RELATIONSHIPS OF Po2, Pco2, AND pH TO ONSET OF BREATHING OF THE TERM LAMB AS STUDIED BY A FLOW-THROUGH CUVETTE ELECTRODE ASSEMBLY

Abstract

1. Study of the relationships of pO2 pCO2, and pH to the onset of breathing of term lambs was performed using a specially designed flow-through cuvette electrode assembly. 2. By altering the blood gas tensions of ewes under spinal anesthesia, changes were elicited in the pO2, pCO2, and pH of the fetal arterial blood supplying carotid bodies and the respiratory center. 3. When 100% oxygen was administered to the ewe, fetal arterial pO2 rose to an average of 29.1 mm Hg, pCO2 rose to 49.4 mm Hg, and pH fell. When 6.5% CO2, 21% oxygen, and 72.5% nitrogen were administered to the ewe, a more marked rise in pCO2 and fall in pH were elicited, and a significant rise in pO2 occurred. When 10% O2 and 90% N2 were administered, a fall in pO2 occurred with slight fall in pCO2. 4. None of these changes in arterial gas tensions of the fetus initiated respirations. 5. After occlusion of the cord, all of the animals initiated rhythmic respirations. 6. When a gas mixture high in CO2 and low in oxygen was administered to the ewe, there was severe spasm of the umbilical veins and usually respirations were initiated in the fetus.