EXCESSIVE OXYGEN DEFICIT DURING LOW-LEVEL EXERCISE IN HEART-FAILURE

Although peak oxygen consumption is reduced in patients with symptomat ic heart failure, the degree of limitation during routine activity oft en appears greater or lesser than expected from peak capacity. This st udy was undertaken to determine whether abnormalities could be detecte d during the initiation of steady-state low-level exercise, approximat ing routine activity, which were distinct from limitation in peak capa city, We sought to determine whether a delay in the integrated respons e to the increased metabolic demand caused by exercise, assessed by th e oxygen deficit incurred between exercise initiation and the achievem ent of steady-state oxygen uptake, was present in heart failure, Low-l evel and symptom-limited maximal exercise tests in 33 ambulatory patie nts with heart failure were analyzed and compared with 9 tests in cont rol subjects, Oxygen deficit was determined during the 8-minute low-le vel exercise at 20 W. During maximal exercise, as expected, patients w ith heart failure had lower peak oxygen uptake (16 +/- 4 vs 31 +/- 6 m l/kg/min) and anaerobic threshold (870 +/- 270 vs 1,180 +/- 370 ml/min ) than controls. After 8 minutes of low-level exercise, the oxygen def icit was higher in patients than in controls (550 +/- 230 vs 270 +/- 1 00 ml, respectively, p <0.01). Among patients with heart failure, the oxygen deficit did not correlate with peak oxygen uptake or anaerobic threshold. Although the time to steady-state heart rate was later in p atients with heart failure, this delay did not correlate with oxygen d eficit. The oxygen deficit represents a distinct abnormality of exerci se response that may reflect impaired central and peripheral responses to the initiation of exercise.