Ventilation / Compliance Flashcards
What is the tidal volume
Volume of air that we breath in and out
Increased in pregnancy
500ml
What is the inspiratory reserve volume
Max volume of air which can be drawn in above tidal volume
3000ml
Relies on lung compliance (elastic recoil) and muscle strength
What is the expiratory reserve volume
Max volume of air which can be expelled below tidal volume
1100ml
What is the residual volume
The. volume of gas in the lung at the end of a max expiration
1200ml
Stops alveoli collapsing
What volume cannot be measured with spirometry
Residual volume
All other volumes can
What are capacities
Lung volumes which do not change with breathing
What is the vital capacity
Max volume of air that can be moved into and out of the lung
ESV + TV + IRV
4.5l
Changes in disease - as relies on compliance / resistance
What is the functional residual capacity
The amount of air in the lung after normal expiration
ESV + RV
3L
What is inspiratory capacity
The amount of air in the lung that can be breathed in
TV. + IRV
3L
What is the total lung capacity
The amount of air in the lung after max inspiration
6L
What measures total lung capacity
Helium dilation
Hyperinflated =120%
Resitricted = 80%
What is anatomical dead space
Air that never reaches the alveoli
150ml
Nitrogen washout measures
What are visual ways of presenting lung volumes
Flow volume loop
Nitrogen washout graph
Vitalograph
What is pulmonary ventilation
Total air in and out
INSIGNIFICANT
RR + TV
What is alveolar ventilation
Fresh air getting to alveoli for exchange RR x (TV-anatomical dead space) Only 350ml of fresh air reaches alveoli when you inspire
Where is alveolar ventilation gretest
Base of the lung
More compliant + stretch more when compressed / contracted
Small change in intrapleural pressure = large change in volume
What is the partial pressure
The pressure of a single gas in a mixture
Equivalent to % of gas x P of whole mixture
What is alveolar partial pressure of O2 and CO2
PO2 = 100mmHg (13.3) PCO2 = 40mmHg (5.3)
What does hyperventilation cause
Increased alveolar as increased tidal volume
PO2 = 120
PCO2 = 20 - which is why a normal CO2 is bad if resp distress
What does hypoventilation cause
Decreased alveolar ventilation
P02 = 30
PCO2 = 100
What is the Law of LaPlace
P (transpulmonary) = 2x Surface tension / radius
What does law of Laplace mean
If alveolar radius decrease s or tension gets larger than P increases and alveoli collapse
The lungs tendency to recoil has to be overcome during inspiration
Harder to fill lungs with air than saline as increased tension to overcome
What does surfactant do
Reduces surface tension on alveoli so stop collapse
Also increase lung compliance and decrease tendency to recoil
How is surface tension greater
Air water interface on wall of alveoli
What is compliance
The change in volume of lung relative to change in pressure
STRETCH over elasticity
A higher lung volume = lungs stretched more so greater intrapleural pressure
What does it mean if lung is high compliance
Large increase in volume for small decrease in intrapleural pressure (more air in)
What occurs in disease
Emphysema = loss of elasticity so expiration needs effort
Fibrosis = increased inspiration as decreased compliance so lungs need to work
What is obstructive lung disease
Air flow is obstructed and increased airway resistance
More on expiration as compression exaggerates
COPD / asthma
What is restrictive lung disease
Loss of lung compliance which restrict expansion of lungs and volumes
Fibrosis / pneumothorax / pleural disease
What is spirometry
Used to measure lung volume
FEV1 - FEV in 1s (4l) / FVC
Should be 80%
What happens in obstruction
Air exhaled slower so total volume of air is reduced
FEV decreased more than FVC
Ratio reduced
What happens in restrictive
Rate of air flow reduced
Total volume reduced due to limitations in expansion
Ratio often constant or increased as large volume can be exhaled in 1s
Not good to use if unwell as doesn’t show change
