Figure 2.

Determination of a safe range using partial pressure of arterial oxygen (PaO₂), NE, and the Borg scale during CPET.

Notes: We measured hypoxemia (PaO₂ <60 mmHg), the NE threshold, and breathlessness onset for each individual during exercise. The NE threshold was determined by using a log-log transformation of the NE–oxygen uptake relationship. The criteria for the safe range were 1) PaO₂ >60 mmHg and 2) lower than the NE threshold and/or Borg scale score of <2. These variables were used together to determine the safe range as indicated by oxygen uptake (mL/min), which was determined from each patient’s SpO₂ (%) reading and pulse rate (beats/min) using a watch-type pulse oximeter, in addition to the Borg scale. The yellow triangles indicates PaO₂; the pink squares indicates norepinephrine (NE); the dark blue diamond is the Borg scale. The dotted line indicates oxygen uptake at the point of NT.

Abbreviations: CPET, cardiopulmonary exercise testing; NE, norepinephrine; NT, norepinephrine threshold; PaO₂, partial pressure of arterial oxygen.