Physiological Responses Of The Modified Shuttle Test In Adults With Cystic Fibrosis

PURPOSE: The modified shuttle test (MST) is increasingly used in clinical practice to assess functional capacity in patients with cystic fibrosis (CF). The purpose of this study was to evaluate the physiological responses of the MST in adults with CF as compared with the gold standard cardiopulmonary exercise test (CPET).METHODS: Participants performed an MST and a CPET on a cycle ergometer in random order. Oxygen (O-2) uptake ((V)Over dotO(2)), carbon dioxide (CO2) retention (end-tidal PCO2; PETCO2), minute ventilation, heart rate, and peripheral O-2 saturation (SpO(2)) were continuously monitored. Whole blood lactate, dyspnea, and leg discomfort were recorded immediately after both exercises.RESULTS: Twenty patients with CF (aged 33 +/- 8 years; forced expiratory volume in 1 second = 48% +/- 17%) completed both tests. Peak values for (V)Over dotO(2) (27 +/- 7 vs 24 +/- 6 mL/kg/min), heart rate (169 +/- 19 vs 163 +/- 16 bpm), end PETCO2 (42 +/- 7 vs 39 +/- 8 mm Hg), and O-2 desaturation (end Sp O 2, 86% +/- 7% vs 90% +/- 6%) were significantly higher during the MST than during the CPET (all Ps<.05). Leg discomfort and whole blood lactate were significantly higher after the CPET (both Ps<.05). Thirty-five percent and 40% of patients showed significant O-2 desaturation and CO2 retention, respectively, during the MST, which was not detected during the CPET. A strong relationship was found between MST peak (V)Over dotO(2) and body weight walking distance product (r = 0.90; P<.01).CONCLUSIONS: The MST may provide a strong indicator of exercise tolerance in adults with CF as indicated by high peak (V)Over dotO(2) values. In clinical practice, body weight walking distance should be considered as the primary outcome. This test is also better than cycle ergometry CPET for detecting O-2 desaturation and CO2 retention, further emphasizing its clinical interest.