Heart response to Static and Dynamic exercise

Question 1

When exercising, what is an achievable heart rate in all individuals, regardless of how fit and unfit?

Answer 1

190-200 beats per minute

Question 2

Label the following points on the ECG

Answer 2

Question 3

Explain why an ECG can be important to examine during exercise

Answer 3

• Blood flow at rest to the heart may be adequete in a person with atherosclerosis
• However, when oxygen demands are increased (such as during exercise)
• This may cause an area of the heart to suffer from hypoxia, leading to angina
• The electrical chemical properties of the ischaemic myocardium will be visible on an ECG reading

Question 4

Define venous return, and describe it’s relationship to Cardiac Output

Answer 4

• Venbous return is the flow of blood back to the heart
• Venous return must equal cardiac output when averaged over time, otherwise blood would accumulate in systemic or pulmonary circulation
• Both are tightly controlled:
  
  • For example, if systemic venous return is suddenly increased, right ventricular preload increases, meaning the subsequent stroke volume and thus Cardiac output will increase
  • This is effectively the franks-starling principle in action

Question 5

Define Frank-Starling Law

Answer 5

The ability of the heart to increase the force of contraction and therefore stroke volume in response to changes in vernous return.

Question 6

GIve factors during exercise which can increase venous return

Answer 6

• Muscle contraction - contraction of limbs during normal activity promotes venous return by the muscle pump mechanism
• Respiratory activity - during respiratory inspiration, the venous return transiently increases because of a decrease in right atrial pressure

Question 7

Give the CV major changes that occur during dynamic exercise

Answer 7

• increased HR
• increased respiratory rate, altered respiratory mechanics
• Increased systolic pressure, static(ish) diastolic pressure
• Total peripheral resistance decreases - since VASODIATION occurs at vascular bed of muscles - this can seem surprising since blood pressure increases - what actually increases the blood pressure is the cardiac output which is massively increased, since blood demand from muscles is massively increased. (MAP = CO *TPR)
• Whilst there is increased flow to muscles due to vasodilation of vessels, there is reduced flow to viscera via vasconstriction

Question 8

GIve the major CV changes that occur in static exercise

Answer 8

• Increase in systolic AND diastolic pressure
• Increase in CO and HR
• The increase in pressure is higher than that of static exercise - there are a few reasons for this:
  
  • ​whilst there is some initial vasodilation group that occurs in the active muscle groups (although these can eventually be occluded if maximal force of contraction is high enough), blood vessels not in the target group experience an increase in pressure since they do not dilate but still have more blood flowing through them
• Increase in pressure is proportional to the size of the muscle involved and the duration of the sustained contraction
• When we preform static (isometric exercises), our muscles contract and mechanically compress blood vessels, causing pressure to rise, as well allowing a build up of local metabolites - also increases venous pooling, reducing the venous return - heart compensates for this by increasing HR

Question 9

Describe changes you would expect to see in an exercise ECG

Answer 9

• common change is in ST segment
• Upsloping ST is unusual but usually not pathological
• Horizonalt ST depression and downsloping ST depression are signs of ischaemia