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BIOC33H3 Lecture Notes - Third-Degree Atrioventricular Block, Heart Failure, Coronary Circulation

Biological Sciences
Course Code
Stephen Reid

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Regulation of Cardiac Output; Blood Flow Regulation
Coronary Artery Blood Flow Occurs Mainly During Diastole
The reason for this is that during systole, when the heart is
contracting, it compresses some (large portion) of the
coronary arteries and completely occludes them and thus
coronary blood flow decreases to the cardiac muscles.
In mammals, the heart muscle has to be supplied
with blood through coronary arteries.
Stroke Volume Regulation Afterload
The afterload is the pressure that the ventricles must work
against during the ventricular ejection phase of the heart
cycle (into systemic circulation). It is equal to the aortic
blood pressure. When the afterload increases, the stroke volume decreases.
On the left side of the heart, the afterload is the pressure from the aorta and on
the right side, the afterload is the pressure from the pulmonary arteries.
A decrease in arterial pressure (afterload) leads to a marginal decrease in EDV
but a substantial decrease in ESV. Since SV = EDV ESV, a decrease in the
afterload means an increase in the SV.
Heart Failure
It is any reduction in the heart’s function that prevents it from maintaining adequate
cardiac output.
Symptoms of Heart Disease
o Breathing difficulties (shortness of breath, trouble breathing lying down)
o Fatigue (exercise intolerance, tiring easily)
o Swelling of feet, ankles, or legs
o Cyanosis (blueness of blood)
Causes of Heart Failure
o Heart Attack (Myocardial Infarction) it is the death of cardiac myocytes
due to blockage of the coronary arteries
o High Blood Pressure, Stenosis (valve doesn’t open wide enough) of the
Aorta (i.e. increases in afterload)
↑ cardiac workload enlargement of the heart (↑ muscle
thickness) ↓ ventricular compliance (harder to stretch thick
muscle) ↓ EDV ↓ SV and CO
Reduction in ventricular contractility
Obstruction of an AV valve
Third Degree heart block (lecture 2 and 3)
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o ↓ decreases HR ↑ increases in EDV (due to increased filling time)
chronic overstretching and weakening
Heart failure can be looked at from the left and right side
of the heart and can lead to different symptoms.
Left Heart Failure (congestive heart failure)
o Left ventricular failure (i.e. ↓ in contractility)
o ↑ Pressure in pulmonary veins as the
blood returning from the lung backs up
o ↑ Pressure in lung capillaries
o Forces fluid into the alveoli of the lungs
(edema) the lung tissues collapse on
each other and decrease gas exchanges
o ↓ Pressure in systemic arteries because of insufficient generation of CO
o Fluid retention by the kidney is triggered
o Veins are volume reservoirs and so venous volume and pressure increase
o Increase in pressure in the pulmonary artery (edema)
If the right heart isn’t functioning well, we get a build up of fluid and pressure in the
systemic circulation (venous system). This leads to a diffusion of fluid from the
capillaries into distal tissue which will lead to swelling which leads to tissue death.
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