Elsevier

American Heart Journal

Volume 134, Issue 2, August 1997, Pages 203-206
American Heart Journal

Assessment of oxygen uptake during the 6-minute walking test in patients with heart failure: Preliminary experience with a portable device,☆☆,,★★

https://doi.org/10.1016/S0002-8703(97)70125-XGet rights and content

Abstract

In patients with heart failure, the 6-minute walking test (6-MWT) is considered a useful measure of submaximal exercise capacity. Few data are available on oxygen uptake (V o2 ) during a standard 6-MWT. The aim of this study was to measure the 6-MWT V o2 by using a recently validated portable instrument in 26 patients (24 men, 2 women; mean age, 56 ± 11 years) with mild to severe heart failure (New York Heart Association class II, 10 patients; III, 10 patients; IV, 6 patients; left ventricular ejection fraction: 22 ± 6%). Peak V o2 was measured during a symptom-limited cardiopulmonary exercise test performed in a period of 1 to 3 days (10 watt/m increment). Peak V o2 was 15 ± 4 ml/kg/m during the symptom-limited test and 12.9 ± 4.4 ml/kg/m during the 6-MWT ( p < 0.05), corresponding to 86% of peak V o2 . Seven (27%) of 26 patients showed a 6-MWT V o2 equal to or higher than peak V o2 . Anaerobic threshold (AT) was identified in 23 of 26 patients during maximal exercise and in 19 of 26 patients during the 6-MWT; V o2 at AT was similar in the two tests (12.2 ± 3.5 ml/kg/m vs 11.9 ± 4.2 ml/kg/m). The distance walked during the 6-MWT (mean, 418 ± 20 m) significantly correlated with 6-MWT V o2 ( r = 0.71) and peak V o2 ( r = 0.63); the 6-MWT V o2 also showed a high correlation with peak V o2 ( r = 0.86). Thus in patients with failing hearts, V o2 during 6-MWT (considered a classic submaximal exercise) is, on average, only 15% lower than peak V o2 and is largely supported by anaerobic metabolism (work above the anaerobic threshold).

Section snippets

Methods

We studied 26 patients (2 women, 24 men; mean age, 56 ± 11 years; range, 22 to 69 years) with heart failure resulting from left ventricular systolic dysfunction (mean left ventricular ejection fraction 22% ± 6%; range 13% to 35%). All of patients had had symptoms of heart failure for ≥6 months, in spite of treatment with diuretics and an angiotensin-converting enzyme inhibitor; 18 patients were receiving additional digoxin therapy. The cause of heart failure was coronary artery disease (without

Results

Demographic, clinical, and exercise data of all patients are shown in Table I . The V o2 at the end of the 6-MWT was lower than peak V o2 at maximal exercise (12.9 ± 4.4 ml/kg/min vs 15 ± 4 ml/kg/min; p < 0.05) and corresponded to 86% of peak V o2 . However, at the end of the 6-MWT, 7 (27%) of 26 patients had a V o2 equal to or higher than the V o2 of maximal exercise. Anaerobic threshold was identified in 23 (88%) of 26 patients during maximal exercise and in 19 (73%) patients during the

Discussion

Our results indicate that, in patients with heart failure, the V o2 measured at the end of a standardized 6-MWT is, on average, only 15% lower than peak V o2 of a symptom-limited exercise test. Furthermore, although the 6-MWT is usually considered a submaximal exercise, in one fourth of our patients V o2 during the test was equal to or even higher than peak V o2 , indicating an almost maximal effort. This observation also was confirmed by the fact that in most of the patients (19 [73%] of 26),

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From the aCardiology Division, Salvatore Maugeri Foundation, IRCCS, Gussago bMI LA, Forniture Medicali.

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Dr. Faggiano is currently with the Cardiology Division, S. Orsola Hospital.

Reprint requests: Dr. Pompilio Faggiano, Via S. Antonio, 6, 25133 Brescia, Italy.

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0002-8703/97/$5.00 + 0 4/1/82316

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