Fig. 1.
Changes in deoxyhemoglobin (Hb) during the calibration pulse of anoxia. The inspired gas was set to zero O2 for 50 s. Total hemoglobin (Hbt) concentration is postulated to be equal to the maximum Hb concentration, under the assumption that all hemoglobin is deoxygenated. The top insert shows the last 10 s of the 50-s anoxia pulse. The bottom insert shows Hb from a subject where the anoxia pulse was extended to 250 s. These show that the maximum Hb occurs during a relatively stable period around 50 s, and more extended periods result in a reduction of Hb. The two traces show the Hb time courses for the same animal before and after acclimation to hypoxia. The large increase in Hbt postacclimation is due to a combination of increased hematocrit and increased CBV.