Exercice and Blood Flow through Special Regions

Question 1

Define the Fick Principle.

Answer 1

Cardiac output (L/min) = Rate of O2 consumption (ml/min) / Arteriovenous O2 difference (ml/L of blood)

Question 2

Describe the effect of decreased alveolar O2 on blood flow.

Answer 2

Decreased alveolar O2 reduces local alveolar blood flow (i.e. vasoconstriction, opposite to effect observed in systemic vessels)
– Mediator unknown

Hence, blood flow in lungs prevents flow going to poorly oxygenated areas (?)

Question 3

Identify the areas supplied by the R coronary artery.

Answer 3

– Walls of RA and RV
– SA and AV node
– Posterior part of interventricular septum (proximal portion of AV bundle of His)
– Small areas of LA and LV (in some people)

Question 4

Identify the areas supplied by the L coronary artery.

Answer 4

– Walls of LA and LV
– Most of the interventricular septum
including AV bundle

Question 5

Identify the areas supplied by the great and small cardiac veins.

Answer 5

– Via coronary sinus into right atrium

Question 6

What happens to the coronary blood supply once systole occurs ?

Answer 6

In systole, constriction of that muscle stopping perfusion to the heart

Question 7

Draw and explain the window for coronary flow.

Answer 7

Refer to slide 6 in lecture on “Exercise and Blood Flow Through Special Reasons”

Coronary flow occurs when pressure within the aorta is higher than pressure within the ventricle. This occurs in a window of time within diastole. This can be reduced by:

1) Increasing HR (i.e. shortening diastole)
2) Increased EDV (increases ventricular pressure)
3) Reduced diastolic atrial pressure

Question 8

Identify issues with coronary blood flow. How is this relevant to dynamic exercise ?

Answer 8

• Myocardium cannot function anaerobically (Anaerobic glycolysis increases lactic acid production which mediate pain response in angina)
• Arterioles close mechanically during systole
• ↓ diastolic filling, ↑ oxygen demand and ↑ metabolic demand, during exercise

This is relevant to dynamic exercise because (similar to the myocardium) contraction of skeletal muscle means blood perfusion is restricted to the time the muscle spends relaxed. If insufficient time is spent in the relaxed state, blood supply may not match demand. Lactic acid can also build up in skeletal muscle during anaerobic exercise.

Question 9

How much does the work output of the heart increase during strenuous exercise ?

Answer 9

Work output of heart ↑ 6-9x during strenuous exercise

Question 10

What proportion of coronary blood flow O2 does the heart use at rest ? What must happen if demand is increased ?

Answer 10

– Uses 70-80% of coronary blood flow O2 at rest

↑ Demand must be met by ↑ flow

Question 11

How is coronary flow controlled ?

Answer 11

1) Primary controller is local metabolism
– In proportion to need of cardiac musculature for O2
– Stimulates release of vasodilators (e.g. adenosine)

2) Sympathetic Stimulation
– Indirectly
• Via ↑ heart rate and ↑ contrac tility which ↑ metabolism
– Directly
• High degree of sympathetic innervation
• Role unclear, but may contribute to pathophysiologies

Question 12

Explain how sympathetic stimulation of skeletal muscle arteries.

Answer 12

Sk. muscle arteries is the only place where SNS can cause both constriction AND dilation

Noradrenaline (from sympathetic nerves) causes vasoconstriction of skeletal muscle arterioles via α1 receptors

Adrenaline (from adrenal medulla) causes vasodilation of skeletal muscle arterioles via β2 receptors (will have some effect on alpha 1 but mainly on beta 2) (also open up the airways)

β2 would dominate

Question 13

Describe the effect of dynamic exercice on the following, explaining your answers: 
Skeletal Muscle Blood Flow:
TPR: 
SV:
HR:
CO:
MABP:
Systolic BP:
Diastolic BP:
Pulse P: 
Renal Blood Flow: 
Renin Release:
Vasopressin Release:
Urine Production:

Answer 13

• Skeletal Muscle Blood Flow: Increase. Use of muscles increases their metabolic activity, resulting in the accumulation of local factors that stimulate vasodilation (active hyperaemia). As a result, blood flow in exercising muscles can increase up to 20x normal flow.
• TPR: Decrease (Huge increase in blood supply to skeletal muscle through dilation of blood vessels means TPR decreases. Although blood flow to non-essential organs and tissues may be reduced to help restrict the amount total peripheral resistance drops by, in whole-body intensive exercise (such as running), the increased blood flow to skeletal muscle may outweigh what’s conserved by reducing blood flow to non-essential organs which results in an overall drop in TPR)

-SV: Increases (because 1) Venous return increases due to muscle pump + breathing movements, which may cause a minor increase in EDV)
+ 2) SNS (fight or flight response, change in the way that the heart stores and mobilized calcium, stronger force of contraction))
The contribution of the Frank-Starling mechanism to increased stroke volume may be small.

