## 4 How to Solve (at Least in Part) These Problems
### Applications and Research Perspectives
[PERSON] used a mannequin (simulating a newborn of 3300 g, with a simple geometric shape and a uniform surface temperature across all body segments), which was exposed in a closed incubator at room air temperatures of between 20 and 30 \({}^{\circ}\)C. In our opinion, it is preferable to (i) make measurements at the lower outside air temperatures encountered during transport and (ii) use anthropomorphic thermal mannequins that simulate premature, low-birth-weight neonates. Inter-infant differences in thermoregulatory control, metabolic heat production, behavioural and vasomotor responses, and skin evaporative heat loss will have to be incorporated in these models. One cannot rule out changes in the neonate's ability to dissipate heat (i.e., the model's performance as a function of skin characteristics, hydration levels, feeding, nursing care, and sleep. In the future, it may be possible to complement mathematical models with an active cybernetic system for predicting thermoregulatory responses (such as shivering, changes in the peripheral vasomotor tone, metabolic heat production, and skin water loss) by incorporating heat capacities and energy fluxes from the different tissues (i.e., internal organs, adipose tissue, muscle, and skin sites). Future research should seek to quantify the strength of the relationship between heat transfer coefficients on one hand and body size and posture on the other. With the exception of [PERSON]'s study [21], there are few published data on the effect of the neonate's body position on heat exchanges inside the incubator. By studying a mannequin representing a newborn with a body mass of 3300 g, [PERSON] showed that the heat transfer coefficient h\({}_{\text{c}}\) was 4.00 W/m\({}^{2}\)/\({}^{\circ}\)C in the foetal position, 3.90 in the relaxed position, and 4.91 in the spread-eagle position; the radiant heat transfer coefficient h\({}_{\text{r}}\) was 3.10, 3.70 and 4.90 W/m\({}^{2}\)/\({}^{\circ}\)C, respectively. Body size modifies the skin surface area to body volume ratio; the greater this ratio, the greater the body's heat losses to the environment. [PERSON] et al. [37] compared dry heat losses from two mannequins simulating infants weighing 900 g and 1800 g, respectively; the heat losses were 20.4% greater for the smaller mannequin. Further studies could usefully analyse the local effects of non-uniform thermal environments and air movement directions, such as those encountered in the incubator. A segment-by-segment approach requires the consideration of interregional skin temperature differences between the body sites, reflecting both the local vascular responsiveness and the heat exchanges with the surroundings. A detailed model can take account of heat transfer coefficients for individual body segments. Using a skin-temperature-controlled adult mannequin, [PERSON] et al. [38] found that the values of h\({}_{\text{c}}\) were higher for peripheral body segments than for central segments. The difference was as much as 60% for lower air speeds, highlighting the errors induced by applying the whole-body value of h\({}_{\text{c}}\) to a non-uniform thermal environment. [PERSON] et al. also reported that air flow direction was a relevant parameter when calculating the heat balance for body segments such as feet and lower legs, where convective heat losses are particularly high. Interestingly, [PERSON] et al. [32] assessed the risks of hyperthermia and hypothermia in neonates by calculating the heat exchanges for 11 body segments. However, as acknowledged by the researchers themselves, this theoretical model of heat transfers has yet to be validated, especially for newborns of various body sizes. The relevance of the thermal instability potentially produced by care procedures has yet to be assessed. The degree of instability is likely to depend on the frequency, type and duration of care.