Muscle Pump Failure (Heart Failure) Flashcards
What is the equation for cardiac output?
CO = heart rate x stroke volume
What is the equation for cardiac reserve?
maximal cardiac output - cardiac output at rest
What is preload?
The level of stretch that a cardiomyocyte is exposed to before ventricular ejection
What is preload equivalent to?
left ventricular end-diastolic volume
What is left ventricular end-diastolic volume?
The volume within the ventricle at the end of diastole, just before it contracts
What is afterload?
The pressure against which the heart is contracting when it ejects blood
During which conditions is afterload increased?
- hypertension
2. increased peripheral vasoconstriction
In cardiac muscle, how does sarcomere length affect tension?
small increases in sarcomere length cause a rapid increase in tension
Using the Frank-Starling curve, what happens when a physiological limit is reached?
There is a decompensation which leads to a sudden and rapid decrease in tension
What is described by the Bowditch phenomenon?
As the heart rate increases, cardiac output increases
Increasing heart rate to an extreme can lead to a reduction in cardiac performance
What is on the x and y axis of the Bowditch curve?
Cardiac performance - y
Heart rate - x
What is described by the Anrep effect?
Increasing the afterload, through increasing systemic vascular resistance, increases cardiac performance up until a limit
What is on the x and y axis of the Anrep curve?
cardiac performance - y
afterload - x
what is the consequence of reducing cardiac output?
reduced organ perfusion
What is the role of the baroreceptor reflex?
It is an autonomic reflex that helps to detect changes in pressure of the blood
What do baroreceptors detect?
Arterial stretch
This determines whether the blood pressure is high or low
What does the afferent end of the baroreceptor end in?
The nucleus tractus solitarius and rostral ventrolateral medulla
How do the baroreceptors augment vagal tone?
What is the result of this?
They activate the vagus nerve which:
- reduces the heart rate
- reduces stroke volume
- causes vasodilation
What is the baroreceptor reflex pathway when blood pressure is too high?
- The parasympathetic NS innervates the SAN and AVN via the vagus nerve
- This decreases the heart rate
- This leads to reduced cardiac output
What is the baroreceptor reflex pathway when blood pressure is too low?
How does it affect the heart?
- The sympathetic NS innervated the SAN, AVN, conducting tissue and myocytes of the atria and ventricles
- This increases heart rate and contractility
- This increases cardiac output
How does the sympathetic nervous system in the baroreceptor reflex affect the blood vessels?
It causes constriction of blood vessels
This increases systemic vascular resistance
This acts to increase blood pressure
What happens when blood pressure is too high?
- baroreceptors detect increased arterial stretch
2. they activate the parasympathetic nervous system to increase vagal tone
What happens when vagal tone is increased?
The heart rate is lowered and cardiac output is reduced
What is the result of increasing systemic vascular resistance?
It leads to an increase in afterload
This causes a temporary increase in cardiac output
What does the juxtoglomerular apparatus detect?
- renal perfusion pressure at the glomerulus
2. sodium concentration in the fluid surrounding the distal convoluted tubule
What is the role of the juxtoglomerular apparatus?
If either renal perfusion or sodium concentration is reduced, it releases renin
What is the process in the kidney that occurs in order for renin to be produced?
Inactive prorenin is converted to renin and active prorenin
Where is angiotensinogen released from?
The liver
How does angiotensinogen interact with renin?
It is cleaved by renin to form angiotensin I
This is inactive
what is the main role of angiotensin converting enzyme (ACE)?
Where is it released from?
The lungs release ACE
It converts angiotensin I to active angiotensin II
What is the secondary role of angiotensin converting enzyme (ACE)?
It breaks down bradykinin (vasodilator)
This prevents vasodilation
What are the actions and effects of angiotensin II?
- increases water retention
- increases sodium reabsorption
- causes vasoconstriction
These act to increase systemic vascular resistance
What group of chemicals does angiotensin II cause the release of?
Catecholamines
These increase cardiac output and systemic vascular resistance
What main chemical does angiotensin II cause the release of, and what is the consequence?
Aldosterone release from adrenal glands
It increases plasma volume, which increases preload and consequently cardiac output
What is aldosterone and where is it released from?
A mineralocorticoid
It is released from the zona glomerulosa in the adrenal cortex
Where does aldosterone act on?
Why is it released?
Released in response to angiotensin II
It has effects on the distal convoluted tubule and collecting duct
What is meant by aldosterone being ‘internalised’?
It binds to an intracellular aldosterone receptor