physiology Flashcards
How can you measure FRC/RV/TLC?
- Body plethysmograpthy
- Helium dilution
- Nitrogen washout
What can you not measure using spirometry?
- TLC
- Reserve volume
- Functional residual capacity
What is dead space?
- Ventilation but no perfusion
- Anatomical
- Physiological
- Alveolar (e.g V/Q mismatch)
How is dead space increased?
- Bronchodilators (inc airway size)
- High RR & low TV
- Standing (due to gravity= stretch)
- Neck extension/jaw protrusion
- Face mask/catheter mount
- Pregnancy (dilated airways by progesterone)
- Old age (loose elastic tissue of lungs)
- Reduced no. of perfused alveoli
How is dead space decreased?
- Bronchoconstriction
- ETT/Trache
- Inc no. perfused alveoli (inc CO)
How is dead space measured?
- Anatomical: Fowler’s method
- Physiological: Bohr Equation
What is Fowler’s method?
- Single breath of 100% O2
Measure Nitrogen concentration on expiration
-
What is the Bohr equation?
Vd/Vt =
PaCO2 - PeCO2 / PaCO2
How do lung volumes change with age?
OLD: Inc dead space & Residual Vol
YOUNG: Dec TLC & VC
What does the point on the vol/pressure graph show when chest expansion and lung collapse are equal?
Functional residual capacity
What factors cause reduced compliance?
- Lung fibrosis
- Pulmonary oedema
- Collapse/atelectasis
- Kyphoscoliosis
What factors cause increased compliance?
- Emphysema
- Old age
What is the equation for pressure in an alveolus?
P = 2T / r
What is Laplace’s law?
The wall tension of a hollow sphere/cylinder is proportional to both the pressure of its contents & its radius
P = T / R
Why does decreased FRC cause low V/Q?
As vol of lung decreases, reaches point where terminal bronchioles close, leads to collapse & atelectasis of alveoli (Closing capacity)
