2000 OPEN FORUM Abstracts
Exercise Testing in Cystic Fibrosis - The 3-Minute Step Test
S. Ammani Prasad MCSP Cystic Fibrosis Unit, Great Ormond Street Hospital for Children, London, UK
Exercise tolerance in patients with cystic fibrosis decreases as lung disease progresses. Standard spirometry is not always a good predictor of exercise tolerance, although parameters such as FEV1 and peak oxygen consumption are good prognostic indicators. Measurement of exercise tolerance in patients with respiratory disease can give useful information regarding functional impairment. It can also reassure the patients and carers that exercise is safe and helps to define limits of exercise and formulate exercise programs. It is also useful as an outcome measure in interventional studies
A wide spectrum of tests exists which in one way or another attempt to measure exercise tolerance. The choice of test is of course dependent on the question to be answered. Tests may be maximal or submaximal, incremental or non-incremental. Maximal tests on a cycle ergometer with respiratory gas analysis remain the gold standard. However such tests require specialist equipment, considerable time and resources. In addition they may not reflect daily activity patterns, particularly in children (Cooper 1995). Incremental tests, maximal or sub-maximal, commonly used in CF (without respiratory gas analysis) include bicycle or treadmill ergometry and the original or modified shuttle test (Singh 1992, Bradley 1999). They give useful information on an individual's capacity to undertake physical activity and can be complemented by subjective scores of breathlessness and fatigue. Maximal tests can be stressful and it is vital that they are conducted in a safe environment with necessary resuscitation equipment to hand.
Simpler field tests are also commonly used in CF and include walking tests (Butland 1982, Gulman 1996) and the 3-minute step test (Balfour-Lynn 1998). These are rarely maximal but give valuable information on the effect of a fixed period of defined exercise on an individual's oxygen saturation and heart rate. They too are complemented by subjective scores of breathlessness.
The three-minute step test is modified from step test protocols originally used in adult cardiac assessment. Subjects step up and down a single level (15cm) platform for a fixed time (3 minutes) at a fixed rate (30 steps/minute). Minimal arterial oxygen saturation, maximum pulse rate are measured and both a subjective and an objective score of breathlessness is recorded. The 3 minute step test has been compared with the standard six minute walk for the assessment of exercise tolerance in children with cystic fibrosis (Balfour-Lynn 1998) and in a population of CF children undergoing assessment for lung transplantation (Aurora 1999). An objective measure of breathlessness in children - the fifteen count score - has also been validated (Prasad 200). The advantages of the 3-minute step test are that it is quick, simple, portable and not dependent on patient effort.
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