Figure 3: The illustration of BPV spectrum during different physiological challenges, including (a) baseline, (b) 6 cycles breathing per minute, (c) 30 cycles breathing, (d) head-up tilt (HUT) by using conventional BPV, and (e) baseline, (f) 6 cycles breathing per minute, (g) 30 cycles breathing per minute, (h) HUT by using adaptive BPV.