[Verse 1]
Tidal breath and residual air,
Four liters resting, FRC sitting there,
Functional reserve — the buffer zone we keep,
But lay supine and watch that margin creep,
Closing capacity climbs above FRC,
Small airways collapse, atelectasis breathes,
Obesity, pregnancy, the aging lung —
All choke the reserve before the case is done
[Chorus]
West zones one, two, three — pressure gradients flow,
PA, Pa, Pv — that's how perfusion goes,
Shunt is blood that never meets the gas,
Dead space is breath that doesn't move the mass,
Hypoxic vasoconstriction pulls away,
Redirecting flow to where the alveoli stay,
V-Q mismatch is the root of hypoxic blame —
Know the gradient, know the game
[Verse 2]
Oxygen falls from atmosphere on down,
One-fifty to alveolar — forty torr unwound,
The A-a gradient widens when the shunt is wide,
Alveolar gas equation — nitrogen can't hide,
PAO2 equals FiO2 times the pressure spent,
Subtract the CO2 divided by the quotient meant,
P50 sits at twenty-seven — hemoglobin's hinge,
Right shift in acidosis, fever, CO2 binge,
Left shift in alkalosis, cold, and HbF terrain,
Delivery equals cardiac output times oxygen contained
[Chorus]
West zones one, two, three — pressure gradients flow,
PA, Pa, Pv — that's how perfusion goes,
Shunt is blood that never meets the gas,
Dead space is breath that doesn't move the mass,
Hypoxic vasoconstriction pulls away,
Redirecting flow to where the alveoli stay,
V-Q mismatch is the root of hypoxic blame —
Know the gradient, know the game
[Verse 3]
Central chemoreceptors taste the CSF,
CO2 dissolves to acid — ventilation's ref,
Peripheral bodies — carotid and the aortic arch,
Respond to hypoxia when the PO2 drops sharp,
Opioids blunt the slope of CO2 response,
Volatiles dampen hypoxic drive at once,
Preoxygenate to fill that FRC tank,
Four minutes tidal or eight deep breaths — full rank,
Apneic oxygenation buys the minutes back,
Diffusion down the trachea keeps SpO2 on track
[Bridge]
Compliance — volume change per unit pressure climb,
Resistance — flow impeded over time,
Time constants couple them — three fills the lung,
Work of breathing spikes when either battle's won,
PEEP recruits the alveoli that fold,
Laparoscopy raises pressures, shifts the diaphragm's hold,
One-lung ventilation — the dependent side breathes,
HPV fights the collapse, but shunt still feeds,
Prone positioning — dorsal zones now perfuse,
Lateral: the down lung works, the up lung tends to lose
[Chorus]
West zones one, two, three — pressure gradients flow,
PA, Pa, Pv — that's how perfusion goes,
Shunt is blood that never meets the gas,
Dead space is breath that doesn't move the mass,
Hypoxic vasoconstriction pulls away,
Redirecting flow to where the alveoli stay,
V-Q mismatch is the root of hypoxic blame —
Know the gradient, know the game