Maintenance of ventilatory control by CO2 in the rat during growth and aging.

The long-term adjustment of ventilation and blood gases throughout life was studied in halothane anaesthetized male Wistar rats of various ages (1.5-20 months). Basal metabolic rate (O2 consumption, CO2 production), ventilation and ventilatory response to CO2 changed significantly during growth and aging, whereas arterial partial pressure of CO2 (PaCO2) and pH remained unchanged. Changes in the rate of CO2 production were associated with proportional changes in alveolar ventilation and in the sensitivity of the ventilatory control system to a CO2 stimulus at various ages. Ventilatory equivalent (ratio of alveolar ventilation to CO2 production) and the slope of the CO2/ventilation response line normalized for CO2 production were maintained constant throughout life, despite significant changes in the breathing pattern. These findings suggest that PaCO2 homeostasis is maintained by ventilatory regulation coupled tightly with CO2 production throughout life.