physiology

Question 1

pefr

Answer 1

maximum flow achieved during expiration delivered with maximal force from TLC’ • Contrived test • Physiologically ‘flow is a function of resistance and lung recoil’ • ‘Majority of resistance is encountered in the upper airway’ • Therefore, PEFR is a function of large airway patency and elastic recoil of the lung

Question 2

PEFR 2

Answer 2

• Test performed at maximal inspiration
(TLC)
• The expiratory force (PEFR) is thus a
measure of: -
Muscle contraction + elastic recoil of the
lung – upper airway resistance

Question 3

why use PEFR?

Answer 3

• Asthma
• Diurnal variation (>20%) is diagnostic
• All asthmatics should know their best
PEFR (standard tables)
• Indication of control of condition and
whether there’s an environmental factor
(occupational asthma)

Question 4

asthma continued

Answer 4

• PEFR <50% is an indication of ‘Acute
severe asthma’
• <33% is ‘life threatening’ asthma
• Admitted asthmatics shouldn’t be
discharged until diurnal variation is <25%
• Wide diurnal variation is indicative of
poorly controlled asthma

Question 5

pefr summary

Answer 5

• Diurnal variability is the hallmark of
asthma
• Lack of variability (when well) and low
PEFR is indicative of COPD
• However, there are many causes of a low
PEFR
• A low reading should prompt further
testing

Question 6

spirometry

Answer 6

• Widely used
• Plot of Volume v Time
• Forced Manoeuvre
• Two basic values and one ratio
• FEV1
• FVC
• FEV1/VC * 100 (FEV1/VC ratio)
• FET
• VC

Question 7

things affecting the spirometr

Answer 7

Question 8

FEV1

Answer 8

• Speed of emptying
• Thus indirect measure of airflow
• Physiologically its a function of the lungs
elastic recoil, TLC, airway patency and
muscle strength

Question 9

FEV/FVC ratio

Answer 9

• Physiologically its Rate of flow agin
change in volume
• Normal 70-80%%
• Obstructive <70%
• Restrictive >80%

Question 10

obstruction

Answer 10

• Airway disease affects the flow more than
the volume—it empties more slowly
• Common causes:
• COPD, asthma, bronchiectasis
• The severity of the obstruction is given by
the FEV1 e.g. COPD
• Mild =/>80%, Moderate <80%, severe <50%, very severe <30%

Question 11

restrictive

Answer 11

• Conditions which the expansion of the lung is
restricted
• Physiologically there is a reduction in TLC
• Due to:-
• 1) Loss of alveolar volume
• 2) Diseases of the chest wall (incl pleura)
• 3) Neuromuscular disease
• 4) ‘Space occupying lesion’ within the thorax

Question 12

summary

Answer 12

• FEV1— used to monitor airway disease (asthma/COPD/CF)
• FVC/VC — used monitor restrictive disease and NM weakness
• Obstructive <70% pathophysiology: airway disease leading to
reduced airflow
• Restrictive Normal or >80% pathophysiology: reduced lung filling
causing a proportionate reduction in airflow

Question 13

kco

Answer 13

• ‘Gas exchange capacity’
• Thickness of the alveolar/capillary
membrane
• Volume per unit time Hb passing that
membrane (dependant upon capillary
density and RBCs)
• Reaction rate of CO with Hb

Question 14

summary

Answer 14