CV responses to stress Flashcards
What is the equation for CO?
HR x SV = CO
What is the equation for mean systemic arterial pressure?
CO x Total Peripheral Resistance (TPR) = Mean systemic arterial pressure
Frank-Starling Mechanism
• 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
What are the four things that increase preload?
- 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
What does the graph look like for the Frank-Starling Mechanism?
Preload on the x axis, stroke volume on y axis.
Curve, curving up and then decreasing.
What is the Bowditch (Treppe) effect?
- 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
Bainbridge reflex- what is it?
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
What is sinus arrhythmia?
Sinus arrythmia- is an irregular heartbeat that’s either too fast or too slow.
What are the direct cardiac sympathetic actions in extrinsic cardiac regulation?
CDIL
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
What are the systemic sympathetic actions in extrinsic cardiac regulation?
① Activation of Renin-Angiotensin-Aldosterone-System (RAAS)
② Suprarenal stimulation
-Catecholamines (hormone made by the adrenal glands)
What are direct cardiac sympathetic actions?
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.
Sympathetic actions- RAAS
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.
What are the actions of the RAAS?
• 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
What does adrenaline do?
Adrenaline is a powerful vasoconstrictor.
What are parasympathetic actions of the body?
- Decreased Heart Rate (CHRONOTROPY)
- Decreased AV conduction (DROMOTROPY)
- Decreased Atrial Contractility (INOTROPY)
- Ventricular contractility- NO SIGNIFICANT EFFECT
- RAAS- NO SIGNIFICANT EFFECT
What is the regulation of the ANS?
- Baroreceptors- found in aortic arch and carotid bodies/ sinus
- Local e.g. renal juxtaglomerular apparatus
Where are baroreceptors located?
Located: Carotid sinuses, Aortic Arch
What do baroreceptors do in response to increased and decreased arterial pressure?
• Decreased arterial pressure
– Decreased firing
• Increased arterial pressure
– Increased firing
What does baroreceptor firing do when increased?
– Decreases Sympathetic Tone
– Increases Parasympathetic Tone
What does baroreceptor firing do when decreased?
– Increases Sympathetic Tone
– Decreases Parasympathetic Tone
What would happen to the baroreceptors, sympathetic tone and parasympathetic tone when mean systemic arterial pressure decreases?
If mean systemic arterial pressure decreased, baroreceptor firing would decrease, sympathetic tone would increase and parasympathetic tone would decrease.
What would happen to the baroreceptors, sympathetic tone and parasympathetic tone when mean systemic arterial pressure increases?
If mean systemic arterial pressure increases, baroreceptors fire more, sympathetic tone will decrease down and parasympathetic tone will increase.
Haemodynamic effects when blood is lost?
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.
If things don’t improve after blood loss and sympathetic stimulation what shall you do?
If this doesn’t improve things: IV fluids and bloods would need to be given increasing central venous pressure.
If doctor gave too much fluid to patient what should you do?
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.
What are treatments for too much fluid?
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.
