Questions 20+ Flashcards
What are three other major collateral pathways other than the Circle of Willis?
- ECA to ICA Collaterialization by going through the Opthalmic and its branches
- The Right and Left ECA crossover at the midline to collateralize
- Anterior communicating arteries crossover to collateralize each other
Define the Arterial System:
- This is a multi-branched elastic conduct that carries blood away from the heart to the distant tissues of the body.
- The arterial tree oscillates with each heartbeat, each heart beat pumps 70 ml of blood into the Aorta
- The amount of blood ejected with each heartbeat is known as the stroke volume
- The amount of blood ejected from the LV into Aorta each minute is known as the Cardiac Output
What is the stroke volume and how much is it for a resting pt?
Stroke Volume: the amount of blood ejected with each heartbeat
-Each heartbeat pumps about 70ml/beat of blood into the Aorta
What is the Cardiac Output and how do we calculate it ?
-The amoutn of blood ejected from the LV into the Aorta each min is known as the Cardiac Output
-The normal cardiac output in a resting patient is5.25 L/min
Formula - CO = SV x HR
What is the Cardiac Output for a resting patient?
5.25 L/min
If my patient has a heart rate of 7t beats per min. and a stroke volume of 75 ml, what is the CO?
Answer:
What two criteria must be met for blood to flow?
1) A pressure gradient (or change in pressure)
2) A route for blood flow
- Vessels
- Arteries
- Veins
What creates an Arterial Reservoir?
- The elastic walls of the arteries expand during systolic phase and excess blood volume creates potential energy
- The wall stretches since the capillaries cannot trasmit a large volume of blood all at once.
- This stretching of the vessel wall creates an Arterial Reservoir
Blood flow in the arteries because of the pressure gradient created by ______
heart –> arteries
What creates potential energy in the arteries?
-The elastic walls of the arteries expand during systolic phase. Excess blood volume creates potential energy (pressure) more stretch systolic
What creates kinetic energy in the arteries?
During diastolic pressure the walls of the arteries become stretched and the potential energy is converted into kinetic energy
What are the three different types of energy in the body?
-Potential Energy
-Kinetic Energy
-Hydrostatic Pressure
Define each of the three types of enrgy found in the body:
A) Potential Energy
Potential Energy - Also called Pressure Energy. This is the main form of energy found in the body
- It is present when blood flows during systolic phase
- It is usually measured in mmHg (millimeter of Mercury)
- This is what we measure when we take BP
Define each of the three types of energy found in the body:
B) Kinetic Energy
Kinetic Energy - this is the ability of blood to do work as result of velocity
Define each of the three types of energy found in the body:
C) Hydrostatic Pressure
Hydrostatic Pressure - also called gravitational pressure
-This is the pressure exerted by a fluid due to its height in circulatory system
Define the resistance to flow:
The main form of resistance to blood flow is the blood viscosity, which is the thickness of the blood.
R = change in P / Q
Change in P = P1 - P2
Viscosity is Q; R = P1 - P2 / Q
Define the hematocrit:
Hematocrit is the percentage of RBC per unit volume blood
-Viscosity is related to the hematocrit
-Decreasing the hematocrit = thinner blood = decreased resistance to flow
What is the formula to calculating resistance?
Formula: R = P1 - P2 / Q
Change in P = P1-P2
R = Change in P /Q
R = 8 x n x L / πxr4
What does each variable in the resistance formula mean and what are the relationships?
R = Resistance to flow: unitless P1 = Proximal Pressure:mmHg P2= Distal Pressure:mmHG
Change in P (Triangle) = Change in Pressure: measure gradient: mmHg
Q = Velocity flow rate: L/min or ML/min
*Direct relationship Increases gradient
Energy is lost as a result of two things:
1) Change in flow direction for blood EXL: turture vessel, vessle bifurcation
2) Increased Friction for Example:
- increased hematocrit
- narrowing of vessle; vasoconstriction stenosis
Define Poiseuille’s Law:
It defines the relationship between pressure vessle radius, viscosity, and vessle length to volumeric flow rate
-Used to determine flow in a long straight tube with no stenosis
Formula for Poiseuille’s Law
Q = Change in P (π)(r4)/ 8 nl
or
Q = (P1-P2) πr4/ 8 nl
What are the relationships in the formula?
Q = volumetric flow rate of simply flow units
i.e. Volume/time ; ML/min
P1= Proximal Pressure : units mmHg P2= Distal Pressure: units mmHg π= 3.14 constant units L = Vessel lenght : unit mm or cm λ= viscosity constant ; 0.035 poise: kg/ms or mg/cm r = radius of vessle; units: mm or cm
When do we use this formula?
-When there is normal flow in a long straight tube with no stenosis
