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Use of Six-Minute Walk Test to Measure Functional Capacity After Liver Transplantation
Lisa B VanWagner1, Sarah Uttal2, Brittany Lapin3
1L.B. VanWagner, MD, MSc, Department of Medicine, Division of Gastroenterology & Hepatology, Northwestern University, 676 St Clair St, Ste 1900, Chicago, IL 60611 (USA); Transplant Outcomes Research Collaborative, Northwestern University Feinberg School of Medicine; and Department of Preventive Medicine, Northwestern University. lvw@northwestern.edu.
Background:
Functional impairment is common in people with chronic liver disease (CLD), and improvement is expected following liver transplantation (LT). The Six-Minute Walk Test (6MWT) is an objective measure of functional performance.
Objective:
The aims of this study were: (1) to evaluate the feasibility of 6MWT performance after LT, (2) to compare post-LT 6MWT performance over time between patients with and without CLD, (3) to determine when post-LT 6MWT performance approaches expected values, and (4) to investigate predictors of poor 6MWT performance.
Methods:
The 6MWT was performed by 162 consecutive ambulatory participants (50 healthy controls, 62 with CLD, 50 with LT). Sex, age, and body mass index were used to predict expected 6MWT performance. Chi-square testing, analysis of variance, and Pearson coefficients compared percentage of predicted 6-minute walk distance (%6MWD) across groups. Multivariable mixed models assessed predictors of improvement.
Results:
The participants' mean age was 53.5 years (SD=13.0), 39.5% were female, and 39.1% were nonwhite. At 1-month post-LT, only 52% of all LT recipients met the inclusion criteria for 6MWT performance. Mean %6MWD values for female participants improved from 49.8 (SD=22.2) at 1 month post-LT to 90.6 (SD=12.8) at 1 year post-LT (P<.0001), which did not differ statistically from the CLD group (X̅=95.9, SD=15.6) or the control group (X̅=95.6, SD=18.0) (P=.58). However, at 1-year post-LT, mean %6MWD values for male participants (X̅=80.4, SD=19.5) remained worse than for both the CLD group (X̅=93.3, SD=13.7) and the control group (X̅=91.9, SD=14.3) (P=.03). Six-Minute Walk Test performance was directly correlated with the Medical Outcomes Study 36-Item Short-Form Health Survey (SF-36) physical component score (r=.51, P<.01) and was inversely correlated with nonalcoholic steatohepatitis (r=-.52, P<.01) and diabetes (r=-.48, P<.05). In multivariate analysis adjusted for age and sex, hepatitis C independently predicted 6MWT improvement (estimated β=69.8, standard error=27.6, P=.01).
Limitations:
A significant proportion of patients evaluated for enrollment were excluded due to level of illness early after LT (n=99, 47.4%). Thus, sampling bias occurred in this study toward patients without significant postoperative complications.
Conclusions:
The 6MWT is a simple test of physical functioning but may be difficult to apply in LT recipients. The 6MWT performance improved following LT but was lower than expected, suggesting a low level of fitness up to 1 year following LT.
