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Resp Block Week 1: Respiratory Mechanics
Terms in this set (75)
What are the primary inspiratory muscles? Accessory inspiratory muscles?
Primary respiratory muscles:
Accessory inspiratory muscles:
T/F: Inspiration is mostly a passive mechanism at rest.
False: Expiration is mostly a passive mechanism at rest.
How does the diaphragm cause inspiration?
Contracts and drops in the thoracic cavity, increasing its volume
What are the two major properties that affect air movement in and out of lungs?
1. Static compliance (=1/elastic recoil)
a. Lung internal structure (fibrous elements, surface tension)
b. Chest wall flexibility (thoracic compliance)
2. Dynamic airway resistance (largely a function of tube radius - Poiseuille's law)
What is static compliance?
The structure of the lungs, chest wall itself (= 1/elastic recoil)
"How much volume can the lung hold?"
What is dynamic airway resistance?
Resistance that must be overcome to get air to the alveoli; about the actual pathway of air during inspiration and expiration
What is included in the total effort of breathing?
Static and dynamic resistance
What is the difference between static and dynamic resistance?
Static: overcoming elastic forces and maintaining current lung volume
overcoming resistance and inertia, producing airflow
What is the equation for transmural pressure?
P(tm) = P(A) - P(Pl)
P(A) = alveolar pressure
P(Pl) = pleural pressure (must be negative for inflation)
What is the equation for pleural pressure (i.e. pressure outside)?
P(Pl) = P(A) - P(tm)
What is the equation for change in pleural pressure?
Delta P(Pl) = -delta V/C + (flow x R)
What is the equation for total effort of breathing?
Total effort = static + dynamic
What is compliance? What is the equation?
How much energy you need to put in to get a certain change in volume
The more compliant you are, the more volume you get for a given pressure (i.e. more bang for your buck)
Compliance = 1/elastic recoil = delta V/ delta transmural pressure
What is the relationship between compliance and elastic recoil?
Compliance is the reciprocal of elasticity
Compliance = 1/elastic recoil
What do you need in order to have any volume in the lungs?
Negative pressure outside of the lungs (pleural space) that holds lungs open
Describe the forces immediately after a tidal expiration
Forces are exactly balanced = tendency for lungs to want to go back to original shape and collapse (elasticity)
What is elasticity relative to the lungs?
the tendency for the lungs to want to go back to their original shape and collapse after a normal tidal expiration when forces are exactly balanced
What balances the elastic recoil of the lungs following expiration?
The elastic recoil of the chest wall (which has a tendency to pull outward)
When are the forces of elastic recoils of the lungs and the chest wall in balance?
Immediately after a tidal breath expiration - i.e. functional residual capacity
When is functional residual capacity achieved?
Right after a tidal breath when you expire
What is the equation for lung compliance?
C = V/P
What is compliance on the static lung compliance curve? What are the X and Y axises?
Compliance = V/P = slope of the linear part of curve in the graph
X axis = intrapleural pressure (cm H2O)
Y axis = volume above FRC (L)
What does the slope represent on a static lung compliance curve?
What is the intrapleural pressure (i.e. negative pressure in the pleural cavity that keeps the lungs open) at resting tidal volume (functional residual capacity)?
-5 cm H2O
Which way will the slope shift in a static lung compliance curve with restrictive disease (i.e. scar tissue, fibrosis)?
How do you calculate compliance from a static lung compliance curve?
Changes in values
On a static lung compliance curve what is represented by the area under the curve/line?
Work = [delta P x delta V)/2
What is the equation for work?
Work = (change in pressure x change in volume)/2
Decreased ventilation from decreased compliance is referred to as...
What is restrictive lung disease?
Decreased ventilation due to decreased compliance
What are 2 lung compliance changes that can cause disease?
1. Elastic forces of lung tissue - determined by fibrous elements (collagen and elastin); compliance is reduced by the presence of scar tissue from repeated infections or as a result of some connective tissue diseases (fibrosis)
2. Surface tension - in neonatal respiratory distress syndrome absence of surfactant increases surface tension and makes inspiration require very strong muscular contractions
What determines the elastic forces of the lungs?
The fibrous elements (collagen and elastin)
Compliance is reduced by the presence of scar tissue from repeated infections or as result of some connective tissue diseases (fibrosis)
Describe the structure and molecular characteristics of surfactant
Amphipathic = hydrophilic and hydrophobic components
Is the surfactant film thicker or thinner in small alveoli?
Thicker in small alveolus; thinner in large alveolus
How does surfactant reduce surface tension?
Surfactant molecules insert themselves on the air-liquid surface and push water molecules apart so that you reduce the additive effect of hydrophilic bonds between water molecules
Describe how surfactant changes during inspiration vs. expiration
At the end of expiration, the surfactant molecules are close together = diluting the water, pushing more of the water away, making it easier to expand
When you expand and breath in, surfactant molecules move further apart and more water molecules can insert = dilution of surfactant = more surface tension = helps with elastic recoil when inhaling
What are the effects of changes in surface tension on lung compliance?
