CV responses to stress

Question 1

What is the equation for CO?

Answer 1

HR x SV = CO

Question 2

What is the equation for mean systemic arterial pressure?

Answer 2

CO x Total Peripheral Resistance (TPR) = Mean systemic arterial pressure

Question 3

Frank-Starling Mechanism

Answer 3

• Increase in PRELOAD increases stroke volume
• Decrease in PRELOAD decreases stroke volume
• Preload is best measured as End Diastolic Volume
– ECHO
• High levels of PRELOAD eventually lead to decreased stroke volume

Question 4

What are the four things that increase preload?

Answer 4

• Increasing circulating volume- This increases central venous pressure
• Decreases venous compliance- Increase atrial filling or contraction
• Decreasing heart rate
  
  • Prolongs diastole
  • Increases ventricular compliance
• Increasing aortic or pulmonary pressure

Question 5

What does the graph look like for the Frank-Starling Mechanism?

Answer 5

Preload on the x axis, stroke volume on y axis.

Curve, curving up and then decreasing.

Question 6

What is the Bowditch (Treppe) effect?

Answer 6

• Increase in heart rate increases force of contraction
• Decrease in heart rate decreases force of contraction
• High levels of heart rate eventually lead to decreased force of contraction
• Length of muscle not affected
• Therefore, independent of Frank-Starling

Question 7

Bainbridge reflex- what is it?

Answer 7

① Increased venous return
② Baroreceptors in the atria detect increased stretch
③ Heart rate increased via sympathetic simulation to sinoatrial node
-Antagonistic to carotid baroreceptor response
-Involved in sinus arrhythmia

Question 8

What is sinus arrhythmia?

Answer 8

Sinus arrythmia- is an irregular heartbeat that’s either too fast or too slow.

Question 9

What are the direct cardiac sympathetic actions in extrinsic cardiac regulation?
CDIL

Answer 9

① Positive chronotropy
-SA node regulates- speeds up the HR acting on sinus node- changing the rhythm
② Positive dromotropy (conduction)-AV node
③ Positive inotropy (contraction)
④ Positive lusitropy (relaxation)-Ventricles and atria

Question 10

What are the systemic sympathetic actions in extrinsic cardiac regulation?

Answer 10

① Activation of Renin-Angiotensin-Aldosterone-System (RAAS)
② Suprarenal stimulation
-Catecholamines (hormone made by the adrenal glands)

Question 11

What are direct cardiac sympathetic actions?

Answer 11

Increase in chronotropy, dromotropy, inotropy and lusitropy will speed up impulses on SA node, conducting through AV nodes faster, contraction of atria and ventricles faster and relaxation of atria and ventricles.

Question 12

Sympathetic actions- RAAS

Answer 12

Liver –> Angiotensinogen –>Renin converts angiotensinogen to angiotensin I –> Angiotensin converting enzyme converts AgI to AgII –> Ag II leads to pituitary glands secreting aldosterone and AgII leads to vasopressin.

Question 13

What are the actions of the RAAS?

Answer 13

• Angiotensin II
– Vasoconstriction
– Increased Na+ and H2O retention- more retained, more preload
• Aldosterone
– Increased Na+ and H2O retention- close aquaporins and increases venous pressure, increase SV, increases CO, increase mean systemic arterial pressure
• Vasopressin (Antidiuretic Hormone)
– Promotes H2O retention

Question 14

What does adrenaline do?

Answer 14

Adrenaline is a powerful vasoconstrictor.

Question 15

What are parasympathetic actions of the body?

Answer 15

• Decreased Heart Rate (CHRONOTROPY)
• Decreased AV conduction (DROMOTROPY)
• Decreased Atrial Contractility (INOTROPY)
• Ventricular contractility- NO SIGNIFICANT EFFECT
• RAAS- NO SIGNIFICANT EFFECT

Question 16

What is the regulation of the ANS?

Answer 16

• Baroreceptors- found in aortic arch and carotid bodies/ sinus
• Local e.g. renal juxtaglomerular apparatus

Question 17

Where are baroreceptors located?

Answer 17

Located: Carotid sinuses, Aortic Arch

Question 18

What do baroreceptors do in response to increased and decreased arterial pressure?

Answer 18

• Decreased arterial pressure
– Decreased firing
• Increased arterial pressure
– Increased firing

Question 19

What does baroreceptor firing do when increased?

Answer 19

– Decreases Sympathetic Tone

– Increases Parasympathetic Tone

Question 20

What does baroreceptor firing do when decreased?

Answer 20

– Increases Sympathetic Tone

– Decreases Parasympathetic Tone

Question 21

What would happen to the baroreceptors, sympathetic tone and parasympathetic tone when mean systemic arterial pressure decreases?

Answer 21

If mean systemic arterial pressure decreased, baroreceptor firing would decrease, sympathetic tone would increase and parasympathetic tone would decrease.

Question 22

What would happen to the baroreceptors, sympathetic tone and parasympathetic tone when mean systemic arterial pressure increases?

Answer 22

If mean systemic arterial pressure increases, baroreceptors fire more, sympathetic tone will decrease down and parasympathetic tone will increase.

Question 23

Haemodynamic effects when blood is lost?

Answer 23

Haemodynamic effects- Less preload, less SV, less CO. Less CO, less BP as CO x TPR = Mean systemic arterial P. Thus if mean systemic arterial P decreases, baroreceptors firing decreases, sympathetic tone increases and parasympathetic tone decreases.

Question 24

If things don’t improve after blood loss and sympathetic stimulation what shall you do?

Answer 24

If this doesn’t improve things: IV fluids and bloods would need to be given increasing central venous pressure.

Question 25

If doctor gave too much fluid to patient what should you do?

Answer 25

If doctor gave too much fluid: Increasing preload too far, increase venous pressure too far. SV falls. Fall down the Frank Starling mechanism curve. CO falls. Mean systemic arterial pressure decreases.

Also, high left ventricular pressures, back pressure to the lungs, increase in alveolar capillary pressure, P can leak in wrong tissue, fluid from capillaries into tissue space can cause pulmonary oedema.

Question 26

What are treatments for too much fluid?

Answer 26

Diuretics (dehydrate the patient, removing excess fluid) using furosemide. This will stabilise the central venous pressure. SV and CO would be stabilised. Stabilising the mean systemic arterial pressure.