Concentration effect vs. second gas effect

[hrmm]

Can someone explain the difference. Wiki is not helping:

Wiki:
During induction of general anesthesia when a large volume of nitrous oxide is taken up from alveoli into pulmonary capillary blood, the concentration of gases remaining in the alveoli is increased. This results in effects known as the "concentration effect" and the "second gas effect".

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[Spacedman]

Can someone explain the difference. Wiki is not helping:

Wiki:
During induction of general anesthesia when a large volume of nitrous oxide is taken up from alveoli into pulmonary capillary blood, the concentration of gases remaining in the alveoli is increased. This results in effects known as the "concentration effect" and the "second gas effect".

i keep having to look this up, so now is a good time as any to review-

btw, this is the best breakdown i've found online of the concentration effect and the second gas effect

of the two effects, IMO concentration effect is an easier concept: if you're breathing in 30% nitrous, the uptake from your alveoli is subject to several influences - rate of diffusion, alveolar ventilation, cardiac output etc. Diffusion depends on the concentration gradient. Every time you take a breath and absorb some nitrous, the fresh gas flow fills to take the place whatever you just absorbed. Refilling the supply with high concentration nitrous (eg 70%) obviously improves your concentration gradient for the next breath.

if you can envision the process of nitrous being taken up and replaced with fresh gas, you can get a handle on the second gas effect. if you follow the figure - the important piece is that after 50% of the nitrous is taken up (40 of 80 parts), you're left with 60 total parts of gas- that's how you get the numbers 66.7% nitrous (40 of 60 parts), 31.7% O2 (19 of 60), and 1.7% of your "second gas" (1 of 60). you can follow the math to see how you get a de facto concentration of your second gas beyond the inspired concentration by means of absorbing nitrous.