Open-loop analysis of PaCO2 oscillation in the dog

Venous CO2 loading and/or unloading using an artificial lung was performed on dogs to evaluate whether changes in the rate of carbon dioxide output (VCO2) can be involved in the control of respiration. As the signal providing VCO2 information, small fluctuations in arterial PCO2 (delta PaCO2) which synchronized with the respiratory cycle were estimated from both the mean PaCO2 and the fluctuations in arterial pH (delta pH) measured with a catheter tip ISFET (ion sensitive field-effect transistor) pH sensor inserted in the common carotid artery. The open-loop method was used to analyze the effects of various respiratory parameters such as VCO2, tidal volume, and respiratory frequency on the changes in delta pH and delta PaCO2. Findings are: (1) delta PaCO2 was linearly proportional to VCO2 while the correlation between delta pH and VCO2 was less linear, (2) magnitude of delta pH was dependent on the changes in tidal volume while delta PaCO2 was not, (3) both the amplitude and the positive slope of PaCO2 oscillation were functions of respiratory frequency. These results suggest the possibility that if VCO2 itself takes part in the control of ventilation, it will be CO2 oscillation which links ventilation with VCO2.