One atom carbon-12 12 amu One mole 6.022 × 10²³ particles Avogadro's number On the balance carbon 12 g 1 amu is 1/12th of a carbon-12 atom — which is what makes the two ends of this line agree. Equal volumes of gases, at the same temperature and pressure, hold equal numbers of particles.
fresh gas · centre lane · fastest spent gas · wall layer · dwells longest spent gas · wall layer · dwells longest v(r) = v_max (1 − r²/R²) No-slip at the wall: the layer touching it does not move at all. Oscillate this and the two lanes travel in opposite directions — Taylor dispersion.
Type 1 · lung failure PaO₂ ↓ · PaCO₂ normal or low V/Q mismatch, shunt, diffusion defect. Bronchiolitis, pneumonia, PARDS, oedema. True shunt needs PEEP, not more FiO₂. Type 2 · pump failure PaCO₂ > 50 with pH < 7.30 Alveolar hypoventilation. CNS depression, neuromuscular, exhaustion at the end of severe obstruction. Type 3 · perioperative FRC falls Anaesthesia, positioning, opiates, splinting. Basilar collapse, then V/Q mismatch. Type 4 · shock The diaphragm competes for cardiac output Respiratory muscles take up to 40% of it. Ventilation offloads them, for the organs. Distress is compensated; failure is not. A "normal" PaCO₂ in an exhausted tachypnoeic child is a rising one.
Type I through the physis Type II + metaphyseal corner Type III into the joint Type IV across all three Type V crush Amber: the physis. Red: the fracture line.
Conducting zone Trachea → terminal bronchioles, ~16 generations Convection: bulk flow and streaming. No exchange at all — this is plumbing. Respiratory zone Diffusion; flow velocity ≈ 0. O₂ and CO₂ cross the membrane here. Flow only has to reach the doorstep: across one alveolus, t ≈ x²/D ≈ 2.5 ms.