Respiratory problems

Question 1

Advantages and disadvantages of PEF and FEV1

Answer 1

PEF
A: Easy, cheap, can monitor himself
D: effort dependent, great variation (e.g some big lungs, small airways)
FEV1
A: Reduced variability, less effort dependent, tight normal range (can distinguish between normal and not)
D:

Question 2

Time course of FEV1 lung function in asthmatic exercising

Answer 2

Exercise, raise in FEV1 due to sympathetic drive, and loss of vagal tone increasing lung function.
Decrease in function, potentially due to fluid in airways drying, increase in tonicity, mast cells release bronchoconstrictors (exercise induced asthma)

Question 3

Exercise induced asthma is worse

Answer 3

In cold/dry air

Question 4

The amount of drop of FEV1 in asthmatics, is the? What is this indicative of?

Answer 4

How bad the asthma is

Airway hyper responsiveness, how twitchy the airways are

Question 5

What two things lead to the manifestations of asthma

3 mechanisms by which these come about

Answer 5

Airway hyper responsiveness + Mediator release (leukotrienes, histamine, PG’s)

Abnormal secretions (mucus gland hypertrophy); airway obstruction (oedema, mucus plugs); SM activity (hypertrophy/hyperactivity)

Question 6

How is airway responsiveness tested?

Answer 6

Challenge test, induce bronchoconstriction
Direct: histamine, methacholine that directly narrows
Indirect: Nebulised hypertonic saline (mimics exercise, stimulates mast cell degradation)

Question 7

Diagram in book explaining inspiration and expiration

Answer 7

Palv= Ppl + Pel
At end of tidal breath, alveolar = atmospheric, so pleural and elastic are equal. Makes sense, no flow.
-Normal inspiration, more negative pleural pressure, negative alveolar, so flow into alveolus
-Normal expiration is passive, pleural pressure drops, and elastic pressure the same so expiration

Question 8

Diagram explaining wheeze on forced expirations

Answer 8

• Due to force, pleural pressure becomes MORE positive, so larger pressure gradient along airways for expiration.
• Along airways at some point, there is constriction in the airways.
• The pressure before the constriction is greater than, or the same as pleural pressure.
• NORMALLY, the airway pressure is lower than pleural pressure in extrathoracic/bronchial walls, which DO NOT collapse as cartilage present
• In asthma/airway obstruction, constriction occurs, and airway pressure = pleural pressure.
• Downstream, still in non supported bronchioles, airway pressure is lower than pleural, causing airway compression.
• resistance higher than expiration, causing wheeze

Question 9

Inspiratory wheeze (stridor) model (diagram)

Answer 9

Extrathoracic obstruction causes airway collapse as atmospheric pressure is greate than the negative pressure induced by inspiration, increasing resistance, causing wheeze

Question 10

Airway resistance and airway number
Why?
What are the small airways sometimes dubbed and why?

Answer 10

Increases a bit, then decreases a lot, this is because small airways have a large cross sectional area in total, yet individually have the most resistance.
Silent zone, as pathologies often begin in small airways, and may take sometime to see effects in lung function tests

Question 11

Labelled diagram of flow volume curve

Answer 11

Look

Question 12

Features of airflow obstruction on flow volume loop

Answer 12

Peak flow is reduced.
Reduced flow at all lung volumes, especially small airways
FVC is reduced, so increased RV
Increased FRC, as tidal breathing is shifted left
FEV1 reduced
FVC reduced, but not as much as FEV1, so reduced ratio
Reduced TLC
Breathing at increased lung volumes, hyperinflated

Question 13

Disadvantages and advantages of breathing how we do in asthma

Answer 13

Disadvantages: As on pressure volume loop, at higher volumes, lung is less compliant, such that a same change in pressure elicits a smaller change in volume, increasing work of breathing (elastic)
Advantages: Airway is hyperinflated, so more tension on airways, which increases elastic pressure, (assists expiration) and holds the airways open. reduces resistive work of breathing

Question 14

Features of RESTRICTIVE lung disease on flow volume loop

Answer 14

• reduced TLC, can not distend lungs as well
• Reduced FEV1 and FVC, to same degree, giving a normal or slightly raised ratio (normal is 0.8)
• reduced RV, as increase in elastic recoil

Question 15

In restrictive lung disease, for any given lung volume, the flow is higher than in a normal flow volume loop, why?

Answer 15

Fibrosis increases elastic recoil, increases the expiratory capacity, and reduced inspiratory one
Thus may have an increased peak flow

Question 16

Why does man with restrictive lung disease have fine bilateral late inspiratory crackles (velcro crackles)

Answer 16

Less compliant small airways
During inhalation, lower compliance means negative pleural pressure does not open these small airways until right at the end, and air rushes in

Question 17

Why is SOB indicative of and what are the inputs

Answer 17

Increased work of breathing! Little to do with gases

Inputs: PO2, PCO2, receptors, ventilatory inefficiency

Question 18

Pressure volume relationship in man with restrictive lung disease, and why his elastic work of breathing is so high

Answer 18

For a resting tidal breath, we exert the area denoted (see graph)
Due to right shifted, flatter pressure volume curve, for the same tidal breath, must do more elastic work
On exercise this is augmented a lot, elastic work required to increase tidal volume is large. In order to counteract this massive work, small shallow breaths to maintain alveolar ventilation

Question 19

Read Char’s notes on emphysema after asthma, as obstructive, different mechanism

Answer 19

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