Measuring Outdoor Walking Capacities Using Global Positioning System in People with Multiple Sclerosis: Clinical and Methodological Insights from an Exploratory Study.

We aimed at showing how Global Positioning System (GPS) along with a previously validated speed processing methodology could be used to measure outdoor walking capacities in people with multiple sclerosis (MS). We also deal with methodological issues that may occur when conducting such measurements, and explore to what extent GPS-measured outdoor walking capacities (maximal walking distance [MWDGPS] and usual walking speed) could be related to traditional functional outcomes (6-min total walking distance) in people with MS. Eighteen people with MS, with an Expanded Disability Status Scale score ≤6, completed a 6-min walking test and an outdoor walking session (60 min maximum) at usual pace during which participants were wearing a DG100 GPS receiver and could perform several walking bouts. Among the 12 participants with valid data (i.e., who correctly completed the outdoor session with no spurious GPS signals that could prevent the detection of the occurrence of a walking/stopping bout), the median (90% confidence interval, CI) outdoor walking speed was 2.52 km/h (2.17; 2.93). Ten participants (83% (56; 97)) had ≥1 stop during the session. Among these participants, the median of MWDGPS was 410 m (226; 1350), and 40% (15; 70) did not reach their MWDGPS during the first walking bout. Spearman correlations of MWDGPS and walking speed with 6-min total walking distance were, respectively, 0.19 (-0.41; 0.95) and 0.66 (0.30; 1.00). Further work is required to provide guidance about GPS assessment in people with MS.

Comparison of Activity Monitors Accuracy in Assessing Intermittent Outdoor Walking.

PURPOSE: This study aimed to determine and compare the accuracy of different activity monitors in assessing intermittent outdoor walking in both healthy and clinical populations through the development and validation of processing methodologies. METHODS: In study 1, an automated algorithm was implemented and tested for the detection of short (≤1 min) walking and stopping bouts during prescribed walking protocols performed by healthy subjects in environments with low and high levels of obstruction. The following parameters obtained from activity monitors were tested, with different recording epochs0.1s/0.033s/1s/3s/10s and wearing locationsscapula/hip/wrist/ankle: GlobalSat DG100 (GS) and Qstarz BT-Q1000XT/-Q1000eX (QS) speed; ActiGraph wGT3X+ (AG) vector magnitude (VM) raw data, VM counts, and steps; and StepWatch3 (SW) steps. Furthermore, linear mixed models were developed to estimate walking speeds and distances from the monitors parameters. Study 2 validated the performance of the activity monitors and processing methodologies in a clinical population showing profile of intermittent walking due to functional limitations during outdoor walking sessions. RESULTS: In study 1, GS1s, scapula, QS1s, scapula/wrist speed, and AG0.033s, hip VM raw data provided the highest bout detection rates (>96.7%) and the lowest root mean square errors in speed (≤0.4 km·h-1) and distance (<18 m) estimation. Using SW3s, ankle steps, the root mean square error for walking/stopping duration estimation reached 13.6 min using proprietary software and 0.98 min using our algorithm (total recording duration, 282 min). In study 2, using AG0.033s, hip VM raw data, the bout detection rate (95% confidence interval) reached 100% (99%-100%), and the mean (SD) absolute percentage errors in speed and distance estimation were 9% (6.6%) and 12.5% (7.9%), respectively. CONCLUSIONS: GPS receivers and AG demonstrated high performance in assessing intermittent outdoor walking in both healthy and clinical populations.

Simulator-based assessment of ankle arterial systolic blood pressure measurement skills.

