Carbon dioxide and acid-base transients during hyperventilation

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

Studies were conducted on ten healthy adult males subjected to mechanically induced hyperventilation. Total ventilation was increased approximately 300%. This resulted in a mean arterial carbon dioxide tension decrease to 20 mm Hg and a mean pH increase to 7.60. Observations of the dynamic shifts in carbon dioxide stores were made for a 12-min period after onset of hyperventilation. The total carbon dioxide elimination was determined and compared to the basic metabolic CO₂ production to permit estimation of body carbon dioxide depletion. The total carbon dioxide elimination was partitioned into that coming from the tissues, the blood, the lung parenchyma, and the alveolar air. After the abrupt increase in alveolar ventilation, a significant portion of the expired carbon dioxide comes from the lung tissue store and the alveolar gas compartments; this is approximately 140 cc and is eliminated in the first 3 min. After 3 min most of the expired carbon dioxide can be accounted for as coming from blood and tissues.