The data presented is from a wider systematic review of the minimum important difference of field walk tests further details can be found here: https://www.crd.york.ac.uk/prospero/display_record.php?RecordID=185565
Authors: E. Daynes 1,2, R.E. Barker 3,4, A. Jones 2, J.A. Walsh 3, C.M. Nolan 3,4, N.J. Greening 1,2, S. Singh 1,2, L. Houchen-Wolloff 1,2, R.A. Evans 1,2
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Centre of Exercise and Rehabilitation Sciences, National Institute of Health Research Biomedical Research Centre – Respiratory Theme, University Hospitals of Leicester NHS Trust, Leicester, UK.
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Department of Respiratory Sciences, University of Leicester, Leicester, UK.
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Harefield Respiratory Research Group, Royal Brompton and Harefield NHS Foundation Trust, UK
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National Heart and Lung Institute, Imperial College London, UK
Summarised for the ATS PR Assembly website by L. Houchen-Wolloff 1,2, T Harvey-Dunstan 5 and R.A. Evans 1,2 -
Division of Physiotherapy and Rehabilitation Sciences, School of Health Sciences, The University of Nottingham, Nottingham, UK.
Introduction: Field walking tests are commonly used to assess exercise performance in Chronic Respiratory Disease (CRD) such as the six-minute walk test [6MWT(1)], the incremental shuttle walk test [ISWT(2)] and the endurance shuttle walking test [ESWT(3)]. The aims of exercise testing are to assess the degree of functional limitation, to prescribe treatment and to measure the outcome of an intervention, for example, Pulmonary Rehabilitation (PR). It is important for clinicians and researchers to be able to interpret what constitutes a ‘meaningful change’ in exercise performance to infer whether a treatment has been successful and to inform sample size calculations for research studies (4). But what do we mean by a ‘meaningful change?’
In research trials, treatment effects are often reported as a change in the outcome measure supported by a measure of variability; for example, the mean change with 95% confidence intervals and a probability (p) value to indicate the level of statistical significance for normally distributed data. However, a statistically significant change may not indicate a clinically meaningful or important change for clinicians or patients to interpret. Minimum Important Differences can be calculated using an anchor-based approach (anchored to a global rating of change or another validated outcome measure) or distribution methods e.g. standard error of the measurement (SEM) (6). The anchor-based method typically derives a minimally clinical important difference (MCID) adding clinical relevance or patient experience to the reporting of an outcome measure. The MCID is defined as ‘the smallest difference in score in the outcome of interest that informed patients or informed proxies [who can be clinicians] perceive as important, either beneficial or harmful, and which would lead the patient or clinician to consider a change in the management’ (5).
There have been many studies that have developed an MID for either the ISWT and the 6MWT using a variety of methodologies and therefore it can be difficult for clinicians and researchers to determine which MID is appropriate. It is important to understand the intervention used (Pulmonary Rehabilitation in this example), and population characteristics for the MID derivation as the MID is likely to be affected by disease severity, type of disease and symptoms. Where possible the MID for the intervention and particular population of interest should be used (7)
Studies evaluating a minimum important difference in walking distance to Pulmonary Rehabilitation in chronic respiratory disease
We have included 20 studies conducted in a range of chronic respiratory diseases (CRD’s) with three exercise tests ISWT (n=4), 6MWT (n=12) and ESWT (n=4). The range of CRD’s identified included COPD (n=11; ISWT=2, 6MWT=5, ESWT=4), Non-cystic fibrosis (NCF) Bronchiectasis (n=2; ISWT=1, 6MWT=1), Interstitial Pulmonary Fibrosis (n=5; ISWT=1, 6MWT=4), Lung cancer (n=1 for the 6MWT), Respiratory Failure (n=1 for the 6MWT). Findings for each MID can be seen below and in Table 1. All but one study (10) applied a combined methodological approach employing both distribution and anchor based measures.
ISWT
For patients with COPD (n=372 to 613) an MID of 35-47.5m is suggested by two studies (10, 11). For patients with Non-Cystic Fibrosis Bronchiectasis (n=37) a similar MID of 35m was suggested by one single study (12), and 31-46m has been proposed for patients with Interstitial Pulmonary Fibrosis (n=50 and 72) in a single study (13).
6MWT
For patients with COPD/ severe COPD (n=75 to n=2112), an MID of 25-71m is suggested from five studies when including any proposed ranges (14-18). When excluding any ranges (using absolute values), the suggested MID reduces to 25-54m.
A single study in patients with NCF-Bronchiectasis (n=37), identified an MCID of 25m (no ranges reported: 12). As similar range has been proposed by four studies in patients with Interstitial Pulmonary Fibrosis (n=48 to 822) of 24-37m (19-22).
Only one study reported the MID as a marker for clinical deterioration for patients with lung cancer (n=56). A deterioration of between 22-42m was considered clinically important (23).
A further study has reported an MID of 20-30m for patients diagnosed with acute respiratory failure [ARF (n=641)]. Underlying causes of ARF were not detailed in this paper (24).
ESWT
COPD was the only CRD reporting an MID for the ESWT (n=55 to n=531). Taking the four studies collectively, an MID of 144-279 seconds for time to limitation is proposed (25-28). This included stated ranges for change. One study was unable to accurately estimate an MID due to weak correlations between the anchors and the measured change in ESWT performance (27).
Summary: We have included 20 studies of MID for common exercise tests in CRD. All but one study (10) applied a combined methodological approach employing both distribution and anchor based measures.