OBJECTIVE: Learning basic vascular examination is a complex process. Very few studies have focused on the ability to measure the arterial systolic blood pressure at the ankle (ASBPa). The aim of this study was to objectively assess the effects of a 1-h practical educational intervention on the ability to measure ASBPa among medical students. METHODS: A total of 27 medical students were prospectively recruited. Two evaluation sessions of ASBPa measurement skills were conducted, before (T1) and after a 1-h practical lesson (T2). To assess the learning effect associated to the simulator-based evaluation, a control group composed by nonmedical students, not involved in the practical lesson, was also tested. Objective assessments of ASBPa measurements were performed by an instrumented leg prototype. RESULTS: There was a nonsignificant decreasing trend measurement time after practical lesson. The average pressure determination error (ΔP) was significantly reduced: ΔPT1: 10.5 ± 13.8 mmHg vs. ΔPT2: 5.7 ± 6.0 mmHg (P = 0.002). The mean deflation rate (DR) of the cuff was significantly decreased: DRT1: 12.9 ± 9.2 mmHg/s vs. DRT2: 8.7 ± 4.6 mmHg/s (P = 0.001). The control group did not show significant changes. CONCLUSION: A 1-h practical learning could improve some parameters of the ASBPa measurement among medical students, but was not sufficient to allow the measured technical factors to reach established guidelines.

Accuracy of a low-cost global positioning system receiver for estimating grade during outdoor walking.

The aim of this study was to assess, for the first time, the accuracy of a low-cost global positioning system (GPS) receiver for estimating grade during outdoor walking. Thirty subjects completed outdoor walks (2.0, 3.5 and 5.0 km · h-1) in three randomized conditions: 1/level walking on a 0.0% grade; 2/graded (uphill and downhill) walking on a 3.4% grade; and 3/on a 10.4% grade. Subjects were equipped with a GPS receiver (DG100, GlobalSat Technology Corp., Taiwan; ~US$75). The GPS receiver was set to record at 1 Hz and its antenna was placed on the right shoulder. Grade was calculated from GPS speed and altitude data (grade = altitude variation/travelled distance × 100). Two methods were used for the grade calculation: one using uncorrected altitude data given by the GPS receiver and another one using corrected altitude data obtained using map projection software (CartoExploreur, version 3.11.0, build 2.6.6.22, Bayo Ltd, Appoigny, France, ~US$35). Linear regression of GPS-estimated versus actual grade with R 2 coefficients, bias with 95% limits of agreement (±95% LoA), and typical error of the estimate with 95% confidence interval (TEE (95% CI)) were computed to assess the accuracy of the GPS receiver. 444 walking periods were performed. Using uncorrected altitude data, we obtained: R 2 = 0.88 (p < 0.001), bias = 0.0 ± 6.6%, TEE between 1.9 (1.7-2.2)% and 4.2 (3.6-4.9)% according to the grade level. Using corrected altitude data, we obtained: R 2 = 0.98 (p < 0.001), bias = 0.2 ± 1.9%, TEE between 0.2 (0.2-0.3)% and 1.0 (0.9-1.2)% according to the grade level. The low-cost GPS receiver used was weakly accurate for estimating grade during outdoor walking when using uncorrected altitude data. However, the accuracy was greatly improved when using corrected altitude data. This study supports the potential interest of using GPS for estimating energy expenditure during outdoor walking.

Predicting metabolic rate during level and uphill outdoor walking using a low-cost GPS receiver.

The objective of this study was to assess the accuracy of using speed and grade data obtained from a low-cost global positioning system (GPS) receiver to estimate metabolic rate (MR) during level and uphill outdoor walking. Thirty young, healthy adults performed randomized outdoor walking for 6-min periods at 2.0, 3.5, and 5.0 km/h and on three different grades: 1) level walking, 2) uphill walking on a 3.7% mean grade, and 3) uphill walking on a 10.8% mean grade. The reference MR [metabolic equivalents (METs) and oxygen uptake (V̇o2)] values were obtained using a portable metabolic system. The speed and grade were obtained using a low-cost GPS receiver (1-Hz recording). The GPS grade (Δ altitude/distance walked) was calculated using both uncorrected GPS altitude data and GPS altitude data corrected with map projection software. The accuracy of predictions using reference speed and grade (actual[SPEED/GRADE]) data was high [R(2) = 0.85, root-mean-square error (RMSE) = 0.68 MET]. The accuracy decreased when GPS speed and uncorrected grade (GPS[UNCORRECTED]) data were used, although it remained substantial (R(2) = 0.66, RMSE = 1.00 MET). The accuracy was greatly improved when the GPS speed and corrected grade (GPS[CORRECTED]) data were used (R(2) = 0.82, RMSE = 0.79 MET). Published predictive equations for walking MR were also cross-validated using actual or GPS speed and grade data when appropriate. The prediction accuracy was very close when either actual[SPEED/GRADE] values or GPS[CORRECTED] values (for level and uphill combined) or GPS speed values (for level walking only) were used. These results offer promising research and clinical applications related to the assessment of energy expenditure during free-living walking.

