Adaptation to C02 with Particular Relation to Co, Retention in Diving

Adaptation to C02 produces a typical breathing pattern of increased tidal volume and lowered respiratory rate. Anatomical and physiological deadspace, as well as arterial-alveolar C02 and 02 gradients, are increased under these condions. The relationship of these findings with the well known lowered respiratory response to high C02 concentrations after 0O2 adaptation is discussed. Evidence for C02 adaptation in routine diving is presented. Zusammenfassung — Die Anpassung an längerdauernde Kohlensäure Einwirkung äussert sich in einem typischen Atmungsrhythmus mit erhöhtem Atemvolumen und verminderter Atemfrequenz. Der anatomische und physiologische Totraum ist vergrössert und der AaD(jo, und AaDo, erhöht. Die Beziehung dieser Befunde zu der bekannten verminderten Reaktion der Atmung bei Einatmung hoher C02 Konzentrationen nach C02 —Adaptation wird diskutiert. Es werden Befunde berichtet, die beweisen, dass Kohlensäure adaptation bei regelmässigem Tauchen auftritt. RSsume" — L'acelimatation ä Pabsorption de C02 pour une longue duree se traduit par une augmentation du volume d'air inspire" et une reduction de la frequence respiratoire. Les temps-morts anatomiqueetphysiologique ainsi que les gradients arterioalveolaires en C02 et 02 sont augmented. On discute les relations existant entre ces resultats et le fait bien connu que le Systeme respiratoire devient moins sensible au gaz carbonique apres acclimatation ä l'hypereapnie. II est en outre demontre qu'il y a adaptation au C02 dans le cas de plongees regulieres. IT HAS been established that prolonged exposure to increased C02 concentration results in a reduction of the ventilatory response to C02 (Haebisch, 1949; Schaefer, 1949; Chapin, 1955). C02 tolerance curves obtained after three days of exposure to 3 per cent C02 showed a shift to the right and a decrease in slope (Schaefer, 1949). During acclimatization to 3 per centC02, the tidal volume increased and respiratory rate decreased (Schaefer, 1949) which suggested that the respiratory pattern is an important factor in the respiratory response to C02. Studies of acute exposure to various C02 concentrations on a large group of subjects established clearly the relationship of respiratory pattern and ventilatory response to C02. Subjects with a large tidal volume and a low frequency showed a significantly lower response to C02 than those with a small tidal volume and high respiratory rate (Schaefer, 1958) (Kg. 1). Subjects were classified in a low and high ventilation group, using as criteria a ventilation ratio of 4 at 5.4 per cent C02 and 6 at 7.5 per cent C02. For example,