- Email: [email protected]
Implicit postural control strategies in older hemodialysis patients: An objective hallmark feature for clinical balance assessment
Gait & Posture 40 (2014) 723–726
Contents lists available at ScienceDirect
Gait & Posture journal homepage: www.elsevier.com/locate/gaitpost
Short Communication
Implicit postural control strategies in older hemodialysis patients: An objective hallmark feature for clinical balance assessment Justine Magnard a, Dan Hristea b, Gae¨lle Lefrancois b, Angelo Testa b, Anne Paris b, Thibault Deschamps a,* a b
University of Nantes, Laboratory ‘‘Motricite´, Interactions, Performance’’ (UPRES EA 4334), F-44000 Nantes, France Dialysis Unit, ECHO Nantes Dialysis Association, France
A R T I C L E I N F O
A B S T R A C T
Article history: Received 2 April 2014 Received in revised form 8 July 2014 Accepted 11 July 2014
Elderly patients with end stage renal diseases (ESRD) undergoing hemodialyis (HD) present poorer physical function and higher accident falls than healthy elderly population. Therefore, the aim of this study was to examine the HD-related changes in postural sway in ESRD patients, as an objective hallmark of their functional abilities. We hypothesized that the ESRD symptoms (i.e. uremic syndrome) and the HD therapy affected the postural control, evidenced by higher bounding limits of center-ofpressure (COP) velocity dynamics. Fifty-five participants, including 28 HD patients and 27 age, body mass index and gender-matched healthy participants HS (70.42 13.69 years; 23.46 4.67 kg/m2; 35.7% women vs. 73.62 6.59 years; 25.09 3.54 kg/m2; 37% women), were asked to maintain quiet stance on force platform, with eyes open and eyes closed. COP parameters were mean and standard deviation (SD) of position, velocity and average absolute maximal velocity (AAMV) in antero-posterior and medio-lateral directions. The results revealed a significant main effect of group on velocity-based variables, highlighting that mean velocity, SD velocity and AAMV (p < 0.01) were higher for HD as compared to HS. These findings identified the bounding limits of COP velocity as an objective hallmark feature of HD-related changes in postural sway. The clinical assessment of this active control of COP velocity dynamics could be useful to examine the effects of targeted intradialytic exercise programs on functional performances and for early detection of increased fall risk in HD patients. ß 2014 Elsevier B.V. All rights reserved.
Keywords: Posture Velocity control hypothesis Hemodialysis patients
1. Introduction More than two million people with end stage renal diseases (ESRD) are currently treated worldwide by dialysis. The ESRD are substantially characterized by the uremic syndrome, whose main features are an arterial hypertension, an overall hydration, a metabolic acidosis and retention of nitrogenous substances – urea and creatinine, and an abnormal electrolyte balance [1]. Despite significant progress in dialysis techniques and in the treatment of associated comorbidities, patients with ESRD undergoing hemodialysis (HD) have decreased physical functioning, diminished muscle mass and altered muscle quality, and all of these features are associated with an increased morbidity and mortality risk [2].
* Corresponding author at: University of Nantes, Laboratory ‘‘Motricite´, Interactions, Performance’’ (EA 4334), 25 bis boulevard Guy Mollet, BP 72206, 44322 Nantes Cedex 3, France. Tel.: +33 02 51 83 72 14; fax: +33 02 51 83 72 10. E-mail address: [email protected] (T. Deschamps). http://dx.doi.org/10.1016/j.gaitpost.2014.07.009 0966-6362/ß 2014 Elsevier B.V. All rights reserved.
The relationship between older patients with ESRD and impairments in motor function and balance has been established in several surveys, revealing a greater frequency of falls and fractures in HD patients than in controls [3,4]. For example, the fall risk in HD population is higher than in the general community (a fall rate of 1.60 falls/patient-year vs. 0.6–0.84 falls/people-year in older, frail populations), and fall-related morbidity is high [5]. Because poorer balance stability is identified as a powerful predictor of falls in older adults with and without cognitive impairment [6,7], balance assessment and in particular the analysis of center-of-pressure (COP) trajectories recorded using force platforms could be helpful to understand ESRD-related changes in postural sway that expose to greater fall risk [8]. In this vein, Shin et al. [9] showed that HD patients have poorer postural control than age-matched healthy subjects (mean age 48.7 9.5 years), in particular while quiet standing with a cognitive task. Unfortunately not investigated in [9], this finding is likely to be related to deficits in integration of visual, proprioceptive and vestibular inputs necessary for efficient postural control [10].
