Externally paced exercise tests

Externally paced tests were developed as an alternative to self-paced tests in an attempt to improve standardisation and reproducibility [6]. These tests control the speed of walking by signals generated from a compact disc (CD). The ISWT for patients was derived from a 20-m shuttle running test described in the 1980s for the assessment of cardiorespiratory fitness of athletes [5]. The instructions and protocol are standardised and are pre-recorded on the CD for playing to the patient. The test requires that the patient walk around an elliptical course at speeds dictated by the CD. The speed is indicated by a series of bleeps, indicating when the patient should be turning around the marker and returning along the course. At the end of every minute, there is an additional signal that indicates that the individual should increase the speed of walking. The test is terminated if the patient: 1) feels they are too breathless to continue with the test; 2) fails to reach the cone in the time allowed, i.e. defined as being >0.5 m away from the cone when the signal indicating the patient should have completed that 10-m length occurs; and/or 3) exceeds 85% of their predicted maximal fC. Upon completion of the test, the patient should be seated immediately for recording of end-exercise physiological and subjective responses, e.g. fc, arterial oxygen saturation, perceived breathlessness and exertion. The ISWT is reproducible after one practice walk. The original authors reported a 30-m difference between test 1 and test 2 for the ISWT [6].

Reported baseline responses in the ISWT range 140-457 m [48, 49]. Relationships with spirometric data and health-related quality of life have not been widely reported, but, as anticipated, are largely inconsistent. There is a correlation between ISWT performance and grades 3-5 of the UK Medical Research Council (MRC) dyspnoea scale, Bestall et al. [50] reported significant differences in performance of the ISWT for each MRC grade. A recently published scale of activities of daily living, the London Chest Activity of Daily Living Scale, identified performance in the SWT decreasing with declined reported function (r=0.58) [51]. The ISWT has also been usefully employed in elderly patients with COPD [52]. The mean distance completed in this group was 177 m. These authors also reported a significant relationship with the Nottingham Extended Activities of Daily Living scale and shuttle performance (r=0.51). Predictors of performance in the ISWT are not dissimilar to those in the 6MWT; in 85 stable COPD patients, there was a significant correlation (p<0.005) with quadriceps strength (r=0.47). Linear regression identified that age, FEV1 and quadriceps strength were the only important variables [53].

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