A method and apparatus for determining a user's Respiratory Quotient (RQ) using
just measured O2 and CO2 concentrations without use of a
flow meter. The RQ is determined by measuring the user's real-time inspired O2
concentration (INS O2) and end tidal O2 concentration (ETO2) and
measuring the user's real-time inspired CO2 concentration (INS CO2)
and end tidal CO2 concentration (ETCO2), and then determining the user's
RQ from the measured INS O2, ETO2, INS CO2, and ETCO2 values in accordance with
the following equation: RQ=(ETCO2-INS CO2)/(INS O2-ETO2). In order to avoid error
introduced by the flow rate, the measurement steps are preferably performed while
the user is in a resting condition. Also, ETCO2 is preferably measured as the maximum
CO2 value in a breath cycle of the user, while INS CO2 is preferably
measured as the minimum CO2 value in a breath cycle of the user. Similarly,
ETO2 is preferably measured as the minimum O2 value within a breath
cycle of the user, while INS O2 is measured as the maximum O2 value
within a breath cycle of the user. On the other hand, the values of INS CO2 and
ETCO2 also may be determined in accordance with the invention by analysis of a
CO2 waveform of a breath cycle of the user and the values of INS O2
and ETO2 determined by synchronizing timing of the O2 waveform of a
breath cycle of the user with the CO2 waveform and sampling INS O2 and
ETO2 values simultaneously with sampling of complementary CO2 values
determined by analysis of the CO2 wavefomm. The RQ measuring device
may include the oxygen and CO2 sensors in a mainstream or sidestream configuration.
