Ventilation and Compliance Flashcards
Anatomical dead space
The volume of gas occupied by the conducting airways and this gas is not available for exchange.
Volume is 150ml.
Tidal Volume (TV)
The volume of air breathed in and out of the lungs at each breath.
Expiratory Reserve Volume (ERV)
The maximum volume of air which can be expelled from the lungs at the end of a normal expiration.
Inspiratory Reserve Volume (IRV)
The maximum volume of air which can be drawn into the lungs at the end of a normal inspiration.
Residual volume (RV)
The volume of gas in the lungs at the end of a maximal expiration.
Vital Capacity (VC)
VC = tidal volume + inspiratory reserve volume + expiratory reserve volume
Total Lung Capacity (TLC)
TLC = vital capacity + the residual volume.
Inspiratory Capacity (IC)
IC = tidal volume + inspiratory reserve volume.
Functional Residual Capacity (FRC)
FRC = expiratory reserve volume + residual volume.
What is FEV1:FVC
Fraction of forced vital capacity expired in 1 second.
Pulmonary ventilation
Total air movement into/out of lungs (relatively insignificant).
Alveolar ventilation
Fresh air getting to alveoli and therefore available for gas exchange (much more significant).
Partial Pressure
The pressure of a gas in a mixture of gases is equivalent to the percentage of that particular gas in the entire mixture multiplied by the pressure of the whole gaseous mixture
Pressure commonly expressed in mmHg or kPa units
How does hyper-ventilation affect alveolar PO2 and PCO2?
PO2 rises to about 120 mm Hg and PCO2 falls to about 20 mmHg.
How does hypo-ventilation affect alveolar PO2 and PCO2?
PO2 falls to 30 mmHg and PCO2 rises to 100 mmHg.
What is Surfactant?
Detergent like fluid produced by Type II Alveolar cells
What does Surfactant do?
Reduces surface tension on alveolar surface membrane thus reducing tendency for alveoli to collapse
Increases lung compliance (distensibilty)
Reduces lung’s tendency to recoil
Makes work of breathing easier
Is more effective in small alveoli than large alveoli because surfactant molecules come closer together and are therefore more concentrated.
What is Lung Compliance?
Change in volume relative to change in pressure.
- The ease at which the lungs can expand under pressure.
High Compliance
large increase in lung volume for small decrease in ip pressure
Low Compliance
small increase in lung volume for large decrease in ip pressure
Where is alveolar ventilation and compliance greatest?
Greatest at base of lung.
They decline with height from base to apex.
Obstructive Lung Disorders
Increased airway resistance
E.g. Asthma, COPD
Restrictive Lung Disorders
Loss of lung compliance
- lung stiffness
- Incomplete lung expansion
E.g. fibrosis, infant respiratory distress syndrome, oedema, pneumothorax.
What is spirometry?
Technique commonly used to measure lung function
Measurements can be classed as static (where the only consideration made is the volume exhaled) or dynamic (where the time taken to exhale a certain volume is what is being measured).
