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 Table of Contents  
ORIGINAL ARTICLE
Year : 2018  |  Volume : 2  |  Issue : 2  |  Page : 32-35

Correlation between 6-min walk test and cardiopulmonary exercise test in Chinese patients


Department of Pediatrics, Kwong Wah Hospital, Hong Kong SAR, China

Date of Web Publication6-Jul-2018

Correspondence Address:
Pik-Fung Wong
Department of Paediatrics, Kwong Wah Hospital, Waterloo Road, Hong Kong SAR
China
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/prcm.prcm_24_17

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  Abstract 

Aim: The aim of the study was to evaluate the correlation between the 6-min walk test (6MWT) and the cardiopulmonary exercise test (CPET) in Chinese pediatric patients. Methods: A retrospective review was undertaken for Chinese patients with exercise intolerance who had undergone both 6MWT and CPET on the same day over 21 months. Pearson's correlation analysis was used to examine the correlation between the 6-min walk distance (6MWD) and the maximum oxygen uptake (VO2 max). The 6MWD was defined as abnormal if <10th percentile of height-matched reference, and the VO2 maxwas defined as abnormal if <80% predicted. Results: Twenty-nine patients with a mean age of 14.3 ± 3.6 years were included in the study. The correlation coefficient (r) between the 6MWD and the VO2 maxwas 0.457 with P = 0.013. Twenty-six (three excluded as no reference for VO2 maxwas available for age <10 years) patients were analyzed. Using CPET as the gold standard for functional exercise capacity, 6MWT had a positive predictive value (PPV) of 92%, negative predictive value of 29%, sensitivity of 52%, specificity of 80%, and accuracy of 58% for assessing exercise capacity. Conclusion: 6MWT had a high PPV for abnormal CPET. It could still be used as a simple tool to evaluate patients with exercise intolerance.

Keywords: 6-min walk test, child, exercise test


How to cite this article:
Wong PF, Chan EY, Ng DK, Kwok KL, Yip AY, Leung SY. Correlation between 6-min walk test and cardiopulmonary exercise test in Chinese patients. Pediatr Respirol Crit Care Med 2018;2:32-5

How to cite this URL:
Wong PF, Chan EY, Ng DK, Kwok KL, Yip AY, Leung SY. Correlation between 6-min walk test and cardiopulmonary exercise test in Chinese patients. Pediatr Respirol Crit Care Med [serial online] 2018 [cited 2018 Nov 17];2:32-5. Available from: http://www.prccm.org/text.asp?2018/2/2/32/236138


  Introduction Top


The objective evaluation of functional exercise capacity provides clinicians with a composite assessment of the respiratory, cardiac, hematopoietic, neuropsychological, and skeletal muscle systems. The current gold standard for assessing aerobic exercise capacity is the maximal incremental cardiopulmonary exercise test (CPET),[1] which requires laboratory testing with exercise equipment to assess the maximum oxygen uptake (VO2 max).

Traditionally functional capacity is assessed by patient recall of the flights of stairs they can climb before shortness of breath occurs. However, this is imprecise. Patients may overestimate or underestimate their true functional capacity. Balke developed a simple field test to examine the functional capacity by measuring the distance walked over a defined period of time.[2] This was then modified by Cooper into a 12-min run fitness test for evaluating the physical fitness of US Air Force male officers.[3] McGavin et al. further modified Cooper's test into a 12-min walk test, with the objective of evaluating exercise tolerance of patients with chronic bronchitis.[4] To make allowance for patients with respiratory disease who do not have the capacity to walk for an extended period, a 6MWT was devised with the aim of achieving equally indicative results.[5] A review of functional walking tests by Solway et al. concluded that the 6MWT is easier to administer, better tolerated, and more reflective of daily activities than the other walk tests.[6]

The 6MWT is a simple practical test that can be executed in a 100-foot hallway, without any exercise equipment or highly trained technicians. This test measures the distance that a patient could walk on a flat, hard surface in 6 min.[7] Most studies involving the 6MWT were performed on adult participants with a spectrum of cardiopulmonary diseases such as heart failure or chronic obstructive pulmonary disease.[8],[9] There was only a limited number of pediatric studies on 6MWT. However, they were mostly confined to a specific chronic disease.[10],[11],[12],[13],[14] A strong correlation between the 6-min walk distance (6MWD) and VO2 max was found in children with cystic fibrosis,[10] congenital heart disease,[12] and obesity.[13] Another study in severely ill children awaiting heart–lung or lung transplantation showed that the 6MWT was an useful alternative screening tool for assessing exercise tolerance.[14] However, few local studies had been performed, one of which by Li et al. concluded that the 6MWT was a valid and reliable functional test for assessing exercise tolerance and endurance in healthy children.[15] Standard reference was established for the 6MWT in Chinese healthy children.[16]

