[Time course study on the stability of the electrode in the oxygen consumption analyzer RM-200]

We investigated the stability of the polarographic electrode, the CO2 electrode and the expired minute ventilation value (VE value) in the oxygen consumption analyzer RM-200 over a 6-month duration. A total of analyses 363 were performed on 71 normal subjects. Two methods were used; one is the gas response curve which directly shows the property of the polarographic electrode and the CO2 electrode, and the other is the Douglas bag method which is considered to be a standard method of O2 consumption (VO2) and CO2 output (VCO2) measurement. The gas response curve analyses were performed just after setting a new polarographic electrode, at the third month and at the sixth month. Measurement by the Douglas bag method was usually done once a week. The effects of respiratory rate on the values of VE, VO2 and VCO2 were evaluated from the ratio of each value measured by RM-200 to that obtained by the Douglas bag method. Evaluation by the gas response curve, revealed that the polarographic electrode was stable for 3 months, but not at the six month. The Douglas bag method revealed that a decrease in VO2 value had already occurred after a 4-month use of the polarographic electrode. However, a definite correction of the time constant allowed the use of the electrode up to six months. The VCO2 value and the VE value were stable for 6 months. Increase in the respiratory rate caused a slight but significant difference between VO2 and VCO2 values measured by RM-200 and those obtained by the Douglas bag method, but did not influence the VE values.(ABSTRACT TRUNCATED AT 250 WORDS)