Canonical Question
CVS – Responses
Master answer
Definition:
Exercise = Strenuous physical activity where there is increased metabolic activity leading to increased requirement for energy and oxygen
CVS changes to accommodate and compensate for such increase in metabolism
Normal parameters at rest:
| Cardiac output | C.O. | 5L/min |
| Heart rate | HR | 60-100 bpm |
| Systemic vascular resistance | SVR | 1600 dynes.s.cm-5 |
| Stroke volume | SV | 70mls |
| Blood pressure | BP | 120/80 |
| Central venous pressure | CVP | 0-5mmHg |
Changes to CVS parameters:
| Cardiac output | ↑ | Can increase up to 4-5 folds CO plateaus at near-maximal workload |
| HR | ↑ | Max HR = 220-age Increases and plateaus at max |
| SV | ↑→↓ | Initially increases, then decreases due to diminishing diastolic time |
| Contractility | ↑ | Increased HR → increased contractility (treppe effect)Activation of sympathetic nervous system → increased contractility |
| CVP | ↑ | Increases |
| Systolic BP | ↑ | Increases |
| Diastolic BP | ↓ | Decreases |
| MAP | ↑ | Increases slightly |
| Pulse pressure | ↑ | Widens |
| PVR | ↑ | Decreases overall |
Redistribution of blood flow
- Increased muscle activity -> increased o2 demand
- Regional vasodilation
- Increased local concentration of metabolites ie Co2, lactate, K+
- Vasoactive mediator released by endothelium ie NO, ATP
- Sympathetic stimulation -> B2 adrenoceptor activation
- Overall: decrease in vascular resistance to muscles -> increased blood flow
- Corresponding vasoconstriction of viscera and skin
Increase in cardiac output
- Cardiac output can increase up to 0L/min
- Due to both increase in HR and SV and decreased afterload
- With increasing workload HR increases but SV decreases due to dec diastolic time
Guo 2021
Exam appearances
| Exam | Exact wording | Relationship | Success |
|---|---|---|---|
| 2020B Q11 | Describe the changes in the circulatory system that occur during exercise. | historical_member | — |