ANALYSIS OF THE RESPIRATORY RESPONSE TO CARBON DIOXIDE INHALATION IN VARYING CLINICAL STATES OF HYPERCAPNIA, ANOXIA, AND ACID-BASE DERANGEMENT

Abstract

By relating effective alveolar ventilation to changes in arterial CO2 tension and pH, the diminished ventilatory response to CO2 inhalation in patients with pulmonary emphysema and chronic respiratory acidosis was investigated. Increased buffering capacity of the blood did not account for the reduced ventilatory response in these patients, since a reduced sensitivity to the chemical stimulus in terms of pH as well as CO2 tension was found. The diminished response was independent of mechanical ventilatory impairment and congestive heart failure. Further observations on patients with chronic anoxemia secondary to cyanotic congenital heart disease, or chronic metabolic acidosis associated with uremia, revealed no reduction in sensitivity to the CO2-pH stimulus under these conditions. However, patients with chronic hypercapnia and an increased alkaline reserve associated with metabolic alkalosis were found to have substantial reductions in sensitivity. It is concluded that chronic hypercapnia per se results in a diminished sensitivity of the respiratory neural regulatory mechanism to the CO2-pH stimulus.