Lung volume, pressure, flow, and density relationships during constant-flow ventilation in dogs

Lung volume changes during constant-flow ventilation (CFV) using cannulas in the main stem bronchi were examined in six beagle dogs. The increase in lung volume was found to depend mainly on the outflow resistance to gas flow in the trachea and tracheal tube. The resistance changed with gas flow, indicating that gas flow was transitional between laminar and turbulent flow (resistance varies; is directly proportional to flow1.5). There was a small pressure gradient between trachea and alveoli (1.1-1.3 cmH2O) that was independent of flow rate or gas velocity out of the CFV cannulas. This was attributed to momentum transfer from the gas jet from the CFV cannulas modified by friction between the gas jet and the airway wall.