Metabolic variability: ¿Noise or new physiological information?

Abstract

The aim of this paper is to propose the measurement a new type of physiological variability. The premise is that there is embedded information in the form of short-term metabolic variability (MV) when the human gas exchange is measured using the mixing chamber and the breath by breath indirect calorimetry technique (ICT). This two measurement methods are compared to observe metabolic dynamics when subjects are subdue to physiological stimulus. Variances and low frequency power spectrums (0-0.5 Hz) are use to measure the MV activity. The hypothesis is proved measuring the MV in a population of 17 young volunteers subdue the clino-ortho maneuver. The test protocol was adapted using 30 minutes of data acquisition to include both mixing chamber and breath by breath ICT. Subjects were measured after 8 hours of fasting. The results showed a MV increment from 32.5 to 40 ml/min (p<0.01) for de VO2 standard deviation with none significance change for de the VCO2 using the mixing chamber ICT. Analogously the ICT breath by breath MV showed a total power spectrum change from 34.9 to 60 (ml/bth)2 for the VO2 and from 24 to 37 (ml/bth)2 for the VCO2 (p<0.05), mainly in the frequency region from 0.01 to 0.03 Hz. Therefore, it was concluded that breath by breath MV was approximately 3 times more relevant than the mixing chamber MV with the possibility to evidence metabolic control mechanism. © Springer-Verlag Berlin Heidelberg 2007.