In this study, we aimed to evaluate the functional exercise capacity among Chinese patients with different underlying diseases and to access the correlation between the simpler 6MWT and the more complex and resource demanding CPET.


  Methods Top


This was a retrospective study in which records of all patients with exercise intolerance who had performed CPET at the author's department from November 2014 to July 2016 were reviewed. Patients were included for analysis if they had performed both CPET and 6MWT on the same day. CPET was performed 1 h after the 6MWT to allow the patients to rest. The baseline anthropometric parameters including body weight and height were recorded.

The 6MWT was performed by physiotherapists according to the protocol outlined by the American Thoracic Society.[7] The hallway distance of the test was modified from 30 m to 20 m due to space constraints. No “warm up” period before the test was allowed, and the patients had to rest on a chair for 10 min before commencement. The test was self-paced and the patients could rest at his or her own wish. Words of encouragement spoken to patients throughout the test were standardized as per protocol. The distance walked over 6 min (6MWD) was recorded in meters. The 6MWT was regarded as abnormal if the 6MWD was less than the 10th percentile of height-matched reference.[16]

The CPET was performed by trained technicians according to the guideline published by the American Thoracic Society,[1] with a treadmill, with a Medgraphics oxygen analyzer (Ultima Series™ Cardiorespiratory Diagnostics Systems, Medical Graphics Corp., St. Paul, MN, USA).

Data including baseline heart rate, blood pressure, carbon dioxide, and oxygen content of the respiratory gas were measured. The patient then ran on the treadmill with increasing speed according to the incremental Bruce Exercise Protocol.

The results of CPET was regarded as abnormal if the VO2 max was <80% predicted.[17]

Statistical analysis

The mean and standard deviation for age, body weight, height, and body mass index (BMI) z-score were calculated. The respiratory exchange ratio (RER) and maximal heart rate in the CPET were also recorded. Shapiro–Wilk test was used to test for normality on datasets. Pearson's correlation analysis was used to calculate the correlation coefficient (r) between variables. The 6MWT and CPET results were represented in a 2 × 2 table. All statistical analyses were performed using IBM SPSS Statistics for Windows, Version 22.0 (IBM Corp., Inc., Armonk, NY, USA) and P < 0.05 was taken as statistically significant. Sensitivity, specificity, accuracy, and positive predictive value (PPV) and negative predictive value (NPV) were calculated.

The study was approved by the Research Ethics Committee of Hospital Authority Kowloon West Cluster (reference: KW/EX-17-031(108-10]).


  Results Top


Patient demographics

Twenty-nine patients, 17 male (59%) and 12 female (41%), were included in this study. The mean age was 14.3 ± 3.6 years old, mean body weight was 51.6 ± 19.3 kg, mean height was 156.6 ± 16 cm, mean BMI was 20.6 ± 6.1 kg/m 2, and mean BMI Z-score was 0.23 ± 1.5 [Table 1]. Underlying diseases were listed in [Table 2].
Table 1: Patient demographics

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Table 2: Patients disease types

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Relationship between 6-min walk test and cardiopulmonary exercise test

Data from all 29 Chinese patients who had completed both the CPET and 6MWT were included in the analysis. The mean VO2 max was 32.1 ± 7.5 ml/kg/min and the mean of 6MWD was 574.3 ± 98.7 m.

The mean RER was 1.08 ± 0.11 (range 0.82–1.27) and the mean percentage of predicted maximal heart rate was 85% ± 8.7% (range 65%–100%), indicating most patients had performed maximal exercise effort.[18]

In view of the small number of patients in our study, the Shapiro–Wilk normality test on datasets for both 6MWD and VO2 max was used. The P values of the normality test for 6MWD and VO2 max were 0.419 and 0.478, respectively, meaning there is no statistically significant difference from a normal distribution for both datasets.

