Exercise flow-volume loops in prepubescent aerobically trained children

Abstract

We studied mechanical ventilatory constraints in 13 aerobically trained (Tr) and 11 untrained (UT) prepubescent children by plotting the exercise flow-volume (F-V) loops within the maximal F-V loop (MFVL) measured at rest. The MFVL allowed to determine forced vital capacity (FVC) and maximal expiratory flows. Expiratory and inspiratory reserve volumes relative to FVC (ERV/FVC and IRV/FVC, respectively) were measured during a progressive exercise test until exhaustion. Breathing reserve (BR) and expiratory flow limitation (expFL), expressed in percentage of tidal volume (V(T)) and defined as the part of the tidal breath meeting the boundary of the MFVL, were measured. Higher FVC and maximal expiratory flows were found in Tr than UT (P < 0.05) at rest. Our results have shown that during exercise, excepting one subject, all Tr regulated their V(T) within FVC similarly during exercise, by breathing at low lung volume at the beginning of exercise followed breathing at high lung volume at strenuous exercise. In UT, ERV/FVC and IRV/FVC were regulated during exercise in many ways. The proportion of children who presented an expFL was nearly the same in both groups (approximately 70% with a range of 14 to 65% of V(T)), and no significant difference was found during exercise concerning expFL. However, higher ventilation (V(E)), ERV/FVC, and dyspnea associated with lower BR, IRV/FVC, and SaO2 were reported at peak power in Tr than UT (P < 0.05). These results suggest that, because of their higher Ve level, trained children presented higher ventilatory constraints than untrained. These may influence negatively the SaO2 level and dyspnea during strenuous exercise.

Maximal Oxygen Uptake Validation in Children With Expiratory Flow Limitation

“…accurate measurement of VO 2 max, children present a substantial challenge; not least of which is the high prevalence of EFL in this population (28,29,40). One approach has been to estimate VO 2 max indirectly from submaximal tests whereas another has been to accept secondary criteria (e.g., HR, RER) to provide confidence that VO 2 max has been achieved.…”

“…Anatomically children have smaller airways in comparison with lung size than adults (24) which, combined with greater ventilations at any given metabolic rate, leads to a high prevalence of EFL irrespective of VO 2 max per se (28,29,40). EFL leads to dynamic hyperinflation (40) thereby mechanically disadvantaging the inspiratory muscles and increasing the likelihood of respiratory muscle fatigue which has been documented in adults during high intensity exercise (20).…”

“…What has not been established in children is whether this procedure is effective across the spectrum of lower fitness levels as might be expected in a randomly recruited population, for example, in the United States. It is also pertinent that among this population of prepubescent children there may be a high prevalence of expiratory flow limitation (EFL, 28,29,40) and possibly exercise-induced arterial hypoxemia (EIAH,27). Whether the two-test protocol can effectively determine VO 2 max across a broad spectrum of fitness levels and in the presence of EFL in children which, in and of itself may increase fatigability and modulate the respiratory response to exercise, has not been determined.…”

Control of Breathing During Exercise

“…However, the airways occasionally do present a significant limitation to expiratory airflow resulting in dynamic hyperinflation, increased respiratory muscle work andV E limitation during heavy-intensity exercise. Healthy subjects most susceptible to mechanical airway limitations to expiratory flow during heavy exercise include fit prepubescent children (251), fit aging adults with reduced lung elastic recoil (185) and highly fit young adult females (229,230). In the latter group, it was shown that theV E response to inhaled CO 2 (via rebreathing) decreased in slope at heavy-intensity exercise (vs. rest or mild exercise), coincident with evidence of expiratory flow limitation.…”

Ventilation and Respiratory Mechanics

“…Children involved in high levels of physical activity tend to have larger maximal flow-volume loops (FVLs) than untrained children at comparable ages and body size (393). Moreover, several studies have reported an increase in static lung volumes, over that expected from the age-dependent increase in stature, with long-term swim training (32,152,586), running training (146), and additional physical education (477).…”