Coordinated response of the CVS Flashcards
What does the cardiovascular system respond to?
Physiological conditions
What is the principle of adaptation of the CVS?
Integration of responses due to lots of small changes
Examples of different activities that require the integration of the CVS
- Exercise
- Diving
- Fight or flight
- Sleeping
- Gravity
What is orthostasis?
Standing up
How does the cardiovascular system change according to the effect of gravity during orthostasis?
- 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
What are the three small changes that the baroreflex integrates during Orthostasis?
- Heart rate
- Heart contractility
- Total peripheral resistance
What is the arterial pressure gradient and how is this beneficial in terms of blood flow?
Arterial pressure gradient is 95-185 mmHg, this helps blood flow from the feet to the heart
What is the Arterial blood pressure in the head (lying down)?
95 mmHg
What is the Arterial blood pressure in the chest (lying down)?
100 mmHg
What is the Arterial blood pressure in the feet (lying down)?
95 mmHg
What is the Venous blood pressure in the head (lying down)?
10 mmHg
What is the Venous blood pressure in the chest (lying down)?
3-5 mmHg
What is the Venous blood pressure in the feet (lying down)?
10 mmHg
What is the Arterial blood pressure in the head (standing up)?
60 mmHg
What is the Arterial blood pressure in the chest (standing up)?
95 mmHg
What is the Arterial blood pressure in the feet (standing up)?
180 mmHg
What is the Venous blood pressure in the head (standing up)?
-35 mmHg
What is the Venous blood pressure in the head (standing up)?
0-5 mmHg
What is the Venous blood pressure in the chest (standing up)?
0-5 mmHg
What is the Venous blood pressure in the feet (standing up)?
90 mmHg
Describe the effects of gravity on blood pressures during Orthostasis?
- 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
Bernouilli’s law in terms of Orthostasis
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
What happens at the feet of people with heart failure?
Poor perfusion
What is the high pressure in the venous system due to?
Hydrostatic pressure
How is pressure calculated for fluid in a solid tube?
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.
Describe gravity induced high venous blood pressures
- 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
How does Orthostasis cause Hypotension?
- 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
How is cardiac output increased whilst lying down?
The blood is evenly distributed in the veins
- > Increased central venous pressure
- > Increased end diastolic volume
- > Increased stroke volume
- > Increased cardiac output
Describe the reflex response to Orthostasis
- 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
What are five ways that postural hypotension can be made worse?
- 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
- Varicose veins: Imp[airs venous return so that blood pools in legs
- Lack of skeletal muscle activity: Due to paralysis or forced inactivity, e.g. long term bed rest, soldiers that are on guard
- Reduced circulating blood volume: e.g. Haemorrhage
- Increased core temperature: peripheral vasodilation, less blood volume available, e.g. standing up after bath
Describe the effect of microgravity (space) on the cadriovascular system
- 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
What are the initial effects of microgravity (space) on the cardiovascular system?
- 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%
What are the long term effects of microgravity (space) on the cardiovascular system?
- Less blood volume
- Reduced stress on the heart
- Heart reduces in muscle mass
- General drop in blood pressure
What occurs on return to gravity from microgravity?
- Severe postural hypotension
- much lower blood volume and smaller heart
- the baroreceptor reflex cannot compensate
Describe coordinated cardiovascular responses to exercise
- 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
Cardiovascular responses to dynamic exercise
Constantly shortening and relaxing with lots of different muscle groups involved
Cardiovascular responses to static exercise
One specific muscle group is being worked without constant movement
By how much does oxygen uptake by pulmonary circulation increase during strenuous exercise?
10-15 times
Describe how the integration of several small adaptations can create an overall large response to exercise
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
Describe the graph that shows increase in O2 uptake from the lungs
- Increased blood flow and greater O2 gradient: increased lung uptake
- Arterio-venous oxygen difference reaches a plateau at high exercise levels
Describe the graph that represents increase in cardiac output during exercise
- 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
Describe exercise induced tachycardia
- 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
How is maximum heart rate calculated?
220 - age
approximate increase 65 to 95 (x3)
Effect of increasing cardiac output
Cardiac output increased by 4.5 x (5 to 22 l/min) = Heart rate (3x) x Stroke volume (1.5x)
Describe exercised induced stroke volume
- 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
What is the size of increase in cardiac output from the resting state to when the leg is exercising in the Leg muscle?
x 9
What is the size of increase in cardiac output from the resting state to when the leg is exercising in the Heart?
x 2
What is the size of increase in cardiac output from the resting state to when the leg is exercising in the Skin?
x 3
What is the size of increase in cardiac output from the resting state to when the leg is exercising in the Brain?
There is no increase in cardiac output, it stays the same
Explain the increase in cardiac output in the leg muscle from the resting to exercising state
- 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
What happens to blood pressure when cardiac output is increased by x 4.5?
- 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
What is the need for compensatory vasoconstriction of non-essential circulations?
- They prevent hypotension due to exercise-induced decreased TPR
- In inactive or unrequired tissues, e.g. kidney, GI tract, inactive muscle
Describe central control of non-essential circulations
The RVLM controls specific pre-ganglionic sympathetic nerves in the spinal cord which send out post-ganglionic nerves to specific tissues
Describe why static exercise raise blood pressure more than dynamic exercise?
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
What are metaboreceptors?
Small diameter sensory fibres in the skeletal muscle
What are metaboreceptors stimulated by?
They are chemosensitive and so stimulated by K+, H+, lactate; which increase in the exercising muscle
Describe the reflex effects of metaboreceptors
- 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
Cardiovascular response to increased oxygen uptake
- Increased heart rate
- Increased stroke volume
Cardiovascular response to increased oxygen transport around the body
- Increased extraction of O2 from blood Bohr shift
Cardiovascular response to directing the increased O2 supply to the exercising muscle
Decreased vascular resistance in exercising muscle: muscle metabolism
Cardiovascular response to stabilization of blood pressure
Vasoconstriction in non-exercising and non-required tissue