J. Magnard et al. / Gait & Posture 40 (2014) 723–726
724
In this context, we have recently demonstrated a key role for COP velocity-based variables in postural sway in older healthy individuals, with cognitive impairment and/or history of falls [11,12]. By assessing the most sensitive velocity-based variables, namely the average absolute maximal velocity (AAMV in mm/s), we specifically showed that the highest AAMVs that bound the COP velocity dynamics of postural sway were associated with cognitive impairment and fall risk. Our findings highlighted the COP velocity-based corrective control process as a hallmark feature of cognitive impairment-related changes in postural sway. This point might be of special interest for clinical balance assessment and falls prevention in older HD patients [12]. Thus we aimed to characterize the implicit postural control strategies in 28 older HD patients in comparison with 27 agematched controls (mean age 72 10.8 years). Because the physiological functions induce continuous body sways [13], our hypothesis was that the ESRD symptoms (e.g. uremic syndromerelated liquid movements) and the HD therapy affected the postural control leading to higher bounding limits of COP velocity dynamics, apart from the fact that HD patients have low levels of daily physical activity [2].
EO conditions, they were instructed to look at a black spot (with a diameter 2 cm diameter) placed on a white wall in the front of them at a 2 m distance. For a trial of 51.2 s duration (sampling frequency of 5 Hz), the system was linked to BioWare1 5.2.2 software, providing COP series on the antero-posterior (AP) and medio-lateral (ML) axes. 2.3. Statistics The COP parameters were mean and standard deviation (SD) of position and velocity in AP and ML directions. We also computed the AAMV from the COP velocity series by extracting the maximum and minimum values of series within non-overlapping windows (of a length of 2 s). Then the absolute values of these extremes were averaged (see [11,12] for details). For testing the effects of Group (HD vs. HS) on the postural control, a one-way ANOVA was first carried out for each aforesaid dependent variable. Then betweengroup comparisons were performed using 2 (Group) 2 (Vision) ANOVAs to test the effects of visual information processing on the postural control. Partial eta square (ph2) values are reported as measures of effect size, with very large effects considered for 2 ph 0.14 [14].
2. Methods
3. Results
2.1. Participants 55 individuals volunteered to take part in this investigation, including 28 HD patients (10 women) and 27 age, body mass index and gender-matched healthy participants HS (10 women. Control subjects were admitted to the study if they had no history of renal impairment, no past history or current symptoms of neuromuscular dysfunction. All participants gave informed signed consent before enrollment. Independent sample t-tests were performed for HD vs. HS age, and body mass index [t(19) = 0.39, p = 0.69, t(19) = 1.53, p = 0.14, respectively]. A Chi square test was conducted for the gender variable [x2 = 0.03, p = 85] (see Table 1 for participants’ baseline characteristics). All HD patients are on thrice-weekly HD therapy for longer than 3 months and were recruited in the outpatient HD Laennec Dialysis unit and Confluent Dialysis unit of the ECHO Dialysis Association in Nantes (France).
We first focused on the postural performance considering only the effects of Group factor (all statistical results are summarized in Table 2). The analysis found a main effect of Group on velocity-based variables, revealing that mean, SD velocity and AAMV were significantly higher in HD patients compared with HS. Besides the analyses for many COP position variables showed that postural sway is not significantly different according to groups. Secondly, the two-way ANOVAs confirmed these findings, with significant effects of Group for all velocity-based variables (Fs > 7.32; p < 0.01). Moreover a significant effect of Vision revealed alterations in postural control in EC vs EO conditions, as found for the mean velocity [13.86 7.31 vs. 12.22 6.02 mm/s; +13.42%; p = 0.02; ph2 = 0.096], the SD velocity [19.1 10.89 vs. 16.09 8.39 mm/s; +18.7%; p = 0.008; ph2 = 0.124] and the AAMV [22.75 13.43 vs. 18.91 10.12 mm/s; +20.3%; p = 0.004; ph2 = 0.147] in the AP direction (Fig. 1). Note that no significant Group Vision interaction was found [all Fs < 4.34, p > 0.07].
4. Discussion
2.2. Procedure
The results confirmed the bounding limits of COP velocity as an objective hallmark feature of HD-related changes in postural sway. Contrary to most of position variables, mean velocity, SD velocity and AAMV are actually higher for HD, as compared to healthy participants (Table 2). Even if these results corroborate changes in
For all data collection of postural sway, the participants were asked to maintain standing position on a Kistler force platform (model 9286BA) according to two trials of quiet stance: stance with eyes open (EO) and stance with eyes closed (EC) (random order across participants). Participants were instructed to stand quietly while barefoot, with the head in a straight-ahead position, their arms along the body, and each foot positioned on the platform plate that maintained the distance between the medial sides of the heel at 8.4 cm with an external rotation angle of 98 [11,12]. During
[(Fig._1)TD$IG]
Table 1 Clinical characteristics of the participants (n = 55).
