Same two-compartment (core/shell) bioheat model as the 3D version, drawn here as a live strip chart and a phase-plane trajectory instead of a rotating sphere — the two views that clinicians and physiologists actually use to read a heat-balance simulation:
C_core · dT_c/dt = M − W − Q_c→s
C_shell· dT_s/dt = Q_c→s + M_shiver − Q_s→env
Q_c→s = BF · k_blood · (T_c − T_s)
Q_s→env = h·(T_s − T_amb) + E_sweat
Integrated here with an explicit midpoint (RK2) stepper (vs. the 3D page's forward Euler) for a more accurate trajectory at the same visual frame rate.
Fixed vs. the 3D engine: with the 3D page's original constants (k_blood = 1.15, h-base = 2.1), resting metabolic heat (M ≈ 55) is roughly 13× larger than the heat-transfer capacity at baseline skin blood flow, so core temperature never actually settles near 37 °C — it drifts to the hard clamp even at a comfortable 22 °C at rest. This page recalibrates k_blood and h-base so the default state (37.0 °C / 33.5 °C, BF ×1, resting, 22 °C, 1 clo) is a genuine heat-balance equilibrium, matching the "Reset to Normothermia" button's own premise. Push the sliders away from that baseline and the same aging mechanics apply: reduced vasomotor gain, a higher sweat-onset threshold with a lower ceiling, and weaker shivering, all scaled continuously by the age slider.
- Strip chart — T꜀ (orange) and Tₛ (blue) plotted against elapsed sim-time, with shaded hypothermia/heat-stress bands so you can see how fast the margin narrows.
- Phase plane — T꜀ vs Tₛ trajectory; a tight loop near the crosshair means the system is holding equilibrium, a trajectory that runs off toward a corner means the effectors have been overwhelmed.
- Core/shell diagram — concentric core and shell discs colored by temperature, with dots marking blood flux (speed ∝ skin blood flow) and droplets appearing once sweating is triggered.