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Cardiovascular system anatomy and physiology
Lymphatic system anatomy and physiology
Blood pressure, blood flow, and resistance
Pressures in the cardiovascular system
Laminar flow and Reynolds number
Resistance to blood flow
Compliance of blood vessels
Control of blood flow circulation
Microcirculation and Starling forces
Measuring cardiac output (Fick principle)
Stroke volume, ejection fraction, and cardiac output
Law of Laplace
Cardiac and vascular function curves
Altering cardiac and vascular function curves
Changes in pressure-volume loops
Physiological changes during exercise
Cardiovascular changes during hemorrhage
Cardiovascular changes during postural change
Normal heart sounds
Abnormal heart sounds
Action potentials in myocytes
Action potentials in pacemaker cells
Excitability and refractory periods
Cardiac excitation-contraction coupling
Electrical conduction in the heart
Cardiac conduction velocity
ECG normal sinus rhythm
ECG QRS transition
ECG rate and rhythm
ECG cardiac infarction and ischemia
ECG cardiac hypertrophy and enlargement
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Robyn Hughes, MScBMCViviana Popa, MD
Sam Gillespie, BSc
David G. Walker
Cardiac work, also known as stroke work, is similar to the concept of work in physics. In physics, work is defined as force times distance.
Stroke work can be thought of as the work performed by the left ventricle to eject a volume of blood, defined as stroke volume multiplied by mean aortic pressure.
And here, stroke volume corresponds to distance, whereas mean aortic pressure corresponds to force. Stroke work is best represented by a pressure-volume loop.
Pressure- volume loops are graphs, where the pressure inside the left ventricle is on the y axis and the volume of the left ventricle is on the x axis.
Each loop represents changes in ventricular pressure and volume over the course of one cardiac cycle, or one heartbeat, which includes both ventricular systole, or contraction, and diastole, or relaxation.
The lower right hand corner is the end-diastolic point, and it’s the point in the cardiac cycle when diastole is over. Αt this point, the mitral valve between the left atrium and the left ventricle, closes, leaving the left ventricle filled with the maximum volume of blood, called the end-diastolic volume.
And then, systole begins, which is when the left ventricle contracts to push that blood into the aorta. Ventricular contraction makes the pressure shoot up, but for a brief period of time, both the mitral and aortic valves are closed, so left ventricular volume doesn’t change.
This phase is isovolumetric contraction, but it doesn’t last long, because eventually the pressure inside the left ventricle exceeds aortic pressure, making the aortic valve pop open, and that starts the ejection phase.
The cardiac cycle, also called the stroke work, is the work performed by the heart's left ventricle during an ejection of a blood volume. It is the performance of the heart from the beginning of one heartbeat to the beginning of the next, and equals to the product of the mean aortic pressure and stroke volume, which is the amount of blood pumped by the left ventricle in one beat. Cardiac work done in a full minute will be referred to as cardiac minute work. It is equal to the product of mean aortic pressure and cardiac output, since the cardiac output equals heartbeats in one minute times the stroke volume.
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