Age (years) [95% CI] Male gender, n (%) BMI (kg/m2) [95% CI] Duration of HD (months) min–max
HD group (n = 28)
HS group (n = 27)
Total (n = 55)
70 13.64 [64.81; 75.18] 18 (64.3) 23.41 4.59 [21.41; 25.16] 87.10 80.56 11–308
73.62 6.59 [64.81; 75.18] 17 (63) 25.09 3.54 [23.69; 26.49] NA
72 10.8 [64.07; 74.92] 35 (63.6) 24.26 4.2 [23.13; 25.4]
Fig. 1. Effects of vision (open eyes – in gray vs. closed eyes – in black) on the average absolute maximal velocity (AAMV) (mm/s) in antero-posterior axis, as a function of Group (healthy controls vs. hemodialys patients). Error bars correspond to the standard deviation. Significant differences at **p < 0.01.
J. Magnard et al. / Gait & Posture 40 (2014) 723–726
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Table 2 Comparisons between HD patients and age- and BMI-matched HS group (one-way analysis of variance results). Statistically significant results (p < 0.05) are indicated in bold. Outcomes (Significant values) 1. COP position-based variables 1.1 Eyes Open Mean position_AP (mm) SD position_AP (mm) Mean position_ML (mm) SD position_ML (mm) 1.2 Eyes Closed Mean position_AP (mm) SD position_AP (mm) Mean position_ML (mm) SD position_ML (mm) 2. COP velocity-based variables 2.1 Eyes Open Mean velocity (mm/s) Mean velocity_AP (mm/s) SD velocity_AP (mm/s) Mean velocity_ML (mm/s) SD velocity_ML (mm/s) AAMV_AP (mm/s) AAMV_ML (mm/s) 2.2 Eyes Closed Mean velocity (mm/s) Mean velocity_AP (mm/s) SD velocity_AP (mm/s) Mean velocity_ML (mm/s) SD velocity_ML (mm/s) AAMV_AP (mm/s) AAMV_ML (mm/s)
HS group, mean [95% CI]
19.28 4.81 1.09 3.13
[ 26.35; 12.19] [4.22; 5.41] [ 5.49; 3.3] [2.59; 3.68]
HD group, mean [95% CI]
28.28 5.69 1.95 4.62
F
h2
p
p
[ 39.74; 16.82] [5.81; 6.58] [ 3.62; 7.53] [3.64; 5.61]
1.85 2.82 0.771 7.234
0.179 0.09 0.384 0.01
0.034 0.051 0.014 0.12a
14.6 [ 21.73; 7.46] 5.113 [4.39; 5.83] 1.82 [ 6.65; 3.01] 2.64 [2.15; 3.14]
25.91 [ 35.04; 16.78] 5.66 [4.69; 6.63] 1.6 [ 4.16; 7.37] 3.73 [2.99; 4.47]
3.982 0.875 0.865 6.177
0.051 0.354 0.356 0.016
0.07 0.016 0.016 0.104a
9.74 4.48 12.65 7.68 7.37 14.84 8.46
[7.93; 11.54] [3.57; 5.4] [10.31; 14.99] [6.27; 9.1] [5.89–8.86] [11.85–17.82] [6.73–10.18]
14.61 6.67 19.41 11.36 13.81 22.84 13.81
[12.15; 17.07] [5.35; 7.98] [15.86; 22.96] [9.51; 13.2] [9.28; 18.34] [18.63; 27.05] [9.28; 18.34]
10.59 10.41 10.47 7.71 7.45 10.02 9.09
0.002 0.002 0.002 0.008 0.009 0.003 0.004
0.167a 0.164a 0.165a 0.127a 0.123a 0.159a 0.146a
11.43 [8.88; 13.98] 4.84 [3.86; 5.83] 15.42 [11.82; 19.03] 9.32 [7.09; 11.55] 7.91 [6.31–9.51] 18.1 [13.69–22.51] 9.36 [7.44–11.28]
16.21 6.26 22.65 13.55 10.98 27.23 12.38
[13.32; 19.09] [5.25; 7.27] [18.21; 27.09] [10.92; 16.18] [8.89; 13.08] [21.77; 32.7] [10.28; 14.48]
6.45 6.3 6.68 4.28 5.68 7.07 4.74
0.014 0.015 0.013 0.043 0.021 0.01 0.023
0.109a 0.106a 0.112a 0.075a 0.097a 0.118a 0.082a
COP: center of pressure; AP: anteroposterior; ML: mediolateral. SD: standard deviation; AAMV: average absolute maximal velocity. HS: healthy controls; HD: hemodialysis patients. a Significant difference between HS and HD groups.
