Question

1. A decrease in VCO ₂ without any change in ventilation will cause:
   1. An increase in PaCO2
   2. An increase in VD/VT
   3. A decrease in PaO₂
   4. A decrease in VD/VT
   5. A decrease in arterial and alveolar CO2

Which one is a correct answer and explain in detail.

I hope to receive a new and better answer because there is answer for this question has posted but it was wrong.

Answer 1

Ventilation refers to the normal exchange of air between the atmosphere and the lungs. This enables the exchange of oxygen with carbon dioxide present in the alveoli.

VCO₂ refers to the carbon dioxide produced by the body. In other terms, it is the difference between the carbon dioxide that is exhaled by the body and carbon dioxide inhaled by the body.

In this case, the ventilation has not changed, therefore the ratio of dead space and tidal volume (VD/VT) remains unchanged. Dead space refers to the volume of inhaled air that does not include in the gaseous exchange and tidal volume refers to the displaced air during normal inhalation and exhalation.

Here, the VCO₂ has decreased this means there will be a decrease in the arterial CO₂. This also corresponds to the alveolar carbon dioxide. This leads to a decrease in the partial pressure of carbon dioxide. As ventilation has not changed, the partial pressure of oxygen will not change, however, it tends to cause hyperventilation.

Hence the correct option is e).