Flow and Pressure Flashcards
Definition of venous return
Volume/min into heart (5L/min)
Must equal cardiac output
Definition of central venous pressure
Filling pressure (preload) of right heart
Definition of stroke volume
Volume/beat (70mls)
Definition of cardiac output
Volume/min (5L/min)
Definition of total peripheral resistance
Pressure load on left heart, resistance to flow (afterflow)
Definition of axial streaming
Where the largest molecules flow in the center to reduce viscosity
Slowest flow occurs at sides of tubes
Why do we need a cardiovascular system
Rate of diffusion too slow to sustain life (O2, CO2, nutrients)
Describe the circulatory system
2 pumps in the heart in series
Properties of the systemic circulation
High resistance and pressure (92mmHg)
Mostly in parallel with each other
Properties of pulmonary circulation
Low resistance and pressure (16mmHg)
In series with the systems
What is the flow into the heart
Volume/min, venous return (5L/min)
Must equal cardiac output
What is the flow out of the heart
Stroke volume (70mls), volume per beat Cardiac output (5L/min), volume per minute
What is the cardiac output equation
CO=SVxHR
What is the filling of the heart
Determined by central venous pressure (CVP)
Filling pressure=preload
What is the resistance to flow
Total peripheral resistance (TPR), determines pressure on left heart
Afterload
Found in arterioles
How are substances moved in the blood to the cells
Bulk flow
Passive diffusion
How does bulk flow work
Transport within blood/air due to pressure differences
How does passive diffusion work
Movement down con grad
What is Fick’s Law
Rate of diffusion= ∆C x A/∆x x solubility/√MX
What does Fick’s Law depend on
Area over which diffusion occurs (A)
Difference in conc of diffusing substances (∆C)
Distance over which it has to travel (∆x)
What affects the diffusion of a substance
Temperature
Solubility
√molecular weight (√MX)
What is diffusion proportional to
Conc gradient
Permeability
Darcys Law
Flow = (P1-P2)/R
If flow changes, what else changes
Pressure differences change too
Resistance does not change
If resistance changes, what else changes
Flow and pressure differences will change
Flow changes by n^4
Poiseuilles Law
R= 8VL/πr^4
What happens when diameter changes
Large resistance and flow changes
What is flow proportional to
r^4
What is resistance proportional to
1/r^4
What is viscosity and how does it affect blood flow
More viscous, more thick
Blood is a non Newtonian fluid
What is laminar flow
Viscous drag at tube sides slows fluid down
Fastest flow in center, cells aligned here in axial streaming
In small vessels, decreased viscosity in Fahraeus Lindqvist effect
How does blood flow through the capillaries and why
RBC 7um diameter
Capillaries 6um diameter
Ensures more contact, more O2 diffusion
V deformable cells, slip easily through, viscosity similar to plasma
How does turbulence arise
High velocity movement
Sharp edges, branch points especially in large tubes disrupt laminar flow, cause vibrations
The effects of greater turbulence
Increased resistance, causes vibrations
Increased velocity blood flow in narrow heart valves => murmurs
Increased velocity air flow in narrow airway => wheezes
Damages vessel walls, activation of clotting mechanism
How does flow change in distensible vessels as pressure increases
As pressure increases, flow increases in a linear manner
At a certain point, small increases in pressure lead to massive increases in flow
How does flow change in rigid Poiseuille tubes as pressure increases
Direct linear relationship between flow and pressure
How does flow change in distensible vessels with myogenic tone as pressure increases
As pressure increases, flow increases in a linear manner
At a certain point, massive increases in pressure leads to very small increases in flow as muscles are actively contracting to maintain constant flow
How does resistance change in a series circuit
R total = R1 + R2 + …
How does resistance change in a parallel circuit
1/R total = 1/R1 + 1/R2 + …
Control of organ blood flow
Changing perfusion pressure changes flow
Blood flow through organs/tissues regulated independently by resistance regulation
What happens in a parallel circuit when P1-P2 is constant but the resistance in resistance arteries in 1 tissue increases
If resistance of 1 tissue rises in the resistance arteries, the overall flow will decrease
The resistances and flows of the other tissues in the parallel circuit are unaffected
Flow controlled independently of tissue by constriction/dilation of its blood vessel
What happens in a parallel circuit when P1-P2 is variable but the resistance in the resistance arteries in 1 tissue increases
Flow through capillaries from resistance arteries in 1 tissue will decrease
To compensate for the decreased flow in 1 tissue, the others will increase the flow
What is the mean arterial blood pressure equation
MABP=COxTPR
TPR controls arteriole radius
Resistance and pressure in aorta
Large artery, low R
Diastolic pressure determined by resistance
CO > afterload
Resistance and pressure in arteries and arterioles
Branch into arterioles, diameter decreases, R increases
Pressure differences increase, P falls
Small changes in radius= large difference in R and pressure differences
Arterioles, v important in total peripheral R and MABP control
Resistance and pressure in arterioles to capillaries
Increased branching, increased R in parallel
Total R falls, P falls
Capillary pressure sufficient to maintain flow into venules
Resistance and pressure in venues to veins
Fewer vessels in parallel, R rises
But diameter increases so R falls
Overall, P falls
Overall resistance and pressure in pulmonary and systemic segments
Overall R and P lower in pulmonary than systemic
