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72 Cards in this Set

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  • Back
What is the equilibrium position of the chest wall?
60% TLC
What is the effect of the chest wall equilibrium position being at 60% TLC?
The lungs are not collapsed.
What happens if the chest wall is compressed to residual volume?
The chest wall will attempt to expand and exerts an outward force of 40 cm H2O
What happens if the chest wall is forced to expand to total lung capacity?
It attempts to collapse and exerts a pulling inward force of 15 mm Hg
So what two forces oppose each other in lungs at equilibrium?
-Chest wall expanding to 60% TLC
-Lungs elasticly collapsing to 0
What is the net equilibrium position of the lungs?
40% TLC
What do we call the equilibrium point of the lungs?
FRC - functional residual capacity.
What 3 factors determine Airway Resistance? Which is most important?
1. Airway length
2. Airway diameter (main!)
3. Air density
What mainly determines airway diameter?
The lung's elastic tissue
What happens to airway diameter and hence resistance as lung volume increases?
Diameter increases so resistance decreases.
What causes the lungs to inflate during inhalation?
The elastic tissue in alveoli acting like springs on neighboring airways so they progressively dilate.
Where is airway resistance highest? Why?
In the early upper generations of airway. Because the total cross-sectional area is lowest there.
Where is airway resistance lowest? why?
In the alveoli - because they collectively have a huuuuge surface area.
What is the first generation of the bronchial tree that has alveoli?
Where in the airway is there smooth muscle?
All the way up to the alveolar ducts - but not in the sacs.
Where is the most smooth muscle?
In small bronchi
Where are alveoli first seen?
Respiratory bronchioles
How can airway resistance be regulated?
Via smooth muscle
How can airway compliance be regulated?
It's not physiologically regulated, remember?
What is the relationship between maximum expiratory flow and lung volume?
Flow is max at high lung volume, then gets progressively slower.
What happens to airflow at 40% of vital capacity (low lung volumes)?
Airflow becomes effort independent.
Why does Airflow decrease as lung volume decreases during expiration? 2 reasons:
1. Alveolar driving pressure decreases
2. Airway resistance increases
Why does alveolar driving pressure for airflow decrease during expiration?
Because the recoil tendency of the lungs is lessened - decreased transpulmonary pressure.
Why does airway resistance increase during expiration?
Because as the lungs deflate, the elastic tissues of alveoli have less springy effect on neighboring airways - less dilating effect.
So the 2 reasons why airflow decreases as expiration proceeds:
1. Recoil tendency decreased
2. Resistance increased
Why is airflow effort independent below 40% VC?
Because the Lung and Chest wall compliance remains the same below that point.
Why doesnt chest/lung compliance change beyond 40% VC?
Because this is past the lung equal pressure point.
What is the Equal Pressure Point?
The point when alveolar pressure no longer exceeds pleural pressure, because resistance increases and airway pressure decreases from alveoli->mouth.
How does the max expiratory airflow-volume curve shift in
Emph: shifts to left b/c max airflow is at higher volumes

Fibrosis: shifts to right b/c max volume is so decreased
Normally, what is the:
-Max expiratory airflow
Max airflow = 400 L/min
TLC = 5.6 L
In emphesyma, what is the:
-Max expiratory airflow
Max airflow = 200 L/min
TLC = 7L
In fibrosis, what is the:
-Max expiratory airflow
Max airflow = 200 L/min
TLC = 3 L
When does airway flow become effort independent?
When an increase in alveolar driving pressure is offset by an increase in airway compression.
2 main features that characterise emphesyma:
-Very high compliance
-Low elasticity
Result: imbalanced equilibrium of lungs/chest - FRC abnormal
Overall effect of imbalanced lung/chest wall equilibrium in emphesyma:
Expanded FRC - 7L instead of 5.5
How much of our ability to increase flowrate during expiration and inspiration do we normally use at rest? What does that tell us?
A very small bit - baby bear; tells us that we have tremendous reserve available to increase airflow during breathing.