poor postural stability in HD patients [3,9], these findings demonstrate that the velocity information is the most sensitive form of sensory information to (de)stabilize posture in HD as compared to age-matched healthy participants. In accordance with [11,12], we argue an adverse impact of ESRD on the active corrective control process of COP velocity dynamics, especially in anteroposterior direction. Even if quiet standing under eyes closed condition induces adverse changes in intermittent velocity-based control of posture (i.e. highest velocity thresholds), no Group Vision interaction was found. This lack of interaction indicates that visual information processing causes alterations in postural control to the same extent whatever the status of older participants. Thus we suggest that the impaired balance in ESRD might be more related to deficits in integration of proprioceptive and/or vestibular inputs rather than the visual input [10], probably because of their specific physiopathology (e.g., atrophy in the lower extremity muscles, low muscle strength, acidosis, abnormalities in vitamin D metabolism or in serum calcium concentration, prolonged inactivity, malnutrition, inadequate dialysis or hyperparathyroidism [1]). To this aim, further research is required to test the specific HD-related adverse changes in postural sway by removing/attenuating the sensory information from the visual, somatosensory and vestibular systems. In support of our purpose, the present finding is of special interest for clinical balance assessment in order to examine the effects of long-term targeted intradialytic exercise programs on functional performances [15]. Moreover, the assessment of this active control of COP velocity dynamics might be also useful for early detection of increased fall risk in HD patients [11,12]. Author contributions All authors meet all of the following criteria: (1) contributing to the conception and design, or analyzing and interpreting data; (2)
drafting the article or revising it critically for important intellectual content; and (3) approving the final version to be published. Acknowledgements The study was sponsored by the University Hospital of Nantes. The research is also sponsored in part by the ACTICLAN prize provided by Fresenius Kabi, France. The sponsors had no role in the design and conduct of the study, in the collection, management, analysis, and interpretation of the data, or in the preparation, review, or approval of the manuscript. Conflict of interest statement The authors report no conflicts of interest.
References [1] Johansen KL, Shubert T, Doyle J, Soher B, Sakkas GK, Kent-Braun JA. Muscle atrophy in patients receiving hemodialysis: effects on muscle strength, muscle quality, and physical function. Kidney Int 2003;63:291–7. [2] Johansen KL, Chertow GM, Ng AV, Mulligan K, Carey S, Schoenfeld PY, et al. Physical activity levels in patients on hemodialysis and healthy sedentary controls. Kidney Int 2000;57:2564–70. [3] Blake C, O’Meara YM. Subjective and objective physical limitations in highfunctioning renal dialysis patients. Nephrol Dial Transplant 2004;19(12): 3124–9. [4] Desmet C, Beguin C, Swine C, Jadoul M, Universite´ Catholique de Louvain Collaborative Group. Falls in hemodialysis patients: prospective study of incidence, risk factors, and complications. Am J Kidney Dis 2005;45:148–53. [5] Cook WL, Tomlinson G, Donaldson M, Markowitz SN, Naglie G, Sobolev B, et al. Falls and fall-related injuries in older dialysis patients. Clin J Am Soc Nephrol 2006;1:1197–204. [6] King MB, Tinetti ME. Falls in community-dwelling older persons. J Am Geriatr Soc 1995;43:1146–54. [7] Horikawa E, Matsui T, Arai H, Seki T, Iwasaki K, Sasaki H. Risk of falls in Alzheimer’s disease: a prospective study. Intern Med 2005;44:717–21. [8] Brauer SG, Burns YR, Galley P. A prospective study of laboratory and clinical measures of postural stability to predict community-dwelling fallers. J Gerontol A Biol Sci Med Sci 2000;55:M469–76.
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[9] Shin S, Chung HR, Fitschen PJ, Kistler BM, Park HW, Wilund KR, et al. Postural control in hemodialysis patients. Gait Posture 2014;39:723–7. [10] Doumas M, Krampe RT. Adaptation and reintegration of proprioceptive information in young and older adults’ postural control. J Neurophysiol 2010;104: 1969–77. [11] Deschamps T, Beauchet O, Annweiler C, Cornu C, Mignardot JB. Postural control and cognitive decline in older adults: position versus velocity implicit motor strategy. Gait Posture 2014;39:628–30. [12] Mignardot J-B, Beauchet O, Annweiler C, Cornu C, Deschamps T. Postural sway, falls and cognitive status: a cross-sectional study among older adults. J Alzheimers Dis 2014;41:431–9.
[13] Conforto S, Schmid M, Camomilla V, D’Alessio T, Cappozzo A. Hemodynamics as a possible internal mechanical disturbance to balance. Gait Posture 2011;14:28–35. [14] Cohen J. Statistical power analysis for the behavioural sciences. 3rd ed. New York: Academic Press; 1988. [15] Magnard J, Deschamps T, Cornu C, Paris A, Hristea D. Effects of a six-month intradialytic physical ACTIvity program and adequate NUTritional support on protein-energy wasting, physical functioning and quality of life in chronic hemodialysis patients: ACTINUT study protocol for a randomised controlled trial. BMC Nephrol 2013;14:259.
