In patients with severe chronic heart failure, rapidly increased peripheral oxygen extraction acts as a crucial compensatory mechanism to maintain exercise capacity during mild physical activity despite reduced cardiac output.
To elucidate the role of oxygen extraction during exercise in chronic heart failure (CHF), 26 patients underwent the symptom-limited maximal exercise. Hemodynamics, oxygen uptake (VO2) and blood gas were examined during exercise. Group I (n = 16, VO2max less than 20 ml/min/kg) showed severe cardiac dysfunction during exercise compared with group II (n = 10, VO2max greater than or equal to 20 ml/min/kg). Though VO2 was similar in both groups at rest and with a 25-watt load, oxygen extraction was significantly higher in group I than in group II. At the maximal work load, VO2max was significantly lower in group I, whereas there was no significant difference in oxygen extraction between the two groups. With a 25-watt load, mixed venous partial oxygen tension was similar, however, oxygen saturation was significantly lower in group I. It was concluded that oxygen extraction during exercise rapidly increased in group I, and this may play an important role in the maintenance of exercise capacity during mild physical activity in CHF.
Takata et al. (1990) studied this question.