Global positioning system use in the community to evaluate improvements in walking after revascularization: a prospective multicenter study with 6-month follow-up in patients with peripheral arterial disease.

UNLABELLED: Revascularization aims at improving walking ability in patients with arterial claudication. The highest measured distance between 2 stops (highest-MDCW), the average walking speed (average-WSCW), and the average stop duration (average-DSCW) can be measured by global positioning system, but their evolution after revascularization is unknown.We included 251 peripheral artery diseased patients with self-reported limiting claudication. The patients performed a 1-hour stroll, recorded by a global positioning system receiver. Patients (n = 172) with confirmed limitation (highest-MDCW <2000m) at inclusion were reevaluated after 6 months. Patients revascularized during the follow-up period were compared with reference patients (ie, with unchanged lifestyle medical or surgical status). Other patients (lost to follow-up or treatment change) were excluded (n = 89).We studied 44 revascularized and 39 reference patients. Changes in highest-MDCW (+442 vs. +13 m) and average-WSCW (+0.3 vs. -0.2 km h) were greater in revascularized than in reference patients (both P < 0.01). In contrast, no significant difference in average-DSCW changes was found between the groups. Among the revascularized patients, 13 (29.5%) had a change in average-WSCW, but not in highest-MDCW, greater than the mean + 1 standard deviation of the change observed for reference patients.Revascularization may improve highest-MDCW and/or average-WSCW. This first report of changes in community walking ability in revascularized patients suggests that, beyond measuring walking distances, average-WSCW measurement is essential to monitor these changes. Applicability to other surgical populations remains to be evaluated. REGISTRATION: http://www.clinicaltrials.gov/ct2/show/NCT01141361.

Time and reliability issues associated with automatic vs. manual measurements of Ankle to Brachial pressure Index (ABI) following heavy load exercise.

OBJECTIVES: Ankle to brachial index after heavy load exercise is the most accurate way of diagnosing minor arterial lesions in athletes, such as endofibrosis. The reliability and practical aspects of ankle to brachial index measurements after heavy-load exercise have not been studied. The purpose of this study was to analyze the interest of oscillometric automatic vs. manual Doppler measurements, for the calculation of ankle to brachial index, after heavy-load exercise in athletes. DESIGN: Prospective single-center study. METHODS: Fifteen healthy trained athletes performed an incremental test twice. Ankle to brachial index measurements were performed at Rest, as soon as possible after exercise (Rec-0), and then started at the 3rd minute of recovery (Rec-3), by two operators using each one of the two ankle to brachial index measurement methods. RESULTS: Mean times for automatic vs. manual ankle to brachial availability were 99 ± 18 s vs. 113 ± 25 s (p = 0.005) and 44 ± 25 s vs. 53 ± 12 s (p = 0.001) respectively at Rec-0 and Rec-3. Ankle to brachial index values from the two methods were highly correlated (r = 0.89). Mean absolute differences of automatic vs. manual ankle to brachial values from test-retest were 0.04 ± 0.05 vs. 0.08 ± 0.08 (p > 0.05) and 0.07 ± 0.05 vs. 0.09 ± 0.10 (p > 0.05) at Rest and Rec-0. CONCLUSIONS: Automatic method allows obtaining faster and simultaneously post-exercise ankle to brachial index measurement compare to the manual Doppler. This time issue does not result in a significant change in absolute ankle to brachial index values, nor in the absolute differences of these in test-retest. Nevertheless, the test-retest variability of post-exercise ankle to brachial index results seems smaller with the automatic than the manual method.

