Combined action of hypoxia and hypercapnia on functional state of the respiratory center

Discharges of bulbar respiratory neurons and electrical activity of the diaphragm and intercostal muscles were studied and pO2, pCO2, pH, and the oxygen saturation of the arterial blood were determined in cats anesthetized with pentobarbital and exposed to the combined action of hypoxia and hypercapnia. During inhalation of a hypoxic gas mixture the developing hypocapnia disturbed the firing pattern of the respiratory neurons and respiration of the Cheyne-Stokes type was established. Addition of 2% CO2 to the hypoxic gas mixture restored the arterial blood gas composition to its initial level, prevented the development of hypocapnia, and prevented the disturbance of the rhythmic firing pattern of the respiratory neurons. Addition of 5% CO2 to the hypoxic gas mixture had a negative action: respiratory unit activity was first stimulated, then inhibited, metabolic and respiratory acidosis was induced, and asphyxia developed.