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A step test to assess exercise-related oxygen desaturation in interstitial lung disease

Pulmonary Function and Clinical Exercise Physiology Unit (SEFICE), Division of Respiratory Diseases, Federal University of São Paulo (UNIFESP), São Paulo, Brazil.

CORRESPONDENCE: J. A. Neder, Respiratory Division, Dept of Medicine, Federal University of São Paulo, Paulista School of Medicine (UNIFESP-EPM), Rua Francisco de Castro 54, Vila Clementino, CEP 04020-050 São Paulo Brazil. Fax: 55 1155752843. E-mail: albneder{at}pneumo.epm.br

Keywords: Exercise induced, exercise tests, interstitial lung diseases, oxygen saturation, oxygen uptake, pulmonary dysfunction

Received: July 17, 2006
Accepted September 18, 2006

A 6-min step test (6MST) may constitute a practical method for routinely assessing effort tolerance and exercise-related oxyhaemoglobin desaturation (ERD) in the primary care of patients with interstitial lung disease.

In total, 31 patients (19 males) with idiopathic pulmonary fibrosis (n = 25) and chronic hypersensitivity pneumonia were submitted, on different days, to two 6MSTs. Physiological responses were compared with those found on maximal and submaximal cycle ergometer tests at the same oxygen uptake (V'_O2). Chronic breathlessness was also determined, as measured by the baseline dyspnoea index (BDI).

Responses to 6MST were highly reproducible: 1.3±2.0 steps·min^-1, ±5 beats·min^-1 (cardiac frequency), ±50 mL·min^-1 (V'_O2), ±7 L·min^-1 (minute ventilation) and ±2% (arterial oxygen saturation measured by pulse oximetry (S_p,O2)). The number of steps climbed in 6 min was correlated to peak V'_O2 and the BDI. There were significant associations among the tests in relation to presence (change in S_p,O2 between rest and exercise 4%) and severity (S_p,O2 <88%) of ERD. Four patients, however, presented ERD only in response to 6MST. Resting diffusing capacity of the lung for carbon monoxide and alveolar–arterial oxygen tension difference were the independent predictors of the number of steps climbed.

A single-stage, self-paced 6-min step test provided reliable and reproducible estimates of exercise capacity and exercise-related oxyhaemoglobin desaturation in interstitial lung disease patients.

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