L4.2 Cardiovascular Responses

Question 1

What is the Fick principle?

What is MAP determined by?

Answer 1

VO2 = Q x (CaO2 (arterial O2 content) – C­vO2 (venous O2 content))

MAP = Q x TPR

Question 2

What are the cardiovascular responses to exercise?

Answer 2

• ↑Q → ↑O2 supply to skeletal & cardiac muscles
• Facilitate CO2 & heat removal
• Maintain mean arterial BP

Question 3

What is the relationship between O2 consumption and Q during exercise?

Answer 3

• ↑exercise → ↑Q & O2 uptake
• Every ↑L of O2 uptake → need ~↑5L of Q

Question 4

Where is Q directed/constricted/maintained during exercise?

Answer 4

• ↑Q → muscles (v.↑↑), skin (↓at max output), others – e.g. heat (↓at max output)
• ↓Q → splanchnic, renal
• ↔Q → Cerebral (blood diverted from skin and others at max output to ↔)

Question 5

How is hyperaemia (increase blood flow) achieved during exercise?

Answer 5

• Metabolic vasodilators from contracting skeletal muscles, endothelium &/or RBC
• Muscle pumps (1st muscle contraction → ↑Blood flow) → maintains venous return
• Conducted vasodilation
  
  • Dilates large arteries leads to dilation of distal capillaries
• Functional sympatholysis
  
  • Blunts effect of sympathetic nerves (↑vasodilation)
  • Desensitises sympathetic nerves

Question 6

What are the vasodilator metabolites?

Answer 6

• K+, H+, adenosine, ATP (From muscles/RBC)
• Reactive Oxygen Species (ROS)
• NO, prostacyclin, PGE2

Question 7

What are the cardiovascular responses from training?

Answer 7

• ↑VO2 max, due to ↑CO
• A-VO2 diff not that big

Question 8

What is the BP response to exercise?

Answer 8

• Not markedly different btw trained & untrained
• Systole → influenced by Q
• Diastole → influenced by TPR
• ↑MAP → ↓HR (Baroreflex)
• Baroreflex is reset during exercise → allows a higher output
  
  • Baroreflex reset by central command

Question 9

What is the A-VO2 difference during exercise?

Answer 9

• ↑exercise → muscle use ↑O2
  
  • At high intensity exercise → mixed CvO2 becomes closer to CaO2
  • A-VO2 difference becomes smaller

Question 10

What happens to CV during prolonged exercise?

Answer 10

• ↓SV (main determinant) → ↓CO
• ↓skin blood flow
• ↑TPR (counter drop in Q)
• ↑HR (counters ↓SV)
• ↓MAP & BV

Question 11

What is the CV drift?

Answer 11

• ↑in HR → contributes to O2 drift
• Hyperthermia (↑temp → SA node depolarise more quickly)
• Dehydration (losing blood volume)
• ↑ plasma [A] (↑HR, related to dehydration & hypoglycaemia)
• Peripheral displacement of BV due to cutaneous vasodilation

Question 12

How does autonomic innervations control CV parameters at different exercise intensities?

Answer 12

• Initial ↑HR due to ↓parasym activity
• Secondary ↑intensity → ↑HR from ↑sym activity

Question 13

What is the effects of training on CV output?

And what are the microvascular adaptations?

Answer 13

• ↑Q by:
  
  • ↑BV → ↑SV (major training adaptation) (from frank-starling mechanism → ↑SV from ↑BV)
  • ↑heart size → ↑L. ventricular mass & size
  • Heart more sensitive to adrenergic stimulation
• ↑capillary density & recruitment (major training adaptation) → ↑O2 delivery & exchange in muscles