The mechanics of obstructive and restrictive lung disease

Question 1

What helps you determine how short of breath someone was?

Answer 1

Get them to semi quantify it e.g. could they speak? words, phrases, sentences?

Question 2

FEV1 vs PF

Answer 2

PF
- easy 
- Cheap machine 
- Effort dependant 
- good for daily monitoring of an individual 
FEV1
- More accurate 
- Reduced variability 
- Less effort dependant 
- Relatively tight normal range, easier to distinguish between normality and abnormailty

Question 3

What happens to FEV1 when you’re exercising?

Answer 3

Increases as the airways expand slightly
Exercise is associated with an increase in smooth muscle activity and there are beta1 receptors on the smooth muscle of the trachea so the circulating catecholamines promote smooth muscle relaxation and therefore airway dilatation

Question 4

What is the supposed mechanism of asthma?

Answer 4

probably from the drying of the mucous layer in the airways. During exercise the tonicity of this fluid increases causing degradation of mast cells and release of bronchoactive mediators, worse when exercising in cold dry air.

Question 5

Challengers of asthma

Answer 5

Direct stimulants: histamine, methacholine
Indirect stimulants: Hypertonic saline (increases tonicity of the airway surface lining fluid, triggering release of chemicals from mast cells –> airways constriction)

Question 6

Wheeze?

Answer 6

Results from localised of diffuse airway narrowing or obstruction from the level of the larynx to the small bronchi. The noise is generated by oscillations of vibrations of nearly closed walls

Question 7

Stridor?

Answer 7

noise on inspiration, airway narrowing in the extra thoracic party of the airway

Question 8

Air way resistance as you move through the lungs? and the significance of this in common airway diseases?

Answer 8

Resistance decreases with increasing airway number (the total cross sectional area increases exponentially)
Most of the important and chronic airway diseases either predominate or begin in the small airways, therefore you can have a big change in small airway resisitance before you can pick it up in lung function tests “the silent zone of the lung”

Question 9

Draw the flow volume loop and label the important points

Answer 9

look at notes haha

Question 10

How do you measure FEV1 on a flow volume loop?

Answer 10

cant read it directly off the diagram until the machine with the clock marks it on the curve

Question 11

From the pressure volume loop what part indicates pathology in small airways

Answer 11

flows at very low lung volumes at you get down towards residual volumes.

Question 12

Pressure volume loop of characteristic obstructive lung disease patient e.g. asthma

Answer 12

has reduced flows over all lung volumes but they’re disproportionately reduced over these mid and lower volumes indicating small airways disease.
Has increased residual volume and tidally breathes at a higher FRC.
Both FEV1 and FRC reduced so their ratio unchanged

Question 13

Why is an asthma patients work of breathing increased?

Answer 13

work of breathing increased as he has to breathe through narrower tubes

Question 14

what is the advantage to the asthma patient of breathing at higher lung volumes?

Answer 14

more elastic recoil pressure, less resistive pressure.

Question 15

Why is it uncomfortable to breathe at higher lung volumes

Answer 15

because naturally we do tidal breathing at the steepest bit of the the pressure volume curve. for the same change in pressure at higher lung volumes you get a smaller change in volume

Question 16

Characteristic PV loop of person with restrictive mung disease
DRAW THE LOOP

Answer 16

reduced TLC and FEV, FVC also reduced therefore their ration still normal.
Reduced residual volume
in the restrictive loop all the flows are above that of the standard flow for that volume, because more elastic recoil causing greater tension

Question 17

What is the normal FEV1:FVC ratio

Answer 17

0.8-0.75

Question 18

Why does a asbestosis patient have fine late basal inspiratory crackles

Answer 18

With age airways at the lung bases close with tidal breathing, normal airways open as you take a big breath, the man has basal airway closure as well but his small airways are abnormal, theyre stiff and non-compliant because of the CT around them but eventually if be breathes in enough they pop open. supposed to sound like velcro.

Question 19

Why does the restrictive lung disease patient get short of breath when he walks across the room?

Answer 19

A health person would increase respiratory frequency and tidal volume, but ifMr Jones wants to take the same tidal breath as a normal person he needs to do heaps more work he cant do this amount of work so he maintains alveolar ventilation by doing rapid breaths more often