Ventilation Mechanics Flashcards
Transpulmonary pressure
Difference between the alveolar and pleural pressures
- pleural pressures are determined via the esophagus
Compliance
(Difference in volume from two points / difference of pressures from two points)
Also can be measured by then slope between two points on a transpulmonary pressure vs lung volume graphs
- steeper the slope, greater the compliance
Effects of emphysema and fibrosis on lung compliance
Emphysema
- increases the lung compliance beyond normal values
- also increases the FRC of the lungs
- is an obstructive Lung disease, causes increased stagnant volume of air since it is an exhalation dysfunction
Fibrosis
- decreases the lung compliance beyond normal values
- also decreases the FRC of the lungs
- is a restrictive lung disease, causes decreased stagnant volume of air since it is an inhalation dysfunction
Which part of the breathing cycle has the higher compliance?
Deflation (exhalation)
- this is due to surfactant
What is the normal (quiet) breathing cycles normal TLC range?
50-60%
Hysteresis
Changes in the physical properties of the body due to changes in the forces
- quiet breathing has less hysteresis than forced breathing
Effect of surface tension on compliance
Increases in compliance
- compliance slope gets steeper, since the walls cannot stick with each other
note that liquid increases compliance more than air does
Pulmonary surfactant consists of what
Lipids
Dipalmitoylphosphatidylcholine (DPPC)
Apoproteins
What cells create surfactant?
Type 2 alveolar cells
Surfactant generation
Occurs usually around week 24 of infancy, but is almost always done by week 35
Requires a DPPC: sphingomyelin ratio of 2:1 or higher
- this ratio indicates mature surfactant production
Decreases surface tension in the lungs, increasing compliance
Neonatal respiratory distress syndrome
Occurs in premature infants whose surfactant is nor being produced on a mature level
Produces atelectasis, decreased compliance, hypoxemia
Law of Laplace for a sphere equation
P = 2T/r
P = collapsing pressure
T = tension of the sphere
R = radius of the sphere
- used for the respiratory and circulatory system to describe the relationship of collapsing pressure to radius*
- note that this equation suggests smaller alveolus have higher collapsing pressures (want to collapse), but dont in normal people due to surfactant prescience *
When is the system at functional residual capacity
At rest (no inspiration of expiration)
Changes in pressures and the respiratory system during inspiration
Inspiration muscles contract and chest expands
- increases volume in the chest and alveoli
- decreases pressures in the alveoli below the atmospheric pressure (lower than 760mmHg, usually 759mmHg), allowing air to move into the alveoli
Changes in pressures and the respiratory system during expiration
Inspiratory muscles relax, decreasing chest volume and increasing the pressures in the alveoli and lungs (above 760mmHg, usually 761mmHg)
Causes collapsing of the alveoli and air leaves back into the system from the lung
Principles Muscles of inspiration
External intercostals
Internal intercostals
Diaphragm
Accessory muscles of inspiration
SCM
Scalenes
Trans mural pressure
((Alveolar pressure) - (intrapleural pressure))
Does atmospheric/barometric pressures change during breathing?
No .
Intrapleural pressure
Pressure in the lungs at any time
At rest, hovers around -5cmHg
Gets more negative in inspiration and more positive (but not past -5cmHg) during expiration
Changes in volume, intrapleural pressure and alveolar pressures during the respiratory cycle
Inhalation:
- volume goes up (max is 500ml)
- intrapleural pressure goes down (usually around -8 H20cm)
- alveolar pressure goes more negative at the inspiration peak
Expiration:
- volume goes down to baseline
- intrapleural pressure goes back to baseline (from -8 -> -5)
- alveolar pressure becomes more positive at the peak of expiration
Airflow relationship between alveolar pressure, atmospheric pressure and airway resistance
Directly proportional
- alveolar and atmospheric pressures
Inversely proportional
- airway resistance
What does COPD do to airway resistance
Increases the resistance in all airways except in the pharynx/larynx
Increases are most apparent in the SMALLER airways
Lung volume differences in restrictive lung diseases
Residual volume (RV) = down
Functional residual capacity (FRC) = down
Total Lung Capacity (TLC) = down
Forced Vital Capacity (FVC) = 2x down
Forced Expiratory Volume (FEV) = down
FEV/FVC ratio = up or normal
- examples are pulmonary fibrosis*
Lung volume differences in obstructive Lung diseases
Residual volume (RV) = 2x up
Functional residual capacity (FRC) = up
Total Lung Capacity (TLC) = up
Forced Vital Capacity (FVC) = down
Forced Expiratory Volume (FEV) = 2x down
FEV/FVC ratio = down
examples are emphysema, chronic bronchitis, asthma, COPD
Why does the FEV and FVC decrease in the amount of air that can be pushed out of the lungs during obstructive lung diseases?
Two reasons
1)The transpulmonary pressure in the alveoli of obstructive disorders is less positive, so less oxygen moves in and out
2) the bronchioles will collapse due to inverted transpulmonary pressure gradient in the bronchioles, causing less air to be expired.
- this generates high resistance