Clinical evaluation of respiratory function Flashcards
What is spirometry?
investigation of airway
obstruction and lung restriction
What is FVC?
Forced vital capacity
What is FEV1?
Forced expiratory volume in 1 second
What is the equation to determine % of total lung capacity an individual can exhale in
the first second ?
100 x FEV1/FVC
At what percentage is 100xFEV1/FVC indicative of obstructive airway disease?
<70% is indicative of obstructive airways disease
How does obstructive airway disease appear in spirometry and what is an example of a disease?
Obstructive:
FEV1/FVC <70%
FVC >80%
E.g. Asthma
↑Resistance
How does restrictive airway disease appear in spirometry?
Restrictive:
FVC < 80%
FEV1/FVC > 70%
E.g. Fibrosis
↓Compliance
What is the rule for spirometry for an obstructive respiratory disease?
FEV1/FVC<70%, FVC = Normal
What is the rule for spirometry for restrictive respiratory disease?
FVC <80% of predicted volume, FEV1/FVC = Normal
What is the rule for mixed obstructive and restrictive respiratory disease?
FEV1/FVC <70% and FVC<80%
What is lung compliance?
Lung compliance is the relationship between
transpulmonary pressure and lung volume
What is the equation for compliance?
Compliance(CL) = change in volume/change in pressure
What is static compliance?
Measurements taken whilst airflow = 0
What is dynamic compliance?
Measurements taken during movement of air
What are the axis when measuring static compliance?
x axis - Transpulmonary pressure
y axis - Lung volume
What are the axis when measuring dynamic compliance?
x axis - (-)intrapeural pressure
y axis - Lung volume
What does the size of the internal area or ‘fatness’ of the loop in a dynamic compliance graph measure?
The size of the internal area or
‘fatness’ of the loop is proportional
to the level of airway resistance.
How do lungs and kidneys maintain blood pH homeostasis?
The lungs & kidneys maintain blood pH homeostasis
by regulating PaCO2 & [HCO3-], respectively
What does an increase in ventilation do to PaCO2 and pH?
↑Ventilation = ↓ PaCO2 = ↑ pH
What does a decrease in ventilation do to PaCO2 and pH?
↓Ventilation = ↑ PaCO2 = ↓ pH
What does a decrease in HCO3- excretion do to [HCO3-] and pH?
↓ HCO3 excretion = ↑ [HCO3-] = ↑ pH
What does an increase in HCO3 excretion do to [HCO3-] and pH?
↑ HCO3 excretion = ↓ [HCO3-] = ↓ pH
What is the equation to calculate PAO2?
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
What is the respiratory exchange ratio?
the relationship
between CO2 elimination & O2 consumption
What is the equation for RER?
RER=VCO2 produced/VO2 consumed
What is the main determinant of RER?
Main determinant of RER is the particular metabolic substrate being
used (e.g. fat or carbohydrate, RER for modern diet ≈ 0.8)
What gradient is used to investigate hypoxaemia?
The alveolar gas equation and alveolar-arterial
oxygen gradient are used to investigate hypoxaemia
What is the Alveolar-arterial gradient?
A-a O2 gradient is the
difference between
alveolar and arterial
pressure:
= PAO2 – PaO2.
What is alveolar-arterial oxygen gradients normal value?
Normally around <2kPa
