Respiration I Flashcards
In normal conditions of lamina flow, what is the movement of air proportional to?
The PRESSURE GRADIENT
In normal conditions of lamina flow, what is the movement of air inversely proportional to?
The RESISTANCE
What is the total volume of air into the lungs at normal lamina flow proportional to?
DIFFERENCE in PRESSURE / Resistance
How do you calculate the ‘difference in pressure’?
Pressure in the ALVEOLI - pressure in the ATMOSPHERE
What is laminar flow?
STEADY flow down a tube in UNIFORM speed and direction
Describe the flow speed in laminar flow?
In the centre of the tube - maximum speed
As go to the edge of the tube - flow rate drops off in linear fashion
Where does laminar flow occur?
In the smaller airways
- TERMINAL BRONCHIOLES
- ALVEOLAR DUCTS
When does turbulent flow occur?
When air reaches CRITICAL VELOCITY in a the and starts to become IRREGULAR and TUMBLES
In the higher airways:
- TRACHEA
- BRONCHI
What is the flow rate in the turbulent airways proportional to?
SQUARE ROOT of the pressure gradient
With what type of air flow is it more difficult to get air into the lungs and why?
Turbulent flow:
- Proportional to sq rt and pressure gradient
- Need larger changes in the pressure gradient to produce same changes in flow rate at laminar flow (proportional to pressure gradient)
With what type of air flow is it more difficult to get air into the lungs and why?
Turbulent flow:
- Proportional to sq rt and pressure gradient
- Need larger changes in the pressure gradient to produce same changes in flow rate at laminar flow (proportional to pressure gradient)
What is the relationship between FLOW under laminar or turbulent conditions?
At LOW driving pressures: not much difference between the different flows
As the driving pressure increases:
- Laminar flow increases in LINEAR fashion
- Turbulent flow increases at a LOWER rate and PLATEAUS
When does transitional flow occur?
In airways that are:
- Bumpy
- Continuously BRANCHING
What occurs in terms of flow at a branch point?
Movement from laminar flow to transitional flow
How do you determine the flow type?
By the Reynolds number
What is the calculation for Reynolds number?
Re = 2rvp/n
Where: 2 - radius v - velocity p - density n - viscosity
What is viscosity?
How thick/sticky a substance is
What Re determines LAMINAR flow?
LOW:
<1000
What Re determines TURBULENT flow?
HIGH:
>1500
What Re determines UNSTABLE flow?
In between 1000-1500
What is unstable flow?
Switching between laminar and turbulent (transitional?)
What is the ‘real’ value for laminar flow in the lungs?
Why?
Re = 1
Lungs in the airways aren’t smooth
Describe the air flow in the lungs
- Velocity slightly goes up in the first few branches as the cross-sectional area slightly decreases
As go through the lungs:
- Cross-sectional area in the lungs INCREASE
- Velocity of the gas decreases
What happens at generation 16 of branching of the airways?
What does this do to the VELOCITY of flow in the lungs?
Why?
Conversion between the CONDUCTING ZONE and the RESPIRATORY ZONE
- Cross-sectional area INCREASES DRAMATICALLY
- Huge drop off in VELOCITY
Velocity decrease as easier to get the same volume of gas to the same place - doesn’t have to travel as fast (more travel through at the same time)
Why does the velocity decrease when the cross-sectional area increases?
Same volume of blood must get to the same place in the same amount of time - must travel faster
At generation 16 of branching, what speed does the air move at?
Moves at 1.5% speed it did when it came into the body
What is the Re in the alveoli?
Very low - laminar flow
What is the IMPACT of RESISTANCE on FLOW determined by?
Describe this
POISEULLE’S LAW:
Resistance is INVERSELY proportional to r^4
Where r - radius
(Resistance = 1/r^4)
So, very small changes in the radius have a very large impact on the resistance
Large impact on flow rate as flow rate is linked to resistance through V = change in pressure/resistance
What happens to the FLOW RATE when the radius increase?
What happens to the velocity?
Flow rate increases
Velocity decrease
What happens to the FLOW RATE when the radius decrease?
What happens to the velocity?
Flow rate decreases
Velocity increase
When is the relationship between radius and flow rate more exaggerated?
In TURBULENT flow
What is the total airway resistance in a normal person?
1.5cm H20 .s.litres^-1
Where in the respiratory system does most of the resistance in the lungs come from?
Why is this not the other way around?
In the upper airways (where there is a large diameter)
In the large airways - airways are in SERIES, so the resistance adds together (R1 + R2 + R3…)
In the smaller airways - airways are in PARALLEL, so the INVERSE of the resistances are added together (1/R1 + 1/R2 + 1/R3…)
What occurs in COPD patients?
What causes this?
Large increase in the TOTAL airway resistance
Caused by:
- Inflammation in the LOWER AIRWAYS
- Causing a huge increase in the resistance of the SMALLER airways
What is the increase in airway resistance in COPD patients?
