Development of a thermal regulation response simulation model for human infants

Fanfoni, Alida (2014-12)

Thesis (MEng) -- Stellenbosch University, 2014.

Thesis

ENGLISH ABSTRACT: The thermal regulation response of a neonate has to maintain temperature homeostasis, thus resisting the changes to core temperature caused by the unstable external environment. In this thesis a theoretical thermal regulation response model for human infants subject to a well-defined environment is presented. This model will aid in understanding the influences of environmental effects on core and skin temperature. The respiratory system was also included in the thermal regulation response model. A literature study was undertaken emphasising thermal regulation of neonates. The blood circulation system, skin tissue physiology and the respiratory system physiology were reviewed and helped to provide a better understanding of the thermal regulation mechanisms and how heat transfer theory can be used to analyse heat loss in neonates. The thermal heat transfer properties of skin tissue was specified and used in the development of the theoretical simulation model. The bioheat equation developed by Pennes was reviewed as well as a mathematical model developed by Fiala et al. The theoretical model was developed by applying the conservation of energy and the applicable properties to one dimensional layers to generate a set of time dependent differential equations. The set of equations was solved using an explicit numerical finite difference method, given the initial conditions. The mathematical model included heat loss through the skin, heat loss through the respiratory system, as well as the effect of environments (in incubator or in a bassinette) with different temperatures, relative humidity’s and air velocities. Clothing was also incorporated. A clinical trial was conducted to facilitate a better understanding of thermal stability in neonates. The data acquired during the clinical trial was also used to verify/validate the theoretical simulation model. The results from the simulation temperatures were compared with the average outer skin layer temperature measured during the clinical trial and an average deviation of only 0.22 °C was found, thereby proving that the simulation model gives realistic results. An experimental respiratory model was designed to simulate the respiratory system and illustrate the functioning thereof with regards to heat transfer. This was done by designing an experimental mechanical lung apparatus. The apparatus was tested and successfully imitated the respiratory system with regards to heat transfer. The results obtained from this experiment indicated that the trachea must be moistened continuously in order to condition inhaled air. The outcome of this project identified two possible applications. For the first application it can be used as a test tool for quickly evaluating the influence of different environmental conditions in the transient temperature distribution of neonates. The second application would be to enable medical professionals to monitor the influence of the thermal environment, including the temperature, relative humidity and air velocity, on the neonate’s temperature change to allow for a speedier thermal intervention strategy.

AFRIKKANSE OPSOMMING: Die hitte regulering reaksie van 'n pasgebore baba moet temperatuur homeostase handhaaf, en sodoende die veranderinge aan die kern temperatuur weerstaan wat veroorsaak word deur ‘n onstabiele eksterne omgewing. In hierdie tesis word 'n teoretiese hitte regulerings reaksie model vir menslike babas, onderhewig aan 'n goed-gedefinieerde omgewing, aangebied. Hierdie model sal help met die verstaan van die invloed wat omgewings effekte het op die kern en vel temperatuur. Die respiratoriese sisteem is ook ingesluit in die hitte regulering reaksie model. 'n Literatuurstudie is onderneem met die klem op hitte regulering van pasgebore babas. Die bloed sirkulasie sisteem, vel weefsel fisiologie en die respiratoriese sisteem fisiologie is hersien en help met beter begrip van die hitte regulering meganismes en hoe hitteoordrag teorie kan gebruik word om hitte verlies in pasgebore babas te analiseer. Die hitte-oordrag eienskappe van vel weefsel is gespesifiseer en word gebruik in die ontwikkeling van die teoretiese simulasie model. Die ‘bioheat’ vergelyking ontwikkel deur Pennes is hersien asook 'n wiskundige model wat ontwikkel is deur Fiala et al. Die teoretiese model is ontwikkel deur die toepassing van die behoud van energie tesame met die gebruik van toepaslike eienskappe en een dimensionele lae om 'n stel tyd afhanklike differensiaalvergelykings op te wek. Die stel vergelykings is opgelos met behulp van 'n eksplisiete numeriese eindige verskil metode, gegewe die aanvanklike toestande. Die wiskundige model sluit in die hitte verlies deur die vel, hitte verlies deur die respiratoriese stelsel, sowel as die effek van die omgewing (broeikas of in 'n bassinette) met verskillende temperature, relatiewe humiditeit en lug snelhede. Klere is ook in ag geneem. 'n Kliniese proef is gedoen om 'n beter begrip van termiese stabiliteit in pasgebore babas te fasiliteer. Die data wat tydens die kliniese proef verhaal is, is ook gebruik om die die teoretiese simulasie model te verifieer. Die resultate van die simulasie temperature is vergelyk met die gemiddelde buitenste vel laag temperatuur gemeet tydens die kliniese proef en 'n gemiddelde afwyking van slegs 0.22 °C is gevind, wat dus bewys dat die simulasie model realistiese resultate gee. 'n Eksperimentele respiratoriese model is ontwerp om die respiratoriese stelsel te simuleer en die funksionering daarvan te illustreer met betrekking tot hitte-oordrag. Dit is gedoen deur die ontwerp van 'n eksperimentele meganiese long apparaat. Die apparaat is getoets en slaag daarin om die respiratoriese stelsel suksesvol na te boots met betrekking tot hitteoordrag. Die resultate verkry uit hierdie eksperiment het aangedui dat die tragea kostant klam gemaak moet word om ingeasemde lug te kondisioneer. Die uitkoms van hierdie projek het twee moontlike toepassings geïdentifiseer. Die eerste is dat dit as 'n toets instrument vir die vinnige evaluering van die invloed van verskillende omgewingsfaktore in die temperatuur verspreiding van pasgebore babas gebruik kan word. Die tweede toepassing sal wees om medici in staat te stel om die invloed van die termiese omgewing te monitor, insluitend die temperatuur, relatiewe humiditeit en lug snelheid, om die neonaat se temperatuur verandering te monitor en voorsiening te maak vir 'n vinniger verwarmings intervensiestrategie.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/95896
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