DeCoursey Respiratory Mechanics II Flashcards
2 types of flow
Laminar and turbulent
Poiseuilles equation
R=8(n=viscosity)(length)/3.14)radius^4
Radius is total cross sectional area
Where is airway resistance the greatest?
at the beginning/segmental bronchi because they have the smallest Cross sectional area.
Alveoli have the greatest SA so they have very little resistance
What happens when you double driving pressure in laminar flor? Turbulent?
Laminar flow= you proportionally increase the flow rate
Turbulent- you increase the flow rate by a square root factor
Equation for reynolds number
What does it mean?
R= 2radius(flow rate)(rho(density)/eta(viscosity))
Large reynolds number means that flow is tuburlent
Where is flow always turbulent?
Trachea- has a large reynolds number due to it’s radius (DON”T THINK TOTAL CROSS SECTIONAL FOR REYNOLDS)
What decreases the diameter of the airway
AKA increase resistance
- Compression of airway
- Bronchoconstrictors (ach, parasym agonist), histamine, bradykinin, bronchitis
- Crud in airways (mucous, inhaled particles)
- Low lung volumes (less traction on airways)
- Increased air density (deep sea diving)
Decreased airway resistance occurs with
- Bronchodilation (sym (NE))
2 High lung volumes - Breathing in air with low density
How should patients with asthma breath?
Breath at higher volumes- this decreases the resistance in patients
When is flow rate the largest for expiration? Why
Just after starting forced expiration beciuase Flow rate= Delta P/Resistance and at the start of expiration the gradient is high and the resistance is low
Why does flow rate slow down during the end of expiration?
Flow rate=delta P/Resistance as the lungs empty the airways become smaller (smaller airway is more resistance=pousiles) so flow rate decreases.
The pressure gradient also gets smaller
What is a key factor to expiratory and work?
Its effort independent over most of the curve, so even if a subject “tries harder” they won’t increase expiration because there is dynamic compression of the airways
Describe shape of inspiratory curve.
Explan it
It’s even and like a parabola
Initially expand chest quickly but the resistance is still high because the radius is small
As lung volume increases so does airway radius but now the pressure gradient is gone
The inspiratiory flow rate is relatively constant and has a low peak than Expiratory
Describe volume flow curve in fibrosis
Emphysema
Fibrosis- shifts to lower volumes (right) because the luing is smaller. The airways are normal and elastic recoild may expel the air
Emphysema- shifts to the left/higher volumes, but the expiratory part is greatly reduced because of dynamic compression of the airways. THe lungs are large and floppy so theres lower elastic recoil and the brochioles are likely to collapse
What is obstructive?
Examples
Can’t get air out due to increase airway resistance
Examples- asthma, chronic bronchitis, and emphysema (due to the bronchi collapsing because the lungs lack elastic recoil ability)
Causes of Obstructive
- Foreign Object
- Increase airway resistance from thickening (bronchitis) or constriction (asthma)
- Increased airway closure (emphysema)
What happens to the pulmonary test in obstructive disease?
Spirometry- The FEV/FVC decreases
Flow-volume loop-inspiratory is the same but the expiratory shifts to high volumes
Emphysema- its scooped. They can fill lungs but can’t expel
Restrictive Disease
Examples
Can’t get air in characterized by increase recoil
Examples- fibrosis, stiff chest wall, wall respiratory muscles
What happens to the pulmonary test in resitrive? FVC, FEV, ratio?
What helps expel the air?
Spirometry- FEV and FVC decrease the ratio either decreases or stays the same
Flow and volume are low
Lung is smaller but since the airways are normal and you have greater recoil this may help expel some air
What happens to the emphysema volume loop curve
It overlaps with the normal breathing tidal breathing curve which means that expiratory is maxed out during normal breathing and they can’t increase expiration much
Describe FRC muscles? Air flow? Pressure in lungs? Transmural?
Muscles are relaxed
NO air flow
Lungs are pulliing inward making a negative pleural pressure
Pressure through the airway and alveoli is 0
So the transmural= 0 In (airway)- (+5)out(pleural)= -5
What happens to pressure gradient during inspiration
We contract the inspiratory muscles and this increases volume so decreases pressure in the airway making a gradient so air flows in.
As the lungs fill the pressure gradient dissipates and airway pressure goes back to zero
What happens at end inspiration
ASK!
