Effects of an acute change in volemia on CgH2S. (A) Recording during withdrawal (W) or infusion (I) of 2 ml of blood before and after infusing 2 ml of MetHb solution. Respiratory flow (), alveolar fraction of H2S (FAH2S), and additional air flow (add) signals are shown. (B) Effect of blood versus MetHb infusion on mean CgH2S, th esymbol B related the basleine values before withdrawal (W) or infusion (I) of blood. (C) Change in CgH2S after withdrawal or infusion of blood or MetHb compared with values obtained before each treatment. Withdrawing and infusing blood produced a small rise and decrease in CdH2S, respectively. Infusing MetHb, instead of blood, produced a dramatic decrease in CgH2S (p < 0.01) that persisted, and in most cases prevented, any other effects of volemia on CgH2S. *Significantly different at p < 0.05, **Significantly different at p < 0.01.