title: Ventilation-perfusion inequality during constant-flow ventilation.
abstract: Previous work by Lehnert et al. (J. Appl. Physiol. 53:483-489, 1982) has demonstrated that adequate alveolar ventilation can be maintained during apnea in anesthetized dogs by delivering a continuous stream of inspired ventilation through cannulas aimed down the main-stem bronchi. Because an asymmetric distribution of ventilation might introduce ventilation-perfusion (VA/Q) inequality, we compared gas exchange efficiency in nine anesthetized and paralyzed dogs during constant-flow ventilation (CFV) and conventional ventilation (intermittent positive-pressure ventilation, IPPV). Gas exchange was assessed using the multiple inert gas elimination technique. During CFV at 3 l X kg-1 X min-1, lung volume, retention-excretion differences (R-E*) for low- and medium-solubility gases, and the log standard deviation of blood flow (log SD Q) increased, compared with the findings during IPPV. Reducing CFV flow rate to 1 l X kg-1 X min-1 at constant lung volume improved R-E* and log SD Q, but significant VA/Q inequality compared with that at IPPV remained and arterial PCO2 rose. Comparison of IPPV and CFV at the same mean lung volume showed a similar reversible deterioration in gas exchange efficiency during CFV. We conclude that CFV causes significant VA/Q inequality which may be due to nonuniform ventilation distribution and a redistribution of pulmonary blood flow.
mesh_terms: D000818:Animals; D002245:Carbon Dioxide / Q000097:blood; D002302:Cardiac Output; D004285:Dogs; D010100:Oxygen / Q000097:blood; D010313:Partial Pressure; D011652:Pulmonary Circulation; D012039:Regional Blood Flow; D012119:Respiration; D012121:Respiration, Artificial; D014692:Ventilation-Perfusion Ratio
chemical_list: D002245:Carbon Dioxide; D010100:Oxygen