Ventilatory response to hypercapnia by rebreathing in successive trials.

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Abstract
The ventilatory response to CO2 at rest was determined repeatedly by the rebreathing method; 3 successive CO2 response lines, with 30 min intervals, were examined in 12 healthy human males. Overall mean slopes obtained at 30, 60 and 90 min were 2.95, 2.47 and 2.28 l/min .cntdot. mmHg, respectively, the difference not being statistically significant. The slopes of 4 high responders, who were subjects with higher slopes than that of the mean values obtained here, decreased significantly (P < 0.05) at 60 min as compared with the 30 min 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 1st rather than the 60 or 90 min trials, suggesting incomplete recovery in the humoral agents released during the CO2 test. 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.