The Power Course

When ventilation-perfusion ratio V/Q is infinite, it means


1 ) Dead Space
2 ) The PaO2 of alveolar air is 159 mmHg and PCO2 is 40mmhg
3 ) The partial pressure of O2 and CO2 is equal
4 ) None of the above


Ventilation-perfusion ratio infinite

When perfusion is zero with preserved ventilation ratio of ventilation to perfusion becomes infinite. With zero perfusion CO2 will not be eliminated in alveolus and oxygen will not be absorbed. Thus alveolar air will be similar to external air. This is nothing but physiological dead space.

Ventilation-perfusion ratio zero

If the ventilation is zero and perfusion is preserved the ratio of ventilation to perfusion becomes zero. The alveolar air will same as for venous blood. This is similar to the right to left shunt.



Dead Space

Last Modified : 16-Jan-2020

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