Ventilatory Response to Hypercapnia by Rebreathing in Successive Trials

Abstract

The ventilatory response to carbon dioxide at rest was determined repeatedly by the rebreathing method;three successive CO₂ response lines, with 30-min intervals, were examined in 12 healthy male subjects.Overall mean slopes obtained at 30, 60 and 90min were 2.95, 2.47 and 2.28 liters/min⋅mmHg, respectively, the difference being statistically not significant.However, the slopes of four high responders, who were subjects with higher slopes than that of the mean values obtained here, decreased significantly (p<0.05) at 60min as compared with the 30min test, but this did not occur in the other subjects.Better reproducibility in obtaining the CO₂ response slope in the high responders was observed in the first rather than the 60 or 90min trials, suggesting incomplete recovery in the humoral agents released during the CO₂ test. These results indicated that the CO₂ response curve by rebreathing should be determined carefully, especially in the high responder, taking into consideration its individual variability and the interval in consecutive measurements.