Re: [MATHEDCC] Kirby Urner's comments

Kirby Urner (pdx4d@teleport.com)
Mon, 13 Apr 1998 17:25:26 -0700

>Well, yes; but human proportions change with age, which offsets the
>geometric relations a bit. Children do have a higher surface to mass ratio
>than adults (they tolerate heat remarkably well, but are for more
>susceptible to cold). An adult's limbs are proportionately longer, though
>(missionaries used to judge when children were ready for school by when
>they could reach one ear with the opposite hand across the top of their
>heads; long legs are considered attractive, possibly because they are a
>sign of sexual maturity). In the interest of realism, BSA calculations
>should have a factor for age -- do they?
>

These are good points re body shape (angles) changing, not just scale
(frequency). Only when shape is rigidly adhered to may we assume a direct
F, F^2, F^3 relationship between edge, area, and volume -- why classroom
chatter around geometric shapes, e.g. tetrahedra and cubes, is apropos.

The BSA formulae I've seen do not factor in age, are empirically derived
and/or matched to data with tolerable error and therefore routinely employed
across a large range of ages for administering heparin for example, an
anti-coagulant, pre-surgery. But possibly pediatrics has a special formula
for the very youngest (and pre birth, we approach a more spherical beginning
-- back to simple geometry again).

Kirby
Curriculum writer
4D Solutions

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