Effects of breathing through external dead space on ventilation at rest and during exercise. II

We used a new non-invasive monitor of ventilation, the respiratory inductive plethysmograph, to determine the effects of breathing through a mouthpiece (with nose clip) and breathing through external dead spaces on ventilation at rest and during exercise. Six normal young subjects were studied during 5-min sequential periods at rest, submaximal exercise on a bicycle at a work load of 800 kgm/min, and recovery. Not surprisingly, the imposition on the respiratory system of breathing through a mouthpiece (with nose clip) and with external dead spaces of 150, 250, and 350 ml produced progressively greater ventilation than natural breathing during rest and submaximal bicycle exercise. However, when the actual tidal volumes were corrected for the increase in ventilation caused by the external dead space, ventilation both at rest and during exercise with mouthpiece breathing still remained higher than natural breathing. These data suggest that breathing through a mouthpiece (with nose clip) and breathing through external dead spaces stimulates ventilation both at rest and during exercise.