ASSESSMENT OF OXYGEN-UPTAKE DURING THE 6-MINUTE WALKING TEST IN PATIENTS WITH HEART-FAILURE - PRELIMINARY EXPERIENCE WITH A PORTABLE DEVICE

In patients with heart failure, the 6-minute walking test (6-MWT) is c onsidered a useful measure of submaximal exercise capacity, Few data a re available on oxygen uptake (VO2) during a standard 6-MWT. The aim o f this study was to measure the 6-MWT VO2 by using a recently validate d portable instrument in 26 patients (24 men, 2 women; mean age, 56 +/ - 11 years) with mild to severe heart failure (New York Heart Associat ion class II, 10 patients; III, 10 patients; IV, 6 patients; left vent ricular ejection fraction: 22 +/- 6%). Peak VO2 was measured during a symptom-limited cardiopulmonary exercise test performed in a period of 1 to 3 days (10 watt/m increment). Peak VO2 was 15 +/- 4 ml/kg/m duri ng the symptom-limited test and 12.9 +/- 4.4 ml/kg/m during the 6-MWT (p < 0.05), corresponding to 86% of peak VO2. Seven (27%) of 26 patien ts showed a 6-MWT VO2 equal to or higher than peak VO2. Anaerobic thre shold (AT) was identified in 23 of 26 patients during maximal exercise and in 19 of 26 patients during the 6-MWT; VO2 at AT was similar in t he two tests (12.2 +/- 3.5 ml/kg/m vs 11.9 +/- 4.2 ml/kg/m). The dista nce walked during the 6-MWT (mean, 418 +/- 20 m) significantly correla ted with 6-MWT VO2 (r = 0.71) and peak VO2 (r = 0.63); the 6-MWT VO2 a lso showed a high correlation with peak VO2 (r = 0.86). Thus in patien ts with failing hearts, VO2 during 6-MWT (considered a classic submaxi mal exercise) is, on average, only 15% tower than peak VO2 and is larg ely supported by anaerobic metabolism (work above the anaerobic thresh old).