Fig. 1.

1D model of gas transfer and signal replenishment in the barrier tissue and RBCs. (A) Simplified depiction of the alveolar capillary unit and corresponding ¹²⁹Xe NMR resonance frequencies in airspace, barrier, and RBCs. (B) Replenishing of the ¹²⁹Xe magnetization profile across the entire tissue block including barrier (green) and RBC (red). (C) Replenishing of the barrier signal (197 ppm) for barrier thicknesses ranging from 1–7.5 μm, assuming D_Xe = 0.33 × 10⁻⁵ cm² · s⁻¹. (D) Replenishing of the RBC signal (211 ppm) for the same range of barrier thickness and constant capillary diameter of 8 μm. As barrier thickness increases, return of the RBC signal is delayed.