Abstract
Background: Alveolar oxygen pressure and alveolar-arterial oxygen gradient calculation are important in the assessment of respiratory system function. It needs estimation of respiratory exchange ratio (RER). Although RER is influenced by the dietary variation, is usually replaced by a constant value of 0.8. In this study, we evaluated the effect of time from last food intake on RER. Methods: After recording time from last food intake (Tf), RER was measured at rest and in sitting position with PowerCube ergospirometer (Ganshorn) in 147 volunteers. Results: 75 males and 72 females with mean age of 34.7±13.7 years were enrolled in the study (7 smokers). Tf mean was 4.8±4.4 hours (0.08-15). Mean RER was 87±0.11(0.63-1.35). There was a negative correlation between mean RER and Tf (R2=0.36, P<0.001). Within 90 minutes from last food intake, there was significant RER dispersion (mean RER = 0.97±0.11,R2=0.03,P=0.21). After this time, the dispersion was decreased (mean RER=0.82±0.08,R2=0.23, P <0.001). Conclusion: We found a significant relationship between RER and time lapsed from last food intake, especially within the first 90 minutes. The assumption of RER∼0.8 is reasonable after this time period.
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