Open-loop Analysis of Pa_CO2 Oscillation in the Dog

Abstract

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 (V_CO2) can be involved in the control of respiration. As the signal providing V_CO2 information, small fluctuations in arterial P_CO2 (ΔPa_CO2) which synchronized with the respiratory cycle were estimated from both the mean Pa_CO2 and the fluctuations in arterial pH (ΔpH) 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 V_CO2, tidal volume, and respiratory frequency on the changes in ΔpH and ΔPa_CO2. Findings are: (1) ΔPa_CO2 was linearly proportional to V_CO2 while the correlation between ΔpH and V_CO2 was less linear, (2) magnitude of ΔpH was dependent on the changes in tidal volume while ΔPa_CO2 was not, (3) both the amplitude and the positive slope of Pa_CO2 oscillation were functions of respiratory frequency. These results suggest the possibility that if V_CO2 itself takes part in the control of ventilation, it will be CO₂ oscillation which links ventilation with V_CO2.