Somatic Reflexes and Blood Oxygenation Under Positive Intrapulmonic Pressure

¹ From the Department of Physiology, University of Michigan, Ann Arbor, Michigan

Abrupt or gradual application of positive intrapulmonic pressure (20 cm H₂O) in young adult men caused an augmentation of the patellar reflex, an increased respiratory minute-volume and a shift from abdominal to thoracic breathing; all of which persisted throughout the period of increased pressure. In controlled ventilation and frequently also in free breathing, positive intrapulmonic pressure caused a predominant decrease, following an inconstant and transient initial increase in O₂ saturation of the blood in the tissues as determined by continuous oximeter readings from the ear. This decreased O₂ saturation is explained not only by the diminished blood flow but also by the finding that in dogs under constant ventilation in air, positive intrapulmonic pressure decreased oxygenation of the blood in the lungs. It is concluded that the augmentation of the knee-jerk induced by positive intrapulmonic pressure is due in large part to the resultant diminished blood flow and decreased oxygenation of the blood in the lungs, and that the attendant hypo-oxia and increased acid metabolites may potentiate the reflex through an anticholinesterase action on the neuromyal junction and possibly also central nervous structures. The increased respiration induced by positive intrapulmonic pressure is a counterpart of, and has etiological factors in common with, the augmentation of the patellar reflex.