Haemodynamics Flashcards
What is haemodynamics?
the movement of blood and the physical factors that control blood flow
How do metabolic demands dictate blood flow? How does blood generally move through different regions of the body?
High metabolic demand = high blood flow
- Kidneys have high metabolic demands, so it requires 20% of CO
Blood moves from a relative high pressure to low pressure
What is serum?
Plasma without clotting factors
In which conditions is high blood viscosity observed in?
polycythaemia (high RBCs), thrombocythaemia (high platelets), leukaemia (WBCs)
Which proteins cause minor changes to plasma viscosity what are these changes an indicator of?
fibrinogen, compliment, c-reactive protein
indicator of infection
Define flow
volume transfer per unit time (blood: mL/min)
Define pressure
force per unit area
(SI unit is Pascal; mmHg used when measuring BP)
What pattern do flow and pressure in circulation display?
Pulsatile
blood flow from relative high to low pressure
equation for FLOW (Darcy’s Law)
Flow = ΔP/R
P: pressure difference
R: resistance
flow = K(ΔP)
R = -1/K
K: measure of ease of flow
Define resistance and give the equation (Darcy’s Law)
The difference in mean pressure needed to move one unit of flow in steady state (mmHg/min/mL)
R = ΔP/Flow
What is the relationship between i) flow and resistance ii) resistance and ΔP (at any give flow)
i) they are reciprocally related
ii) directly proportionate
What is laminar and turbulent flow?
laminar - smooth, silent flow; parabolic flow profile; blood moves in streamlined and concentric fluid layers; blood moves fastest in the middle
turbulent - disorganised flow; noisy
describe the relationship between flow and perfusion pressure to maintain laminar flow. And how do flow become turbulent?
As pressure increases, flow increases to match the increase (linear relationship). When flow can’t match the increase in pressure, the CRITICAL REYNOLDS NUMBER IS EXCEEDED
Which factors primarily influence resistance to flow?
- diameter (most important)
- vessel length (doest change)
- viscosity (maintained with in a narrow range)
Describe the changes in resistance across vessel types. (aorta to capillaries)
- low resistance in aorta (due to large diameter and short)
- small arteries and arterioles have higher resistance and pressure and contribute to total peripheral resistance
What is velocity? Give the equation used to calculate flow from velocity and area of the cross-section.
the distance fluid moves in a given time (cm/s)
Flow = Velocity x A (area of cross-section)
How does cross-sectional area influence velocity? Why is this factor important in capillaries?
High cross-sectional area = Low velocity
- capillaries have a combined cross-sectional area that is a thousand time larger than that of the aorta
What has the greatest impact on resistance within a vessel?
Cross-sectional area
Which vessel type has the greatest effect on total peripheral resistance?
arterioles
What is pulse pressure and give the equation
PP = SYS BP - DIA BP
Give the two arterial pressure equations (1. w/ CO and TPR 2. w/ DBP and PP)
MAP = CO x TPR
MAP = DBP + (1/3PP)
What is high pulse pressure described and which factors increase pulse pressure?
- described as ‘bounding pulse’
- Heart block (poor heart conduction) resulting in bradycardia (slow HR) -> results in lower DIA BP and high PP
- Vasodilation - low peripheral resistance
- athletes - high SYS BP and low DIA BP
How does blood flow differ before and after passing a stenosis? How does the velocity change as blood passes through the stenosis?
Before: laminar + silent
While passing: velocity increases
After: turbulent
How is blood pressure measured using Korotkoff sounds?
- when cuff pressure is above systolic pressure, there is no flow
- when cuff pressure of below systolic pressure, there turbulent flow which produces Korotkoff sounds in the brachial artery
- when cuff pressure is below diastolic pressure, Korotkoff sounds stop and laminar flow resumes
