Respiratory measurements Flashcards
Name an obstructive airway disease
COPD
Name a restrictive airway disease
Asthma
What is the difference between a restrictive and obstructive airway disease
restrictive = limits amount of air getting to lungs
Obstructive = reduces ventilation capcity by reducing surface area for gas exchange
What is lung compliance
strechibility/expandibility
Describe the difference in lung compliance at low and high pressures
High = lung is stiffer, so compliance is lower
Low = lung more collapsed, compliance is higher
Which is more compliant the base or apex of lung?
Base = better ventilation
What is the reason for lung compliance?
elastic recoil
What diseases when lung compliance is increased or decreased?
Decreased = pulmonary fibrosis, alveolar oedema
Increased = normal ageing lung
For efficient ventilation, what do healthy people tend to have?
High lung compliance
Low alveolar surface tension due to surfactant secreted by alveoli
What is pulmonary fibrosis?
Scarring of the lungs = reduces capacity of lung to perform function
What do lung tests need to assess and what do they need to diagnose?
Mechanical condition of the lungs- pulmonary fibrosis
Resitance of the airways- asthma
Diffusion across the alveolar membrane- pulmonary fibrosis
What is used to measure lung volumes?
spirometer
Name 4 measurements of lung volumes
- Tidal volume
- Inspiratory reserve volume
- Expiratory reserve volume
- Vital capacity
How does a spirometer work?
- Must be closed system = clip on nose with mouth piece attached- told to breath in and out
- Connected to apparatus that measures the movement
- Everytime there is a movement, a needle moves on chart
Define: Tidal volume
the amount of air that passes in and out of lungs during normal breathing
Define: inspiratory reserve volume
= extra volume of air inspired above the normal tidal volume with full force
Define: Expiratory tidal volume
extra volume of air expired by forceful expiration at the end of normal tidal expiration
Define: vital capacity
maximum amount of air expelled from the lungs after first filling the lungs to a maximum then expiring to a maximum
How do you work out the vital capacity?
Tidal volume + inspiratory reserve volume + expiratory reserve volume
How do you work out the vital capacity?
Tidal volume + inspiratory reserve volume + expiratory reserve volume
Name + define 3 measurements not using spirometry?
Residual volume = volume of air remaining in the lungs after the most forceful expiration
Functional residual capacity = amount of air that remains in the lungs at the end of normal expiration
Total lung capacity = maximum volume of air the lungs can hold
What can be used to measure forced vital capacity?
Vitalograph
What is the forced vital capacity?
= total volume of air that is exhaled
What happens to air when we force a breath out?
90% of air will move out in 1st second- takes 3-5 seconds to complete forced exhalation
What does FEV1 refer to?
= volume expired in the first second of a breath- typically above 70%
what is used to determine the relationship between FEV1 and the FVC?
defined as a ratio- FEV1/FVC
Apart from disease, what are the physiological/environmental factors affecting lung volumes?
Age
Height
Gender
How do you measure functional residual capacity?
Using helium dilution or nitrogen washout
Why are inert gases used in helium diluation or nitrogen washout?
They diffuse in and out of lung without any gas exchange
Describe the process of nitrogen washout
Patient inspires 100% O2
Expires into the spirometer system
Procedure repeated until N2 in lungs is replaced with O2
FRC calculated from exhaled N2 and estimated alveolar N2
