Final answer:
An a. increased heart rate during exercise leads to an increased cardiac output, as the heart is pumping more blood each minute to meet the body's higher oxygen and nutrient demands.
Step-by-step explanation:
The change that would lead to an increase in cardiac output during exercise is an a. increased heart rate. Cardiac output is the volume of blood the heart pumps in one minute, which is the product of heart rate and stroke volume.
During exercise, the heart rate increases, which directly increases cardiac output, provided that the stroke volume does not decrease significantly.
In a healthy young adult, when heart rate increases above 160 bpm, the cardiac output continues to increase as well.
Exercise has multiple effects on the cardiovascular system; not only does it increase heart rate, but it also enhances the heart's strength and efficiency, leading to an increase in stroke volume.
Enhanced tissue perfusion occurs as a result of these changes, ensuring that oxygen and nutrients are efficiently delivered to the muscles during periods of physical exertion.