Cardiovascular integration in exercise and mental stress Lecture 3

Question 1

Describe the changes in dynamic exercise

Answer 1

Requires an increase in ventilation and cardiac input O2 consumption is graded with work load up to a maximum the anaerobic threshold Recovery after exercise to repay the oxygen debt

O2 consumption

• Gradually rises until plateau (DO2 crit)
• Upon stopping there is an O2 debt where ventilation must be kept at the same rate to recover
• Recovery depends on whether anaerobic was used
• Increase in O2 consumption requires an increase in ventiliation and cardiac output to get O2 taken up in lungs to exercising muscle.

Shear Rate / Stroke volume / CO

• Increase progressively
• SV is dependent on ventricular contractility and venous return - this is greater during exercise due to skeletal muscle/respiratory pump

mABP

• Progressive increase in mABP and in systolic pressure with graded dynamic exercise
• Accompanying decrease in diastolic pressure
• refelcts the progressive vasodilation happening in the skeletal muscle.
• increase in muscle blood flow, increasing and decreasing in phase with relaxation and contraction

Question 2

Describe the local effects of exercising muscles on the cardiovascular and respiratory system

Answer 2

Exercise hyperaemia- local vasodilation K, P, adenosine released by muscle into interstitial space Graded with exercise intensity PGI2, NO from endothelium Causes relaxation of vascular smooth muscle Counteracted by mechanical influence of contracting muscles

Exercise hyperaemia

• K+, Pi and adenosine released by muscle into interstitial space (during action potential) - graded with excerise intensity.
• PGl2 and NO released from endothelium - due to increased blood flow and shear stress
• All cause relaxation of VSM -> vasodilatation

Counteracted by mechanical influences of contraction:

-So increase in blood flow is rhythmic in dynamic exercise - tends to decrease TPR, then DP. Skeletal pump helps to maintain or increase EDV.

Question 3

What is the exercise reflex?

Answer 3

Afferent activity from metaboreceptors/mechanoreceptors -> medulla -> STLR (subthalamic locomotor region) in hypothalamus - prododuces a pttern of response.

Reflex responses:

• Increase respiration (diaphragm and intercostal activity)
• Increase HR and contractility (increased sympathetic, decreased sympathetic)
• Increased sympathetic NA activity to cause vasoconstriction in GIT and kidney. Leads to increased TPR
• Increase set point of baroreceptor reflex

Question 4

Describe the central command involved in dynamic exercise

Answer 4

Subthalamic locomotor region (SLR) in the hypothalamus

Exercise integrating area received inputs from the cortex

Result in increase respiration, HR, CO and vasoconstriction in GIT

Also increase set point of baroreceptors

Question 5

Describe static exercise

Answer 5

Graded increase in SP and DP

• Reflex increases in respiration, HR and vasoconstriction (muscle/GIT/kideny/skin - increase in TPR and mean ABP
• As TPR goes up muscle contraction impairs muscle blood flow
• Exercise hyperaemia still happens after contraction - even stronger due to metabolites trapped in contracting muscle causing greater stimulation of metaboreceptors
• Exercise reflex is greater for given workload than during dynamic exercise.
• Exercise hyperaemia occurs after static exercise- mean ABP may then fall

Question 6

What is the fight or flight response?

Answer 6

• Prefrontal cortex senses threat, feed information to amygdala, hypothalamus and dorsal medulla
• These act to inhibit the Baroreceptor reflex at the NTS, allowing ABP to reach very high values
• These also activate the ventral medulla which:
• Increases respiration
• Decreased para / increased symp to the heart via NA/RVLM to increase HR and CO
• Increased vasodilatation to skeletal muscle due to increased beta2 adrenoceptor activation and decreased symp. NAd activity to muscle (both via RVLM)