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Cardiovascular system > Coordinated response of the CVS > Flashcards

Coordinated response of the CVS Flashcards

1
Q

What does the cardiovascular system respond to?

A

Physiological conditions

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2
Q

What is the principle of adaptation of the CVS?

A

Integration of responses due to lots of small changes

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3
Q

Examples of different activities that require the integration of the CVS

A
  • Exercise
  • Diving
  • Fight or flight
  • Sleeping
  • Gravity
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4
Q

What is orthostasis?

A

Standing up

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5
Q

How does the cardiovascular system change according to the effect of gravity during orthostasis?

A
  • Blood pressure falls at first: postural hypotension, lack of blood flow to brain which could lead to fainting
  • Quickly recovering: due to homeostatic mechanisms such as baroreflex
  • Baroreflex integrates three smaller changes
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6
Q

What are the three small changes that the baroreflex integrates during Orthostasis?

A
  1. Heart rate
  2. Heart contractility
  3. Total peripheral resistance
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7
Q

What is the arterial pressure gradient and how is this beneficial in terms of blood flow?

A

Arterial pressure gradient is 95-185 mmHg, this helps blood flow from the feet to the heart

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8
Q

What is the Arterial blood pressure in the head (lying down)?

A

95 mmHg

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9
Q

What is the Arterial blood pressure in the chest (lying down)?

A

100 mmHg

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10
Q

What is the Arterial blood pressure in the feet (lying down)?

A

95 mmHg

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11
Q

What is the Venous blood pressure in the head (lying down)?

A

10 mmHg

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12
Q

What is the Venous blood pressure in the chest (lying down)?

A

3-5 mmHg

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13
Q

What is the Venous blood pressure in the feet (lying down)?

A

10 mmHg

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14
Q

What is the Arterial blood pressure in the head (standing up)?

A

60 mmHg

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15
Q

What is the Arterial blood pressure in the chest (standing up)?

A

95 mmHg

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16
Q

What is the Arterial blood pressure in the feet (standing up)?

A

180 mmHg

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17
Q

What is the Venous blood pressure in the head (standing up)?

A

-35 mmHg

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18
Q

What is the Venous blood pressure in the head (standing up)?

A

0-5 mmHg

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19
Q

What is the Venous blood pressure in the chest (standing up)?

A

0-5 mmHg

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20
Q

What is the Venous blood pressure in the feet (standing up)?

A

90 mmHg

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21
Q

Describe the effects of gravity on blood pressures during Orthostasis?

A
  • The pressure at the head and feet is the same when lying down: no real pressure gradient
  • Upon standing up, the blood pools at the legs: lower pressure here than at the heart
  • Blood therefore flows from the feet to the heart
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22
Q

Bernouilli’s law in terms of Orthostasis

A

Blood flow = pressure energy + potential energy + kinetic energy

  • Increased potential energy at the heart level vs the feet = increased kinetic energy of ejected blood
  • Potential energy is the energy due to gravity
  • Total energies means that the blood therefore flows from the feet to the heart
  • Therefore not just due to Darcy’s law, which focuses just on pressure
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23
Q

What happens at the feet of people with heart failure?

A

Poor perfusion

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24
Q

What is the high pressure in the venous system due to?

A

Hydrostatic pressure

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25
Q

How is pressure calculated for fluid in a solid tube?

A 
Pressure = p x g x h 
p= fluid density
g= gravitational acceleration constant 
h= height 
- The pressure is higher at the bottom of the tube.
26
Q

Describe gravity induced high venous blood pressures

A
  • Veins are examples of tubes with compliant walls
  • Veins are compliant capacitance vessels: there is lower pressure than on the arterial side
  • The blood causes the veins to distend, which is why blood pools at the feet
27
Q

How does Orthostasis cause Hypotension?

A
  • Venous pooling of 500 ml in the legs reduces the blood returning to the heart
  • > This means that less blood will fill the left ventricle
  • > The left ventricle then gets stretched a bit less and contracts more softly
  • > Decreased end diastolic volume
  • > Decreased stroke volume
  • > Decreased cardiac output
  • > Decreased perfusion of the brain
28
Q

How is cardiac output increased whilst lying down?