- The airway pressure is zero
- The chest wall is expanded above FRC so there is an elastic recoil so the transmural is more negative that at FRC
- The transmural is increased
- IF we relax our inspiratory muscles the pressure there is an outward gradient pushing air out the lungs
What does positive transmural pressure mean?
Pressure is greater inside so the tube stays open
What happens in forced expiration
- We compress the thoracic cavity so we increase the pleura pressure
- The pressure in the airway > pleural pressure
- IN forced expiration the pressure drops as you leave the airway and at some point is half pleural making negative transmural
- Negative transmural means the airway will shut and pressure will build behind it forcing air out
- after the outflow pressure decreases again and pinches shut
DYANMIC COMPRESSION and alot of wasted work.
WHat is the key to dynamic compression>
???
Finding equal pressure where the Ptransmural is zero. and distal to this point there will be dynamic compression
How should patients with emphysema breath?
With pursed lips. This increases the pressure distal to the lips and the airways stay open
What is the pleural pressure lower than the airway pressure
In a normal individual the pleural pressure is totally occupied by fluid
3 identifying characterisics of laminar flow
- streamlined flow in which gas molecules move parallel to each other and the wall
- High axial velocity
- Efficient
5 characteristics of turbulent flow
- Chaotic movement with irregular changes in velocity and pressure
- Cannot be prevented
- Occurs preferentially in large airways
- Is less efficient that laminar flow
- is audible
Two factors that determine airway flow
Pressure and resistance
Vdot (airflow ml/min)= Pressure/resistance
What decreases the radius AKA …….? (5)
Increase resistance
- Compression of airways
- Bronchoconstrictors (AcH, parasym agonists, histamine, braykinin)
- Crud in airways (mucus, inhaled particle)
- Low lung volume- less traction on airways so more resistance
- INcreased air density as in deep sea diving
WHere is there the most resistance?
Large airways…. seems counter to Poiseuilles law but isn’t because the total area is greater in the small ariways hence the very minimal resistance
How can you predict likelihood of turbulent flow?
Where do we normally find turbulent flow? What does it mean else where?
Reynolds number
R=2(radius)(Vdot)(density rho/viscosity eta)
Large airways always have turbulent flow (consider individual radius for terminal parts not additive) but turbulence in terminal indicates pulmonary disease
What happens when you double driving pressure in laminar flow?
In turbulent flow?
Laminar- you double flow rate (proportional)- hence efficient
Turbulent- you increase flow rate by a square root- hence not effieicient
3 ways to decrease airway resistance
- Bronchodilation
- high lung volumes- high volume decreased airway
- Breathing in air with decreased density
Why is flow rate the greatest in expiration?? Why?
Just seconds after starting forced expiration because at this point pressure gradient is the highest and resistance is the lowest. because as the lungs empty the radius gets smaller (initially larger though)
Affects of working harder to increase flow rate
None- flow rate is effort independent over much of the curve and if the subject tries to breath out faster there is dynamic compression of the airways
Explain what happens in terms of volume/resistance/pressure gradient when inspiring
- initially great expansion because the pressure gradient is large even though airways are small so resistane is high
- With increase volume the airway widen but the pressure gradient decreases so flow is tentatively constant
3.
What happens to flow volume curve in
fibrosis?
Emphysema?
Fibrosis-lower peak and more narrow
Emphysema- lower peak and much wider
what happens in obstrutive disease?
Causes?
Makes it hard to get air out due to increase airway resistance
- Mechanical obsttruction
- Increased airway resistance from constriction or thickening
- Increased airway closure
What happens to flow volume loop in obstrutive disease?
Discuss expiratory and inspiratory
Shifts to high max values. Max expiratory begins and ends at higher volumes
Patients can expand their lungs to great volumes but can’t expire
Inspiratory flow rates can still be normal
Define restrictive disease
Makes it difficult to get air in characterized by increased recoil
Examples of resitrive disease
Fibrosis, stiff chest wall, respirator muscle weakness
What happens to the FEV, FVC, FEV/FVC ratio, and the flow volume loop in restrictive disease
Fev decreases
FVC decreases
FEV/FVC decreases or stays the same
Flow volume are low because the lung is smaller than normal
Flow rate may be normal or larger to attempt to correct
