Can Maximal Cardiopulmonary Capacity be Recognized by a Plateau in Oxygen Uptake: ConclusionThe ramp treadmill protocol employed in the present study may offer several advantages for cardiopulmonary assessment. It has been suggested that an optimal test duration, determined by individualized work increments that yield the highest oxygen uptake, is approximately ten minutes in duration. Redwood and coworkers demonstrated that tests which use large work increments in patients with angina resulted in reductions in exercise capacity and poor reliability for studying the effects of therapy. Standardized protocols that are commonly used clinically employ large and/or unequal work increments resulting in a nonlinear relation between oxygen uptake and work rate. A number of investigators have therefore described the importance of adapting the exercise test to the subject and purpose of the test. Thus, the ability to individualize ramp rates to reproduce exercise capacity, a given myocardial oxygen demand, the onset of angina, or other symptoms when evaluating interventions is provocative. A simple computer prograin was developed for the present study, from which ramp rates were individualized resulting in good reproducibility and a test duration of approximately 9.1 ±1 minute.

Intuitively, the body’s cardiorespiratory and metabolic systems must reach some finite limit beyond which oxygen uptake can no longer be increased. The factors that limit exercise capacity are not entirely clear, however, exercise capacity depends on disease, fitness, and the type and duration of exercise. The traditional interpretation of the plateau concept assumes oxygen delivery always limits exercise capacity. However, this may not be the case under all conditions. This may explain the fact that, subsequent to the studies of Taylor et al, researchers have reported between 7 and 80 percent of subjects demonstrate a plateau.2*’ It should be noted also that these studies differed greatly in population, protocol, and criteria. The considerable variability in the slope of the change in oxygen uptake during progressive exercise in the present study suggests that the plateau concept has limitations for general application during standard exercise testing.