Map the acute responses that cause stroke volume to increase during large muscle
ID: 53464 • Letter: M
Question
Map the acute responses that cause stroke volume to increase during large muscle cardiorespiratory endurance exercise.
Box at the top of map: Initiation of Exercise.
Box at the bottom of the map: Increase in Stroke Volume
Include all the factors listed below on the map.
Afterload
Blood Pressure Gradient (left ventricle to aorta)
End diastolic volume
Left ventricular contractility
Left ventricular contraction strength
Muscle arteriole auto-regulation
Muscle arteriole radius
Muscle arteriole vasodilation
Peripheral resistance(include formula)
Preload
Respiratory Pump Effect
Skeletal muscle pump
Venoconstriction
Venous return
You must include the direction of change (i.e. – either increase or decrease in afterload) for each of these factors.
Explanation / Answer
The stroke volume is detremined by three factors preload, contractility and afterload.
1. The increase in stroke volume results from an increase in venous return, which, in turn, increases the left ventricular end–diastolic volume (LVEDV) which is also known as preload. An increase in the left ventricular end–diastolic volume and a decrease in the left ventricular end–systolic volume (LVESV) account for the increase in stroke volume during light to moderate dynamic exercise.
2. The Total peripheral resistance (TPR) decreases owing to vasodilation in the active muscles. The decrease in TPR can be calculated by the formula TPR= MAP/Q where MAP is mean arterial pressure and Q is the cardiac output.
3. The reduction in stroke volume during high-intensity contractions is probably the result of both a decreased preload and an increased afterload.
4. Stroke volume is less during upper-body exercise than during lower-body exercise because of the absence of the skeletal muscle pump augmenting venous return from the legs.
5. The increase in stroke volume results from an increase in venous return.
6. The increase in heart rate is proportional to the decrease in stroke volume, so cardiac output is maintained during exercise.