Validation of the Portable VmaxST System for Oxygen-uptake Measurement

The aim of this study was to validate the accuracy of a new type of portable gas-analysis system (Sensormedics VmaxST) for the measurement of oxygen-uptake at expenditure levels that are reached during walking in patients with movement disorders. The criterion method was the Douglas Bag (DB) method, which is considered to be the gold standard. Accuracy evaluations were made in two trials, randomly using the VmaxST (ST) and the Douglas Bag method. Ten healthy adult subjects participated in the trials (age: 28.8 (4.3) years; body mass: 75 (13.3)kg; height: 179.3 (8.9)cm). Each trial consisted of two time periods: 5 min of resting in a comfortable chair and 5 min of cycling at an 80 W workload. During the fifth minute of each block, mean minute ventilation (VE), oxygen-uptake (VO2), and carbon dioxide production (VCO2) were measured or calculated for both systems. Energy expenditure (EE) values were calculated and net values calculated by subtracting resting measurements from gross measurements. The results show that no significant differences were found between the VmaxST and the Douglas Bag method for the primary parameters: EEnet and VO2net. Significantly higher values were found for rest and exercise values. However, these differences were very small. Therefore, the validity of the VmaxST is sufficient for use in gait studies to determine the energy cost of walking, especially when net values are calculated.