[Influence of body position on human gas exchanges. Role of age (author's transl)].

We measured blood gases, steady state diffusing lung capacity, global and partial lung ductances in 16 subjects aged from 20 to 63 in supine and seated position. We obtained three types of response. In group I, (n = 6) blood gases and TLCO increased probably chiefly due to an increase of perfusion of lung apices and a more even distribution of regional VA/Q (all these subjects are young and thin). In group II, (n = 4) blood gases and TLCO decreased probably due to a ventilation at closing volume level with a decrease of ventilation in the dependent parts of the lung (2 subjects with abdominal obesity and a third who is the oldest one). In group III (n = 7), PaO2 decreased but DLCO increased. Probably ventilation took a slight place in closing volume. The increase of the exchange surface area is likely to be unable to compensate the arterial hypoxemia induced by the low VA/Q in the dependent parts of the lung. Influence of body position seems to be a function of age which increases closing volume.