In the schematic of maximal insp and exp flow-volume curve:
-What does Papa bear represent?
-What does Mama bear represent?
-What does baby bear represent?
Papa = maximum value for airflow and lung volume
Mama = airflow/volume increase during heavy exercise
Baby = values during resting
Where does mama bear touch papa bear during exercise?
Only briefly during expiration
Why does mama bear only touch papa bear BRIEFLY?
Because it is inefficient to continue expiring at max ability, b/c of the point at which airflow becomes effort independent.
What is the most significant change to breathing during heavy exercise?
Inspiration flow rate
So which reserve do we use most? Why?
Inspiratory reserve - it's more efficient.
3 Types of Work accompilshed during inspiration:
-Tissue Resistance
-Airway resistance
What diagram shows respiratory work?
Change in lung volume vs change in pleural pressure
What is the slope of the volume vs pressure diagram for breathing?
What is the area to the left of the compliance curve?
Compliance work - Elastic work
What is the area to the right of the compliance curve?
Tissue Resistance work (closest to the line) + Airway resistance work (outermost)
What do we call the sum of Tissue Resistance + Airway Resistance work?
Inspiratory work
How can you esimate the Elastic and Flow Resistive work of breathing from the compliance diagram?
By multiplying the change in pressure times change in volume.
What would change in the respiration work diagram if the upper airway diameter was reduced by 90% from normal?
The loop/area to the right of the diagonal compliance curve would increase, but not the compliance curve itself.
Why would the area to the right of the compliance diagnoal increase if airway diameter was decreased?
Because of the huge increase in airway resistance.
What are 4 diseases in which airway resistance is increased?
1. Emphysema
2. Bronchitis
3. Asthma
4. Obstructive sleep apnea
Why is airway resistance increased in emphysema?
Because the lung elastic tissue tethering of airways is decreased - so airways are not as dilated.
Why is airway resistance increased in Bronchitis?
Because of increased mucous and airway inflammation reducing the diameter
Why is airway resistance increased in Asthma?
Because the airway smooth muscle is hyperreactive, and excessive contractions narrow the airways.
Why is airway resistance increased in Obstructive sleep apnea?
Because of excessive fat and/or reduced airway dilator muscle activity, closing/compressing the pharyngeal airway.
Does changing breathing frequency effect Elastic (compl) work and flow (airway) resistive work of breathing?
How does an Increased Tidal Vol and Low Breathing Frequency affect Elastic/flow work?
-Elastic work is high
-Flow resistant work is low
Why is airway resistive work low at high tidal volumes and low breathing frequency? (2 reasons)
1. Airway is dilated
2. Air flow rate is low
What happens to breathing when tidal volume is LOW but breathing FREQUENCY is high?
-You're mainly replacing dead space volume repeatedly
-Flow rates are high
So what work values change in high breathing freq and low TV?
-High resistive work
-Low elastic work
Where is optimal breathing work?
At the middle of the graph of work vs. breathing freq
How do we achieve optimal work of breathing?
By our respiratory control centers in the medulla
What do the medullary respiratory control centers do?
Set a TV and frequency that is most efficient for each individual.
What is the Time Constant of an airway?
The rate of alveolar filling when a pressure change is applied.
What determines the time constant of an airway-alveolar unit?
Compliance and resistance
What will increase the time constant?
-Increased resistance
-Decreased compliance
How should the time constants for individual alveoli be related?
They should be equal/uniform
What happens at low breathing frequency when the time constants are not uniform throughout the lung?
It's not a big deal because there is a pause when lagging alveoli can fill and catch up.
What happens at high breathing frequency when the time constants are not uniform throughout the lung?
There is no pause so while alveoli with long time constants
are still filling, those with short time constants are emptying.
What are the results of alveoli simultaneously filling/emptying?
The emptying fast ones will dump their old air into the slow alveoli; Hypercapnia + Hypoxemia
What is the term that denotes alveoli having different time constants?
Pendelluft Effect
finish looking at frequency dependent dynamic lung compiance in asthmatic humans