[Development and disease in the newborn infant from the viewpoint of the thermodynamics of irreversible processes].

The newborn baby was considered thermodynamically as an open system in stationary state and its rate of entropy production determined. Three groups of newborns were studied: (1) healthy, premature newborns (34 weeks gestational age) at the age of 1, 7, 14, 21 and 28 days, (2) healthy, mature newborns (39 wks GA) and mature newborns with a hypoplastic-left-heart syndrome (39 wks GA), both in their first week of life. The entropy production rate was determined by using a diagnostic procedure, based on temperature measurements and a thermodynamic model. The entropy production rate (EPR) indicates the direction and stadium of development of a system. The results show, that the EPR in prematures increases during the first four postpartal weeks i. e. up to the 38th postconceptual week and then still is lower than in mature newborns. The EPR in prematures after birth develops in the same manner as the EPR of animal organisms before birth and approaches the one of newborns at term. The EPR in newborns with a lethal congenital heart disease was significantly lower (p less than 0.01) than in healthy newborns of the same age and already during the first week of life similar to the EPR of a 70 year old persons. These results support the hypothesis that the rate of entropy production could be used as an index to indicate biological, non-chronological developmental stadium and to assess the severity of a disease respectively its tendency to heat or to deteriorate. This would be especially helpful in patients with a very complex therapeutic regime.