Lung volumes and capacity can be measured directly with a spirometer.
2 types: Volume Displacement and Flow Sensing
It also measures:
Forced Vital Capacity (FVC)
Total volume lower than the VC.
Forced expiratory Volume in 1 second (FEV1)
2.1 Diseases and Changes to the Graph
FEV1 is reduced because the airway is narrow
FVC is reduced due to chest wall diseases.
3 Residual Volume
Indirect measurement of the lung volume.
Uses Boyle's Law
RV= v1 X (c1/c2)/C2
P3/v2=P4 (V2 + change in V)
Alveolar Ventilation: Fresh gas that enters 4200ml/min.
Measured using Fowler's Method or Bohr's Method.
Fowler's Method is measured by expired N2 as indicator.
Bohr's Method is based on a measure of Carbon dioxide tensions in expired and alveolar gases.
Dead Space = VT x (1- (mixed expired /mixed alveolar))
Determines dead space
Dead space ventilation from normal ventilation.
5 Respiratory Exchange Ratio
Amount of oxygen used is dependent on body size and activity.
Respiratory exchange ratio (R)
is carbondioxide output/oxygen consumption.
Normal value is about 0.8 to 0.85
The higher the R value (carbohydrate). lower, fatty.