Validity of Alfred Step Test Exercise Protocol (A-STEP) as a Surrogate VO_2Max Cardiopulmonary Exercise Test (CPET) to...

The Alfred Step Test Exercise Protocol (A-STEP) and feasibility study were previously published. The aim here was to determine the validity of the A-STEP compared to cycle ergometry (CPET) in adults with CF.

The A-STEP and CPET were carried out in random order 2 weeks apart. A wearable, portable metabolic system was used to measure breath-by-breath and minute-by-minute sampling of O₂, CO₂, heart rate, and VO₂. The main outcome measures were VO_2max and HRmax.

Seven stable-state adults (3 male) on CFTR modulator therapy with a mean (SD) and range of age 38.2 (13.4) 26-64 years; height 169.9 (10.9) 149.7-185.3 cm; BMI 22.8 (2.10) 19.5-28 kg/m²; FEV1 79.4 (18.9) 38.0-106.0; and FVC 95.1 (16.7) 63.0-114.0 percent predicted (pp) completed both A-STEP and CPET. The VO_2Max had high correlation and good agreement between the A-STEP 31.3 (5.9) and CPET 29.8 (6.2) mL/min/kg, r = 0.88. The HR_MAX was strongly correlated with the A-STEP 174 (17) bpm and 95.7 (7.4) pp versus 168 (15) bpm and 92.4 (5.3) pp with r = 0.92 and 0.86, respectively. The SpO_2Nadir for A-STEP was 91.0 (4.0) and CPET 92.0 (3.3), r = 0.82. The VO₂ at the anaerobic threshold (VO_2@AT) occurred significantly earlier for the CPET at 1021 (260) versus A-STEP 1361 (234) mL/minute, p < 0.05. The VE_Max for CPET was 84.1 (18.8) and A-STEP 73.5 (15.8) L/minute, p < 0.05. The AWESCORE also ensured baseline stability. The number of levels completed during the A-STEP was 10.7 (12.9) ranging from 9 to 15.

The A-STEP may be a portable, valid surrogate to cardiopulmonary exercise testing using cycle ergometry.