Ventilatory response to inhaled and infused CO₂: Relationship to the oscillating signal

The purpose of this study was to determined the relationship between the respiratory oscillations of CO₂ and the ventilatory response to CO₂. Cats anaesthetized with chloralose and urethane were given CO₂ either by exchange transfusion into the inferior vena cava or by inhalation. Changes of amplitude of the respiratory oscillations of CO₂ (amp P_CO2 ) were assessed from measurements of the amplitude of the arterial pH oscillations (amp pH). For short periods of CO₂ loading (2-8 min), the ventilaory response to CO(in2) was greater for venous than for airway loading; this differences of the respiratory response to the route of administration of Co₂9 could not be related to amp P_CO2 . For long periods of CO₂ loading (20 min or more) there was no marked changed of minute ventilation when the route of administration was changed from airway to venous route, despite an increase of amp pH at both low and intermediate loads. We suggest that the dependence of ventilatory response to CO₂ on the route of administration observed in this study was mainoy due to a longer period required to attain steady state conditions for CO₂ inhalation, and that the respiratory oscillations of CO₂ do not affect the ventilatory response to CO₂.