A

The blood is evenly distributed in the veins

  • > Increased central venous pressure
  • > Increased end diastolic volume
  • > Increased stroke volume
  • > Increased cardiac output
29
Q

Describe the reflex response to Orthostasis

A
  • Stand up, less blood goes to he heart and so there is less stimulation (unloading) of the baroreceptors in the aorta and carotid
  • Afferent fiber activity is lowered
  • Neurons in the Nucleus Tractus Solitarius (NTS) are stimulated in the medulla oblongata
  • This switches off inhibitory nerves that go from Caudal Ventrolateral Medulla (CVLM) to Rostral Ventrolateral Medulla (RVLM)
  • This results in the RVLM being more active sending efferent signals to the heart and arterioles
  • This leads to:
    • Increased sympathetic drive to the SA node and increased heart rate
    • Myocardium increased contractility
    • Vasoconstriction (arterioles, veins) increases TPR
    • Less vagal parasympathetic activity to the SA node: overall increase in blood pressure
30
Q

What are five ways that postural hypotension can be made worse?

A
  1. a-adrenergic blockade/generalized sympathetic blockade/other drugs that reduce vascular tone: e.g. side effect with voltage gated calcium channels used to treat hypertension, angina
  2. Varicose veins: Imp[airs venous return so that blood pools in legs
  3. Lack of skeletal muscle activity: Due to paralysis or forced inactivity, e.g. long term bed rest, soldiers that are on guard
  4. Reduced circulating blood volume: e.g. Haemorrhage
  5. Increased core temperature: peripheral vasodilation, less blood volume available, e.g. standing up after bath
31
Q

Describe the effect of microgravity (space) on the cadriovascular system

A
  • There is no difference in pressures when lying down or standing up in space
  • The blood pools are the centre due to redistribution of blood into the chest region
  • SUMMARY:
    • Normal slight pooling in the lower body
    • Fluid shifts towards the head in microgravity
    • Adaptation is reduces blood volume and pressure
    • Return to gravity postural hypotension
32
Q

What are the initial effects of microgravity (space) on the cardiovascular system?

A
  • Initially blood doesn’t pool in the feet and returns to the heart easily, this increases atria/ventricle volume and so preload and cardiac output.
  • This is sensed by cardiac mechanoreceptors leading to a reduction in sympathetic activity
  • This reduces ADH and increases atrial natriuretic peptide (ANP), there is increased glomerular filtration rate (GFR) and reduced RAAS. Overall the blood volume is reduced by 20%
33
Q

What are the long term effects of microgravity (space) on the cardiovascular system?

A
  • Less blood volume
  • Reduced stress on the heart
  • Heart reduces in muscle mass
  • General drop in blood pressure
34
Q

What occurs on return to gravity from microgravity?

A
  • Severe postural hypotension
  • much lower blood volume and smaller heart
  • the baroreceptor reflex cannot compensate
35
Q

Describe coordinated cardiovascular responses to exercise

A
  • Integrated by central command in the brain
  • Anticipation of exercise will cause some changes to be initiated
  • Once exercise commences there is feedback from the muscles via mechanoreceptors and metaboreceptors
  • The receptors increase sympathetic activity and reduce vagus circulation
36
Q

Cardiovascular responses to dynamic exercise

A

Constantly shortening and relaxing with lots of different muscle groups involved

37
Q

Cardiovascular responses to static exercise

A

One specific muscle group is being worked without constant movement

38
Q

By how much does oxygen uptake by pulmonary circulation increase during strenuous exercise?

A

10-15 times

39
Q

Describe how the integration of several small adaptations can create an overall large response to exercise

A

During strenuous exercise, oxygen uptake by pulmonary circulation increases 10-15 times:

  • Heart rate is increased: x3 (60 bpm to 180 bpm)
  • Stroke volume is increases: x 1.5 (70 ml to 120 ml)
  • Arteriovenous O2 difference: x 3 (gradient + Bohr effect)

3 x 1.5 x 3: 13.5 times

40
Q

Describe the graph that shows increase in O2 uptake from the lungs

A
  • Increased blood flow and greater O2 gradient: increased lung uptake
  • Arterio-venous oxygen difference reaches a plateau at high exercise levels
41
Q

Describe the graph that represents increase in cardiac output during exercise

A
  • Heart rate increase is the main factor at high workloads
  • Increase in SV reaches maximum value
  • Plateau phase on Starling’s curve and maximum contractility
42
Q

Describe exercise induced tachycardia

A
  • The brain is the central command (ready for exercise) and muscle mechanoreceptors (fast feedback on exercise being carried out)
  • This causes vasodilation of vessels in the muscles, which increases blood flow
  • Vagal tone in the SA and AV nodes is decreased
  • Sympathetic activity at the SA and AV nodes is increased
43
Q

How is maximum heart rate calculated?

