DeCoursey Respiratory Mechanics I Flashcards
Which pressures are greater when air flows Out?
In?
Out- Pressure Alveolar> Pressure B/Air
in- Pressure Air/B > Pressure Alveolar
Boyles Law is?
PV/T= Constant in an enclosed container
P1V1=P2V2- for fixed amount of gas (enclosed container) at constant temp
Membranes Surrounding of lungs?
- Visceral Pleura- internal boundary, attached to lung
- Parietal pleura- outside boundary, lines the chest wall
Space between forms the potential space- pleural space
What 3 conditions can come from disruption to the visceral space/pleurae
- Pneumothorax- air enters the potential spae
- Pleural effusion- fluid enters the potential space
- Empysema- fluid enters the same in severe infection
What is the favorable volumes of the lung and chest wall?
Why don’t they reach these values?
Lung- 800ml
Chest wall- 4500ml
They don’t reach these values because they are virtually attached by the pleura
What happens during pnemothorax?
Pleural has negative pressure so when you poke a hole, air enters the potential space and the chest wall expands and the lungs collapse
Why is pleural pressure negative at FRC?
ADD TO/Review THIS CARD
Lungs pull inward, chest wall pulls outward
pleural pressure «< Alveolar Pressure alwayss!
Steps of breathing in
- Contract inspiration muscles (diaphragm and external intercostal)
- Decrease in Pleural Pressure
- Increase in Alveolar Volume
- Decrease Alveolar pressure
- Air in (Palveolar«_space;Pressure atmos.)
- Return Pressure Alveolar to Pressure atmos.
Steps of breathing out
What happens in increased ventilation?
- Relax inspiration muscles (passive) causes elastic recoil of the lungs
- Increase in pleural pressure
- Decrease in Alveolar volume
- Increase in Alevolar pressure
- Air out (alveolar pressure» Atm pressure)
- Return to Palv to Patm
Increased ventiliation internal intercostal become active and pull inward and downward on ribs opposing the external intercostals
Importance of diaphragm in respiration
- It’s the main inspiration muscle
- When this dome shaped muscle contracts it pushes the abdominal contents
down and forward increasing lateral dimension of thoracic cavity
Four forces that have to be overcome by respiratory muscles?
- Elastic recoil of chest cavity
- Elastic recoil of lungs
- Surface tension
- Airway resistance
What is elastic recoil of lungs measured by?
Compliance= DeltaV/DeltaP
How does compliance change with volume in the lungs?
At high volumes the pressure volume curve is flatter and compliance is low- same work produces smaller change in volume when compliance is low
At moderate volumes (near FRC), the compliance is high (steep slope) because the lung is unfolding and can easily increase volume
4 situations where compliance is reduced
- Pulmonary Fibrosis
- Alveolar edema-makes alveoli harder to inflate
- Unventilated Lung regions-collapsed alveoli or increased surface tension
- Increase in pulmonary venous pressure- causes lungs to be engorged with blood
What happens in pulmonary fibrosis?
Infiltration of lymphocytes/plasma cells–> increased fibroblast–> these lay down collagen thickening the alveolar walls
Ultimately decreasing compliance
When is compliance too high?
Pulmonary Emphysema- due to the change in the elastic recoil of the lung tissue
Define COPD
Airway obstruction due to chronic bronchitis, emphysema or a mixture of the two.
Why is Pressurepleural«_space;Pressure Alveolar ALWAYS
The lungs are always pulling inward decreasing alveolar volume and increasing alveolar pressure above whatever the pleural pressure is
At what percentage of TLC capacity is chest wall relaxed?
80% So this means the chest is pulling outward over most physiological ranges
What happens at values near 100% of VC?
Both the chest wall and lungs are pulling inward so respiratory muscle have to work hard to inflate lungs to TLC
Diseases that affect compliance of the chest wall
These are more rare than affect compliance of lung but
- Ankolsing spondylitis (spinal joint inflammation)
- Kyphoscoliosis
- Obesity
What is complaince of the system compared to lungs and chest wall alone?
Compliance of the system is less (flatter slope)
What is happening at FRC with forces? What percentage of Vital capacity?
Inward of lung is equal and opposite to outward of chest cavity so the system is at rest/equilibrium
About 40%
What is surface tension? What does it do in the lungs?
Its the tension force at the interface between two phases.
IN the lungs there is an air/water interface that tends to collapse the alveoli
Explain the saline/air experiment of surface tension
For Saline the lungs inflate and deflate easily and the same because we have eliminated the air/water surface tension
With air it takes 3-4 more work to inflate lungs
Also there is hysteresis-meaning deflation and inflation follow different curves. This is partially due to pulmonary surfactant.
Define atelectasis
Law that determines atelectasis
collapsed alveoli
LaPlaces law
LePlaces Law
P= 2(T)ension Surface/radius in sphere
Small radius collapse more
Large radius stay open
Effects of surfactant
- Reduce Surface tension and atelectasis
- Increase compliance
- Reduce work of breathinig
How does surfactant work?
Where is it secretated from?
It’s a thin layer of fluid that lines the alveolus that reduces surface tension by opposing intermolecular forces.
Hydrophobic- towards air
Hydrophilic towards water
Secreted from Type II alveolar endothelial cells
Surfactant in fetus appears when?
Premature lacking surfactant have?
Type appears ~6 months and surfactant Week 24-35 (7-8 months)
Infant Respiratory Distress Syndrome leading cause of death in premature
Two forces that oppose atelectasis
- Surfactant
2. Interconnectedness of lung tissue- when alveoli begins to collapse it pulls on neighboring alveoli and they pull back
Where is surfactant packaged?
What is it composed of?
Lamellar bodies
DPCC
Where do you find Type I and Type II alveolar epithelial cells?
Type 1- thin, flat that lines 95% of alvelar surface
Type 2- cubodial in the corners of alveoli
Situations that reduce surfactant
PAAAID ASS O
- Pulmonary Embolu- prevents “food” from getting to Type II so no production
- Acidosis
- Atelectasis
- ARDS (adult resp. distress syndrom)
- IRDS (infant)
- Drowning
- Abdominal Surgery
- Smoking
- Shock
- Oxygen related abnormalities (low/too much O2)
Increase surfatant
- Mechanical Stretch (Yawning)
- Birth (hormonal effects)
- Secretagogues (Beta agonist)
Discuss elastic recoil at
High volumes
Low Volumes
High- elastic recoil is stronger– makes sense, lower compliance so can’t inflate much more
Low volume- counter-intuitive large pressure is required to inflate because surface tension is greatest at smaller volumes. So you have to pass a critical opening pressure
Think balloon hard to start but once it starts its easeir
