A 4-min, self-paced step test to assess exercise impairment in COPD patients GOLD I-to-IV

Background : There is a long-standing interest in developing “field” exercise tests for patients with chronic obstructive pulmonary disease (COPD) which can be easily performed in the consulting room with a minimum of technical support. Objectives : To investigate whether a 4-min, self paced step test (4MST) would be useful to assess exercise tolerance and oxyhemoglobin desaturation by pulse oximetry (SpO2) in a large group of outpatients with COPD. Methods : 191 patients (GOLD stages: I= 16, II= 63, III= 79, IV= 33) prospectively underwent the 4MST. Patients were allowed to stop the test as needed and re-start it within the allowed 4-min. Results : There were no significant test-related complications. There was a large variability in the steps climbed (ranging from low 20's to more than 100). Based on the tertiles of steps climbed, patients were separated into sub-groups of progressive impairment (Group A, N= 62; Group B, N= 61; Group C, N= 68). Group A patients were significantly younger than those of Group B and C (p<0.05). The number of interruptions during the tests increased from Group A to C; in addition, this variable and the steps climbed were significantly correlated (r= -0.53; p<0.01). 11/16 GOLD I patients were on Group A whereas 30/33 GOLD IV patients were on Groups B or C (p<0.05). In addition, from 36 patients with disabling breathlessness (MRC scores IV to V) 30 of them were on Groups B or C (p<0.05). Decreases in SpO2 corrected by steps climbed decreased as exercise tolerance diminished (p<0.05). Conclusions : A 4-min, self paced step test (4MST) was useful in discriminating COPD patients into progressive levels of exercise and pulmonary gas exchange impairment.