Applicability of global positioning system for the assessment of walking ability in patients with arterial claudication.

OBJECTIVE: This study determined for the first time the clinical applicability of a global positioning system (GPS)-monitored community-based walking ability assessment in a large cohort of patients with peripheral artery disease (PAD). METHODS: A multicenter study was conducted among PAD patients who complained of intermittent claudication. Patients equipped with a GPS device performed a community-based outdoor walk. We determined the number of technically satisfactory GPS recordings (attempt No. 1). Patients with unsatisfactory GPS recordings were asked to perform a second attempt (attempt No. 2). From the satisfactory recordings obtained after attempts No. 1 and No. 2, we analyzed several GPS parameters to provide clinical information on the patients' walking ability. Results are reported as median (interquartile range). RESULTS: A total of 218 patients performed an outdoor walk. GPS recordings were technically satisfactory in 185 patients (85%) and in 203 (93%) after attempts No. 1 and No. 2, respectively. The highest measured distance between two stops during community walking was 678 m (IQR, 381-1333 m), whereas self-reported maximal walking distance was 250 m (IQR, 150-400 m; P < .001). Walking speed was 3.6 km/h (IQR, 3.1-3.9 km/h), with few variations during the walk. Among the patients who had to stop during the walk, the stop durations were <10 minutes in all but one individual. CONCLUSIONS: GPS is applicable for the nonsupervised multicenter recording of walking ability in the community. In the future, it may facilitate objective community-based assessment of walking ability, allow for the adequate monitoring of home-based walking programs, and for the study of new dimensions of walking in PAD patients with intermittent claudication.

The inter- and intra-unit variability of a low-cost GPS data logger/receiver to study human outdoor walking in view of health and clinical studies.

PURPOSE: The present study evaluates the intra- and inter-unit variability of the GlobalSat® DG100 GPS data logger/receiver (DG100) when estimating outdoor walking distances and speeds. METHODS: Two experiments were performed using healthy subjects walking on a 400 m outdoor synthetic track. The two experiments consisted of two different outdoor prescribed walking protocols with distances ranging from 50 to 400 m. Experiment 1 examined the intra-unit variability of the DG100 (test-retest reproducibility) when estimating walking distances. Experiment 2 examined the inter-unit variability of four DG100 devices (unit to unit variability) when estimating walking distances and speeds. RESULTS: The coefficient of variation [95% confidence interval], for the reliability of estimating walking distances, was 2.8 [2.5-3.2] %. The inter-unit variability among the four DG100 units tested ranged from 2.8 [2.5-3.2] % to 3.9 [3.5-4.4] % when estimating distances and from 2.7 [2.4-3.0] % to 3.8 [3.4-4.2] % when estimating speeds. CONCLUSION: The present study indicates that the DG100, an economical and convenient GPS data logger/receiver, can be reliably used to study human outdoor walking activities in unobstructed conditions. This device let facilitate the use of GPS in studies of health and disease.

The accuracy of a simple, low-cost GPS data logger/receiver to study outdoor human walking in view of health and clinical studies.

