Hemodynamics Flashcards
How are organs arranged in the circulatory system and how does the blood flow vary in the organs
Organs are arranged in parallel, there is different pressure through different organs as they offer different resistance to blood flow
Dicrotic notch, runoff and ejectione closes
Blood is ejected into the aorta, the valve opens up and when the pressure gets to 115 mm Hg the valve closes. This point is called the dicrotic notch.
The oscillation in blood pressure is can be divided into two phases, the run off phase and the ejection phase.
Run off phase starts at the dicrotic notch when the aortic valve close and ends when the aortic valve opens whereas the ejection phase is when the pressure is rising so starts at aortic valve closing and ending at aortic valve opening
What happens in the runoff phase in the systemic circulation and why is this term a misnomer
Blood moves from the large arteries to the large veins. Runoff occurs during both the runoff and the ejection phase except in ejection phase its effect is hindsighted by the ejection of blood in the aorta
Pulse pressure
Difference in systolic and diastolic pressure
What determines the rate of runoff
Resistance of the arterioles
How to find MAP
MAP = diastolic pressure + 1/3*(pulse pressure), where pulse pressure is systolic p - diastolic p.
The reason it is 1/3rd is because systolic time is 1/3rd and diastolic time is 2/3rds
What are the 2 factors that determine the diastolic pressure
The rate and time of runoff, runoff time being proportional to diastole
Arteriolar pressure changes with changes in volume of blood into the arteries. This is in turn determined by the run off rate and the flow of blood into the arteries
How is the slope of rate of runoff change with TPR
A decrease in TPR allows the blood to leave the arteries faster so the runoff increases and vice versa
Explain the mechanism of action of baroreceptors on the aortic arch and other places where they exist
When the aorta is stretched, there is an increase in the firing of the baroreceptors, which causes a decrease in sympathetic firing to the heart causing a decrease in the inotropic state of the heart.
The opposite happens when the aorta relaxes (there is decreased in baroreceptor signaling and increased firing of the sympathetic nervous system to the heart to increase the inotropic state of the heart)
How does the runoff change when the heart rate is reduced
The runoff time increases linearly and the diastolic pressure is lower
What minimizes the fall of pressure in the aorta during diastole
The elastic energy stored in the aorta, this decreases with aging
When the elasticity is lost in the vessels due to aging or possible arteriosclerosis what happens to the systolic and diastolic pressure and what can casue the same effect
They have a larger difference, systolic pressue is higher and diastolic pressure is lower
Increase in stroke volume can also cause the same effect
What is compliance
Change in volume versus change in pressure. The slope of this line in the graph is compliance
What are the causes and what is one dangerous effect of arteriosclerosis
Hypertension, a rise in systolic pressure can cause arteriosclerosis which can damage the endotherlial cells and promote plaque formation
Vessel complaince
Veins are much more compliant than arteries, hence their slope is much steeper, the compliance of a vein can change by giving alpha 1 agonist
What happens when the veins are constricted
Only the peripheral veins are constricted, they dont significantly change the diameter since they are so big and hence no significant change in resistance occurs but at the same time venous return is increased.
Hence venous return is increased without changing the resistance of the veins significantly
In series we just add
Poiseuille’s law
Resistance mainly depends on radius in the body
How does viscosity changes
Changes with hematocrit
What is the disease associated with it
Anemia will cause decrease in viscosity and polycythemia will cause hematocrit to increase as high as 70%
What are the sounds from turbulent flow in a vessel called
bruits
How does turbulent flow develop in the vessels
When the vessels narrow, maybe due to plague formation
Ankle brachial index
Ratio of systolic pressure in the leg to systolic pressure in the artery, normal values are 1 to 1.4
What causes a change in ankle brachial index
Coarctation of the aorta and plaques in the legs
What happens when youre standing, what is this phenomena called
The pressure in the veins increases in the foot, the walls of the veins increase, the volume of blood in the bottom of the legs is increasing called the venous pooling, which will cause a decrease in venous return.
Orthostatic hypotension
Explain the S2 splitting mechanism during inspiration on the left ventricle
Pressure of the thoracic cavity is lower which causes the pulmonic veins to expand, pressure difference in the left atrium and the lungs is decreased and hence blood returning to the left atrium is decreased (while it increases in the right atrium) and hence valve splitting occurs
What is he trying to explain here
Expiration causes a decrease in heart rate since the cardiac output is increasing due to increased blood flow to the right and then to the left ventricle. This causes baroreflex to change the heart beat rate.
It is also important to know that this change is very fast as it can be seen in this slide here
Mnemonic for this rule
What is the Valsalva Maneuver
When someone tries to breath out with their mouth and nose closed, the pressure inside the thoracic cavity increases causing more pressure on the pulmonic vains. At the onset of valsalva maneuver the filling of the left ventricle is increased and then it is decreased owing to the less filling of the right ventricle.
People with heart problems who do a valsalva maneuver for a prolonged period can have sudden cardiac death
What is an example of alpha 1 agonist and where does it intiates an alpha 1 response (on what vessels)
Phenylephrine, in the arterioles and veins
What does phenylephrine do to pulse pressure
Pulse pressure will decrease, he explains why here since the baroreflex will kick in and it will reduce the stroke volume by decreasing the inotropic state of the heart
What is isoproterenol
It is a nonselective beta 1 agonist. Non selective means that on smaller doses it acts on beta 1 (it activates them since it is an agonist, just in this case) and in larger doses it acts on beta 2 receptors that are present in the arterioles to the skeletal muscles, part of the fight or flight response
