Ventilatory control during exercise with increased external dead space

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Abstract
Effects of increased external dead space (VD) on ventilatory control in steady-state exercise were determined in 3 healthy human adults. The subjects performed cycle ergometer exercise on 6 occasions, each with a different VD (range: 0.1-1.0 l); work rate was incremented every 5 min by 15-20 W. Minute ventilation (.ovrhdot.VE), CO2 output (.ovrhdot.VCO2) and mean alveolar PCO2 (P.hivin.ACO2) were measured in the steady state. Without VD, the .ovrhdot.VE-.ovrhdot.VCO2 relationship was linear, having a small positive .ovrhdot.VE intercept, and P.hivin.ACO2 was constant, independent of .ovrhdot.VCO2. Increased VD was associated with an upward shift of the .ovrhdot.VE-.ovrhdot.VCO2 relationship, and an elevated P.hivin.ACO2, again independent of .ovrhdot.VCO2. At each work rate, the increases in .ovrhdot.VE accompanying increased VD were no greater than could be expected from a conventional CO2 inhalation study. Increasing external dead space does not impair the ability of the human respiratory system to regulate P.hivin.ACO2 during exercise except for resetting the regulated PCO2 [CO2 partial pressure] level.