Stroke volume Flashcards
How much can CO increase during exercise
4-5 normals
7 athletes
Discuss the factors regulating stroke volume
Preload: during exercise there is an increase in venous return due to control of blood flow and muscular pumps. This causes an increase stretch on the cardiac chambers, this increase in stretch directly increases the force of contraction known as the frank-starling law mechanism.
Cardiac muscle fibres rest in a slightly shortened position, length tension relationship.
Contractility: this is independent of muscle stretch and EDV and is the contractile strength at a given length.
It is caused by an influx of calcium into the sarcoplasm which promotes cross bridge activation, increasing force of contraction. Chemicals that cause this effect are called positive inotropic factors (epinephrine and norepinephrine)
Chemicals that the block the effects of these by blocking calcium channels are called negative inotropic doctors. (Beta blockers)
Afterload: The pressure that needs to be overcome in the pulmonary and aortic trunk in order for blood to be expelled. Hypertension will increase this as it reduces the ventricles ability to expel blood during systole, ESV will increase.
