In a diving-chamber experiment, a human subject breathed a mixture of O2, and He while small areas of his skin were exposed to nitrogen gas. After some time the exposed areas became blotchy, with small blisters forming on the skin. Model the skin as consisting of two adjacent layers, one of thickness δ1, and the other of δ2. If counterdiffusion of He out through the skin occurs at the same time as N2 diffuses into the skin, at what point in the skin layers is the sum of the partial pressures a maximum? If the saturation partial pressure for the sum of the gases is 101 kPa, can the blisters be a result of the sum of the gas partial pressures exceeding the saturation partial pressure and the gas coming out of the solution (i.e., the skin)?
Before answering any of these questions, derive the concentration profiles for N2 and He in the skin layers. Hint: See Side Note.
Diffusivity of He and N2 in the inner skin layer
=5 × 10-7cm2/s and 1.5 × 10-7 cm2/s, respectively
Diffusivity of He and N2 in the outer skin layer
=10-5 cm2/s and 3.3 × 10-4 cm2/s, respectively
| External Skin Boundary Partial Pressure | Internal Skin Boundary Partial Pressure |
N2 He | 101 kPa 0 | 0 81 kPa |
δ1 δ2 | 20 μm 80 μm | Stratum corneum Epidermis |
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