FEV1 Forced expiratory capacity
Volume of force exhale after 1 sec.
- fx of lung size, elasticity and airway diameter (resistance)
FVC Forced Vital Capacity
Max forced exhale that starts after a inhaling max amnt (volume) of air.
- generally VC (vital capacity) > FVC
FEV (forced expiratory volume)/FVC (forced vital capacity) ratio is higher or lower in Obstructed Pulm dz?
ratio (%) is lower (airway is clogged with mucus debris): can’t move air very fast (and in addition, amount/volume of air out is smaller than that of a normal person)
In restrictive pulm dz the FEV/FVC ratio is higher or lower?
its normal: moves air very quickly but smaller amount of air than normal person
Does change in diameter of airway affect FVC the same way it affect FEV1?
No, change in diameter doesn’t affect FVC (total forced expired volume):
when d is decreased, FEV1 (forced expired volume per minute) is decreased more (but total volume expired (FVC) is not decreased - it just takes it longer to get out??)
Both are affected by lung size and elasticity
Surface Tention (ST or T) is interaction of H2O molecules that tends to collapse the lung Surfactant
dicreases the intermolecular forces between H20 molecules and decreases ST
delta V/delta P
As volume increases, C decreases
high C= easy to inflate lungs
When pressure around lung is decreased, lung inflates/expands
Lung have high C (distensible):
large volume change per unit pressure change
Recoil (collapsing) forces of lung are due to
- alveolar ST
- elastic fibers in lung (collagen and elastin)
- increase STa or elastic fibers = DECREASE C
What decreases lung C?
- high lung volume (as volume increases, C decreases)
- pulm fibrosis (restrictive lung dz due to decreased lung+/- wall expansion)
- pulm congestion (blood)
- surfactant deficiency
- edema (in IF or in alveoli itself)
Increase surfactant = decrease ST (bc breaks down H2O) = Increase C?
What increases lung compliance?
- lower lung volumes
- emphysema (loss of elastic lung elements)
- age increase (loss of elastic tissues)
Why does compliance increase in emphysema (obstructive)?
elastic fibers destroyed by protease and elastases
Why does compliance decrease in restrictive lung disease?
fibrotic tissue in parenchyma of lung makes expansion more difficult