The effects of breath-holds and muller manoeuvres on upper airway carbon dioxide concentration in humans

Background: Obstructive sleep apnoea is caused by collapse of the upper airway. The presence of CO₂ in the upper airway lumen evokes a number of reflexes which favour upper airway re-opening, and we have proposed previously that CO₂ would build up in the upper airway following airway collapse and that this would contribute to reflex airway re-opening. However, it is not known if CO₂ can transfer from the alveoli to the anatomical dead space of the upper airway during apnoea. Objectives: To determine if alveolar CO₂ can enter the upper airway during breath-holds and Muller manoeuvres. Material and Methods: With local ethics committee approval, 6 male volunteers (aged 22-48 years), following a quiet inspiration, carried out breath-holds and Muller manoeuvres until breaking point. CO₂ was measured continuously in samples obtained from the hypopharynx using an infrared analyser with a sample rate of 50 ml/min. Muller manoeuvres (forced inspirations against a closed upper airway) mimic the respiratory efforts which occur during obstructive apnoeas. Results: In all cases, CO₂ increased progressively during apnoeas. There was a much larger increase in Muller manoeuvres (3.78 ± 0.51%, mean ± SEM at breaking point) compared to breath-holds. Discussion: These results show that upper airway CO₂ concentration rises substantially during apnoeas and suggest that transfer of CO₂ from the lungs to the upper airway may evoke a number of reflex effects which could affect breathing and upper airway re-opening during obstructive apnoeas.