projects, “Effects of Simulated Altitudes and Load Carriage of Cardiac Output” and “The Effects of Heavy Load Carriage and Simulated Altitude on Ventilatory Physiology.”
Doody explained the heart functions as a pump to supply the body with blood enriched with oxygen. When the heart contracts and all the blood in the ventricles is ejected, the amount of blood pumped during one beat is known as stroke volume. The number of times a heart beats per minute is known as heart rate. Cardiac output is the total volume of blood pumped by the ventricles per minute, the product of heart rate and stroke volume.
“Heart rate is an important indicator of cardiovascular stress and strain,” Doody said. “During exercise, the heart rate increases in direct response to increased exercise intensity, to supply working muscles and organs with enough oxygen and nutrients to function. As exercise intensifies, HR approaches a maximum heart rate. Research has shown SV also changes to meet the demands of exercise, up to and including the point of exhaustion.”
At high altitudes, where the air is thinner, the lungs and the heart must work harder to supply the bloodstream with enough oxygen. This causes shortness of breath, increased heart rate, and increased blood pressure.
“The delivery of oxygen to the muscles during intense exercise begins with the movement of air into and out of the lungs—breathing,” said Buchanan. “Carrying a heavy load, a common task for soldiers, is known to add to the difficulty of breathing. As the heart and lungs work together to deliver oxygenated blood to the muscles, it is possible that the heart must overwork during such challenging conditions, causing important implications for soldiers engaged on the battlefield.”
The research involved healthy male subjects who were tested on six separate occasions by performing exercise tests in VMI’s privately funded hypoxic chamber, which simulates a high-altitude environment. First, a baseline for oxygen consumption was established through three exercise tests. The first test was without weight with normal oxygen levels and the second was with a 65-pound rucksack. The third test was loaded under hypoxic conditions of 12,000 feet. For reference, many of the Rocky Mountains have summits that are between 12,000 and 14,000 feet tall.
After those three tests have been completed, three walking tests are done for comparison, with varying weight loads, speeds, and oxygen levels.
“The military does not stop when they reach high altitudes or when they need to carry everything on their backs, so results of the study will provide more insight into the effects carrying a heavy load at high altitudes has on the body’s ability to get oxygen to the muscles and all other vital organs,” Doody commented. “The effects of load carriage at altitude on cardiac output are mostly unknown. By furthering our understanding of altitude and load carriage on cardiac output, we can begin to further understand how to help make it easier on the body.”
The Baurs, meanwhile, have been pleased with the research. “Buchanan and Doody have assisted me with research at various points over the last year, and I’ve been lucky to have them,” said Dan Baur. “They have worked hard, and I believe their efforts will result in data that they can present at a national conference and publish in a prominent journal. Their project will likely have important implications for the health and performance of soldiers, and both understand and value their role in producing knowledge that may someday support their peers who serve.”
“Buchanan and Doody have each embraced their individual roles in the research process and take their responsibilities seriously,” Katie Baur added. “They work well alongside one another and ask questions that exemplify their interest and understanding of our larger research question.”
Doody came to VMI from Ladera Ranch, California. After graduation, she plans to go to graduate school where she will pursue a degree in physical therapy.
Buchanan is from Richmond, Virginia. After graduation, she plans to go to graduate school, where she will study sports medicine or pharmacy.
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