Contents lists available at ScienceDirect
Gait & Posture journal homepage: www.elsevier.com/locate/gaitpost
Short Communication
Implicit postural control strategies in older hemodialysis patients: An objective hallmark feature for clinical balance assessment Justine Magnard a, Dan Hristea b, Gae¨lle Lefrancois b, Angelo Testa b, Anne Paris b, Thibault Deschamps a,* a b
University of Nantes, Laboratory ‘‘Motricite´, Interactions, Performance’’ (UPRES EA 4334), F-44000 Nantes, France Dialysis Unit, ECHO Nantes Dialysis Association, France
A R T I C L E I N F O
A B S T R A C T
Article history: Received 2 April 2014 Received in revised form 8 July 2014 Accepted 11 July 2014
Elderly patients with end stage renal diseases (ESRD) undergoing hemodialyis (HD) present poorer physical function and higher accident falls than healthy elderly population. Therefore, the aim of this study was to examine the HD-related changes in postural sway in ESRD patients, as an objective hallmark of their functional abilities. We hypothesized that the ESRD symptoms (i.e. uremic syndrome) and the HD therapy affected the postural control, evidenced by higher bounding limits of center-ofpressure (COP) velocity dynamics. Fifty-five participants, including 28 HD patients and 27 age, body mass index and gender-matched healthy participants HS (70.42 13.69 years; 23.46 4.67 kg/m2; 35.7% women vs. 73.62 6.59 years; 25.09 3.54 kg/m2; 37% women), were asked to maintain quiet stance on force platform, with eyes open and eyes closed. COP parameters were mean and standard deviation (SD) of position, velocity and average absolute maximal velocity (AAMV) in antero-posterior and medio-lateral directions. The results revealed a significant main effect of group on velocity-based variables, highlighting that mean velocity, SD velocity and AAMV (p < 0.01) were higher for HD as compared to HS. These findings identified the bounding limits of COP velocity as an objective hallmark feature of HD-related changes in postural sway. The clinical assessment of this active control of COP velocity dynamics could be useful to examine the effects of targeted intradialytic exercise programs on functional performances and for early detection of increased fall risk in HD patients. ß 2014 Elsevier B.V. All rights reserved.
Keywords: Posture Velocity control hypothesis Hemodialysis patients
1. Introduction More than two million people with end stage renal diseases (ESRD) are currently treated worldwide by dialysis. The ESRD are substantially characterized by the uremic syndrome, whose main features are an arterial hypertension, an overall hydration, a metabolic acidosis and retention of nitrogenous substances – urea and creatinine, and an abnormal electrolyte balance [1]. Despite significant progress in dialysis techniques and in the treatment of associated comorbidities, patients with ESRD undergoing hemodialysis (HD) have decreased physical functioning, diminished muscle mass and altered muscle quality, and all of these features are associated with an increased morbidity and mortality risk [2].
* Corresponding author at: University of Nantes, Laboratory ‘‘Motricite´, Interactions, Performance’’ (EA 4334), 25 bis boulevard Guy Mollet, BP 72206, 44322 Nantes Cedex 3, France. Tel.: +33 02 51 83 72 14; fax: +33 02 51 83 72 10. E-mail address: [email protected] (T. Deschamps). http://dx.doi.org/10.1016/j.gaitpost.2014.07.009 0966-6362/ß 2014 Elsevier B.V. All rights reserved.
The relationship between older patients with ESRD and impairments in motor function and balance has been established in several surveys, revealing a greater frequency of falls and fractures in HD patients than in controls [3,4]. For example, the fall risk in HD population is higher than in the general community (a fall rate of 1.60 falls/patient-year vs. 0.6–0.84 falls/people-year in older, frail populations), and fall-related morbidity is high [5]. Because poorer balance stability is identified as a powerful predictor of falls in older adults with and without cognitive impairment [6,7], balance assessment and in particular the analysis of center-of-pressure (COP) trajectories recorded using force platforms could be helpful to understand ESRD-related changes in postural sway that expose to greater fall risk [8]. In this vein, Shin et al. [9] showed that HD patients have poorer postural control than age-matched healthy subjects (mean age 48.7 9.5 years), in particular while quiet standing with a cognitive task. Unfortunately not investigated in [9], this finding is likely to be related to deficits in integration of visual, proprioceptive and vestibular inputs necessary for efficient postural control [10].
