NEET PG Medical – 2018 – Question – 14
When Va / Q is infinity?
a) Partial pressure of O2 becomes zero
b) No exchange of O2 & CO2
c) Partial pressure of CO2 alone becomes zero
d) Partial pressure both CO2 and O2 remain normal
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Correct Answer – B
Answer: B – No exchange of O2 & CO2
- Va represents the ventilation in alveoli.
- Q represents the blood flow through the alveolus.
- The ratio of Va and Q explains the respiratory exchange when there is an imbalance between alveolar ventilation and alveolar blood flow. The ventilation-perfusion ratio is considered normal there is an equal amount of blood flow & ventilation through alveolus.
- Va /q ratio is Zero –
- There is inadequate or nil, but perfusion persists
- Va /q ratio is infinity –
- There is adequate ventilation but no perfusion.
- Both in the Zero and infinity Va /Q ratio, there is no exchange of gases through the respiratory membranes of corresponding alveoli.
- When Va /Q ratio is infinity,
- The alveolar air equilibrates the humidified inspired air No exchange of oxygen and carbon-di-oxide occurs.
- Partial pressures of the O2 and CO2 are 149mmHg & 0 mmHg respectively
