Threshold Pco₂ dependence on arterial pH for the respiratory system of dogs

¹ Department of Physiology, Kanazawa University School of Medicine, Kanazawa, Japan

By observing respiratory discharges of the phrenic nerve, the threshold values of Pco₂ (Ptco₂) as chemical stimulus for the respiratory system were examined at varying arterial pH's on anesthetized dogs with and without vagotomy. 1) The reliability of the Ptco₂ obtained by this method was high, the standard deviation being 0.48 mm Hg of Pco₂. 2) The Ptco₂ was lowered as the arterial cH (Ht) was increased by ammonium chloride infusion. The relationship between the Ptco₂ and the Ht was linear and the regression line was calculated to be Ptco₂ + 0.429 Ht = 44.0 for vagotomized and Ptco₂ + 0.361 Ht = 46.1 for nonvagotomized dogs. 3) By combining this equation with that previously obtained expressing the partial effect of increased arterial cH and Pco₂ on alveolar ventilation ratio (VR), the general chemical stimulation equation for ventilation in anesthetized normal dogs was derived to be VR = 0.194 Pco₂ + 0.071 H – 8.94. 4) The Ptco₂ of vagotomized dogs was several millimeters Hg lower than that of nonvagotomized dogs.

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