Resp. function tests Flashcards
What limitations/ problems may arise when completing respiratory function tests
- Need to understand orders
- Max effort
- Mouthpiece leak
- Ability to carry out orders
What is normal resp rate
<25
What is plotted in spirometry
Volume/ time
What is the FEV1/ VC if there is an obstructive defect
<75%
What is an obstructive defect typical in
Asthma, COPD, upper airway obstructions
What is the FEV1/ VC ratio in a restrictive defect
> 75%
What is restrictive defect typical in
Lung fibrosis, reduced chest wall movement and muscle disease
When is peak flow typically reduced
Large airway obstruction
Upper airway obstruction
Asthma
What diseases effect peak flow less
COPD
Small airway disease
When is peak flow lowest
Morning
What pattern is seen on peak flow charts with asthma
Saw tooth pattern
What changes in peak flow must be observed with asthma to determine diagnosis
- > 20% dirunal variation for 3 days a week for 2 weeks
With what kind of training may peak flow increase
Inspiratory muscle training
What changes in FEV1 must be seen after use of bronchodilators to determine obsuctive disease is reversible
Increase by >15% or 200ml
A 15% increase in FEV1 is adequate to suggest reversibility after….
a) 400mg salbutamol via spacer
b) 2.5mg by nebuliser
c) 30mg/day of steroids for 14 days
What may be the problem if there is reduced inspiratory limb flow with normal expiratory flow
Extra-thoracic obsutrction
What may be the problem if there is reduction in both inspiratory and expiratory flow
Intra-thoracic obsutrction such as a goitre
How do you measure vital capacity
Spirometry
How can you measure total lung capacity
- Inspiration of gas mixture including helium
- Rebreathing
- Dilution of helium and decrease in concentration * vital capacity= TLC
Where do oxygen and co2 diffuse
Oxygen diffuses into circulation
CO2 diffuses out of the lungs
How can you calculate alveolar volume and gas transfer
- Single large breath of air with CO and helium
- Calculate total CO transfer and per l of lung volume
What does TLCO stand for and how do you calculate it
Transfer factor for CO
=kco*va
What can cause decreased TLCO (4)
- Anaemia
- Decreased perfusion
- Decreased ventilation
- V/Q mismatch
What can cause increased TLCO (3)
Increased CO
Polycythaemia
Alveolar haemorrhage
Describe the Fick principle
Volume of gas per unit time which diffuses across a tissue sheet is
a) proportional to sheet area
b) inversely proportional to thickness
c) proportional to difference in pressure on either side
d) dependent of permeability coefficient for gas
What equation can be derived from the Fick principle
= area/thickness * pressure * diffusion constant
What does diffusion constant depend upon
Solubility and molecular weight of gas
What is Grahams law
Rate of diffusion of a gas is inversely proportional to square root of molecular weight
What are the real life causes of reduced surface area causing reduced gas transfer
Pneumonectomy, lobectomy or reduced ventilation from obsutrction
Reduced effective area with emphysaemia or increased dead space
What are the real life causes of increased membrane thickness
Pulmonary fibrosis
Alveolar proteinosis
Acute lung injury
What are the real life causes of reduced oxygen concentration
High altitude
Define airway resistance
Pressure difference between alveolae and the mouth
How can airway resistance be measured
Body plethysmograph
Direct measurment of intrathoracic oesophageal pressures
What is lung compliance defined as
Volume change per unit of pressure
What does lung compliance depend upon
Alveolar surface tension and distensibility of lung tissue
When is lung compliance increased/ decreased
Increased: emphysaema
Decreased: Lung fibrosis
What is the effect of thorax deformities on chest wall compliance
Compliance is reduced
Where is perfusion and ventilation highest
At the base
How does pneumonia lead to hypoxia
Reduced ventilation
Increased perfusion
What does anaerobic threshold correlate with
Cardiopulmonary capacity
Operative risk
What is the effect of muscle wasting in COPD
Reduces maximum inspiratory muscles
Problems with mitochondrial dysfunction
