A Pickwickian Problem: How Is Breathing Controlled?

[...]adding weight to the chest and abdomen in the form of adipose tissue reduces chest wall compliance and decreases functional residual capacity, expiratory reserve volume, and, much less commonly, vital and total lung capacities. CO2, however, diffuses freely into the CSF, where its chemical combination with H2O is catalyzed by carbonic anhydrase, yielding dissociated HCO2 and H1 and reducing pHCSF (Figure 2). Because the CSF protein concentration is relatively low, CSF is a poor buffer, and small changes in PaCO yield large and rapid changes in pHCSF. [...]oxygen decreases the affinity of hemoglobin for CO2 (the Haldane effect), thereby increasing the Pco2 for a given blood CO2 content. Urine eliminated through the kidneys contains very little HCO2. [...]as the extravascular volume "contracts" with a loop diuretic-mediated diuresis, it does so around a relatively constant HCO2 content, and the blood [HCO2] increases.