Fick’s Law of diffusion
Vgas = (c ΔP A)/T diffusion constant is proportional to the gas solubility and inversely
proportional to the square root of its molecular weight
Partial Pressue – total pressure times the fractional concentration. In the lungs must subtract 47
mmHg because of water saturation.
-BGB is 0.5 um thick. But surface area is 50-100 square meters. 300 million alveoli.
- 23 generations of airways. 1-16 trachea terminal bronchiole is conducting zone, 17-23
respiratory bronchiole to alveolar sac is transitional and respiratory zone.
- Intrapleural space has negative pressure
Major Inspiratory muscles: diaphragm (innervated by phrenic nerves) and external intercostals.
Major expiratory muscles: muscles of the abdominal wall, internal intercostals.
Pulmonary compliance = difference in volume / difference in pressure
- Lung is most compliant between 10-20 cm H2O. 1/3 of the lungs pressure is caused by
the elastic forces and 2/3 is the surface tension.
- Tidal Volume – Volume of air inhaled with each breath
- Vital Capacity – Volume of air that can be forcibly exhaled after a maximal inspiration
- Residual Volume – volume of air remaining in the lungs after a maximal expiration
- Functional Residual Capacity – volume of air remaining in the lungs at the end of a
- Inspiratory Reserve Volume – volume of air that can be forcibly inhaled following a
- Expiratory Reserve Volume – volume of air that can be forcible exhaled following a
- Total Lung Capacity – volume of air in the lungs at the end of a maximal inspiration
- Minute Volume or Pulmonary Volume – Volume of air inhaled per minute, tidal
volume x frequency of respiration
- Forced Expiratory Volume – fraction of vital capacity expired in one second. Normally
it is about 80%. In restrictive diseases, the vital capacity is lowered so the FEV is normal
(pulmonary fibrosis), but in obstructive diseases (asthma) FEV is reduced much more.
- Maximal Voluntary Ventilation – Volume of air that can be moved into and out of the
lung in one minute by voluntary effort.
- TLC, RV and FRV cannot be measured
Helium Dilution method
C1V1 = C2(V1+V2)
V2 = FRC
Alveolar Ventilation = pulmonary ventilation – Dead Space Anatomical Dead Space – 150 ml, air in conductive zone
Physiological total dead space – total amount of air that does not participate in gas exchange.
Normal subjects would have similar anatomical and physiological dead spaces.
Bohr equation for dead space
VD (PaCO2− PeCO2)
= VD = deadspace VT = tidal volume
Alveolar Ventilation = (tidal volume – dead space) x respiration rate (breathing through a tube
will create a larger tidal volume and less exhaled PCO2 more inhaled CO2)
O2 – highest in inspired gas expired alveolar arteries veins
CO2 – Veins alveolar gas, arteries expired gas inspired gas
H20 – higher inside
N2 – higher outside
VO2 (l/min) = [(tidal volume x bpm) x %O2 inhaled] – [(tidal volume x bpm) x %O2 exhaled)]
VO2 max – 30-40 ml/min/kg. Affected by CV, musculoskeletal and respiratory
Henry’s Law Concentration of a dissolved gas = pressure * solubility
- O2’s not very soluble
- O2 transport on hemoglobin is the major form of transport