The 6MWD showed a significant correlation with VO2 max (r = 0.457, P = 0.013). A scatterplot of the relationship between 6MWD and VO2 max was shown in [Figure 1].
Figure 1: Scattergram of 6-min walk distance and maximum oxygen uptake.

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Analysis based on the results of the tests was performed as shown in the 2 by 2 table [Table 3]. In the calculation for sensitivity, specificity, PPV, and NPV, there were five patients with normal CPET and 21 patients with abnormal CPET.
Table 3: Results of cardiopulmonary exercise test and 6-min walk test

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Using CPET as the gold standard for functional exercise capacity, 6MWT had a PPV of 92%, NPV of 29%, sensitivity of 52%, specificity of 80%, and accuracy of 58% [Table 3]. Three patients were excluded as they were under 10 years old and there was no reference value for VO2 max for this age group to define abnormality.[17] The positive and negative likelihood ratios were 2.62 and 0.59, respectively. Among the patients with an abnormal CPET, 10 cases were due to deconditioning, 9 cases were due to respiratory causes, and 3 cases were due to cardiac causes. We interpreted the abnormal results and classified their causes according to the ATS guideline.[1]


  Discussion Top


This was the first local study to evaluate the correlation of the 6MWT with maximal CPET in Chinese patients who complained of exercise intolerance. Previous studies on adult patients with diverse cardiopulmonary disease all showed statistically significant correlations between 6MWD and VO2 max, with correlation coefficient (r) ranging from 0.21 to 0.7.[19],[20],[21] The 6MWT was shown to be an independent predictor of mortality in adult patients with primary pulmonary hypertension [21] or heart failure.[22] Within the pediatric population, previous studies evaluating the correlation were either in healthy Chinese children,[15],[16] or in children with specific diseases,[11] for example, children with cystic fibrosis (r = 0.76, P < 0.001),[10] severely cardiopulmonary disease awaiting heart or lung transplant (r = 0.7, P < 0.01),[14] and congenital heart disease (r = 0.76, P < 0.01).[12]

The current study assessed whether the 6MWT was useful for identifying abnormal exercise capacity in Chinese patients with exercise intolerance.

The current study confirmed a statistically significant correlation between the 6MWT and the CPET in Chinese patients. Being a submaximal exercise test, the 6MWT is valuable in patients with moderately or severely impaired exercise tolerance because a full CPET could put them at risk of clinical deterioration. The 6MWT may be used as a quick test as it is easy to perform, less time-consuming, well tolerated by patients, and is a good reflection of daily activity performance compared to the CPET which is more expensive and time-consuming.

In view of the high PPV of 6MWT, it is a convenient and simple tool to identify patients with abnormal CPET. The main drawback of the 6MWT is its low sensitivity. The main limitation of the current study was the small number of patients.


  Conclusion Top


6MWT has a high PPV for an abnormal CPET result and can be used as a simple tool to confirm impaired aerobic exercise capacity even though the sensitivity was low.

Financial support and sponsorship

This work was financially supported by the Tung Wah Group of Hospitals' Research Fund 2016/2017.

Conflicts of interest

There are no conflicts of interest.

 
  References Top

1.
American Thoracic Society; American College of Chest Physicians. ATS/ACCP Statement on cardiopulmonary exercise testing. Am J Respir Crit Care Med 2003;167:211-77.  Back to cited text no. 1
    
2.
Balke B. A simple field test for the assessment of physical fitness. Civ Aeromed Res Inst US 1963; 63:1-8.  Back to cited text no. 2
    
3.
Cooper KH. A means of assessing maximal oxygen intake. Correlation between field and treadmill testing. JAMA 1968;203:201-4.  Back to cited text no. 3
    
4.
McGavin CR, Gupta SP, McHardy GJ. Twelve-minute walking test for assessing disability in chronic bronchitis. Br Med J 1976;1:822-3.  Back to cited text no. 4
    
5.
Butland RJ, Pang J, Gross ER, Woodcock AA, Geddes DM. Two-, six-, and 12-minute walking tests in respiratory disease. Br Med J (Clin Res Ed) 1982;284:1607-8.  Back to cited text no. 5
    
6.
Solway S, Brooks D, Lacasse Y, Thomas S. A qualitative systematic overview of the measurement properties of functional walk tests used in the cardiorespiratory domain. Chest 2001;119:256-70.  Back to cited text no. 6
    
