Question

Which of the following increases stroke volume?

1)exercise
2)decrease in preload
3)severe blood loss
4)decrease in end diastolic volume (EDV)

Answer 1

Exercise increases stroke volume by enhancing the heart rate and force of contraction, which increases the end diastolic volume (EDV), or preload, and thereby strengthens the heart's pumping efficiency.

Step-by-step explanation:

Exercise is the factor that increases stroke volume (SV). Stroke volume, defined as the amount of blood ejected by a ventricle during a single contraction, is dependent on several factors, mainly preload, contractility, and afterload. Preload refers to the end diastolic volume (EDV), which is the volume of blood in the ventricles at the end of diastole. An increased EDV or preload stretches the cardiac muscle fibers and, through the Frank-Starling mechanism, leads to a stronger contractile force and increased SV. During exercise, the heart rate and force of contraction increase, enhancing the pumping effectiveness of the heart, and thereby increasing SV.

Options 2) a decrease in preload, 3) severe blood loss, and 4) a decrease in end diastolic volume (EDV) would lead to a reduced preload and consequently a decreased stroke volume, contrary to the increase observed with exercise. Therefore, only option 1) exercise aligns with the conditions that increase stroke volume.