Comparison of Ventilatory Response between Dead Space and CO₂ Breathing in Humans

Abstract

Ventilatory response during external dead space (tube) breathing and CO₂ inhalation for given increase in PET_CO2 were compared at different levels of PET_O2 (hyperoxia, normoxia, and hypoxia) in human subjects. At all the PET_O2 levels studied, magnitude of increment in minute ventilation (VE) and tidal volume were larger in the dead space breathing than in the CO₂ inhalation. The slope of CO₂-ventilation response line was significantly steeper in the dead space breathing only in the hypoxic condition. There was no significant difference in frequency response to CO₂ between the two methods. These results suggested that augmented ventilatory response to CO₂ in the dead space breathing occurs in the condition of peripheral chemoreceptor activation.