7.
ATS Committee on Proficiency Standards for Clinical Pulmonary Function Laboratories. ATS statement: Guidelines for the six-minute walk test. Am J Respir Crit Care Med 2002;166:111-7.  Back to cited text no. 7
    
8.
Paggiaro PL, Dahle R, Bakran I, Frith L, Hollingworth K, Efthimiou J, et al. Multicentre randomised placebo-controlled trial of inhaled fluticasone propionate in patients with chronic obstructive pulmonary disease. International COPD Study Group. Lancet 1998;351:773-80.  Back to cited text no. 8
    
9.
O'Keeffe ST, Lye M, Donnellan C, Carmichael DN. Reproducibility and responsiveness of quality of life assessment and six minute walk test in elderly heart failure patients. Heart 1998;80:377-82.  Back to cited text no. 9
    
10.
Gulmans VA, van Veldhoven NH, de Meer K, Helders PJ. The six-minute walking test in children with cystic fibrosis: Reliability and validity. Pediatr Pulmonol 1996;22:85-9.  Back to cited text no. 10
    
11.
Bartels B, de Groot JF, Terwee CB. The six-minute walk test in chronic pediatric conditions: A systematic review of measurement properties. Phys Ther 2013;93:529-41.  Back to cited text no. 11
    
12.
Moalla W, Gauthier R, Maingourd Y, Ahmaidi S. Six-minute walking test to assess exercise tolerance and cardiorespiratory responses during training program in children with congenital heart disease. Int J Sports Med 2005;26:756-62.  Back to cited text no. 12
    
13.
Elloumi M, Makni E, Ounis OB, Moalla W, Zbidi A, Zaoueli M, et al. Six-minute walking test and the assessment of cardiorespiratory responses during weight-loss programmes in obese children. Physiother Res Int 2011;16:32-42.  Back to cited text no. 13
    
14.
Nixon PA, Joswiak ML, Fricker FJ. A six-minute walk test for assessing exercise tolerance in severely ill children. J Pediatr 1996;129:362-6.  Back to cited text no. 14
    
15.
Li AM, Yin J, Yu CC, Tsang T, So HK, Wong E, et al. The six-minute walk test in healthy children: Reliability and validity. Eur Respir J 2005;25:1057-60.  Back to cited text no. 15
    
16.
Li AM, Yin J, Au JT, So HK, Tsang T, Wong E, et al. Standard reference for the six-minute-walk test in healthy children aged 7 to 16 years. Am J Respir Crit Care Med 2007;176:174-80.  Back to cited text no. 16
    
17.
Sheng LW, Ye JC, Qing ZY, Z Ivic Njak M, Xin SL, Jie GM, et al. Maximal aerobic power in children and adolescents of Beijing, China. Am J Hum Biol 1996;8:497-503.  Back to cited text no. 17
    
18.
Fox SM, Haskell WL. The exercise stress test: Needs for standardization. Cardiology: Current Topics and Progress. New York: Academic Press; 1970. p. 149-54.  Back to cited text no. 18
    
19.
Ross RM, Murthy JN, Wollak ID, Jackson AS. The six minute walk test accurately estimates mean peak oxygen uptake. BMC Pulm Med 2010;10:31.  Back to cited text no. 19
    
20.
Prichard RA, Juul M, Gazibarich G, Davidson PM, Mason C, Keogh AM, et al. Six-minute walk distance predicts VO2 (max) in patients supported with continuous flow left ventricular assist devices. Int J Artif Organs 2014;37:539-45.  Back to cited text no. 20
    
21.
Miyamoto S, Nagaya N, Satoh T, Kyotani S, Sakamaki F, Fujita M, et al. Clinical correlates and prognostic significance of six-minute walk test in patients with primary pulmonary hypertension. Comparison with cardiopulmonary exercise testing. Am J Respir Crit Care Med 2000;161:487-92.  Back to cited text no. 21
    
22.
Bittner V, Weiner DH, Yusuf S, Rogers WJ, McIntyre KM, Bangdiwala SI, et al. Prediction of mortality and morbidity with a 6-minute walk test in patients with left ventricular dysfunction. SOLVD investigators. JAMA 1993;270:1702-7.  Back to cited text no. 22
    


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  [Table 1], [Table 2], [Table 3]



 

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