Ventilation and Compliance Flashcards
Tidal volume (TV)
The volume of air breathed in or out of the lungs at each breath (500ml).
Expiratory reserve volume (ERV)
The maximum volume of air that can be expelled from the lungs at the end of a normal expiration (1100ml).
Inspiratory reserve volume (IRV)
The maximum volume of air that can be drawn into the lungs at the end of a normal inspiration (3000ml).
Residual volume (RV)
The volume of gas in the lungs at the end of a maximal expiration (1200ml).
Vital capacity (VC)
VC = TV + IRV + ERV
Total lung capacity (TLC)
TLC = VC + RV
Inspiratory capacity (IC)
IC = TV + IRV
Functional residual capacity (FRC)
FRC = ERV + RV
FEV1
Forced expired volume in 1 second.
FEV1:FVC
Fraction of FVC in 1 second.
Describe pulmonary (minute) ventilation
Total air movement into and out of the lungs (functionally insignificant).
Describe alveolar ventilation
Fresh air getting into alveoli and thus, available for gas exchange (functionally significant).
Define partial pressure
The pressure of a gas in a mixture of gases is equivalent to there percentage of that particular gas in the entire mixture multiplied by the pressure of the whole gaseous mixture.
All gas molecules exert the same pressure, so partial pressure increases with increasing conc. of gas mixture.
What is the normal value for the partial pressure of oxygen in alveolar and arterial gas?
O2 = 100mmHg, 13.3kPa
What is the normal value for the partial pressure of carbon dioxide in alveolar and arterial gas?
CO2 = 40mmHg, 5.3kPa
State the role of pulmonary surfactant
Surfactant is a detergent-like fluid produced by type II alveolar cells.
- Reduces surface tension on the alveolar surface membrane, thus reducing tendency for alveoli to collapse
- Increases distensibility (lung compliance)
- Reduces lung’s tendency to recoil
- Makes work of breathing easier
State the Law of Laplace
P = 2T/r
Where P = pressure, T = surface tension and r = radius
Define compliance
Change in volume relative to change in pressure. It represents the stretchability of lungs, not elasticity.
List factors that affect compliance
Changes in disease states/age.
Emphysema (obstructive) - loss of elastic tissue means expiration requires effort.
Fibrosis (restrictive) - inert fibrous tissue means effort of inspiration increases.
Describe the pressure-volume relationship in terms of respiration
In inspiration, a bigger change in pressure is required to reach a particular lung volume, than to maintain that volume in expiration. This is because the work of inspiration is recovered in expiration due to elastic recoil.
Summarise the basic characteristics of obstructive lung disease
- Obstruction of air flow, especially on expiration
- Increased airway resistance
e. g. asthma, COPD, chronic bronchitis, emphysema
Summarise the basic characteristics of restrictive lung disease
- Loss of lung compliance: lung stiffness, incomplete lung expansion
e. g. pulmonary fibrosis, IRDS, oedema, pneumothorax
Describe the tests used to identify abnormal lung function
Spirometry;
- Static: consider only volume exhaled
- Dynamic: consider time to exhale a certain volume
- Can measure TV, IRV, ERV, IC and VC
How does an obstructive lung disease affect spirometry?
- Rate of exhalation much slower
- FRC is reduced
- FEV is reduced more so than FRC, due to major effect on airways
- FEV1:FRC is reduced
How does an restrictive lung disease affect spirometry?
- Absolute rate of air flow is reduced
- Total volume is reduced due to restricted lung expansion
- Ratio remains constant or increases
- FEV1:FRC remains constant, thus is not always indicative of good health
