Clinical evaluation of respiratory function

Question 1

What is spirometry?

Answer 1

investigation of airway
obstruction and lung restriction

Question 2

What is FVC?

Answer 2

Forced vital capacity

Question 3

What is FEV1?

Answer 3

Forced expiratory volume in 1 second

Question 4

What is the equation to determine % of total lung capacity an individual can exhale in
the first second ?

Answer 4

100 x FEV1/FVC

Question 5

At what percentage is 100xFEV1/FVC indicative of obstructive airway disease?

Answer 5

<70% is indicative of obstructive airways disease

Question 6

How does obstructive airway disease appear in spirometry and what is an example of a disease?

Answer 6

Obstructive:
FEV1/FVC <70%
FVC >80%
E.g. Asthma
↑Resistance

Question 7

How does restrictive airway disease appear in spirometry?

Answer 7

Restrictive:
FVC < 80%
FEV1/FVC > 70%
E.g. Fibrosis
↓Compliance

Question 8

What is the rule for spirometry for an obstructive respiratory disease?

Answer 8

FEV1/FVC<70%, FVC = Normal

Question 9

What is the rule for spirometry for restrictive respiratory disease?

Answer 9

FVC <80% of predicted volume, FEV1/FVC = Normal

Question 10

What is the rule for mixed obstructive and restrictive respiratory disease?

Answer 10

FEV1/FVC <70% and FVC<80%

Question 11

What is lung compliance?

Answer 11

Lung compliance is the relationship between
transpulmonary pressure and lung volume

Question 12

What is the equation for compliance?

Answer 12

Compliance(CL) = change in volume/change in pressure

Question 13

What is static compliance?

Answer 13

Measurements taken whilst airflow = 0

Question 14

What is dynamic compliance?

Answer 14

Measurements taken during movement of air

Question 15

What are the axis when measuring static compliance?

Answer 15

x axis - Transpulmonary pressure
y axis - Lung volume

Question 16

What are the axis when measuring dynamic compliance?

Answer 16

x axis - (-)intrapeural pressure
y axis - Lung volume

Question 17

What does the size of the internal area or ‘fatness’ of the loop in a dynamic compliance graph measure?

Answer 17

The size of the internal area or
‘fatness’ of the loop is proportional
to the level of airway resistance.

Question 18

How do lungs and kidneys maintain blood pH homeostasis?

Answer 18

The lungs & kidneys maintain blood pH homeostasis
by regulating PaCO2 & [HCO3-], respectively

Question 19

What does an increase in ventilation do to PaCO2 and pH?

Answer 19

↑Ventilation = ↓ PaCO2 = ↑ pH

Question 20

What does a decrease in ventilation do to PaCO2 and pH?

Answer 20

↓Ventilation = ↑ PaCO2 = ↓ pH

Question 21

What does a decrease in HCO3- excretion do to [HCO3-] and pH?

Answer 21

↓ HCO3 excretion = ↑ [HCO3-] = ↑ pH

Question 22

What does an increase in HCO3 excretion do to [HCO3-] and pH?

Answer 22

↑ HCO3 excretion = ↓ [HCO3-] = ↓ pH

Question 23

What is the equation to calculate PAO2?

Answer 23

PAO2 = F1O2 x (PB-PH20) - PaCO2/RER
PAO2 - Alveolar O2 pressure
F1O2 - Fraction of oxygen present in inspired gas
PB - Barometric pressure
PH20 - H20 Vapour pressure
PaCO2 - Arterial CO2 pressure
RER - Respiratory exchange ratio

Question 24

What is the respiratory exchange ratio?

Answer 24

the relationship
between CO2 elimination & O2 consumption

Question 25

What is the equation for RER?

Answer 25

RER=VCO2 produced/VO2 consumed

Question 26

What is the main determinant of RER?

Answer 26

Main determinant of RER is the particular metabolic substrate being
used (e.g. fat or carbohydrate, RER for modern diet ≈ 0.8)

Question 27

What gradient is used to investigate hypoxaemia?

Answer 27

The alveolar gas equation and alveolar-arterial
oxygen gradient are used to investigate hypoxaemia

Question 28

What is the Alveolar-arterial gradient?

Answer 28

A-a O2 gradient is the
difference between
alveolar and arterial
pressure:
= PAO2 – PaO2.

Question 29

What is alveolar-arterial oxygen gradients normal value?

Answer 29

Normally around <2kPa