Figure 3: Different Patterns in VO₂ vs WR Linear Increase During Maximal Exerciset Test.

During a maximal symptom-limited exercise, VO₂ increase lineraly to the increase in work rate (WR) and accurately reflects the extent of aerobically regenerated ATP. In physiological conditions, the VO₂/WR linearity corrisponds to 10 ml/min increase (a). In HF, the pattern of VO2 increase may change in a shallow downward shift (b) or in a VO₂ flattening at a given WR c). There are then unfrequent worrysome conditions with a VO₂ downsloping associated with acute drop in blood pressure and cardiac output (d).