EFFECT OF ADDED DEAD‐SPACE ON PULMONARY VENTILATION DURING SUB‐MAXIMAL, STEADY‐STATE EXERCISE

Six normal subjects exercised for 6 min at 30%, 50%, and 70% of their predicted Vo 2 max, with and without an added respiratory dead‐space of 1,200 ml. The added dead‐space caused a marked increase of V 2 /MVV 15 %, the values at the three work loads being, respectively: without dead‐space, 20·4%, 30·1%, and 44·2%; and, with dead‐space, 41·1%, 48·6%, and 68·7%. These increases of V 2 were due mainly to increases of tidal volume, but ventilatory frequency increased also, the values being: without dead‐space, 21·0, 25·5, and 30·4 breaths/min; and with dead‐space 25·4, 28·4, and 33·9 breaths/min. At the highest work load the V 2 /VC ratio without dead‐space was 44·0%, and with the dead‐space 62·6%. Possible reasons for the breathing pattern adopted by the subjects are discussed.