Muscle Blood Flow: Lecture 6&7

Question 1

Define The Oxygen-Conforming Response

Answer 1

Refers to the rapid adjustment of force production at a given motor neuron activation to match changes in muscle oxygenation

Question 2

Describe the relation between perfusion and force production

Answer 2

When muscle perfusion is reduced(i.e. thus reducing muscle oxygenation), force production is also reduced

Question 3

When must motor neuron activation absolutely increase?

Answer 3

During exercise where muscle oxygenation is reduced AND force production must be maintained, motor neuron activation must increase to compensate
–Equals need for greater recruitment and greater metabolite production!

Question 4

To what expense does the increase of muscle activation happen, when PcellO2 is low?

Answer 4

At the expense of disturbances to muscle metabolic and contractile function (i.e., accumulation of metabolites leading to fatigue) as well as symptoms of muscular fatigue/discomfort.

Question 5

Effects of muscle oxygenation (PcellO2) on muscle metabolism & contractile function

Answer 5

H+ (from lactic acid): Inhibits Ca2+binding to troponin = Fatigue

Pi: decrease in SR release of Ca2+; decrease in myofibrillar Ca2+ sensitivity; and inhibits cross-bridge formation = Fatigue

Question 6

How can motor drive be increased to maintain muscle production? (voluntary ex)

Answer 6

-Self encouragement
-Outside encouragement
- Nerve stimulation (has to be outside stimulation???)
albeit at the expense of higher ratings of perceived exertion

Question 7

What does ADP and Pi stimulate?

Answer 7

ADP and Pi stimulate glycolysis = increase lactic acid production

Question 8

Simply Define Hypoxia, Normoxia, Hyperoxia

Answer 8

Hypoxia: Low oxygenation
Normoxia: Normal oxygenation
Hyperoxia: High oxygenation

Question 9

Compare power output, time to exhaustion, PCr & Pi levels in normoxia, hypo/hyperoxia (Hogan et al)

Answer 9

Compared to normoxia

-power output achieved & time to exhaustion (i.e.,exercise performance) was DECREASED with hypoxia INCREASED with hyperoxia
-BUT exhaustion occurred at the same “muscle metabolic state” across FiO2 trials([PCr] and [Pi] levels were similar at end-exercise)

Question 10

What will happen to [PCr] and­
[Pi] and [ADP] when theres a decrease in PcellO2 but we need to maintain
V’O2 and power output

Answer 10

DECREASE of [PCr] and­ INCREASE of [Pi]&[ADP] to maintain V’O2 and power output

Question 11

Which factors stimulate glycolysis and what reactions does it result in?

Question 12

How does an Increase in [Pi] and [H+] affect contractile function?

Answer 12

INCREASED [Pi] and [H+] combine to DECREASE muscle force production and ­INCREASE the rate of development of skeletal muscle fatigue (performance limitation - i.e., inability of muscle to produce force required to perform a given activity).

Question 13

Why/when do ratings of perceived exertion increase?

Answer 13

As the skeletal muscle(s) fatigue and muscle force generating capacity DECREASES, neural drive to the contracting muscle(s) must INCREASE (i.e., recruit more and larger motor units) to MAINTAIN any given power output à ­ ratings of perceived exertion.

Question 14

Define blood flow

Answer 14

The volume of blood travelling through a blood vessel, organ or entire body through time

BLOOD FLOW (BF): VOLUME/TIME

Question 15

General effect of metabolites on blood flow during exercise

Answer 15

Metabolites cause VASODILATATION

Question 16

What counteract is necessary when metabolites cause vasodilation in certain parts of the body during exercise?Why?

Answer 16

Vasoconstriction elsewhere or else high risks of fainting because of low BP while blood flow is still high

Question 17

Name examples of metabolites

Answer 17

CO2
Lactic Acid (La+ + H+)
K+
ATPs
O2
Temperature

Question 18

Define BF response

Answer 18

Dynamic response of O2 delivery to a step increase in exercise intensity

Question 19

Feedforward VS Feedback mechanisms

Answer 19

Feedforward: mechanisms that happens to cause a chain of reaction
Feedback: loop

Question 20

Name different phases of BF response profile

Answer 20

Rest
Phase 1 (0-20sec): Feedforward
Phase 2 (20-…sec): Feedback

Question 21

Which phase of BF response profile is mechanically induced and why/how? Chemically induced?

