[A technical evaluation of 5 brands of O2 concentrators. The Asturias Project]

To check the technical specifications of 5 O2 concentrators pertaining to 5 different brands: Mark 4, Zefir, Puritan-Bennet, Drager and MHF prototype. The concentrators worked continuously for 37 days. External filters were cleaned after 400 hours and measurements were taken when theoretical flows were between 1 and 3 l/min. One-way analysis of variance and Scheffe's method were used to compare the different brands. Flow measurements were taken with Costrema and Drager debitmeters. O2 concentrations were measured with Drager, Cepo and Oxidig oximeters. Emitted sound was measured with Cel, Spyri Ag Thun, Bruel Kjaer and General Radio meters. Electrical consumption was determined with a Siemens counter. All the concentrators produced flows that were under theoretical values, though the Zefir and MHF models came the closest. Accuracy and precision of flow varied from 1% to -32%, and from 1.1% to 11.7%, respectively. The value of 4 expressing linearity of flows oscillated between 0.959 and 0.991. When flow was 2 l/min or less, all achieved O2 concentrations greater than 90%, but this level was reached only by the Drager and MHF concentrators when flows were 3 l/min. With the exception of the MHF prototype, all the models emitted noise over 50 dB, the Drager machine being the noisiest. Electrical consumption was similar in all models. O2 concentrators can be recommended as sources of oxygen supply, but they have their limitations. Improvements must be made in accuracy of flow and monitoring of the apparatus ability to concentrate; noise must be reduced as well.