L7 Dynamics of Ventilation Flashcards Preview

Respiratory System Module > L7 Dynamics of Ventilation > Flashcards

Flashcards in L7 Dynamics of Ventilation Deck (10):
1

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)

2

Ventilation essentials

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

3

Equation of motion of respiratory system

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

4

Dynamic effects of elastance and Resistance

requires measurement of intrapleural pressure
Pip
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

5

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

6

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

7

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

8

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

9

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)

10

Work of breathing

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