J. Magnard et al. / Gait & Posture 40 (2014) 723–726
724
In this context, we have recently demonstrated a key role for COP velocity-based variables in postural sway in older healthy individuals, with cognitive impairment and/or history of falls [11,12]. By assessing the most sensitive velocity-based variables, namely the average absolute maximal velocity (AAMV in mm/s), we specifically showed that the highest AAMVs that bound the COP velocity dynamics of postural sway were associated with cognitive impairment and fall risk. Our findings highlighted the COP velocity-based corrective control process as a hallmark feature of cognitive impairment-related changes in postural sway. This point might be of special interest for clinical balance assessment and falls prevention in older HD patients [12]. Thus we aimed to characterize the implicit postural control strategies in 28 older HD patients in comparison with 27 agematched controls (mean age 72 10.8 years). Because the physiological functions induce continuous body sways [13], our hypothesis was that the ESRD symptoms (e.g. uremic syndromerelated liquid movements) and the HD therapy affected the postural control leading to higher bounding limits of COP velocity dynamics, apart from the fact that HD patients have low levels of daily physical activity [2].
EO conditions, they were instructed to look at a black spot (with a diameter 2 cm diameter) placed on a white wall in the front of them at a 2 m distance. For a trial of 51.2 s duration (sampling frequency of 5 Hz), the system was linked to BioWare1 5.2.2 software, providing COP series on the antero-posterior (AP) and medio-lateral (ML) axes. 2.3. Statistics The COP parameters were mean and standard deviation (SD) of position and velocity in AP and ML directions. We also computed the AAMV from the COP velocity series by extracting the maximum and minimum values of series within non-overlapping windows (of a length of 2 s). Then the absolute values of these extremes were averaged (see [11,12] for details). For testing the effects of Group (HD vs. HS) on the postural control, a one-way ANOVA was first carried out for each aforesaid dependent variable. Then betweengroup comparisons were performed using 2 (Group) 2 (Vision) ANOVAs to test the effects of visual information processing on the postural control. Partial eta square (ph2) values are reported as measures of effect size, with very large effects considered for 2 ph 0.14 [14].
2. Methods
3. Results
2.1. Participants 55 individuals volunteered to take part in this investigation, including 28 HD patients (10 women) and 27 age, body mass index and gender-matched healthy participants HS (10 women. Control subjects were admitted to the study if they had no history of renal impairment, no past history or current symptoms of neuromuscular dysfunction. All participants gave informed signed consent before enrollment. Independent sample t-tests were performed for HD vs. HS age, and body mass index [t(19) = 0.39, p = 0.69, t(19) = 1.53, p = 0.14, respectively]. A Chi square test was conducted for the gender variable [x2 = 0.03, p = 85] (see Table 1 for participants’ baseline characteristics). All HD patients are on thrice-weekly HD therapy for longer than 3 months and were recruited in the outpatient HD Laennec Dialysis unit and Confluent Dialysis unit of the ECHO Dialysis Association in Nantes (France).
We first focused on the postural performance considering only the effects of Group factor (all statistical results are summarized in Table 2). The analysis found a main effect of Group on velocity-based variables, revealing that mean, SD velocity and AAMV were significantly higher in HD patients compared with HS. Besides the analyses for many COP position variables showed that postural sway is not significantly different according to groups. Secondly, the two-way ANOVAs confirmed these findings, with significant effects of Group for all velocity-based variables (Fs > 7.32; p < 0.01). Moreover a significant effect of Vision revealed alterations in postural control in EC vs EO conditions, as found for the mean velocity [13.86 7.31 vs. 12.22 6.02 mm/s; +13.42%; p = 0.02; ph2 = 0.096], the SD velocity [19.1 10.89 vs. 16.09 8.39 mm/s; +18.7%; p = 0.008; ph2 = 0.124] and the AAMV [22.75 13.43 vs. 18.91 10.12 mm/s; +20.3%; p = 0.004; ph2 = 0.147] in the AP direction (Fig. 1). Note that no significant Group Vision interaction was found [all Fs < 4.34, p > 0.07].
4. Discussion
2.2. Procedure
The results confirmed the bounding limits of COP velocity as an objective hallmark feature of HD-related changes in postural sway. Contrary to most of position variables, mean velocity, SD velocity and AAMV are actually higher for HD, as compared to healthy participants (Table 2). Even if these results corroborate changes in
For all data collection of postural sway, the participants were asked to maintain standing position on a Kistler force platform (model 9286BA) according to two trials of quiet stance: stance with eyes open (EO) and stance with eyes closed (EC) (random order across participants). Participants were instructed to stand quietly while barefoot, with the head in a straight-ahead position, their arms along the body, and each foot positioned on the platform plate that maintained the distance between the medial sides of the heel at 8.4 cm with an external rotation angle of 98 [11,12]. During
[(Fig._1)TD$IG]
Table 1 Clinical characteristics of the participants (n = 55).
