Exercise-induced breathing patterns of youth are related to age and intensity

Abstract

The influences of sex, age, exercise intensity, and end-tidal CO₂ on the inspiratory drive ([V _T kg⁻¹]·T _i ⁻¹) and respiratory timing (T _i·T _tot ⁻¹) components of ventilation were examined in 295 youth (138 females, 157 males); similarly distributed 8–18 years of age. Ventilatory and metabolic measures were collected breath-by-breath at rest and during a slow walk (4.0 km h⁻¹), fast walk (5.6 km h⁻¹) and run (8.0 km h⁻¹). Regression modeling for drive (age, sex, and P_ETCO₂) found that sex was significant (R ² < 0.017; P < 0.05) for rest and running, but not walking. Compared to rest, drive increased by 120% for the slow walk, 217% for the fast walk and 258% for the run (P < 0.0001). Drive decreased with age (P < 0.0001): rest = 0.41 ml kg⁻¹ s⁻¹ year⁻¹; slow walk = 0.90 ml kg⁻¹ s⁻¹ year⁻¹; fast walk = 1.30 ml kg⁻¹ s⁻¹ year⁻¹; and run = 1.47 ml kg⁻¹ s⁻¹ year⁻¹. In the regression models for timing, sex provided ∼ 1% of the variance during the run, but was not significant during rest or walking. Timing increased with exercise intensity by approximately 0.02 units (P < 0.001), but decreased by ∼ 0.002 units year⁻¹ with age for all conditions (P < 0.003). Changes in drive and timing were marginally related to end-tidal CO₂ (exercise R ² < 0.063 for all models). These results suggest that in the control of inspiratory drive and timing during exercise in youth, sex is of minor importance but there are age-related changes which are marginally associated with CO₂.