A

220 - age

approximate increase 65 to 95 (x3)

44
Q

Effect of increasing cardiac output

A

Cardiac output increased by 4.5 x (5 to 22 l/min) = Heart rate (3x) x Stroke volume (1.5x)

45
Q

Describe exercised induced stroke volume

A
  • Increasing sympathetic activity 70 ml to 150 ml for 30 year old male= 1.5x
  • Increased end -diastolic volume:
    • Increases venous return/CVP through veno-constriction
    • Increases sympathetic activity and calf muscle pump which activates Starling’s law and increases preload
  • Faster ejection
    • Increases contractility by sympathetic activation of B1 receptors (inotropic increase in Ca2+)
  • Decreased end-systolic volume: increases ejection fraction
  • Accounts for increase in stroke volume
  • Increases contractility by sympathetic activation of B1 receptors and Starling’s law
46
Q

What is the size of increase in cardiac output from the resting state to when the leg is exercising in the Leg muscle?

A

x 9

47
Q

What is the size of increase in cardiac output from the resting state to when the leg is exercising in the Heart?

A

x 2

48
Q

What is the size of increase in cardiac output from the resting state to when the leg is exercising in the Skin?

A

x 3

49
Q

What is the size of increase in cardiac output from the resting state to when the leg is exercising in the Brain?

A

There is no increase in cardiac output, it stays the same

50
Q

Explain the increase in cardiac output in the leg muscle from the resting to exercising state

A
  • There is a fall in the local resistance due to metabolic hyperaemia vasodilation
  • Local sympathetic response and B2-mediated vasodilation via circulating adrenaline
  • B2 receptor expression is high in skeletal muscle and coronary artery
51
Q

What happens to blood pressure when cardiac output is increased by x 4.5?

A
  • There is obviously a large increase in cardiac output
  • There is a relatively small increase in mean blood pressure due to dilated skeletal muscle arterioles decreasing TPR
  • There is a large decrease in TPR
52
Q

What is the need for compensatory vasoconstriction of non-essential circulations?

A
  • They prevent hypotension due to exercise-induced decreased TPR
  • In inactive or unrequired tissues, e.g. kidney, GI tract, inactive muscle
53
Q

Describe central control of non-essential circulations

A

The RVLM controls specific pre-ganglionic sympathetic nerves in the spinal cord which send out post-ganglionic nerves to specific tissues

54
Q

Describe why static exercise raise blood pressure more than dynamic exercise?

A

STATIC:

  • Constant contraction of small number of muscles, high loads e.g. weight lifting
  • Not unloading/loading : just static
  • Heart rate dosent go as high

DYNAMIC:

  • Shortening/lengthening of many muscles
  • Low load e.g. Running
  • Not a massive change in blood pressure
  • Massive heart rate change
55
Q

What are metaboreceptors?

A

Small diameter sensory fibres in the skeletal muscle

56
Q

What are metaboreceptors stimulated by?

A

They are chemosensitive and so stimulated by K+, H+, lactate; which increase in the exercising muscle

57
Q

Describe the reflex effects of metaboreceptors

A
  • Tachycardia (via increased sympathetic activity)
  • Increased blood pressure
  • ‘Pressor response’ to exercise
  • Especially important during isometric exercise (increased muscle load). Static exercise raises BP more than dynamic exercise
  • Raised BP maintains blood flow to contracted muscle to try to force blood into the contracted muscle
  • Contracted muscle supplied by dilated resistance vessels due to metabolism, selective metabolic hyperaemia
58
Q

Cardiovascular response to increased oxygen uptake

A
  • Increased heart rate

- Increased stroke volume

59
Q

Cardiovascular response to increased oxygen transport around the body

A
  • Increased extraction of O2 from blood Bohr shift
60
Q

Cardiovascular response to directing the increased O2 supply to the exercising muscle

A

Decreased vascular resistance in exercising muscle: muscle metabolism

61
Q

Cardiovascular response to stabilization of blood pressure

A

Vasoconstriction in non-exercising and non-required tissue

Cardiovascular system (16 decks)

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