Age (years) [95% CI] Male gender, n (%) BMI (kg/m2) [95% CI] Duration of HD (months) min–max
HD group (n = 28)
HS group (n = 27)
Total (n = 55)
70 13.64 [64.81; 75.18] 18 (64.3) 23.41 4.59 [21.41; 25.16] 87.10 80.56 11–308
73.62 6.59 [64.81; 75.18] 17 (63) 25.09 3.54 [23.69; 26.49] NA
72 10.8 [64.07; 74.92] 35 (63.6) 24.26 4.2 [23.13; 25.4]
Fig. 1. Effects of vision (open eyes – in gray vs. closed eyes – in black) on the average absolute maximal velocity (AAMV) (mm/s) in antero-posterior axis, as a function of Group (healthy controls vs. hemodialys patients). Error bars correspond to the standard deviation. Significant differences at **p < 0.01.
J. Magnard et al. / Gait & Posture 40 (2014) 723–726
725
Table 2 Comparisons between HD patients and age- and BMI-matched HS group (one-way analysis of variance results). Statistically significant results (p < 0.05) are indicated in bold. Outcomes (Significant values) 1. COP position-based variables 1.1 Eyes Open Mean position_AP (mm) SD position_AP (mm) Mean position_ML (mm) SD position_ML (mm) 1.2 Eyes Closed Mean position_AP (mm) SD position_AP (mm) Mean position_ML (mm) SD position_ML (mm) 2. COP velocity-based variables 2.1 Eyes Open Mean velocity (mm/s) Mean velocity_AP (mm/s) SD velocity_AP (mm/s) Mean velocity_ML (mm/s) SD velocity_ML (mm/s) AAMV_AP (mm/s) AAMV_ML (mm/s) 2.2 Eyes Closed Mean velocity (mm/s) Mean velocity_AP (mm/s) SD velocity_AP (mm/s) Mean velocity_ML (mm/s) SD velocity_ML (mm/s) AAMV_AP (mm/s) AAMV_ML (mm/s)
HS group, mean [95% CI]
19.28 4.81 1.09 3.13
[ 26.35; 12.19] [4.22; 5.41] [ 5.49; 3.3] [2.59; 3.68]
HD group, mean [95% CI]
28.28 5.69 1.95 4.62
F
h2
p
p
[ 39.74; 16.82] [5.81; 6.58] [ 3.62; 7.53] [3.64; 5.61]
1.85 2.82 0.771 7.234
0.179 0.09 0.384 0.01
0.034 0.051 0.014 0.12a
14.6 [ 21.73; 7.46] 5.113 [4.39; 5.83] 1.82 [ 6.65; 3.01] 2.64 [2.15; 3.14]
25.91 [ 35.04; 16.78] 5.66 [4.69; 6.63] 1.6 [ 4.16; 7.37] 3.73 [2.99; 4.47]
3.982 0.875 0.865 6.177
0.051 0.354 0.356 0.016
0.07 0.016 0.016 0.104a
9.74 4.48 12.65 7.68 7.37 14.84 8.46
[7.93; 11.54] [3.57; 5.4] [10.31; 14.99] [6.27; 9.1] [5.89–8.86] [11.85–17.82] [6.73–10.18]
14.61 6.67 19.41 11.36 13.81 22.84 13.81
[12.15; 17.07] [5.35; 7.98] [15.86; 22.96] [9.51; 13.2] [9.28; 18.34] [18.63; 27.05] [9.28; 18.34]
10.59 10.41 10.47 7.71 7.45 10.02 9.09
0.002 0.002 0.002 0.008 0.009 0.003 0.004
0.167a 0.164a 0.165a 0.127a 0.123a 0.159a 0.146a
11.43 [8.88; 13.98] 4.84 [3.86; 5.83] 15.42 [11.82; 19.03] 9.32 [7.09; 11.55] 7.91 [6.31–9.51] 18.1 [13.69–22.51] 9.36 [7.44–11.28]
16.21 6.26 22.65 13.55 10.98 27.23 12.38
[13.32; 19.09] [5.25; 7.27] [18.21; 27.09] [10.92; 16.18] [8.89; 13.08] [21.77; 32.7] [10.28; 14.48]
6.45 6.3 6.68 4.28 5.68 7.07 4.74
0.014 0.015 0.013 0.043 0.021 0.01 0.023
0.109a 0.106a 0.112a 0.075a 0.097a 0.118a 0.082a
COP: center of pressure; AP: anteroposterior; ML: mediolateral. SD: standard deviation; AAMV: average absolute maximal velocity. HS: healthy controls; HD: hemodialysis patients. a Significant difference between HS and HD groups.
