3. Control of Cardiac Output Flashcards
What is meant by the term cardiac output?
Cardiac output is the volume of blood pumped by the left ventricle in one minute
How is cardiac output calculated?
Calculated by multiplying heart rate by stroke volume
What alters the heart rate?
Sympathetic and parasympathetic nervous systems
What effect does the sympathetic nervous system have on the heart?
Speeds up the heart
+ve chronotropic efffect
How does the sympathetic nervous system speed up?
Beta 1 receptor opens Ca++ L channels
Increases slope of prepotential, making it reach firing level quicker, more rapid SA firing.
Speeds AV conduction
R symps to SA node, L to AV node
What effect does the parasympathetic nervous system have on the heart?
Slows down heart (-ve chronotropic effect)
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How does the parasympathetic nervous system speed up?
M2 receptor opens K+ channels, slows opening of Ca++ channels
Hyperpolarises cell, decreases slope of prepotential, making it reach firing level more slowly, slower SA firing.
Slow AV conduction
R vagus to SA node, L vagus to AV node
How is cardiac output influenced?
Altercations in stroke volume
What do changes in the altercations in stroke volume depend on?
These changes may depend on the intrinsic properties of cardiac muscle, on autonomic stimulation and on hormones
What is meant by heterometric regulation?
Changes in C.O. dependent on initial length of cardiac muscle fibre
What is meant by homeometric regulation?
Changes in C.O. independent of such changes
What are the features of a frank-starling relationship?
Stroke volume (and CO) is dependent on the degree of stretch on ventricular walls
Increases in End-diastolic volume stretch ventricular walls increasing stroke volume
More in = more out, elegant!
Preload and afterload
Decompensation
Mechanism now debated
Overlap? Ca++ sensitivity or influx?
What happens in sympathetic stimulation?
Shifts Starling up and to the left (see previous)
Affect on Beta 1 adrenergic receptors
Positive inotropic effect of sympathetic stimulation
What is meant by parasympathetic stimulation?
Negative inotropic effect on atria but no effect on ventricles
What other factors affect contractility?
Catecholamines
Force-frequency relation
What are examples of catecholamines and what do they do?
Noradrenaline and adrenaline
Amplify beta effects
What are examples of force frequency relations?
Post-extrasystolic potentiation
Paired stimuli
Fast heart rates
What is the fick principle?
Amount of a substance taken up per unit time by an organ (or the whole body) equals arterial content – venous content (A – V difference) times the blood flow through the organ (or body).
What is the indicator dye method?
look at slide 18
What is cardiac failure?
insufficient peripheral perfusion despite normal blood volume, a sufficient filling pressure and intact intrinsic and extrinsic compensatory mechanisms
What are some of the causes of cardiac failure?
Common causes - Coronary artery disease
Cardiac tamponade and valvular problems