Eliminating surface tension by filling a lung with saline instead of air increases lung compliance; increasing surface tension by lavage with saline (removes surfactant) before air re-infiltration decreases lung compliance
What happens when you inflate lungs with fluid? Why?
Gets rid of air-water surface so you don't have surface tension to overcome
The trigger for synthesis and secretion of pulmonary surfactant occurs immediately before birth. Infants born prematurely may therefore lack sufficient levels of surfactant and develop infant respiratory distress syndrome (IRDS).
Compared to normal compliance (i.e. ΔV for a given ΔP), which graph represents the P-V relationship, or compliance, for an infant suffering from IRDS?
B (fibrosis on this image)
Lower slope = decreased compliance = less volume change for same amount of pressure
Describe the effect of emphysema on the P-V relationship?
Increased compliance (breakdown of alveolar walls, less tethering = easier to get air in)
But huge effort to get air out
Emphysema results in (increased/decreased) compliance.
Breakdown of alveolar walls, less tethering = easier to get air in
But huge effort to get air out
RDS results in (increased/decreased) compliance.
What is alveolar interdependence?
Alveolar are more hexagonally shaped than spherical; different sizes interconnected/tethered to each other
Helps prevent collapse
Equation for compliance?
delta V/delta P
For the same amount of work (i.e. pressure), decreased compliance results in (increased/decreased) lung volume
What conditions can cause decreased thoracic compliance?
Thoracic cage injury
Skeletal changes as in severe scoliosis
Airway resistance is primarily a function of:
What is emphysema?
Alveolar wall destruction
Emphysema results in (over/under)-inflation
What are the characteristics of chronic bronchitis?
What are the characteristics of asthma?
Bronchial hypperresponsiveness triggered by allergens, infection, etc.
Emphysema and chronic bronchitis are examples of...
Small airway disease = COPD
What is this describing?
Bronchial hypperresponsiveness triggered by allergens, infection, etc.
Persistent coughing with sputum production is a characteristic sign of...
Chronic bronchitis (COPD)
The majority of airway resistance occurs in conducting airways due to...
Turbulent air flow
Airway resistance (decreases/increases) as lung volume and airway radius increases
What is the equation for resistance?
R = 8nl/pi*r^4
R = 1/4^4
People with increased airway resistance (COPD) breath at (higher/lower) lung volumes. Why?
Lower. At higher lung volumes it is easier for them to breath = less resistance (tap into tethering to keep airways open)
What happens to alveolar pressure in obstructive disease?
Increases to move the same amount of air at the same velocity
What is the total work of breathing?
= elastic recoil work + airway resistance work
What is the difference between restrictive and obstructive lung disease?
Restrictive = we don't have problem with airways but we have noncompliant lung = something wrong with thoracic cage or tissue (fibrosis) = have to put in more pleural pressure to achieve and hold volume; pathway is ok
Obstructive = we have compliant lung but we can't get air to the lung to inflate; work to overcome compliance is the same as in normal but we have to add a lot more work to pull air past obstructions and to push out past obstructions
Where does the total effort of breathing come from?
Pleural pressure (i.e. coming from respiratory mm, generating pleural pressure to overcome static compliance and resistance to airflow)
Restrictive disease affects (compliance/airway resistance)
Obstructive disease affects (compliance/airway resistance)
What happens to the diaphragm as you breath in? As you breath out?
Inhalation: diaphragm flattens out and descends towards abdominal cavity
Exhalation: ascends and develops curvature, thoracic volume decreases
What happens to the transverse thoracic diameter and AP diameter during inspiration? Why?
Increase. Bucket handle motion and pump handle motion
Bucket handle motion ribs increase which dimension of the rib cage?
What makes the diaphragm able to do what it does?
Zone of apposition (60% of surface area of diaphragm) = overlap of costodiaphragmatic fibers, alignment of muscle fibers so that portion of the diaphragm that is contracting pulls straight upward (rather than inward)
What is the zone of apposition?
The mechanics of the costovertebral and costochondral articulations that steer the rib into going out wider and up; allows the diaphragm to pull straight up
What is the analogue of the zone of apposition (i.e. 90 deg angle to thoracic diaphragm)?
Transversus abdominus muscle
How might a dysfunction in the transversus abdominus muscle affect the diaphragm?
If you can't push in with transversus abdominus muscle then you will have difficulty building up enough pressure against abdominal contents to mechanically raise ribs
External intercostals drive (inspiration/expiration)
Internal intercostals drive (inspiration/expiration)
Expiration with one exception (innermost intercostals are expiratory)
The innermost intercostals are (inspiratory/expiratory)
Expiratory (the other internal intercostals drive inspiration)
How does COPD affect the diaphragm?
Flattening = a lot of wasted energy for very little return
You no longer have fibers oriented vertically to lift ribs and pull out; rather you have fibers that are oriented transversely = pull ribs inward
Can have reverse mechanics in severe disease = when patient breaths in, their diaphragm goes in opposite direction
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