CO₂ and acid-base transients after hyperventilation

¹ Department of Physiology, Ohio State University College of Medicine; and Cardiopulmonary Laboratory, Ohio Tuberculosis Hospital, Columbus, Ohio

Fourteen male subjects were mechanically hyperventilated by intermittent positive pressure breathing. Tidal volume and respiratory frequency were increased approximately three times and one and one-half times control, respectively. Breath-by-breath analyses of CO₂ output indicate a loss of approximately 2.5 liters of CO₂ from the body stores in 12 min. Only one-third of that volume was restored during the ensuing 12-min recovery period, mostly as a result of hypoventilation rather than apnea. Over the entire recovery period, the volume of CO₂ regained by the blood store approximated 75% of the CO₂ content lost during hyperventilation. Under the conditions of these experiments, tissues regained less than 20% of the depleted CO₂ store. CO₂ retention patterns may be more effective than arterial blood or alveolar air analyses in determining a return to a steady state when tissue stores have been considerably reduced.