The effect of lung volume on the ventilatory response to CO2 during resistive loading in normal subjects.

The ventilatory response to CO2 during resistive loading was determined in normal subjects when the end-expiratory level was allowed to increase and when it was restored to that present in the unloaded state. Restoration of the end-expiratory level of that seen in the unloaded state, during the resistive loading, resulted in an increase in ventilatory response to CO2. The mechanism by which increases in lung volume affect the ventilatory response to CO2 is unknown; multiple factors are likely to be involved. It is suggested that an increase in end-expiratory level plays a major role in limiting the ventilatory response to CO2 during resistive loading and may also be an important factor in the reduced ventilatory response to CO2 that is seen clinically when there is obstruction to air flow.