Influence of vagal blockade on respiratory work in the hypoxic and hypercapneic anesthetized dog

¹ Department of Physiology and Pharmacology, Duke University Medical Center, Durham, North Carolina

The mechanical work of breathing was determined in anesthetized dogs by measurements of intrathoracic pressures and tidal volumes, during inhalation of various gas mixtures while vagi reflexes were functional (warm) and blocked (cool). Pressure-volume loops obtained when vagi reflexes were blocked showed that both elastic and viscous work per breath increased during inhalation of 3.8% and 5.2% CO₂. However, the total work per minute increased during inhalation of 3.8% CO₂, but remained constant during inhalation of 5.2% CO₂. During inhalation of 10.1% O₂ in nitrogen, viscous and elastic work per breath increased when vagi were blocked, with no significant changes in total work per minute. When 6.39% O₂ in nitrogen was inhaled, elastic and viscous work per breath increased with blocked vagi, but a significant decrease in total work per minute occurred. Vagal reflexes do not have as prominent a role in influencing the work of breathing during severe hypoxia and hypercapnia as they do during normal and obstructive breathing.