Stroke Volume responses to exercise in a unique populations cardiovascular physiology.

Question 1

Compare the stroke volume responses in the individuals with quadriplegia and heart transplantation. How are they different and what accounts for this difference?

Answer 1

The individual with quadriplegia has no motor control below the level of the lesion (no muscle venous pump), and therefore venous return does not increase with exercise. In contrast, the individual with heart transplantation is able to increase stroke volume because of a functioning muscle venous pump. This illustrates the importance of the Frank-Starling mechanism. In fact, the individual with heart transplantation has a stroke volume comparable to that of the sedentary individual.

Question 2

Compare the stroke volume response in the sedentary individual with the response in the
individual with heart transplantation. What accounts for the similarity in stroke volume?

Answer 2

Stroke volume response to exercise is determined by end-diastolic volume, cardiac sympathetic efferent activity, circulating catecholamines, and afterload. The muscle venous pump is functioning normally in both individuals, and therefore the stroke volume response to exercise is initially similar; however, the maximum stroke volume achieved in the individual with heart transplantation is lower because of the absence of cardiac sympathetic efferent activity.

Question 3

Compare the stroke volume responses in the sedentary and athletic individuals. How are they different and what accounts for this difference?

Answer 3

The athlete has a much higher stroke volume at similar work loads. The athlete has a larger ventricular volume and slower heart rate, which allows for a greater cardiac filling during diastole
(greater end-diastolic volumes); therefore the stroke volume response in the athlete is much greater compared with that of the sedentary individual.