Lecture 14 - Cardiac Output • Starling's Law Flashcards
What is cardiac output
The volume of blood pumped by each ventricle per minute
What is cardiac output the product of
The heart rate and the stroke volume
What is the stroke volume
The volume of blood ejected per contraction
What is cardiac output controlled according to
Physiological requirements via control of the heart rate and stroke volume
What does intrinsic control of SV depend on
The direct correlation between end diastolic volume (EDV) and SV
What does intrinsic control depend on
The length-tension relationship of cardiac muscle
What causes the difference in length of muscle fibres before contraction
The degree of diastolic filling
What does an increased EDV cause
The heart to be stretched more
What does an increase in length of the muscle fibres cause
A greater force on the subsequence cardiac contraction, and thus in a greater stroke volume
What is the intrinsic relationship between EDV and SV known as
The Frank-Starling Law of the heart
What is the extent of filling known as
Preload
What is preload
The workload imposed on the heart before contraction begins
What is the arterial blood pressure known as
The afterload
What is afterload
The workload imposed on the heart after contraction has begun
How can the heart compensate an increased afterload
By enlarging
What may cause a heart to not be able to compensate with an increased afterload
A diseased or weakened heart
Why is the contractile state of the myocardium important
For determining the severity or progress of valve dysfunction
What is the simplest measurement of myocardial contractility
To use the analysis of the pressure waveform during the isometric contraction phase
What is the advantage of using the analysis of the pressure waveform during the isometric contraction phase for myocardial contractility
It is independent of afterload
What it is used as a global assessment of myocardial contractility
Max dP/dT (the maximum rate of rise of pressure)
What is the cellular basis of the Frank-Starling mechanism
Greater initial length increases the sensitivity of the contractile proteins to Ca2+
What may increased initial length also cause
The increase of Ca2+ release from the sarcoplasmic reticulum
What effect does sympathetic stimulation have on the heart
It increases contractility
What extrinsic control occurs on the SV
Sympathetic stimulation and adrenaline
What triggers increased Ca2+ entry
Noradrenaline and adrenaline
What does an increase in Ca2+ during the plateau phase of the action potential cause
It enhances the intracellular calcium store
What is Ca2+ required for
Excitation-contraction coupling in cardiac muscle cells
How is the rate of relaxation increased in cardiac cells
By stimulating Ca2+ pumps
What are the positive conotropic actions of noradrenalline
The duration of systole is decreased, the ventricular pressure wave rises faster, it has a higher peak tension, the end diastolic pressure is decreased and there is a decrease in the duration of the wave.
