L7 Dynamics of Ventilation Flashcards Preview

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Flashcards in L7 Dynamics of Ventilation Deck (10):

Requirements of lung movement

1) Delta V = a) Air into lung= lung must expand. b) Air out of lung=decrease volume
2) overcome Elastance
3) overcome resistance to airflow (RV.)
Delta P = E x DeltaV + RV.
= DeltaV/C + RV.
(Equation of motion of respiratory system)


Ventilation essentials

Ventilation (V.) cannot occur unless Delta P is large enough to overcome:
1. Tissue elastance
2. Air flow resistance


Equation of motion of respiratory system

Delta P = E x DeltaV + RV.
= DeltaV/C + RV.


Dynamic effects of elastance and Resistance

requires measurement of intrapleural pressure
Faciliated by anatomical peculiarity
P(intrapleural)=- P oesophageal
-needle through ribs into intrapleural space
-ask patient to swallow balloon go down into oesophagus, will become intrapleural pressure when low enough


Graph withDynamic effects of Elastance and Resistance

1. 4sec for one total breath. 15 breaths per min
2. 600ml+ tidal volume
3. Inspiratory downwards. Peak air flow = steepest part of volume-function-of-time curve (rate of change)
-+ coincides with 1 unit magnitude arrow in both graphs
4. Passive elastance curve: Total change in pressure vs elastance of lung.
-inhale/exhale VERY SLOWLY = negligible airflow resistance = dotted line
-exercise = airflow resistance= adds compliance
5. Difference= direction and magnitude of the arrows
6. Pip starts negative= lung collapsing= chest wall resisting= subatmospheric pressure


Airflow Resistance

Air-Flow resistance introduces a phase-shift (time-lag) between pressure and Flow
-minimum value of elastance doesnt co-incide with minimum value of elastance or 0 crossing point of airflow


Flow-Volume Diagram

inhale 1L Volume= small fraction of Total lung capacity = resting/walking up stairs (not exercising)
Pressure= Airway opening/barometric pressure - oesophageal pressure(Pip approximate) = increasingly negative axis
Up= inspiration
Compliance through middle
Pst= static pressure to overcome lung tissue compliance
Inspiration --> Expiration change= point where no air is being moved at all = Ventilation=0


Flow-Diagram second diagram

c) -20 intrapleural pressure
larger loop= faster drawing in same volume
expiratory= Pip becomes positive= exhale 1L very rapidly
a) very slow breath = almost no airflow resistance = only be overcoming elastance = dotted line on first graph


Flow-Diagram graph compared to Mechanics of breathing graph

1. + airway pressure = active = point at which lung volume is at FRC
2. imagine vital capacity if 5, but our gas is 1L
3. Centre line in the loop corresponds with lung compliance
Note: Scale difference ( flow-diagram narrower)


Work of breathing

W = P x dV
Work (energy) is expended against:
1. tissue elastance
2. air-flow resistance