Local regulation of collateral ventilation by oxygen and carbon dioxide

Abstract

The effects of changes in CO2 and O2 on the mechanics of collateral ventilation were studied in anesthetized paralyzed dogs. A double-lumen catheter was wedged into a peripheral airway obstructing a segment of lung distal to the catheter. Through one lumen of the catheter, air, 5% CO2 in air, 10% CO2 in air, 5% O2 in N2, or 5% O2 with 5% CO2 in N2 was infused at a constant flow (.ovrhdot.V). Pressure (Ps) was monitored through the other lumen. At functional residual capacity the resistance to collateral flow Rcoll = Ps/.ovrhdot.V. When .ovrhdot.V was interrupted, the time for Ps to fall 63% was defined as the time constant for collateral ventilation, Tcoll. The effective compliance (Cs'') = Tcoll/Rcoll. When air was replaced by 5% CO2, Rcoll fell 46.3% (.+-. SE 2.8) and Tcoll fell 41.5% (.+-. SE 3.0). When the CO2 concentration was increased from 5%-10%, Rcoll fell an additional 9.2% (.+-. SE 2.2) and Tcoll fell an additional 5.1% (.+-. SE 4.4). When air was replaced by 5% O2 in N2, Rcoll rose 36.6% (.+-. SE 6.0) and Tcoll rose 13.6% (.+-. SE 10.5). No signigicant changes in Cs'' were noted. Varying concentrations of CO2 and O2 apparently provide potent mechanisms for the control of collateral ventilation which may be of importance in the regulation of ventilation perfusion relationships at the local level.