EBME Forums Forums Maintenance Technical Assistance Infrared radition & infant radiant warmers

Hello

I've been trying to do some background literature searching on the use of infrared radiation for warming (specifically in neonatal care). I've come up fairly blank on the topic of the output spectrum of radiant warmers. I've trawled Medline with all the relevant words I can think of. Does anyone know of, or has carried out, any radiometry work on these devices?
Thanks

Sue

Sorry Sue,

I head up the Radiation protection Services within our Trust. What is the question and what is it you are after?

alex

I'm after some spectrographic information on the output of the various heaters. What is the range and irradiance levels? Are they designed to produce a particular spectrum or a particular temperature? Why might one source type be more effective at heating tissue than another?
I'm also having trouble finding information about optical properties of tissue, particularly beyond the NIR range (this seems fairly well characterised due to the use of NIR spectroscopy). I have some old reports from the seventies which refer mostly to work done in the 1950's. I'd like information particularly on the penetration/absorption in neonatal skin, but I don't think I'm going to find this anywhere.

The heating effect of warmers/heaters is the issue isn't it Sue? Is thermometry not a satisfactory method of ascertaining the effectiveness of therapy? Or are you interested in secondary effects of depositing radiated energy at wavelengths other than I.R?

Well, yes. As the aim of the warmer is to heat an infant then the ultimate test is how well it does this. Clinical trials should therefore provide the best evidence for warming devices. However, clinical trials have so many uncontrolled variables (as is the human condition). The main instigator for this work was a device that claimed to screen out the longer wavelengths and use the more penetrating IR-A radiation.

To the uninitiated (i.e. me before I did any background reading) this sounded vaguely like microwaving babies, but now I realise it's more of a skin-sparing effect. There may be a difference between how warm a heater feels (skin heating) and how good it is at preventing/treating hypothermia.

So this is why I'm interested in the wavelength dependence of tissue absorption/penetration and the output spectra of different warmers. I imagine that the latter is mostly determined by the nature of the heating element, the temperature it reaches and the element surface. The heating effect will be determined by the output power/irradiance, the spectra, the reflector and the distance.

The AAMI water-filled tube phantom and the black aluminium disk test object will not mimic tissue absorption characteristics, as far as I know. Therefore, they may not reproduce physiological warming effects very well.

Sue (Inveterate Scientist)

Yes I understand that, I think. So, given a particular incident wavelength in the I.R. spectrum, you're looking at the rate of energy absorption (heating effect) in different tissues, at different depths, as the energy is deposited in a non-homogenous, non-uniform, mass (baby).

At different incident wavelengths then tissues will absorb I.R energy and the heating effect is likely to vary at different depths and possibly in different tissues, of course. In much the same fashion as heating may occur as a consequence of gamma irradiation in radiotherapy applications, eh? I guess that "skin sparing" is a common and appropriate term that can be applied in this context as well.

I suppose ambient temperature, effects of physiological processes, conduction and convection will also have to be considered since they must also play a part as well as the radiative processes at I.R. wavelengths. Shame someone clever has not come up with a model for a baby that takes into account all these processes yet.

Suggest you look at the following web site. They have avery good design guide for ceramic infrared heaters. (Not necessarily medical)
http://www.infraredheaters.com/links.htm

In the real world the distribution of radiated I.R. energy, transmitted from the source and eventually deposited in target tissue, is unlikely to heat the target uniformly due to the physical and complex characteristics of tissue, tissue colour, shape and mass, physiological processes, evaporation, conduction, convection, re-radiation, etc, and all these processes will probably be highly dependent upon ambient temperature.

Calculating emissivity and irradiance of a single I.R. source is obviously very important in determining the range of incident wavelengths, radiated power, etc, as is characterising the absorptive, transmissive and radiative properties of superficial and deeper tissues (i.e. how I.R. energy is deposited in these tissues; thus heating effect) at different I.R. wavelengths.

Determination of how effective I.R. energy is for alleviating the effects of hypothermia over a particular range of wavelengths can only really be established by using this data to model these processes or at least to estimate the most desirable properties of the I.R. source. This theoretical foray would would need to be followed by clinical trials in any case because of the complex nature of the problem (clinical and purely scientific) and the risk of burn injuries.

Richard (Not a Scientist)

>>"Shame someone clever has not come up with a model for a baby that takes into account all these processes yet. "

How about a leg of lamb with temperature sensors at appropriate depths?

(Shame on me, I'm vegetarian)

Sounds like a good idea.

Richard (Not a Scientist nor a Vegetarian)