Exercise test | Outcome Measure | Condition | Population Demographics | Suggested MID (range) | Assessment Method | Author (n=) |
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Response to Pulmonary Rehabilitation or detecting clinical deterioration | ||||||
ISWT | Distance (m) | COPD | Age=69.4(8.4); Gender % Male=55%; FEV 1=1.06(0.53)L; FEV 1/FVC=50.8(18.1)%. | 47.5mAdditional benefits identified at 78.7m. | Anchor based | Singh 2008 (n=372)Ref 10 |
Cohort 1: Age=68.8(9.3); Gender % Male=55.2%; FEV 1=1.06(0.51)L; FEV 1/FVC=44.2(12.3)%. Cohort 2: Age=69.5(8.4); Gender % Male=56.5%; FEV1=0.95(0.0.43+D11)L; FEV1/FVC=45.1(11.1)%. |
35-36.1m | Anchor and distribution based | Evans 2019 (=613)Ref 11 | |||
NCF-Bronchiectasis | Age=63.0(13.0); Gender % Male=NR; FEV 1 % Predicted=76.9(18.3)%; FVC % Predicted=83.8(17.6)% | 35m | Anchor and distribution based | Lee 2014 (n=37)Ref 12 | ||
IPF | Study 1 : Age=75.0(7.0); Gender % Male=72%; FVC =2.17(0.68)L; FVC % Predicted=70.0(19.9)%. Study 2: Age=74.0(7.0)); Gender % Male=69%; FVC =2.30(0.70)L; FVC % Predicted=76.7(19.8)%. |
31-46m | Anchor and distribution based | Nolan 2017 (Study 1 n=50; Study 2 n=72)Ref 13 | ||
6MWT | Distance (m) | COPD | Age=70.3(8.5); Gender % Male=58.6%; FEV 1=1.26(0.55); FEV 1/FVC=49.0(16.0)%. | 25m (no range reported) | Anchor and distribution based | Holland 2010 (n=75)Ref 14 |
Age=63.4(7.1); Gender % Male=65.0%; FEV 1% Pred=48.4(15.7)%. | - 30m | Anchor based approach in the context of worsening clinical status | Polkey 2013 (n=2112)Ref 15 | |||
Age=67.0(10.0); Gender % Male=53.0%; FEV 1=0.98(0.45). | 54 (37-71)m | Anchor and distribution based | Redelmeier 1997 (n=112)Ref 16 | |||
Age=68.9(8.3); Gender % Male=71.0%; FEV 1 % Predicted=39.2(14.1)%. | 35 (30-42)m | Systematic review of 9 studies Anchor and distribution based | Puhan 2008 (n=460)Ref 17 | |||
Severe COPD | Age=66.4(6.1); Gender % Male=61.2%; FEV 1 % Predicted=26.9(7.1). | 26 (24-28)m | Anchor and distribution based | Puhan 2011 (n=1218)Ref 18 | ||
NCF-Bronchiectasis | Age=63.0(13.0); Gender % Male=NR; FEV 1 % Predicted=76.9(18.3)%; FVC % Predicted=83.8(17.6)% | 25m | Anchor and distribution based | Lee 2014 (n=37)Ref 12 | ||
Idiopathic Pulmonary Fibrosis | Age=65.1(8.7); Gender % Male=73%; FVC =2.60(0.71)L; FVC % Predicted=67.8(11.8)%. | 28m | Anchor and distribution based | Swigris 2010 (n=123)Ref 19 | ||
Age=69.0(9.0); Gender % Male=NR; FVC % Predicted=78.0(16.0)%. | 29-34m | Anchor and distribution based | Holland 2009 (n=48)Ref 20 | |||
Age=66.0(7.8); Gender % Male=71%; FVC % Predicted=72.5(12.7)%. | 24-45m | Anchor and distribution based | Du Bois 2011 (822)Ref 21 | |||
Age=66.5(5.6); Gender % Male=73%; FVC % Predicted=74.7(14.9)%. | 21.7-37m | Anchor and distribution based | Nathan 2015 (n=338)Ref 22 | |||
Lung Cancer | Age=65.0(10.0); Gender % Male=61%. | - 22-42m | Anchor and distribution based in the clinical context of deterioration. | Granger 2015 (n=56)Ref 23 | ||
Acute Respiratory Failuresurvival | Study 1*: Age=48.0(14.0); Gender % Male=57%; Lung function=NR. Study 2**: Age=48.0(15.0); Gender % Male=61%; Lung function=NR. Study 3~: Age=57.0(16.0); Gender % Male=72%; Lung function=NR. Study 4 #: Age=59.0(15.0); Gender % Male=60%; Lung function=NR. |
113m (94-132)m | Anchor and distribution based | Chan 2015 (n=641; *162; **183; ~180; #126)Ref 24 | ||
ESWT | Time (sec) | COPD | Age=62.0(9.0); Gender % Male=58%; FEV 1=0.84(0.34); FEV 1/FVC=31.8(9.2)%. | 144 (186-199)sec | Anchor and distribution based | Altenburg 2015 (n=55)Ref 25 |
Age=70.0(8.0); Gender % Male=NR; FEV 1=1.11(0.40); FEV 1/FVC=43.0(13.0)%. | 227 (70-156)sec | Anchor and distribution based | Hill 2019 (n=78) | |||
Age=68.0(11.0); Gender % Male=57%; FEV 1=1.19(0.56); FEV 1/FVC=50.0(17.0)%. | Unable to estimate | Anchor and distribution based | Pepin 2011 (n=132) | |||
Age=69.4(9.1); Gender % Male=57%; FEV 1=1.29(0.58); FEV 1/FVC=51.2(16.4)%. | 174-279sec | Anchor and distribution based | Zatloukal 2019 (n=531) | |||
MD= mean; (SD)=standard deviation; Med=Median; [IQR]=Interquartile range; n=number of subjects; m=metre; NR=not reported; FEV 1=forced expiratory volume in one second; FVC=forced vital capacity; L=litre; Sec=second; |
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