Figure 8. The concept of peri-infarct hot zones susceptible to PID initiation.

a. Three-dimensional rendering of a hypothetical CBF defect upon focal arterial occlusion, depicting the conceptual framework consisting of the severely ischemic depolarized core (red), the penumbra (yellow), and the metastable hot zone surrounding it (lavender). The narrow critical CBF range defining the hot zone is also shown from Figure 2d (yellow bar, residual CBF in shoulder S1 where a PID is triggered upon shoulder stimulation).

b. Two-dimensional projection of the perfusion defect. In the metastable hot zone, increased demand during functional activation of the tissue worsens the supply-demand mismatch to trigger a PID. Because penumbra is electrophysiologically silent, by definition it cannot be activated upon somatosensory stimulation; therefore, it is only susceptible to reduced O₂ supply during hypoxic and hypotensive transients to trigger a PID.