Respiratory muscle deoxygenation and ventilatory threshold assessments using near infrared spectroscopy in children

The aim of this study was to assess respiratory muscles deoxygenation and to determine ventilatory threshold using near infrared spectroscopy (NIRS) in children during incremental cardiopulmonary exercise. Fourteen healthy children with a mean +/- SD age of 12.8 +/- 1.4 yrs performed an incremental exercise test on a cycle ergometer. NIRS was used to assess deoxygenation of the respiratory muscles. Ventilatory parameters (oxygen uptake, carbon dioxide production, and ventilation minute), power output, and tissue saturation (StO2) were measured. Ventilatory threshold was determined by the two following methods: the V-slope method which corresponds to the breakpoint in VCO2 as a function VO2 relationship (VT(V-slope)) and the NIRS method which corresponds to the point of rapid fall in StO2 (VT(nirs)). During exercise, the respiratory muscles deoxygenated as the exercise intensity increased. StO2 decrease progressively until an abrupt decrease was observed. No significant differences were observed between cardiorespiratory variables corresponding either to VT(V-slope) or to VT(nirs). The two methods showed a good agreement (data were inside the 95 % confidence interval). Likewise, a significant relationship was found between VT(V-slope) and VT(nirs) for each parameter measured (r = 0.87 to 0.94, p < 0.001). We concluded that respiratory muscles deoxygenate during incremental exercise in children and that ventilatory threshold could be determined by NIRS.