[The determination of oxygen consumption from temperature measurements with the use of a thermodynamic model ]

A thermodynamic model is described which allows to calculate the oxygen consumption from 4 temperatures as input-variables. These input-variables are: one core-temperature (Tesoph), two skin-temperatures (one at the chest, one at the calf) and the incubator-air temperature. This model is based on the close relationship between oxygen consumption and heat production. The rate of heat production is derived from heat loss to the environment plus heat storage in the body. The data are smoothened by a special mathematical procedure and processed by a HP-85 Computer. Oxygen consumption was synchronously determined by the thermodynamic model and by a conventional method 155 times in four newborns. The flow-through method was used as conventional reference method. The results show that the thermodynamic model yields values for oxygen consumption which are closely related to directly measured values; which indicate the increase in oxygen consumption with activity and decreased environmental temperature; and which follow rapid changes in oxygen consumption of 5 ml/kg per minute. Consequently this thermodynamic model seems suitable to predict the relative changes in oxygen consumption. However the absolute values of oxygen consumption obtained by the model and obtained by direct measurement differ by 5 to 25% the thermodynamic model yielding systematically higher values than the direct measurement. The reasons for this difference are discussed. We demonstrated that a maximum of reliable information can be obtained from a minimal number of measuring sites on the patient by using a theoretical-analytical model.