Ventilatory Responses During Arterial Homeostasis of P_{CO 2} at Low Levels of Inspired Carbon Dioxide

Summary

Ventilatory responses in anesthetized chickens were measured during arterial ${\operatorname{P} _{{{\operatorname{CO} }_2}}}$ (${\operatorname{P} _{{{\operatorname{aCO} }_2}}}$) homeostasis at low levels of inspired carbon dioxide (${\operatorname{P} _{{{\operatorname{ICO} }_2}}}$). The ${\operatorname{P} _{{{\operatorname{aCO} }_2}}}$ and hydrogen ion concentration in arterial blood ([H⁺]_a) were regulated at control levels (partial pressure of CO₂ in inspired gas, ${\operatorname{P} _{{{\operatorname{iCO} }_2}}}$ = 0) as ${\operatorname{P} _{{{\operatorname{aCO} }_2}}}$ was varied between 0 and 21 torr under both normoxic (Series I) and hyperoxic (Series II) conditions. During normoxia, mean expiratory minute volume (V_T) increased by 53%, mean tidal volume (V_T) increased by 82%, and mean respiratory frequency (f) decreased by 25%. We conclude that CO₂-sensitive intrapulmonary chemoreceptors mediate the ventilatory response to inhalted CO₂ during arterial isocapnia and that parabronchial ventilation is the regulated variable accounting for arterial hemoestasis of ${\operatorname{P} _{{{\operatorname{aCO} }_2}}}$.