Ventilation of lungs in infant and adult rats and its responses to hypoxia

Abstract

Do the controls of breathing differ with age? Pulmonary ventilation was measured by body plethysmograph and pressure transducer. After birth, breathing was irregular (pneumotaxic); steadiness from breath to breath was gained at 3 days; extraction of oxygen from the inspired air became more uniform after 10 days. In pO2 20–40 mm Hg only infants survived a half hour; ventilation did not usually increase, and often decreased. Hyperventilation even in 40 mm Hg was not sustained for many minutes in the newborn, but by 6 days was large and enduring. Heartbeats decreased in frequency during severe hypoxia. Oxygen consumption decreased 75% during hypoxia that allowed survival of infants; it sometimes recovered only slowly after hypoxia ended. Tolerance of infants to low oxygen thus consisted in ability to utilize some oxygen at low pressures and to dispense with some oxygen. Some factor other than pCO2 or pO2, possibly centrogenic, often controlled ventilation in infancy. Low oxygen maximally accelerated the breathing at an age when endurance of hypoxia remained. Submitted on May 12, 1960