G6i / 20B11: Describe the changes in the circulatory system that occur during exercise.

20B11: Exam Report

Describe the changes in the circulatory system that occur during exercise.

22% of candidates passed this question.

This is an applied physiology question. Better answers categorised the changes in some manner and included a measure of the degree of change as applicable (e.g., what increases, what decreases and what may stay the same). The question was to describe the changes so that the detail behind the mechanisms enabling these changes to occur was expected (e.g., neurohumoral, local factors). Marks were also awarded for any regional variation that occurs.

G6i / 20B11: Compare and contrast rocuronium and cisatracurium

Definition

Exercise = strenuous physical activity where there is increased metabolic activity leading to increased requirement for energy and oxygen  

CVS Parameters

CVS changes to accommodate and compensate for such increase in metabolism

Parameter

Degree of Change

Mechanism of Change

Cardiac Output

Degree of Change

Increase up to 4-5 folds

CO plateaus at near-maximal workload 

Mechanism of Change

Cardiac output can increase up to 20L/min

Due to both increase in HR (mediated by SNS activation) and SV and decreased afterload

With increasing workload HR increases but SV decreases due

Heart Rate

Degree of Change

Increases

Max HR = 220-age

Mechanism of Change

Increases due to SNS activation -> increased circulating catecholamines

Stroke Volume

Degree of Change

Increases

Mechanism of Change

Initially increases – up to 40-60% of the person’s VO2 max

After which it reaches a plateau 2’ to increased heart rate

Contractility

Degree of Change

Increases

Mechanism of Change

Increased HR -> increased contractility (treppe effect)

Activation of sympathetic nervous system -> increased contractility  

CVP

Degree of Change

Increases

Mechanism of Change

Cardiac output and venous return are equally matched

Increased blood returned to the heart 2’ to increased cardiac

SVR

Degree of Change

Decreases

Mechanism of Change

Vasodilation 2’ to muscle hypoxia and accumulation of metabolic byproducts

Increased concentration of vasoactive mediators – NO/ATP/prostaglandins

Activation of B2 receptor in skeletal muscles -> further vasodilation

SBP

Degree of Change

Increases

Mechanism of Change

Increases due to increase in stroke volume and Velocity of

DBP

Degree of Change

Decreases

Mechanism of Change

Due to decrease in peripheral vascular resistance

MAP

Degree of Change

Increase

Mechanism of Change

Increases slightly

Increase in cardiac output > decrease in peripheral vascular

Pulse Pressure

Degree of Change

Widens

Mechanism of Change

Due to changes seen in SBP & DBP

Coronary Blood Flow

Degree of Change

Increases

Mechanism of Change

Due to increase in perfusion pressure of the coronary arteries + coronary vasodilation as mediated by increased catecholamines

Flow is coupled with increased metabolism

Skeletal Muscle Blood Flow

Degree of Change

Increases

Mechanism of Change

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

Author: Zoe Guo