Estimation of the respiratory ventilation rate of preschool children in daily life using accelerometers

Inhalation rate is an essential factor for determining the inhaled dose of air pollutants. Here, accelerometers were used to develop regression equations for predicting the minute ventilation rate (V(E)) to estimate the daily inhalation rate in young children. Body acceleration and heart rate were measured in 29 Japanese preschool children (6 yr of age) during nine different levels of activities (lying down, sitting, standing, playing with plastic bricks, walking, building with blocks, climbing stairs, ball tossing, and running) using the Actical omnidirectional accelerometer, the ActivTracer triaxial accelerometer, and a heart rate monitor. Measurements were calibrated against the V(E) measured by the Douglas bag method. ActivTracer accelerometer measurements gave a strong correlation with V(E) (Pearson's r = 0.913), which was marginally stronger than that for the Actical counts (r = 0.886) and comparable to the correlation between heart rate and logarithmic V(E) (r = 0.909). According to the linear regression equation, the V(E) for lying down, sitting, standing, playing with plastic bricks, walking, and running was overestimated by 14-60% by the Actical and by 14-37% by the ActivTracer. By comparison, for building with blocks, climbing stairs, and ball tossing, the V(E) was underestimated by 19-23% by the Actical and by 13-18% by the ActivTracer. When these three activities were excluded, a stronger correlation was found between the V(E) and ActivTracer measurements (r = 0.949); this correlation was 0.761 for the three excluded activities. Discriminant analysis showed that the ratio between vertical and horizontal acceleration obtained by the ActivTracer could discriminate walking from building with blocks, climbing stairs, and ball tossing with a sensitivity of 75%. The error in estimating V(E) was considerably improved for the ActivTracer measurements by the use of two regression equations developed for each type of activity.