Chapter 41, Problem 6TY

In the animal iii question 5, what could explain why the stroke volume remained normal?

1. Stroke volume is not usually affected by hemorrhage.
2. The heart muscle cannot contract more forcefully than it normally does at rest.
3. The hemorrhage may have been so severe that venous return to the heart cannot be significantly increased.
4. It is a compensatory response to prevent blood pressure from increasing too much.
5. Stroke volume increases only when the heart rate does not change from normal.