32 Questions
What is heart failure?
Heart failure is any condition whereby the heart fails to meet the perfusion demands of the body.
Define Pre-load in relation to the heart.
Pre-load is the initial stretching of the cardiac myocytes prior to an active contraction; it is the initial passive length to which muscle is stretched before the start of a contraction.
What is After-load in the context of the heart?
After-load is the load the heart must eject blood against; it is the force a muscle experiences after it has begun to pump blood.
Explain the Frank-Starling Law.
The Frank-Starling Law states that the stroke volume of the heart increases in response to an increase in the volume of blood filling the heart when all other factors remain constant.
What percentage of blood is pumped out of the left ventricle during a normal heart cycle?
Only 2/3 (two-thirds) of the blood is pumped out of the left ventricle during a normal heart cycle.
How does the stroke volume change with an increase in Pre-load in a normal heart?
In a normal heart, as Pre-load increases, the stroke volume also increases.
How does overstretching of cardiomyocytes affect contractility?
Reduced contractility
Explain the relationship between increased sympathetic venoconstriction and venous return.
Increased sympathetic venoconstriction enhances venous return.
How does a decrease in resistance affect maximum cardiac output?
Decreased resistance leads to an increase in maximum cardiac output.
What is the short term compensation mechanism for Acute Myocardial Infarction?
Positive feedback loop
How does persistent low cardiac output lead to salt and water accumulation?
Persistent low cardiac output causes salt and water accumulation.
What happens when the Right atrial pressure becomes very high (20 to 30 mm Hg)?
High Right atrial pressure may lead to cardiac dilatation, pulmonary and peripheral oedema.
How does sympathetic arteriolar constriction in the skin and viscera affect blood pressure?
Increases blood pressure
What is the purpose of sympathetic veno-constriction?
Increase venous return to the heart
What is the effect of the sympathetic nervous system on cardiac stimulation?
Increases myocardial contractility
What is the consequence of excessive calcium accumulation due to sympathetic stimulation?
Receptor uncoupling and desensitization
How does venoconstriction affect cardiac output?
Increases cardiac output by increasing preload
What is the risk associated with chronic myocardial hypertrophy in response to heart failure?
Loss of contractility and elasticity
What initiates the RAAS system in response to a fall in renal blood flow?
Secretion of renin by juxtaglomerular cells
How does angiotensin 2 contribute to an increase in blood pressure?
Facilitates sympathetic potentiation and vasoconstriction
What is the role of aldosterone in response to angiotensin 2?
Promotes excess sodium retention
What is the term used to describe the elevated pressure in the jugular vein indicative of heart failure?
Elevated jugular venous pressure
What term describes the shifting of the heart's apex towards the left hand side in congestive heart failure?
Laterally displaced apex beat
How does hypertrophied myocardium affect the heart's ability to contract?
Decreases the ability to contract in unison
What is the term for the third heart sound that can be heard in heart failure patients?
3rd heart sound
Why do patients with heart failure experience cold extremities?
Due to inefficient pumping of blood by the heart
What is the term for the condition where skin and lips turn blue due to lack of oxygen?
Cyanosis
What is the main cause of chronic myocardial ischemia leading to heart failure?
Hypertension
What is the formula for calculating mean arterial blood pressure?
MABP = CO x TPR
What happens to cardiac output (CO) in heart failure?
CO falls
What do arterial baroreceptors detect in response to a fall in mean arterial blood pressure?
Baroreceptors detect low blood pressure
What is the acute response in heart failure that involves increased sympathetic cardiac stimulation?
Increases sympathetic cardiac stimulation
Study Notes
Heart Failure
- Heart failure: a condition where the heart fails to meet the body's perfusion demands.
- Causes: weak or stiff heart muscle, increased afterload, or decreased contractility.
Preload and Afterload
- Preload: initial stretching of cardiac myocytes prior to contraction; the pressure the heart must fight before pumping blood.
- Afterload: the load the heart must eject blood against; the force a muscle experiences after pumping blood.
Frank-Starling Law
- The stroke volume of the heart increases in response to an increase in blood filling the heart, if all other factors remain constant.
- In a normal heart, as preload increases, stroke volume also increases.
Types of Heart Failure
- Left-sided heart failure: affects the muscular side responsible for pumping blood into the systemic circulation.
- Right-sided heart failure: affects the side responsible for sending blood to the lungs for oxygenation.
Congestive Heart Failure
- Signs:
- Elevated jugular venous pressure
- Laterally displaced apex beat
- 3rd heart sound
- Symptoms:
- Cold extremities
- Pallor
- Fatigue
- Tachycardia
- Tachypnoea
- Pulmonary oedema
- Orthopnoea dyspnoea
- Cyanosis
Causes of Heart Failure
- Acute myocardial infarction
- Chronic myocardial ischaemia
- Hypertension
- Outflow obstruction
- Arrhythmias
- Valve disorders
- Thyrotoxicosis
- Arterio-venous fistulae
- Beri-beri disease
Cardiac Homeostasis and Haemodynamics
- Mean arterial blood pressure (MABP) = cardiac output (CO) x total peripheral resistance (TPR)
- CO = stroke volume (SV) x heart rate (HR)
- CO falls during heart failure, leading to a decrease in MABP
Baroreceptors and Reflexes
- Baroreceptors in the heart and aorta monitor stretch and pressure.
- Decreased blood pressure activates baroreceptors, leading to sympathetic stimulation, increased cardiac output, and increased blood pressure.
Effects of Sympathetic Nervous System
- Increases myocardial contractility
- Increases venous return and cardiac output
- Raises blood pressure and afterload
- Mitogenic response: leads to myocardial hypertrophy, which can increase cardiac output but decrease contractility
Chronic Response to Heart Failure
- Decreased cardiac output leads to decreased renal blood flow, activating the renin-angiotensin-aldosterone system (RAAS)
- RAAS leads to salt and water retention, chronic hypervolemia, and increased venous pressure
- Increased pulmonary pressure and mean arterial blood pressure
- Effects on the kidney: decreased renal blood flow, secretion of renin, and retention of salt and water
Ventricular Function Curves
- Relationship between tension and length affects contractility
- Increased length (stretch) leads to increased tension and contractility
- Overstretching can reduce contractility
Contractility and Venous Return
- Increased cardiac contractility increases venous return
- Sympathetic venoconstriction enhances venous return
- Changing cardiac contractility affects right atrial pressure
Explore the concept of heart failure, where the heart fails to meet the body's perfusion demands, and learn about pre-load and after-load in cardiac physiology. Understand how pre-load and after-load affect the heart's ability to pump blood effectively.
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