INTRODUCTION: Accurate and objective measurements of physical activity and lower-extremity function are important in health and disease monitoring, particularly given the current epidemic of chronic diseases and their related functional impairment. PURPOSE: The aim of the present study was to determine the accuracy of a handy (lightweight, small, only one stop/start button) and low-cost (∼$75 with its external antenna) Global Positioning System (GPS) data logger/receiver (the DG100) as a tool to study outdoor human walking in perspective of health and clinical research studies. Methods. Healthy subjects performed two experiments that consisted of different prescribed outdoor walking protocols. Experiment 1. We studied the accuracy of the DG100 for detecting bouts of walking and resting. Experiment 2. We studied the accuracy of the DG100 for estimating distances and speeds of walking. RESULTS: Experiment 1. The performance in the detection of bouts, expressed as the percentage of walking and resting bouts that were correctly detected, was 92.4% [95% Confidence Interval: 90.6-94.3]. Experiment 2. The coefficients of variation [95% Confidence Interval] for the accuracy of estimating the distances and speeds of walking were low: 3.1% [2.9-3.3] and 2.8% [2.6-3.1], respectively. CONCLUSION: The DG100 produces acceptable accuracy both in detecting bouts of walking and resting and in estimating distances and speeds of walking during the detected walking bouts. However, before we can confirm that the DG100 can be used to study walking with respect to health and clinical studies, the inter- and intra-DG100 variability should be studied. TRIAL REGISTRATION: ClinicalTrials.gov NCT00485147.

Variability and short-term determinants of walking capacity in patients with intermittent claudication.

OBJECTIVE: Global positioning system (GPS) recordings can provide valid information on walking capacity in patients with peripheral arterial disease (PAD) and intermittent claudication (IC) during community-based outdoor walking. This study used GPS to determine the variability of the free-living walking distance between two stops (WDBS), induced by lower-limb pain, which may exist within a single stroll in PAD patients with IC and the potential associated parameters obtained from GPS analysis. METHODS: This cross-sectional study of 57 PAD patients with IC was conducted in a university hospital. The intervention was a 1-hour free-living walking in a flat public park with GPS recording at 0.5 Hz. GPS-computed parameters for each patient were WDBS, previous stop duration (PSD), cumulated time from the beginning of the stroll, and average walking speed for each walking bout. The coefficient of variation of each parameter was calculated for patients with the number of walking bouts (N(WB)) >or=5 during their stroll. A multivariate analysis was performed to correlate WDBS with the other parameters. RESULTS: Mean (SD) maximal individual WDBS was 1905 (1189) vs 550 (621) meters for patients with N(WB) <5 vs N(WB) >or= 5, respectively (P < .001). In the 36 patients with N(WB) >or= 5, the coefficient of variation for individual WDBS was 43%. Only PSD and cumulated time were statistically associated with WDBS in 16 and 5 patients, respectively. CONCLUSIONS: A wide short-term variability of WDBS exists and likely contributes to the difficulties experienced by patients with IC to estimate their maximal walking distance at leisurely pace. Incomplete recovery from a preceding walk, as estimated through PSD, seems to dominantly account for the WDBS in patients with IC.

Measurement of walking distance and speed in patients with peripheral arterial disease: a novel method using a global positioning system.

BACKGROUND: The maximal walking distance (MWD) performed on a treadmill test remains the "gold standard" in estimating the walking capacity of patients who have peripheral arterial disease with intermittent claudication, although treadmills are not accessible to most physicians. We hypothesized that global positioning system (GPS) recordings could monitor community-based outdoor walking and provide valid information on walking capacity in patients with peripheral arterial disease. METHODS AND RESULTS: We studied 24 patients (6 women) with arterial claudication (median [25th to 75th percentile] values: 57 years old [48 to 67 years], 169 cm tall [164 to 172 cm], weight 81 kg [71 to 86 kg], and ankle-brachial index 0.64 [0.56 to 0.74]). MWD on the treadmill was 184 m (144 to 246 m), which was compared with the results of self-reported MWD, the distance score from the Walking Impairment Questionnaire, MWD observed during a 6-minute walking test, and MWD measured over a GPS-recorded unconstrained outdoor walk in a public park. Self-reported MWD, Walking Impairment Questionnaire distance score, 6-minute walking test score, and GPS-measured MWD were 300 m (163 to 500 m), 28% (15% to 47%), 405 m (338 to 441 m), and 609 m (283 to 1287 m), respectively. The best correlation with MWD on the treadmill test was obtained with the MWD measured by the GPS (Spearman r=0.81, P<0.001). CONCLUSIONS: Outdoor walking capacity measured by a low-cost GPS is a potentially innovative way to study the walking capacity of patients with peripheral arterial disease. It opens new perspectives in the study of walking capacity for vascular patients with claudication under free-living conditions or for physicians who do not have a treadmill.

