Mechanics of Ventilation Flashcards
(35 cards)
What are the two general classifications of the respiratory system?
Conducting zone
Respiratory zone
Which zone has a larger surface area?
Respiratory zone
Muscle that accounts for most of inspiratory effort.
Diaphragm
-external intercostals also used in quiet inspiration
Two accessory muscles that aid in forced inspiration.
- Scalenes
2. SCM
Muscles used in quiet expiration and then forced expiration.
Quiet: passive
Forced: abdominals and internal intercostals
What is Tidal Volume (TV)?
volume of air inspired or expired with each normal breath.
What is inspiratory reserve volume (IRV)?
Extra volume of air that can be inspired above normal TV.
What is expiratory reserve volume (ERV)?
Maximum extra volume of air that can be expired after the end of a normal TV expiration.
What is Residual Volume (RV)?
Volume of air remaining in the lungs after the most forceful expiration.
What is Inspiratory Capacity (IC)?
IC = TV + IRV
What is Functional Residual Capacity (FRC)?
FRC = ERV + RV
What is the Vital Capacity (VC)?
VC = IRV + TV + ERV
What is Total Lung Capacity (TLC)?
TLC = VC + RV
What is transpulmonary pressure and how is it calculated?
The pressure difference between the alveoli and the intrapleural space.
TPP = Avleolar pressure - intrapleural pressure
What is the chest pressure and how is it calculated?
Pressure difference between the compressive force exerted on the chest wall by the outside barometric pressure and the recoil pressure created on the inside wall by the intrapleural pressure.
Chest Wall Pressure = Intrapleural pressure - barometric pressure
What is the respiratory system pressure and how is it calculated?
Pressure difference between outside barometric pressure and the alveolar pressure.
RSP = alveolar pressure - barometric pressure
What limits elasticity in the lungs (prevents overexpansion)?
Collagen
(elastin contributes to the elasticity and recoil with exhalation but the collagen actually limits the expansion to prevent tearing of the elastin fibers)
At what transpulmoary pressure is the lung’s compliance high and when is it low?
Compliance is the change in volume/change in transpulmonary pressure.
At high transpulmonary pressure, the compliance is low mainly because the collagen prevents expansion of the lung tissue.
At low transpulmonary pressure, the compliance is high mainly because the elastic fibers have not been stretched to resist expansion.
Why does a saline lung have less hysteresis (difference between inhalation limb and exhalation limb on a lung pressure graph) compared to a normal lung?
Saline filled lungs have less surface tension in the alveoli. The slope in phase 1 of the inhalation limb on the tranpulmonary pressure graph has a low slope due to difficulty overcoming high surface tension in the alveoli, but the slop increases in phase 2 and 3 as the alveoli open and decrease the surface tension.
Which alveoli (large or small) have higher surface tension?
Small alveoli have higher surface tension. This means that a larger pressure is required to keep a smaller alveolus open and that, given the option, air will move to a larger alveolus during inspiration.
What decreases surface tension in the lungs?
Surfactant: secreted by type II alveolar cells
Pneumocyte Type II
What effect does surfactant have on compliance and elasticity of lungs?
Increases compliance: surfactant decreases surface tension which makes alveoli easier to expand with air
Decreases elasticity: surface tension inhibits expansion of alveoli just like elastin fibers, when this is removed the elasticity decreases
most important force holding the lungs and chest wall together.
Transmural pressure
-combination of transpulmonary pressure and chest wall pressure
What causes the lungs to collapse in a pneumothorax?
Intrapleural pressure increases to zero (zero is designated as outside barometric pressure). This was the main pressure holding the lungs open and the negative pressure becomes more positive revering the force it applies on the lungs.