poor postural stability in HD patients [3,9], these findings demonstrate that the velocity information is the most sensitive form of sensory information to (de)stabilize posture in HD as compared to age-matched healthy participants. In accordance with [11,12], we argue an adverse impact of ESRD on the active corrective control process of COP velocity dynamics, especially in anteroposterior direction. Even if quiet standing under eyes closed condition induces adverse changes in intermittent velocity-based control of posture (i.e. highest velocity thresholds), no Group Vision interaction was found. This lack of interaction indicates that visual information processing causes alterations in postural control to the same extent whatever the status of older participants. Thus we suggest that the impaired balance in ESRD might be more related to deficits in integration of proprioceptive and/or vestibular inputs rather than the visual input [10], probably because of their specific physiopathology (e.g., atrophy in the lower extremity muscles, low muscle strength, acidosis, abnormalities in vitamin D metabolism or in serum calcium concentration, prolonged inactivity, malnutrition, inadequate dialysis or hyperparathyroidism [1]). To this aim, further research is required to test the specific HD-related adverse changes in postural sway by removing/attenuating the sensory information from the visual, somatosensory and vestibular systems. In support of our purpose, the present finding is of special interest for clinical balance assessment in order to examine the effects of long-term targeted intradialytic exercise programs on functional performances [15]. Moreover, the assessment of this active control of COP velocity dynamics might be also useful for early detection of increased fall risk in HD patients [11,12]. Author contributions All authors meet all of the following criteria: (1) contributing to the conception and design, or analyzing and interpreting data; (2)
drafting the article or revising it critically for important intellectual content; and (3) approving the final version to be published. Acknowledgements The study was sponsored by the University Hospital of Nantes. The research is also sponsored in part by the ACTICLAN prize provided by Fresenius Kabi, France. The sponsors had no role in the design and conduct of the study, in the collection, management, analysis, and interpretation of the data, or in the preparation, review, or approval of the manuscript. Conflict of interest statement The authors report no conflicts of interest.
References [1] Johansen KL, Shubert T, Doyle J, Soher B, Sakkas GK, Kent-Braun JA. Muscle atrophy in patients receiving hemodialysis: effects on muscle strength, muscle quality, and physical function. Kidney Int 2003;63:291–7. [2] Johansen KL, Chertow GM, Ng AV, Mulligan K, Carey S, Schoenfeld PY, et al. Physical activity levels in patients on hemodialysis and healthy sedentary controls. Kidney Int 2000;57:2564–70. [3] Blake C, O’Meara YM. Subjective and objective physical limitations in highfunctioning renal dialysis patients. Nephrol Dial Transplant 2004;19(12): 3124–9. [4] Desmet C, Beguin C, Swine C, Jadoul M, Universite´ Catholique de Louvain Collaborative Group. Falls in hemodialysis patients: prospective study of incidence, risk factors, and complications. Am J Kidney Dis 2005;45:148–53. [5] Cook WL, Tomlinson G, Donaldson M, Markowitz SN, Naglie G, Sobolev B, et al. Falls and fall-related injuries in older dialysis patients. Clin J Am Soc Nephrol 2006;1:1197–204. [6] King MB, Tinetti ME. Falls in community-dwelling older persons. J Am Geriatr Soc 1995;43:1146–54. [7] Horikawa E, Matsui T, Arai H, Seki T, Iwasaki K, Sasaki H. Risk of falls in Alzheimer’s disease: a prospective study. Intern Med 2005;44:717–21. [8] Brauer SG, Burns YR, Galley P. A prospective study of laboratory and clinical measures of postural stability to predict community-dwelling fallers. J Gerontol A Biol Sci Med Sci 2000;55:M469–76.
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[9] Shin S, Chung HR, Fitschen PJ, Kistler BM, Park HW, Wilund KR, et al. Postural control in hemodialysis patients. Gait Posture 2014;39:723–7. [10] Doumas M, Krampe RT. Adaptation and reintegration of proprioceptive information in young and older adults’ postural control. J Neurophysiol 2010;104: 1969–77. [11] Deschamps T, Beauchet O, Annweiler C, Cornu C, Mignardot JB. Postural control and cognitive decline in older adults: position versus velocity implicit motor strategy. Gait Posture 2014;39:628–30. [12] Mignardot J-B, Beauchet O, Annweiler C, Cornu C, Deschamps T. Postural sway, falls and cognitive status: a cross-sectional study among older adults. J Alzheimers Dis 2014;41:431–9.
[13] Conforto S, Schmid M, Camomilla V, D’Alessio T, Cappozzo A. Hemodynamics as a possible internal mechanical disturbance to balance. Gait Posture 2011;14:28–35. [14] Cohen J. Statistical power analysis for the behavioural sciences. 3rd ed. New York: Academic Press; 1988. [15] Magnard J, Deschamps T, Cornu C, Paris A, Hristea D. Effects of a six-month intradialytic physical ACTIvity program and adequate NUTritional support on protein-energy wasting, physical functioning and quality of life in chronic hemodialysis patients: ACTINUT study protocol for a randomised controlled trial. BMC Nephrol 2013;14:259.