Ten patients with chronic obstructive lung disease, five patients with restrictive lung disease and five normal healthy volunteers were studied to assess the kinetics of oxygen consumption (VO2) at the start of mild exercise by a treadmill.
The VO2 during the steady state period showed no significant differences, but the continuous time of the initial period was longer and the amount of increase in VO2 per second (ΔVO2) was smaller in patients than in normal healthy subjects. The continuous time of the initial period was longer and ΔVO2 was smaller in patients whose arterial oxygen tension (PaO2) decreased during exercise than those with almost no change in PaO2 during exercise. Moreover, ΔVO2 at the start of exercise was smaller in patients whose %VC was less than 80% and FEV1.0% was less than 70%.
Regarding the cause of the VO2 kinetics at the start of exercise, it seems possible that the cardiorespiratory response at the start of exercise is slower in patients with impaired pulmonary function than in normal healthy subjects and patients with normal pulmonary function.
In conclusion, these findings suggest that the studies of the initial period of the exercise load test are useful in assessing the severity and the work capacity in patients with chronic lung disease.