Increase from 1.5 cm H2O .s.litre^-1 to 5.0cm H2O.s.litre^-1
What is the increase in the contribution of the lower airways in COPD patients?
From 20% contribution to 70% contribution
What 2 factors increase resistance of the airways?
How?
1) Increased mucus secretin
2) Oedema
Both decrease the diameter - increasing the resistance
What is oedema?
Increase fluid retention
How does oedema increase resistance of the airways?
Causes swelling
Build up of interstitial fluid
Compresses the airways
What effect does inspiration have on resistance?
Why?
REDUCES resistance
Causes DILATION of the airways
What effect does expiration have on resistance?
Why?
INCREASES resistance
Causes CONSTRICTION of the airways
What is FRC?
Functional residual capacity
When is FRC measured?
At the end of a NORMAL expiration
Describe the pressure gradient at the end of a normal expiration (at FRC)
No pressure gradient:
- No movement of air (resting state)
- Alveolar pressure is at 0 (relative to the atmosphere)
What is the pressure in the intapleural space at rest?
Why?
Subatmospheric (LOWER than that of the atmosphere)
Expansion of the chest wall balances the collapse of the lung
What is transpulmonary pressure (Ptp)?
The DIFFERENCE between the ALVEOLAR pressure and the INTRAPLEURAL pressure
Where is the intrapleural pressure?
In the pleural cavity
What is the Ptp at residual capacity (no airflow)
FIXED at +5 at a specific volume of the alveoli
What is the transmural pressure (Ptm)?
Difference between the pressure in the BRANCHES of the airways and the pressure in the pleural cavity (INTRAPLEURAL pressure)
What is Ptm at residual capacity?
+5
What is Ptm equal to?
Paw (airway pressure) - Pip (intrapleural pressure)
What must the Pa (Alveolar pressure) be for inspiration to occur?
SUBatmospheric (lower than that of atmospheric pressure)
MINUS value
What must the Pa (Alveolar pressure) be for expiration to occur?
MORE than the atmosphere
POSITIVE value
What is the Ptm fixed at at a specific volume of alveoli?
+5
What is Pip?
What is it equal to?
Intrapleural pressure
Pip = Pa - Ptm
= -Transmural pressure - alveolar pressure
What is Ptp?
What is it equal to?
Transplural pressure
Ptp = Pa - Pip
= Alveolar pressure - intraplural pressure
What is Ptm?
What is it equal to?
Transmural pressure
Ptm = Paw - Pip
= Airway pressure - intraplural pressure
What is the Pip if Pa is -15?
Why?
-20
Ptp = Pa - Pip
As Ptp is fixed at +5
What happens to the Paw during INSPIRATION as move from the inside to the outside of the lungs?
What impact does this have on the pressure gradient?
It becomes more POSITIVE
Pressure gradient with the atmosphere DECREASES
What happens to the Ptm as the Paw becomes positive?
Why?
What does this cause?
The Ptm becomes a higher positive
As Ptm = Paw - Pip
Causes:
- Airways to expand
- Decrease in resistance
- Air moves into the lungs
What happens to the Paw during EXPIRATION as move from the inside to the outside of the lungs?
What impact does this have on the pressure gradient?
It becomes more NEGATIVE
Pressure gradient with the atmosphere INCREASES
What happens to the Ptm as the Paw becomes less positive?
Why?
What does this cause?
It eventually becomes NEGATIVE
As Ptm = Paw - Pip
Causes:
- Airways to COMPRESS
- Increase in resistance
- Air moves OUT of the lungs
What is exaggerated in emphysema?
Why?
The compression effect of expiration
Loss of the elastic tissue (elastin) in the alveoli
Loose tethering of the alveoli to the airways - normally keeps the airways open
In emphysema what is the resting lung volume in comparison to normal patients?
What is the resistance? Why?
HIGHER resting volume
Resistance increases - compression effect of expiration increases
In emphysema, what can happen during forced expiration?
Airways can collapse
What happens to the airway resistance as breath in?
Why?
Decreases
Due to the diameter of the tubes increasing
What happens to the airway resistance as breath ou?
Why?
Increases
Due to the diameter of the tubes decreasing
What is the difference between normal patients reaching tidal volume and patients with COPD?
After 1 second in normal patient:
- Lungs reach tidal volume
COPD:
- Only 60% tidal volume
During inspiration, is the intrapleural pressure positive or negative?
Why?
Negative
So that the airways can expand (surrounds the airways)
During expiration, is the intrapleural pressure positive or negative?
Why?
Positive
So that the airways constrict (surrounds the airways)
Why does Paw become more positive during inspiration?
So that the aw can expand and fill with air
Why does Paw become more negative during expiration?
So that the aw can constrict and expel the air out