Answer 21

Phase 1 is a feedforward mechanism mechanically induced by muscle pump which causes rapid vasodilation

Phase 2 is a feedback mechanism chemically induced by local metabolites (plateau observed)

Question 22

How does the muscle pump increase MBF?

Answer 22

The muscle pump increases MBF by increasing the pressure gradient between the arteries and veins with each muscle contraction.

Question 23

When is muscle pump ineffective?

Answer 23

Muscle Pump is ineffective when the exercising muscle is above heart level because the veins are already empty and, therefore, the arterial-venous pressure gradient cannot be increased.

Question 24

What correlation does “Feedforward” vasodilation dilation have with tension development & motor unit recruitment?

Answer 24

It is in proportion to muscle activation (i.e., tension development & motor unit recruitment)

Question 25

Define shear stress

Answer 25

Force of the flowing blood on the endothelial surface of the blood vessel

Question 26

What does shear stress stimulate?

Answer 26

Shear Stress is the stimulus for endothelial production & release of Nitric Oxide (NO) – a potent vasodilator substance that causes rapid dilation of arterioles
stimulataes FMD

Question 27

How muscle vascular conductance & smooth muscle tone affect MBF?

Answer 27

INCREASED muscle vascular conductance, DECREASED smooth muscle tone = an ­ INCREASED MBF

Question 28

When is K+ present in regulation of O2 delivery during exercise?

Answer 28

In Feedforward Regulation of O2 Delivery during Exercise K+ is released from muscle fibre as part of action potential; thus, K+ is immediately present causing rapid vasodilation.

Question 29

Which ion causes rapid vasodilation in Feedforward regulation of O2? What kind of muscle died it act upon?

Answer 29

K+ is released from muscle fibre in proportion to muscle activation as part of action potential

K+ causes smooth muscle relaxation

Question 30

In proportion to what is K+ released during Feedforward Regulation of O2 Delivery during Exercise?

Answer 30

Released in proportion to muscle activation

Question 31

Define the variables of MBF = ∆P x MVK and wether they are increase mechanically or chemically

Answer 31

∆P: Muscle Pump (↑∆P mechanically)

VK: Rapid Vasodilators (↑ VK chemically)

Question 32

Which phase of Regulation of O2 Delivery during Exercise is defined as follows:

• Onset delayed
• Slower adaptation
• Steady-state achieved

Answer 32

PHASE 2: FEEDBACK

Question 33

What is considered the “error signal” of Feedback Regulation of Exercising MBF?Wgat does that entail?

Answer 33

The [metabolites] (concentration of metabolites) which indicates mismatch between metabolism and blood flow

Question 34

What does the [metabolites] reflect? What does it dictate?

Answer 34

The [metabolites] reflects the relationship between O2 demand (work rate-metabolism) & O2 supply (MBF)

It is not the metabolites that are being regulated

[metabolites] dictates the movement of metabolites into and out of the interstitial space.

Question 35

In Feedback Regulation of Exercising MBF what determines production & clearance of metabolites ?

Answer 35

Production = determined by rate of metabolite production (intensity dependent)

Clearance = determined by muscle blood flow

Question 36

What are the consequences of reductions in muscle blood flow….?

Answer 36

DECREASE metabolite clearance & substrate delivery (like O2)

Question 37

How does blood flow change during and after muscle contractions?

Answer 37

During: MBF Increases & decreases with each muscle contraction (feedforward)

After: Blood flow remains high for a few seconds but then returns to normal during the next few minutes (feedback)

Question 38

How does the feedforward mechanism regulate the changes in muscle blood flow during contractions?

Answer 38

MBF Increases & decreases with each muscle contraction

Question 39

How does the feedback mechanism regulate the changes in muscle blood flow during contractions?

Answer 39

Blood flow remains high for a few seconds but then returns to normal during the next few minutes