Breath-to-breath "noise" in the ventilatory and gas exchange responses of children to exercise

The purposes of this investigation were to quantify the noise component of child breath-by-breath data, investigate the major determinants of the brea th-to-breath noise, and to characterise the noise statistically. Twenty-fou r healthy children (12 males and 12 females) of mean (SD) age 13.1 (0.3) ye ars completed 25 min of steady-state cycle ergometry at an exercise intensi ty of 50 W. Ventilatory and gas exchange variables were computed breath-by- breath. The mean (SD) oxygen consumption ((V)over dot O-2) ranged from 0.72 (0.16) to 0.92 (0.26) l . min(-1); mean (SD) carbon dioxide production ((V )over dot CO2) ranged from 0.67 (0.20) l . min(-1) to 0.85 (0.16) l . min(- 1); and mean (SD) minute ventilation ranged from 17.81 (3.54) l . min(-1) t o 24.97 (5.63) l . min(-1). The majority of the breath-to-breath noise dist ributions differed significantly from Gaussian distributions with equivalen t mean and SD parameters. The values of the normalised autocorrelation func tions indicated a negligible breath-to-breath correlation. Tidal volume acc ounted for the majority of the (V)over dot O-2 (43%) and (V)over dot CO2 (4 9%) variance. The breath-to-breath noise can be explained in terms of varia tions in the breathing pattern, although the large noise magnitude, togethe r with the relatively small attainable response amplitudes in children redu ces the certainty with which ventilatory and gas exchange kinetics can be m easured.