Final answer:
A decrease in airway radius increases resistance, which could lead to changes in respiratory rates or tidal volume, but this does not directly cause the residual volume or the expiratory reserve volume to decrease.
Step-by-step explanation:
When the radius of the airway was decreased, it indicates that there is a narrower passage for air to flow into and out of the lungs. This would cause an increase in resistance during breathing and potentially decrease the airflow. However, it does not directly affect volumes such as residual volume, tidal volume, or inspiratory reserve volume. Considering the options provided and the definitions of respiratory volumes:
- Tidal volume is the amount of air that enters the lungs during quiet breathing.
- Inspiratory reserve volume is the amount of air that can be inhaled beyond the tidal volume.
- Expiratory reserve volume is the additional air that can be forcefully exhaled after the expiration of the normal tidal volume.
- Residual volume is the amount of air left in the lungs after expelling the expiratory reserve volume, which helps to keep the alveoli open and prevent lung collapse.
Given that the question is in reference to volumetric changes due to a decreased radius of the airway, the most accurate answer is that neither residual volume nor expiratory reserve volume would necessarily decrease as a direct result.