REGULATION OF RESPIRATION AND BLOOD GASES*

Abstract

Our interest in the relationship of the blood gases to the regulation of respiration was stimulated three years ago when some simple studies undertaken in Puebla, Mexico, pointed to the possible importance of the PcO, of mixed venous blood.These studies showed that the relationship between ventilation and mixed venous PCO, was the same at rest breathing COz mixtures as during exercise breathing air.This suggested that ventilation might be controlled by a common mechanism during exercise and during COz breathing, namely by chemoreceptors bathed in mixed venous blood.Such an hypothesis was particularly attractive because classical concepts seemed inadequate to account for the control of breathing during exercise.Our experiments, like those of everyone who has studied the subject, showed that arterial PCO, rose during the hyperpnea of COz breathing but remained virtually constant during the hyperpinea of exercise.The arterial blood changes were difficult to reconcile with a common control mechanism on the arterial side of the circulaton.On returning to Baltimore we confirmed the consistent relationship between ventilation and mixed venous P C O ~ using a number of different indirect methods for estimating mixed venous Pco,.The idea of mixed venous control of ventilation gained further support from the study of a patient with anomalous pulmonary venous drainage and atrial septa1 defect.Owing to the peculiarities of this patient's congenitalanomaly, the pulmonary and systemic arterial PCO, values were the same regardless of whether the patient was at rest or exercising.Both values rose during exercise thus maintaining the normal relationship between ventilation and pu1,monary arterial PCO, in spite of an abnormal relationship between ventilation and systemic arterial Pco,.Further evidence which seemed consistent with a dominant role for mixed venous PCO* in the control of ventilation was obtained by studying the transient changes in ventilation