Cardiovascular/Cardiorespiratory (lectures 11-13)

Question 1

how is the body able to maintain relatively constant levels of oxygen
and carbon dioxide when metabolic rate is increased during exercise?

Answer 1

• by matching tissue perfusion with the increase tissue metabolic rate (increasing blood flow through tissues as tissue demand increases)
• matching minute ventilation to metabolic rate (increasing oxygen coming into the body to support the increased perfusion, and increasing CO2 offloading)

Question 2

What is the symbol for cardiac output and its unit?

Answer 2

Q, measured in L/min

Question 3

What is the relationship between workload and perfusion?

Answer 3

as workload increases, perfusion increases proportionally

Question 4

by what mechanisms does blood flow to a tissue vary according to
metabolic need?

Answer 4

• increase cardiac output 4-7x (not sufficient to meet 20-30x increase in metabolid demand on its own)
• a variety of vasoactive mechanisms - act by changing the diameters of blood vessels to optimise perfusion to precisely match the demand of each tissue and shunt blood towards active tissues.

Question 5

What was the indicator that increased perfusion due to workload is locally mediated?

Answer 5

subjects with severed sympathetic nerves also had a linear relationship between perfusion & workload

Question 5

What is reactive hyperaemia?

Answer 5

the transient relative excess of blood in a tissue immediately following disruption of blood flow

Question 6

What is the equation for cardiac output?

Answer 6

Q = SV (L) x HR (bpm)

Question 7

What is the Frank-Starling law of the heart?

Answer 7

stroke volume increases as cardiac filling increases (when all other factors equal).
ie more blood in, heart stretches more,more contraction force, increased stroke volume.
Similarly, increased output -> increased return = higher preload, so do get some increase in BP from Q increase