The effect of CO2 on ventilation and breath-holding during exercise and while breathing through an added resistance

摘要

1. Ventilation was measured while subjects were made to rebreathe from a bag containing CO2 and O2 in order to expose them to a steadily rising CO2 tension (PCO2). The object of the experiments was to determine the effect of a variety of stimuli upon the increase in ventilation and fall in breath-holding time which occurs in response to the rising PCO2.2. Steady-state exercise at 200 kg.m/min resulted in a small fall in the slope of the ventilation—CO2 response curve (SV) and a small, though not statistically significant, fall in the PCO2 at which ventilation would be zero by extrapolation (BV). There was a marked fall in the slope of the breath-holding—CO2 response curve (SBH) and an increase in the PCO2 at which breath-holding time became zero by extrapolation (B_BH).3. These results have been interpreted with the aid of a model of the control of breath-holding and it is suggested that there is no change in CO₂ sensitivity on exercise, either during rebreathing or breath-holding.4. An increase in the resistance to breathing caused a marked reduction in S_V and B_V, but no change in the breath-holding—CO₂ response curve. These findings suggest that the flattening of the ventilation—CO₂ response curve is mechanical in origin and acute airway obstruction produces no change in CO₂ sensitivity.5. On the basis of these results, we suggest that more information about CO₂ sensitivity can be obtained by a combination of ventilation and breath-holding—CO₂ response curves.