Figure 5. Impact of lung volume (VL) and blood volume (Qb) on 
.
(A) Effect of three levels of VL, (i) 30, (ii) 20 and (iii) 10 ml kg−1, on arterial (
) and mixed venous (
) O2 desaturation during apnea. (B) Sensitivity of 
to changes in VL. Note that reduced VL has a strong impact on 
and 
but no impact on 
. (C) Effect of three levels of Qb, (iv) 120, (v) 80 and (iv) 40 ml kg−1, on 
and 
during apnea. (D) Sensitivity of 
to changes in Qb. Note that reduced Qb has little impact on 
or 
but has a large impact on 
. n = ‘normal’ values; S1, stage 1 slope; S2, stage 2 slope.