• HR: Increases (through sympathetic innervation and decreased parasympathetic innervation)
• CO: Increases (Must increase, given the drop in TPR, to maintain MABP)
• MABP: Might get a small increase because of CO increase (changes in cardiac output and total peripheral resistance more or less balance out). Normally, tries to regulate everything around set MABP but now, reset set point.

-Systolic BP: Increases, because
SV has increased (which in itself is enough of a reason), but also SNS stimulation is occurring, resulting in a higher force of contraction.

• Diastolic BP: Decreases, because as a result of decreased afterload due to decreased total peripheral resistance
• Pulse P: Increases (it is the difference between systolic and diastolic BP)
• Renal Blood Flow: Decreases
• Renin Release: Increases due to decreased urine production. Other factor contributing is sympathetic stimulating release of renin.
• Vasopressin Release: Increases, because of the change in blood V and osmolarity, losing V of fluid and salt (through sweating).
• Urine Production: Decrease (determined by lower blood flow to the kidneys during exercise + release of renin and vasopressin)

Question 14

Describe the effect of exercise on cardiac output.

Answer 14

During exercise cardiac output increases from 5L/min to:
-~15L/min (moderate intensity)
- ~30L/min (highly trained athlete, at
maximum intensity)

Question 15

Describe the effect of exercise on the distribution of cardiac output.

Answer 15

– Heart & muscle
• Active hyperaemia (essential area)

– Skin
• Initially, vasoconstriction (non-essential area)
• Then, core temp ↑ detected by hypothalamus results in decreased sympathetic innervation to skin, which increases the blood flow to it (Reactive hyperaemia) (in order to get rid of the heat via sweating and radiation) (results in decrease TPR)

Question 16

Describe the effect of moderate exercise

on MABP, pulse pressure, CO and TPR.

Answer 16

Mean arterial pressure may only increase a small amount (if at all) during moderate exercise

Pulse pressure ↑↑
– Systolic pressure increases due to ↑ stroke volume and ↑ speed of ejection

↑↑↑ Cardiac output
– Due to increased Heart rate (decreased parasympathetic stimulation and increased sympathetic stimulation)
-Also due to increased Stroke volume (increased contractility and Frank Starling mechanism)

↓ Peripheral resistance

Question 17

Identify the factors which promote veinous return during exercise. Why is this significant in exercise ?

Answer 17

↑ Skeletal Muscle Pump Activity
↑ frequency and depth of inspiration
↑ venous tone via sympathetic innervation

Because Cardiac output can only be increased to high levels if venous return is ↑ to the same degree (easier flow from arteries to veins through dilated skeletal muscle arterioles)

Question 18

Describe the feedforward mechanism in place in dynamic exercise.

Answer 18

The cardiovascular system is primed, and then activity is modified to suit the demand of the exercise that follows. This “priming” involves:

1. CO and TPR are adjusted in preparation for activity, by decreasing parasympathetic tone and increasing sympathetic activity (to increase CO and vasoconstriction in abdominal organs and kidneys)
2. Antidiuretic hormone release is stimulated as part of this feedforward control to promote retention of water and decrease urine production
3. Resetting of baroreceptors upwards, to mute the effect of increased arterial pressure on the normal reflex mechanisms they would otherwise induce

Question 19

Which of the changes in parameters are different in static exercise (compared to dynamic exercise) ?

Answer 19

In static exercise, it is generally the same but the following parameters change:

1. TPR increase (because lifting heavy weights (a) increases venous return to the heart and (b) occludes arteries and prevents tissue perfusion). Even though local factors may try to cause dilation of arterioles, the physical compression caused by muscle contraction prevents this from occurring)
2. CO still increases (because as local factors accumulate in greater and greater concentration, metabotropic receptors cause an increase in the exercise reflex controlling cardiac output and push this higher. The result is a big increase in heart rate, which increases cardiac output alongside the increased total peripheral resistance)
3. Diastolic BP increases (because of occlusion of downwards vessels meaning increased TPR)
4. Systolic BP still increases (because increased veinous return, resulting in increase stroke V which increases systolic P)
5. MABP increases massively (due to increases in both systolic and diastolic P)