Unlike other links in the oxygen delivery chain, such as cardiac output and muscle aerobic activity, the components of ventilation (Ve, Vt, and fR) are easily measured during exercise testing. Thus, barring technical error, reported data such as that provided in this study can be presumed to provide an accurate assessment of developmental changes in ventilatory function during exercise. In addition, longitudinal observations can be expected to provide a clearer picture of such changes compared with cross-sectional investigations. The findings in this study indicate that at a given level of treadmill work, Ve increases as the child ages. This rise in not, however, simply related to increase in body size. Vt increases in proportion to body mass as the child grows, but the frequency of breathing at a given submaximal work load progressively declines. As a result, submaximal Ve rises slower with age than would be expected for body mass.
This is also reflected in a steady fall in the Ve response to a given submaximal metabolic rate (ie, decline in (Ve/Vo2) with age. When the influence of sex was examined, only the magnitude of the Ve/Vo2 was observed to be gender related, with the girls demonstrating a greater value at all years. The explantation for this effect of gender on ventilatory efficiency is unknown. generic clarinex
Virtually the same patterns were observed at maximal exercise. Vt per kilogram remained stable while fR declined. The scaling exponent of 0.92 for Ve relative to mass indicates that body mass rose more rapidly than Ve during the 5-year study. At maximal exercise, however, the fall the maximal Ve per kilogram was not statistically significant. Ve/Vo2 fell with advancing age only in the boys, with greater values again evident in the girls.
These findings support those of previous studies describing children’s ventilatory responses to submaximal exercise. Robinson2 reported ventilatory responses to a treadmill walk at 5.6 km/h in groups of subjects ages 6 to 17 years. Breathing rate declined from 49 to 29/min over that age span while Ve per kilogram fell from 1.05 to 0.67 1 kg/min. Only small changes were observed in Vt per kilogram (0.021 L at age 6 years to 0.025 L at age 17 years). Andersen et al described a fall in breathing rate of 5 to 10/min between the ages of 8 and 16 years when children were cycling at 50% and 75% of maximal Vo2. The decline in submaximal Ve/Vo2 with age observed in the present study has also been described in crosssectional studies.
Rutenfranz et al reported longitudinal findings in children between ages 8 and 17 years. At the same relative intensity (65 to 70% Vo2max), Ve increased from 52.2 to 68.1 L/min over this age span in the male subjects but changed little in the female subjects (47.8 and 47.6 L/min, respectively). Breathing frequency fell from 39 to 28 and 36 to 26 in the boys and girls, respectively. Vt increased from 1.58 to 2.48 L in the boys and from 1.52 to 1.87 L in the girls. In this study, no influence of age on submaximal Ve/Vo2 was observed.
Previous reports of changes in ventilatory findings at maximal exercise in growing children have been less consistent. Moreover, to what degree increases in lung and body size are responsible for improvements in VEmax with age remains problematic. Mercier et al found that VEmax scaled to the mass exponent of 0.68 and height exponent of 2.06 in a study of boys ages 10.5 to 15.5 years. Compared with the present study, then, these data indicate that maximal Ve increased significantly slower relative to body mass as children became larger. Mercier et al described a close relationship between the development of maximal Vt and body mass (scaling exponent, 0.96). This supports the finding of a constant Vt per kilogram with age in the present longitudinal study as well as the report of Rutenfranz et al that maximal Vt during exercise is linearly related to lung volume.