Lungs volume and testing Flashcards
Long compliance =?
stretchiness
At high pressure the lung is stiffer and less compliant
TRUE!
Lung bases are more compliant
TRUE!
What is compliance ensured by?
Elastic recoil
Give an example of decreased compliance?
Pulmonary fibrosis and alveolar oedema
Give an example of increased compliance?
Normal ageing lung - elastic recoil is compromised
Total lung compliance is dependent on what?
Thoracic cage and elasticity
For efficient ventilation, healthy people tend to have
High lung compliance
Low alveolar surface tension due to surfactant
List the three things tests need to assess for lung function
Mechanical condition (pul. fibrosis - condition of compliance) Resistance of airways (asthma - obstructive deficit) Diffusion across alveolar membrane (pul. fibrosis - gas transfer)
What is the normal tidal volume?
0.5l
What is the equation for vital capacity?
TV+IRV+ERV
What is the equation for the functional residual capacity?
(amount of air that remains in the lungs at the end of a normal expiration)
ERV+RV (residual volume)
What is the equation for total lung capacity and what is the normal value?
VC+RV
7.3l
Forced Vital Capacity (FVC) - total volume exhaled - what kind of deficit and what does it indicate?
Restrictive deficit and indicates the compliance
FEV1.0 - volume expired in the first second
Typically >70%
Obstructive deficit and indicates the lung function
List physiological and environmental factors affecting lung volumes
Smoking, age, weight, exercise, living at high altitude, sex
What is used instead of a spirometer to measure FRC, TLC or RV?
Helium dilution or nitrogen washout
Why do we use helium?
Is not absorbed by the body
List the procedure for nitrogen washout
Patients inspires 100% oxygen
Expires into spirometer system, N2 meter detects N in expired air
As no. of breaths increases, N2 conc, decreases - O2 replaces the N2
Procedure repeats till N2 is replaces
FRC calculated from exhaled N2 and estimated alveolar N2
What happens in a restrictive deficit?
Lung expansion compromised
Lungs don’t fill to capacity - e.g. pulmonary fibrosis and scoliosis
FVC IS REDUCED BUT FEV1 IS RELATIVELY NORMAL
FEV1/FVC remains relatively normal
What happens in a obstructive deficit
Airway obstruction Can still fill to capacity Resistance is increased on expiration - e.g. asthma and COPD FEV1 IS REDUCED BUT FVC WILL BE NORMAL A LOW FEV1/FVC WILL BE REDUCED
Peak Expiratory Flow Rate (PEF) - what is it?
Fully expanded lungs - airways are widest and flow is maximum - it reaches a plateau (means no matter how much they breathe out the flow rate will be unaffected)
Flow falls and ceases at RV
TLC –> PEF
Is EFFORT dependent - incr. effort increases flow rate
PEF–>RV
Is effort INDEPENDENT - incr. effort DOES NOT increase flow rate
PEF–>RV
Is effort INDEPENDENT - incr. effort DOES NOT increase flow rate
What is the normal flow rate? and normal TLC?
11 and 7
How do you measure diffusion conductance
Measure CO crossing alveolar air to blood - higher affinity to haemoglobin.
Patient inhales single breath of dilute CO followed by holding breath for 10 secs
DIFFUSION CAPACITY is calculated from the lung volume and the % of CO in the alveoli at the beginning and end of 10s breath hold
Fibrosis - diffusion is compromised