Study of human outdoor walking with a low-cost GPS and simple spreadsheet analysis.

PURPOSE: To determine whether a low-cost, commercially available global positioning system (GPS) can be used to study outdoor walking of healthy subjects, allowing the detection of walking and resting (nonwalking) periods and the accurate estimation of speed and distance of each walking periods. METHODS: The same EGNOS-enabled GPS receiver was used for all experiments. In experiment 1, various signal-processing methodologies were tested for the detection of both walking and resting bouts from a prescribed walking protocol (PWP) that was performed 21 times by six healthy subjects on an outdoor athletic track. In experiment 2, the accuracies of these processing methodologies were then tested through a blinded analysis of different PWP for 10 other healthy subjects in a designated public park. In experiment 3, speed and distance calculated by the GPS receiver during series of 100-400 m on an outdoor athletic track were compared with actual speed and distance. RESULTS: Raw data were inaccurate, but the combination of a low-pass filter, an adapted high-pass filter, and artifact processing enabled one to detect walking and resting bouts with an accuracy of 89.8% (95% CI, 84.4-93.4). A manual post-processing methodology, used to complete previous automatic processing results, provided the highest concordance with the PWP, reaching an accuracy of 97.1% (95% CI, 93.5-98.8). There was an excellent relationship both between actual and processed distances (R2=1.000) and between actual and processed speeds (R2=0.947). CONCLUSION: Low-cost, commercially available GPS may be accurate in studying outdoor walking, provided that simple data processing is applied. Future validation in diseased subjects could allow for the study of free-living walking capacity, such as maximal walking distance in vascular patients.

Simultaneous arterial pressure recordings improve the detection of endofibrosis.

PURPOSE: Exercise improves the diagnostic performance of ankle-to-brachial index (ABI) in the detection of exercise-induced arterial endofibrosis (EIAE). Pressure values for all four limbs are required to calculate ABI, but rapid systemic pressure changes occur during the recovery period from exercise. We checked whether after exercise, ABI calculated from simultaneous measurements was better than from consecutive measurements for differentiating athletes with EIAE from normal athletes. METHODS: We studied 42 normal athletes and 42 athletes suffering from unilateral pain caused by histologically proven EIAE. Bilateral brachial and ankle (ASBP) systolic blood pressure levels were simultaneously measured in the supine position at rest and every minute during the first 4 min of the recovery from incremental maximal exercise. Using receiver operating characteristics curves (ROC), we compared the diagnostic performance of single-leg ASBP and ABI values and between-leg ASBP (DeltaASBP) and ABI (DeltaABI) differences, calculated from simultaneous (simu) versus consecutive (cons) measurements, to discriminate athletes with EIAE from normal athletes. RESULTS: For single-leg postexercise values, ROC curve area was significantly higher for ABIsimu compared with ASBPsimu (P < 0.05, r = 0.91) and ASBPrand (P < 0.05, r = 0.68). Areas (+/- SE of area) of the ROC curves for postexercise Delta ASBPsimu and Delta ABIsimu were 0.97 +/- 0.01 and 0.97 +/- 0.02, respectively, and were higher than areas for postexercise Delta ASBP and Delta ABI calculated from consecutive and random measurements (P < 0.01). Accuracy for postexercise Delta ASBPsimu and Delta ABIsimu in discriminating EIAE from normal athletes was 93% [95% CI; 85-97], with a cutoff point of 22 mm Hg and 0.10, respectively. CONCLUSION: Delta ASBP and/or Delta ABI calculated from simultaneous pressure measurements should be recommended when searching for unilateral EIAE. Whether this result is applicable in the detection of early atherosclerotic lesions in sedentary subjects requires future investigation.