3B - Hemodynamics Flashcards
What two major variables affect blood flow through arteries?
Pressure and resistance
Q = (change) P / R
units: L/min
What is blood flow (Q)?
Quantity of blood flowing through a vessel, organ, or the entire circulation in a given period of time (L/min)
What is blood pressure?
The force with which blood is pushed against the walls of blood vessels
What causes blood pressure to fall progressively through circulation?
- Increasing distance from the heart
2. Branching of vessels and distribution
What is systolic pressure (SP)?
The highest amount of pressure reached during ventricular ejection of blood
(SP/DP)
What is diastolic pressure (DP)?
The minimum amount of pressure just before ventricular ejection
(SP/DP)
What does the energy generated from ventricular contraction do?
- Provides flow during ventricular systole
2. Provides potential energy for blood and distends the arterial tree
What are the methods of blood pressure measurement?
- Auscultatoric measurement - listening to blood turbulence with a stethoscope
- Oscillometric measurement - using an electronic pressure sensor
What is the “Wind Kessel” effect?
The aorta stores potential energy during its ventricular contraction in order to alternate systolic and diastolic propulsion. This alternation of propulsion will make blood flow “continuous” instead of “pulsatile”.
What is Mean Arterial Pressure (MAP)?
The actual pressure that propels blood to tissues
- the “average” pressure in a cardiac cycle
MAP = 2/3 DP + 1/3 SP
MAP = DP + 1/3 PP
(PP is DP - SP)
What is TPR or SVR?
Total peripheral resistance
Systemic vascular resistance
- The sum of all resistance in the vasculature
What are the three important sources of resistance within a single vessel?
- Blood viscosity
- Vessel diameter or radius
- Vessel length
Which of the three sources of blood flow resistances actually change appreciably in vivo?
Blood viscosity and vessel diameter/radius change appreciably
Vessel length doesn’t really change
What is Poiseuille’s Law?
R = 8 V L / π r^4
Relationship between resistance, viscosity, vessel length, and vessel radius
What is a normal hematocrit level?
40%
Hematocrit = RBC / Blood x 100
What is the most important factor for blood viscosity?
Concentration of the suspended medium (the formed elements)
In a low hematocrit state such as anemia (15-16%):
- What happens to viscosity?
- Vascular resistance?
- Blood flow?
- Oxygen level?
Viscosity: Decreases
Vascular resistance: Decreases
Blood flow: Increases
Oxygen: Low
In a high hematocrit state such as polycythemia (60+%):
- What happens to viscosity?
- Vascular resistance?
- Blood flow?
Viscosity: Increases
Vascular resistance: Increases
Blood flow: Decreases
What is rouleaux?
What is rouleaux formation’s relation to tissue ischemia?
A factor that increases viscosity
- The tendency of RBC’s to aggregate into stacks at lower flow veocities
- Can cause a “sludge” or clumping, severely hindering flow and causing ischemia?
What is the relationship between blood vessel radius and resistance?
Resistance is inversely proportional to the fourth power of the vessel radius
A 2-fold increase in radius will increase flow by 16 fold
Drugs that dilate vessels have a powerful effect on blood flow
Vasoconstriction on arteries has what effect on:
- Resistance
- Pressure
- Blood flow
Resistance increases more than pressure
Blood flow decreases
Q = P/R
Vasoconstriction on veins has what effect on:
- Resistance
- Pressure
- Blood flow
Pressure increases more than resistance
Blood flow increases
Q = P/R
