A 28-year-old professional athlete participates in a sports physiology study. She runs on a treadmill at an incrementally increasing speed. After 15-minutes, her pulse is 90% of the maximal heart rate based on her age, and several physiologic parameters are measured. Which of the following changes have most likely occurred compared to at rest?

Question

A 28-year-old professional athlete participates in a sports physiology study. She runs on a treadmill at an incrementally increasing speed. After 15-minutes, her pulse is 90% of the maximal heart rate based on her age, and several physiologic parameters are measured. Which of the following changes have most likely occurred compared to at rest?
A 28-year-old professional athlete participates in a sports physiology study. She runs on a treadmill at an incrementally increasing speed. After 15-minutes, her pulse is 90% of the maximal heart rate based on her age, and several physiologic parameters are measured. Which of the following changes have most likely occurred compared to at rest? A) A B) B C) C D) D E) E

Quizplus · Accepted Answer

During aerobic exercise, respiratory activity changes to help meet the body's increased metabolic demand. The physiologic changes that occur are most pronounced in highly trained athletes: Increased minute ventilation occurs via an increase in respiratory rate and tidal volume and facilitates an increased rate of oxygen uptake and carbon dioxide removal. The increase in tidal volume can reach up to 50% of resting vital capacity. The increased minute ventilation increases alveolar ventilation throughout the lungs up to 20 times resting levels. Pulmonary vascular resistance is reduced and cardiac output is increased, which allows for more evenly distributed blood flow throughout the lungs and reduced physiologic dead space (ie, reduction in the proportion of air in the respiratory tract that does not participate in gas exchange). Although blood flow through the lungs is increased (the increase in cardiac output maxes out at approximately 8 times resting levels), alveolar ventilation is more increased (ie, ventilatory capacity exceeds cardiac output capacity), resulting in an increased ventilation-perfusion ratio. In addition, an accumulation of lactic acid decreases blood pH and stimulates a rightward shift in the hemoglobin dissociation curve, facilitating increased unloading of oxygen in skeletal muscle. Although increased cardiac output increases the rate of blood flow through the skeletal muscle capillaries and reduces the time allowed for oxygen unloading, the rate of arterial oxygen extraction by skeletal muscle markedly increases during exercise, outpacing cardiac output. This results in increased fractional extraction of arterial oxygen and decreased mixed venous oxygen content. It follows that cardiac output, and not alveolar ventilation or the rate of oxygen uptake by skeletal muscle, is the primary limitation to aerobic exercise. Educational objective: Physiologic changes in the respiratory system that occur with exercise include increased minute ventilation (via both an increase in respiratory rate and tidal volume), reduced physiologic dead space, increased ventilation-perfusion ratio, and increased extraction of oxygen by skeletal muscle (resulting in decreased mixed venous oxygen content).

A 28-Year-Old Professional Athlete Participates in a Sports Physiology Study